Utilization of Thermal Potential of Abandoned Wells: Fundamentals, Applications and Research 0323906168, 9780323906166

Table of contents :
Front Cover
Utilization of Thermal Potential of Abandoned Wells: Fundamentals, Applications and Research
Copyright
Contents
Contributors
Preface
Acknowledgments
Part I: Introduction to geothermal energy
Chapter 1: Historical overview of geothermal energy
1. Introduction
2. First traces of usage of geothermal energy
3. Geothermal energy and ancient Mediterranean civilizations
4. Etruscans and developments in geothermal energy
5. Geothermal energy and Roman period
6. Up to 1000CE
7. Middle ages of geothermal energy (from 1000CE)
8. Developments of technology of chemical productions in 18th century
9. Geothermal energy in 19th century
10. Modernization period
11. Summary
References
Chapter 2: Fundamentals of geothermal energy extraction
1. Introduction
2. Geophysics of the Earths regions
2.1. Core
2.2. Crust
2.3. Mantle
2.4. Mesosphere
2.5. Asthenosphere
2.6. Lithosphere
2.7. Troposphere
2.8. Stratosphere
2.9. Mesosphere
2.10. Thermosphere
2.11. Exosphere
2.12. Ionosphere
3. Sources of Earths internal energy
4. Classes of global geothermal regions
5. Harvesting the geothermal heat
5.1. Heat extracted from dry rock
5.2. Heat extracted from the hot aquifer
6. Geothermal heat extraction techniques
7. Applications of geothermal energy
7.1. Geothermal power generation
7.2. Geothermal direct heating
7.2.1. Greenhouse heating
7.2.2. Space and district heating
7.2.3. Ground source heating and cooling
7.2.4. Crop drying
7.2.5. Snow melting
7.2.6. Aquacultural heating
7.2.7. Industrial process heat
7.2.8. Other uses
8. Conclusions
References
Chapter 3: Optimal simulation of design and operation of geothermal systems
1. Introduction
2. Mathematical model and numerical algorithm
3. Numerical simulation of GCS exploitation
4. Different seasonal regimes
5. Multiple productive well systems
6. Two injection well systems
7. Multiple injection well systems
8. Future prospects
9. Conclusions
Conflicts of interest
References
Part II: Abandoned wells and its global thermal potential
Chapter 4: Harvesting geothermal energy from mature oil reservoirs using downhole thermoelectric generation technology
1. Executive summary
2. Review of geothermal energy development in oil fields
3. Introduction of thermoelectric technology
4. Downhole power generation in oil wells
4.1. Design for a vertical well
4.2. Design for a horizontal well
5. Summary
References
Chapter 5: A brief survey on case studies in geothermal energy extraction from abandoned wells
1. Introduction
2. Features of the stored geothermal energy in oil fields
3. Utilizations of the stored geothermal energy in oil fields
3.1. Direct utilizations
3.2. Indirect utilization method and power generation
4. Methods of harnessing geothermal energy from oil fields
4.1. Converting oil wells (active and abandoned) to borehole heat exchangers
4.2. Geothermal energy extraction from the coproduced water
5. Further studies
6. Opportunities and challenges
7. Conclusions
References
Part III: Energy Extraction from abandoned wells
Chapter 6: Energy Extraction from abandoned wells
1. Introduction
2. Stimulation of abandoned geothermal wells
2.1. Hydraulic fracturing
2.2. Acidizing
2.2.1. Matrix acidizing
2.2.2. Acid fracturing
2.3. Thermal fracturing
2.4. Casing perforation
2.5. High-energy gas fracturing (HEGF) or explosive stimulation
2.6. Acoustic stimulation (active cavitation and ultrasonic)
2.7. Electric stimulation
2.8. Enhanced geothermal systems (EGS) using CO2 as a working fluid
3. Lessons for the reclamation of abandoned geothermal wells from reclamation of petroleum wells
4. Potential environmental impacts of reclamation of abandoned geothermal wells
5. Conclusions
Acknowledgment
References
Chapter 7: Productivity evaluation of geothermal energy production system based on abandoned oil and gas wells
1. Introduction
2. Mathematical model
2.1. Model assumption
2.2. Governing equations
2.3. Coupling process
2.4. Models with different wells
3. Capacity analysis
4. Parameter analysis
4.1. Effect of rock mass parameters
4.1.1. Thermal conductivity and specific heat capacity of rock mass
4.1.2. Rock mass permeability
4.1.3. Rock mass porosity
4.2. Effect of fracture parameters
4.2.1. Fracture permeability
4.2.2. Fracture aperture
4.2.3. Fracture thermal conductivity
4.3. Effect of injection temperature
5. Conclusions
References
Chapter 8: Simulation and thermodynamic modeling of heat extraction from abandoned wells
1. Introduction
2. Definition of modeling
3. The ways for modeling different parameters
3.1. Well temperature
3.2. Properties of materials
3.3. Temperature distribution in the wellbore
3.4. Continuity (mass conversion) equations
3.4.1. Case #1: Ahwaz oil field in southern Iran
3.4.2. Case #2: South Texas oil wells in the United States
3.5. Momentum equation
3.5.1. Case #1: Ahwaz oil field in southern Iran
3.5.2. Case #2: South Texas oil wells in the United States
3.6. Energy equations
3.6.1. Case #1: Ahwaz oil field in southern Iran
3.6.2. Case #2: South Texas oil wells in the United States
3.7. Turbulence intensity
4. Different possibilities for used mesh in numerical simulation
5. Literature review
6. Conclusions
Acknowledgment
References
Part IV: Feasibility, economic, and environmental analysis
Chapter 9: The main utilization forms and current developmental status of geothermal energy for building cooling/heating i
1. Introduction
2. Literature review and categories of geothermal energy utilization
2.1. Literature review on geothermal energy development for building cooling/heating in the developing countries
2.2. Categories of geothermal energy utilization for building cooling/heating
3. Common utilization of the GSHP system and its current application and development
3.1. GCHP system
3.2. GWHP system
4. Common utilization of the UDS system and its current application and development
4.1. Horizontal UDS system
4.2. Vertical UDS system
4.3. UDS-PCM system
4.4. UDS-advanced energy-saving technology system
5. Common utilization of the abandoned wells energy system and its current application and development
5.1. Application of the AWE system
5.1.1. Geothermal heat pump system
5.1.2. Geothermal power generation system (GPGS)
5.1.3. Desalinating produced water system
5.2. Influential of geothermal utilization efficiency
6. The existing issues and in-depth analysis on the practical application of geothermal energy for building cooling/heating
References
Chapter 10: Desalination design using geothermal energy of abandoned oil wells
1. Introduction
1.1. Desalination using renewable energies
1.2. Geothermal energy and desalination
1.3. Desalination and abandoned Wells
2. Multistep desalination method
3. Methods and materials
4. Results
4.1. Scenario 1: Conventional multistage geothermal desalination process
4.2. Scenario 2: Multistage geothermal desalination process with secondary preheating
4.3. Scenario 3: Geothermal desalination process with secondary preheating and external flash box
4.4. Scenario 4: Geothermal desalination process with secondary preheating, external flash box, and internal flash box
4.5. Conventional multistep desalination process simulation results (Scenario 1)
4.6. Multistage desalination simulation results with secondary preheating (Scenario 2)
4.7. Multistage desalination simulation results with secondary preheating and external flash box (Scenario 3)
4.8. Multistage desalination simulation results with secondary preheating, external flash box, and internal flash box (Sc ...
5. Economic analysis
6. Conclusion
References
Part V: Applications and case studies
Chapter 11: Electricity generation using heat extracted from abandoned wells
1. Introduction
2. Geothermal energy resources
2.1. Vapor-dominated resources
2.2. Liquid/hot water resources
2.3. Geo-pressurized resources
2.4. Hot dry rock resources
2.5. Magma resources or molten rock
2.6. Radiogenic resources
3. Electricity generation
3.1. Dry steam power plant
3.2. Flashed-steam power plants
3.2.1. Single flash steam plants
3.2.2. Double flash steam plants
3.3. Binary cycle power plant
3.4. Combined cycle or hybrid plants
4. Conclusion
References
Chapter 12: Thermodynamic modeling of an ORC power plant for abandoned geothermal well
1. Introduction
2. System description
3. Case study: Abandoned geothermal well (NWS3) in the Sabalan field
4. Numerical modeling of a geothermal well
4.1. Model validation
5. Geothermal power plant modeling
5.1. Energy analysis
6. Simulation results
7. Remarks
References
Chapter 13: Application of abandoned wells integrated with renewables
1. Introduction
2. Systematic literature review of abandoned wells for thermal and power generations
2.1. Abandoned wells for thermal energy generation
2.2. Abandoned wells for power generation
2.3. System assessment criteria
3. Renewable integrations with abandoned wells for district heating
3.1. Solar-geothermal energy system integration
3.2. Abandoned wells with waste heat recovery
3.3. Abandoned wells and renewable systems for district heating
4. Strategies for performance enhancement
4.1. Optimal system design
4.2. Smart system operation
5. Applications, challenges, and future prospects
5.1. Techno-economic and environmental performance analysis
5.2. Geothermal integrated energy systems
5.3. Potential assessment of abandoned wells for carbon-neutrality transition
Acknowledgments
References
Chapter 14: Integration of heat extraction from abandoned wells with renewables
1. Introduction
2. Different ways for integration of heat extraction from abandoned wells with renewables
2.1. Solar and geothermal
2.2. Biomass and geothermal
2.3. Wind and geothermal
2.4. Poly-generation
3. Literature review
4. Conclusions
Acknowledgment
References
Chapter 15: A Kalina cycle for low and medium enthalpy abandoned oil and gas reservoirs incorporated with solar technolog ...
1. Introduction
2. Related works
3. Theory and working principle
4. Comparison of Kalina cycle with other cycles
5. Proposed idea
6. Challenges and future scope
7. Conclusion
References
Chapter 16: Abandoned oil and gas wells for geothermal energy: Prospects for Pakistan
1. Introduction
2. Geothermal play types
3. Geothermal reservoir characterization
3.1. Porosity/permeability
3.2. Thermal gradient
3.3. Lithofacies
3.4. Fault/fractures
4. Geothermal energy extraction through AOGW
5. Geothermal energy potential of Pakistan
5.1. Upper Indus Basin
5.2. Central Indus Basin
5.3. Lower Indus Basin
6. Conclusions
References
Chapter 17: Mandaree, North Dakota: A case study on oil and gas well conversion to geothermal district heating systems for
1. Geothermal district heating for the oil patch
2. Innovations in district heating
3. Description of the study site
4. Characterizing Mandaree energy demand
5. Classifying the geothermal resource
6. Geological setting of the Williston Basin
7. Using thermostratigraphy to assess aquifer temperatures
8. Aquifer access through existing wells
9. Decarbonizing Mandarees heat demand with geothermal energy
10. Refining the heat network service area
11. Downhole pump flow rates
12. Production test case
13. Determining industrial heat loads
14. Peak heating source sizing and load allocations
15. Geothermal well energy utilization factor
16. Changing patterns of energy use
17. Economics
18. Hedging against the uncertainty with contingency planning
19. Available funding vehicles for Mandaree geothermal
20. Recompletion and heat network costs
21. Fluid chemistry and maintenance considerations
22. Regulatory conditions
23. Completed design, production costs, tariffs, and payback periods
24. Limitations and future work
25. Conclusions
References
Chapter 18: Geothermal energy from abandoned oil and gas wells in India
1. Introduction
2. Indian petroliferous basins and scope for utilization of abandoned wells for geothermal energy
2.1. Cambay basin
2.2. Krishna-Godavari basin
2.3. Cauvery basin
2.4. Assam-Arakan basin
3. Implementation methodologies adopted by other countries for geothermal energy extraction
3.1. Heat exchange from a single well
3.2. Doublet well system
3.3. Coaxial wellbore heat exchanger (WHE) in abandoned oil and gas wells
3.4. Simulation studies on Earth energy designer model
3.5. Thermal impact graph
3.6. In situ combustion
4. Heat recovery methodologies for Indian AOGWs
5. Conclusions
Acknowledgments
References
Part VI: Revitalization of abandoned oil and gas wells
Chapter 19: Pragmatic steps to the revitalization of abandoned oil and gas wells for geothermal applications
1. Introduction
2. Prefeasibility features favoring geothermal exploitation of abandoned oil and gas wells
3. Main components of thorough feasibility studies
3.1. Thermodynamic feasibility of the project
3.2. Economic feasibility of the project
3.3. Environmental feasibility
4. Viable conversion technologies for power generation
5. Short review of practical case studies
6. Summary
References
Chapter 20: Exploration techniques for the identification of thermal potential zones
1. Introduction
2. Remote sensing techniques
3. Geochemical study
4. Geophysical techniques
4.1. Micrometer survey method (MSM)
4.2. Seismic methods
4.2.1. Acquisition
4.2.2. Interpretation: Velocity and layer thickness calculations
4.3. Gravity methods
4.3.1. Bouguer gravity anomalies
4.3.2. Regional and residual gravity fields
4.3.3. Derivatives of the gravity field
4.3.4. Upward and downward continuation
4.4. Resistivity and magnetotellurics
4.5. Magnetics
References
Chapter 21: Comparative analysis and evaluation of the geothermal system potential to recover thermal resources of&spi
1. Introduction
2. Review of geothermal system application at mining sites
3. Methods
4. Geological and geothermal conditions of the Donetsk coal-mining area
5. Results and discussion
6. Conclusions
Acknowledgment
References
Index
Back Cover

Citation preview

Utilization of Thermal Potential of Abandoned Wells

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Utilization of Thermal Potential of Abandoned Wells Fundamentals, Applications, and Research Edited by

Younes Noorollahi Associate Professor, University of Tehran, Tehran, Iran

Muhammad Nihal Naseer Researcher, National University of Sciences and Technology (NUST), Islamabad, Pakistan

Muhammad Mobin Siddiqi Chair of Registrar, Assistant Professor of Chemistry, National University of Sciences and Technology (NUST), Islamabad, Pakistan

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom Copyright © 2022 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. ISBN 978-0-323-90616-6 For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Charlotte Cockle Acquisitions Editor: Rachel Pomery Editorial Project Manager: Joshua Mearns Production Project Manager: Nirmala Arumugam Cover designer: Matthew Limbert Typeset by STRAIVE, India

Contents

Contributors Preface Acknowledgments

Part I 1

2

Introduction to geothermal energy

Historical overview of geothermal energy Muhammad Azhar, Asad A. Zaidi, Muhammad Nihal Naseer, Younes Noorollahi, and Muhammad Uzair 1 Introduction 2 First traces of usage of geothermal energy 3 Geothermal energy and ancient Mediterranean civilizations 4 Etruscans and developments in geothermal energy 5 Geothermal energy and Roman period 6 Up to 1000 CE 7 Middle ages of geothermal energy (from 1000 CE) 8 Developments of technology of chemical productions in 18th century 9 Geothermal energy in 19th century 10 Modernization period 11 Summary References Fundamentals of geothermal energy extraction Hamdy Hassan 1 Introduction 2 Geophysics of the Earth’s regions 3 Sources of Earth’s internal energy 4 Classes of global geothermal regions 5 Harvesting the geothermal heat 6 Geothermal heat extraction techniques 7 Applications of geothermal energy 8 Conclusions References

xiii xix xxi

1 3

3 3 4 4 4 5 5 6 6 7 8 9 11 11 12 17 17 18 21 24 32 32

vi

3

Contents

Optimal simulation of design and operation of geothermal systems Mikhail Yu. Filimonov and Nataliia A. Vaganova 1 Introduction 2 Mathematical model and numerical algorithm 3 Numerical simulation of GCS exploitation 4 Different seasonal regimes 5 Multiple productive well systems 6 Two injection well systems 7 Multiple injection well systems 8 Future prospects 9 Conclusions References

Part II Abandoned wells and its global thermal potential 4

5

Harvesting geothermal energy from mature oil reservoirs using downhole thermoelectric generation technology Xingru Wu and Kai Wang 1 Executive summary 2 Review of geothermal energy development in oil fields 3 Introduction of thermoelectric technology 4 Downhole power generation in oil wells 5 Summary References

A brief survey on case studies in geothermal energy extraction from abandoned wells Davar Ebrahimi, Mohammad-Reza Kolahi, Mohamad-Hasan Javadi, Javad Nouraliee, and Majid Amidpour 1 Introduction 2 Features of the stored geothermal energy in oil fields 3 Utilizations of the stored geothermal energy in oil fields 4 Methods of harnessing geothermal energy from oil fields 5 Further studies 6 Opportunities and challenges 7 Conclusions References

35 35 37 43 45 47 47 47 49 54 54

59 61 61 61 63 66 70 71

75

75 77 79 82 88 89 91 91

Contents

Part III 6

7

8

Energy Extraction from abandoned wells

97

Energy Extraction from abandoned wells Zachary Siagi and Charles Nzila 1 Introduction 2 Stimulation of abandoned geothermal wells 3 Lessons for the reclamation of abandoned geothermal wells from reclamation of petroleum wells 4 Potential environmental impacts of reclamation of abandoned geothermal wells 5 Conclusions Acknowledgment References

99

Productivity evaluation of geothermal energy production system based on abandoned oil and gas wells Jie Zhang and Xiaohua Zhu 1 Introduction 2 Mathematical model 3 Capacity analysis 4 Parameter analysis 5 Conclusions References Simulation and thermodynamic modeling of heat extraction from abandoned wells Ali Sohani, Ardeshir Mohammadian, Nima Asgari, Saman Samiezadeh, Mohammad Hossein Doranehgard, Erfan Goodarzi, Benedetto Nastasi, and Davide Astiaso Garcia 1 Introduction 2 Definition of modeling 3 The ways for modeling different parameters 4 Different possibilities for used mesh in numerical simulation 5 Literature review 6 Conclusions Acknowledgment References

Part IV 9

vii

Feasibility, economic, and environmental analysis

The main utilization forms and current developmental status of geothermal energy for building cooling/heating in developing countries Zhengxuan Liu, Chao Zeng, Yuekuan Zhou, and Chaojie Xing 1 Introduction 2 Literature review and categories of geothermal energy utilization

99 100 108 109 110 113 113

115 115 116 120 121 131 133

135

137 138 138 149 149 153 153 153

157

159 159 160

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Contents

3

Common utilization of the GSHP system and its current application and development 4 Common utilization of the UDS system and its current application and development 5 Common utilization of the abandoned wells energy system and its current application and development 6 The existing issues and in-depth analysis on the practical application of geothermal energy for building cooling/heating References 10

Desalination design using geothermal energy of abandoned oil wells Nima Norouzi, Maryam Fani, and Saeed Talebi 1 Introduction 2 Multistep desalination method 3 Methods and materials 4 Results 5 Economic analysis 6 Conclusion References

Part V Applications and case studies 11

12

Electricity generation using heat extracted from abandoned wells Hamdy Hassan 1 Introduction 2 Geothermal energy resources 3 Electricity generation 4 Conclusion References Thermodynamic modeling of an ORC power plant for abandoned geothermal well Saeid Mohammadzadeh Bina, Hikari Fujii, Shunsuke Tsuya, and Younes Noorollahi 1 Introduction 2 System description 3 Case study: Abandoned geothermal well (NWS3) in the Sabalan field 4 Numerical modeling of a geothermal well 5 Geothermal power plant modeling 6 Simulation results 7 Remarks References

165 170 178 184 186

191 191 196 196 198 207 208 209

215 217 217 219 226 237 238

239

239 240 241 243 245 249 252 253

Contents

13

14

15

16

Application of abandoned wells integrated with renewables Yuekuan Zhou, Zhengxuan Liu, and Chaojie Xing 1 Introduction 2 Systematic literature review of abandoned wells for thermal and power generations 3 Renewable integrations with abandoned wells for district heating 4 Strategies for performance enhancement 5 Applications, challenges, and future prospects Acknowledgments References Integration of heat extraction from abandoned wells with renewables Ali Sohani, Amir Dehnavi, Farbod Esmaeilion, Joshua O. Ighalo, Abdulmaliq Abdulsalam, Siamak Hoseinzadeh, Benedetto Nastasi, and Davide Astiaso Garcia 1 Introduction 2 Different ways for integration of heat extraction from abandoned wells with renewables 3 Literature review 4 Conclusions Acknowledgment References A Kalina cycle for low and medium enthalpy abandoned oil and gas reservoirs incorporated with solar technology for power production Jainam Panchal and Manan Shah 1 Introduction 2 Related works 3 Theory and working principle 4 Comparison of Kalina cycle with other cycles 5 Proposed idea 6 Challenges and future scope 7 Conclusion References Abandoned oil and gas wells for geothermal energy: Prospects for Pakistan Muhammad Jawad Munawar, Xianbiao Bu, Saif Ur Rehman, Naveed Ahsan, Hafiz Ahmed Raza Hassan, and Muhammad Talha 1 Introduction 2 Geothermal play types 3 Geothermal reservoir characterization 4 Geothermal energy extraction through AOGW

ix

255 255 256 260 266 267 269 269

275

275 276 287 291 292 292

297 297 300 304 307 309 310 311 312

315

315 317 319 323

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Contents

5 Geothermal energy potential of Pakistan 6 Conclusions References

325 333 335

17

Mandaree, North Dakota: A case study on oil and gas well conversion to geothermal district heating systems for rural communities 341 Jessica Eagle-Bluestone, Moones Alamooti, Shane Namie, Jerjes Porlles, Nnaemeka Ngobidi, Nicholas Fry, Matthew Villante, Chioma Onwumelu, Ogonna Obinwa, and Will Gosnold, Jr. 1 Geothermal district heating for the oil patch 341 2 Innovations in district heating 343 3 Description of the study site 343 4 Characterizing Mandaree energy demand 344 5 Classifying the geothermal resource 345 6 Geological setting of the Williston Basin 346 7 Using thermostratigraphy to assess aquifer temperatures 346 8 Aquifer access through existing wells 348 9 Decarbonizing Mandaree’s heat demand with geothermal energy 352 10 Refining the heat network service area 354 11 Downhole pump flow rates 355 12 Production test case 356 13 Determining industrial heat loads 356 14 Peak heating source sizing and load allocations 358 15 Geothermal well energy utilization factor 359 16 Changing patterns of energy use 360 17 Economics 360 18 Hedging against the uncertainty with contingency planning 361 19 Available funding vehicles for Mandaree geothermal 361 20 Recompletion and heat network costs 362 21 Fluid chemistry and maintenance considerations 363 22 Regulatory conditions 364 23 Completed design, production costs, tariffs, and payback periods 364 24 Limitations and future work 364 25 Conclusions 366 References 367

18

Geothermal energy from abandoned oil and gas wells in India Namrata Bist, Anirbid Sircar, and Kriti Yadav 1 Introduction 2 Indian petroliferous basins and scope for utilization of abandoned wells for geothermal energy

373 373 374

Contents

xi

3

Implementation methodologies adopted by other countries for geothermal energy extraction 4 Heat recovery methodologies for Indian AOGWs 5 Conclusions Acknowledgments References

Part VI 19

20

21

Revitalization of abandoned oil and gas wells

Pragmatic steps to the revitalization of abandoned oil and gas wells for geothermal applications Joseph Oyekale and Eyere Emagbetere 1 Introduction 2 Prefeasibility features favoring geothermal exploitation of abandoned oil and gas wells 3 Main components of thorough feasibility studies 4 Viable conversion technologies for power generation 5 Short review of practical case studies 6 Summary References Exploration techniques for the identification of thermal potential zones Kriti Yadav, Anirbid Sircar, and Namrata Bist 1 Introduction 2 Remote sensing techniques 3 Geochemical study 4 Geophysical techniques References Comparative analysis and evaluation of the geothermal system potential to recover thermal resources of closed mines in Ukraine Dmytro Rudakov and Oleksandr Inkin 1 Introduction 2 Review of geothermal system application at mining sites 3 Methods 4 Geological and geothermal conditions of the Donetsk coal-mining area 5 Results and discussion 6 Conclusions Acknowledgment References

Index

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387 389 389 390 391 397 397 398 401

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427 427 428 432 436 440 443 443 443 447

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Contributors

Abdulmaliq Abdulsalam Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX, United States Naveed Ahsan Institute of Geology, University of the Punjab, Lahore, Pakistan Moones Alamooti University of North Dakota, Grand Forks, ND, United States Majid Amidpour Faculty of Mechanical Engineering, Department of Energy System Engineering, K.N. Toosi University of Technology, Tehran, Iran Nima Asgari Sahand University of Technology, Tabriz, Iran Muhammad Azhar National University of Sciences and Technology (NUST), Islamabad, Pakistan Saeid Mohammadzadeh Bina Graduate School of Engineering and Resource Science, Akita University, Akita, Japan Namrata Bist Centre of Excellence for Geothermal Energy, Pandit Deendayal Petroleum University, Gandhinagar, Gujarat, India Xianbiao Bu Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, China Amir Dehnavi Department of Electrical Engineering, Amirkabir University of Technology, Tehran, Iran Mohammad Hossein Doranehgard Department of Civil and Environmental Engineering, School of Mining and Petroleum Engineering, University of Alberta, Edmonton, AB, Canada Jessica Eagle-Bluestone University of North Dakota, Grand Forks, ND, United States Davar Ebrahimi Renewable Energy Research Department, Niroo Research Institute (NRI), Tehran, Iran Eyere Emagbetere Department of Mechanical Engineering, Federal University of Petroleum Resources, Effurun, Delta State, Nigeria

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Contributors

Farbod Esmaeilion Department of Mechanical Engineering, K.N. Toosi University of Technology, Tehran, Iran Maryam Fani Department of Energy Engineering and Physics, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran Mikhail Yu. Filimonov Ural Federal University; Krasovskii Institute of Mathematics and Mechanics UrB RAS, Yekaterinburg, Russia Nicholas Fry Iceland School of Energy, Reykjavik, Iceland Hikari Fujii Graduate School of Engineering and Resource Science, Akita University, Akita, Japan Davide Astiaso Garcia Department of Planning, Design, and Technology of Architecture, Sapienza University of Rome, Rome, Italy Erfan Goodarzi Lab of Optimization of Thermal Systems’ Installations, Faculty of Mechanical Engineering-Energy Division, K.N. Toosi University of Technology, Tehran, Iran Will Gosnold, Jr. University of North Dakota, Grand Forks, ND, United States Hafiz Ahmed Raza Hassan Institute of Geology, University of the Punjab, Lahore, Pakistan; School of Geosciences, China University of Petroleum, Qingdao, China Hamdy Hassan Energy Resources Engineering Department, Egypt-Japan University of Science and Technology (E-JUST), Alexandria; Mechanical Engineering Department, Faculty of Engineering, Assiut University, Assiut, Egypt; Energy Resources Engineering Department, Egypt-Japan University of Science and Technology (E-JUST), Alexandria, Egypt Siamak Hoseinzadeh Department of Planning, Design, and Technology of Architecture, Sapienza University of Rome, Rome, Italy Joshua O. Ighalo Department of Chemical Engineering, Nnamdi Azikiwe University, Awka; Department of Chemical Engineering, University of Ilorin, Ilorin, Nigeria Oleksandr Inkin Dnipro University of Technology, Dnipro, Ukraine Mohamad-Hasan Javadi Renewable Energy Research Department, Niroo Research Institute (NRI), Tehran, Iran

Contributors

xv

Mohammad-Reza Kolahi Energy & Environment Research Center, Niroo Research Institute (NRI), Tehran, Iran Zhengxuan Liu College of Civil Engineering, National Center for International Research Collaboration in Building Safety and Environment, Hunan University, Changsha, Hunan, China; Faculty of Architecture and the Built Environment, Delft University of Technology, Delft, Netherlands Ardeshir Mohammadian Lab of Optimization of Thermal Systems’ Installations, Faculty of Mechanical Engineering-Energy Division, K.N. Toosi University of Technology, Tehran, Iran Saeid Mohammadzadeh Bina Graduate School of Engineering and Resource Science, Akita University, Akita, Japan Muhammad Jawad Munawar Institute of Geology, University of the Punjab, Lahore, Pakistan Shane Namie University of North Dakota, Grand Forks, ND, United States Muhammad Nihal Naseer National University of Sciences and Technology (NUST), Islamabad, Pakistan Benedetto Nastasi Department of Planning, Design, and Technology of Architecture, Sapienza University of Rome, Rome, Italy Nnaemeka Ngobidi University of North Dakota, Grand Forks, ND, United States Younes Noorollahi University of Tehran, Tehran, Iran Nima Norouzi Department of Energy Engineering and Physics, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran Javad Nouraliee Renewable Energy Research Department, Niroo Research Institute (NRI), Tehran, Iran Charles Nzila Department of Manufacturing, Industrial & Textile Engineering, Moi University School of Engineering, Kenya Ogonna Obinwa University of North Dakota, Grand Forks, ND, United States; California Geologic Energy Management Division (CalGEM), Sacramento, CA, United States Chioma Onwumelu University of North Dakota, Grand Forks, ND, United States

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Contributors

Joseph Oyekale Department of Mechanical Engineering, Federal University of Petroleum Resources, Effurun, Delta State, Nigeria Jainam Panchal Department of Chemical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar, India Jerjes Porlles University of North Dakota, Grand Forks, ND, United States Saif Ur Rehman Institute of Geology, University of the Punjab, Lahore, Pakistan Dmytro Rudakov Dnipro University of Technology, Dnipro, Ukraine Saman Samiezadeh Lab of Optimization of Thermal Systems’ Installations, Faculty of Mechanical Engineering-Energy Division, K.N. Toosi University of Technology, Tehran, Iran Manan Shah Department of Chemical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar, India Zachary Siagi Department of Production, Mechanical & Energy Engineering, Moi University School of Engineering, Kenya Anirbid Sircar Centre of Excellence for Geothermal Energy, Pandit Deendayal Petroleum University, Gandhinagar, Gujarat, India Ali Sohani Lab of Optimization of Thermal Systems’ Installations, Faculty of Mechanical Engineering-Energy Division, K.N. Toosi University of Technology, Tehran, Iran Saeed Talebi Department of Energy Engineering and Physics, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran Muhammad Talha Institute of Geology, University of the Punjab, Lahore, Pakistan; School of Geosciences, China University of Petroleum, Qingdao, China Shunsuke Tsuya Graduate School of Engineering and Resource Science, Akita University, Akita, Japan Muhammad Uzair Department of Mechanical Engineering, NED University of Engineering and Technology, Karachi, Pakistan Nataliia A. Vaganova Ural Federal University; Krasovskii Institute of Mathematics and Mechanics UrB RAS, Yekaterinburg, Russia Matthew Villante Iceland School of Energy, Reykjavik, Iceland

Contributors

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Kai Wang The University of Oklahoma, Sarkeys Energy Center, Norman, OK, United States Xingru Wu The University of Oklahoma, Sarkeys Energy Center, Norman, OK, United States Chaojie Xing College of Civil Engineering, National Center for International Research Collaboration in Building Safety and Environment, Hunan University, Changsha, Hunan, China; College of Civil Engineering, Hunan University, Changsha, China Kriti Yadav Centre of Excellence for Geothermal Energy, Pandit Deendayal Petroleum University, Gandhinagar, Gujarat, India Asad A. Zaidi National University of Sciences and Technology (NUST), Islamabad, Pakistan Chao Zeng School of Mechanical Engineering, Southwest Jiaotong University, Chengdu, China Jie Zhang School of Mechatronic Engineering; Geothermal Energy Research Center, Southwest Petroleum University, Chengdu, China Yuekuan Zhou Sustainable Energy and Environment Thrust, Function Hub, The Hong Kong University of Science and Technology, Guangzhou; Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China Xiaohua Zhu School of Mechatronic Engineering; Geothermal Energy Research Center, Southwest Petroleum University, Chengdu, China

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Preface

The earth’s internal heat represents an unlimited thermal energy source initiated from radioactive decay. This form of energy is known as geothermal energy, which has been utilized throughout human history in the form of hot water from hot springs. It is an infinite source of energy for supplying heat demand and electricity production. Geothermal energy does not depend on weather conditions and is capable of supplying base load energy continuously and can, therefore, be an environment-friendly energy source. Modern use of geothermal energy includes the direct use of heat and its conversion to electricity. Geothermal energy as a form of green energy with very little or no CO2 emissions has greatly augmented the effects of climate change. Because of its inexhaustibility, it is evident that the utilization of underground heat will become a foundation for future energy supplies. The major concern of geothermal resource exploration is the expensive investment costs of exploration and drilling. Utilizing abandoned petroleum wells for geothermal energy extraction is a novel idea for green energy production. Abandoned oil and gas reservoirs may not hold oil or gas productivity after a long-term recovery process, but such wells can produce brine fluids with high temperatures. Thus, geothermal energy from such high-temperature depleted wells could be directly or indirectly recovered back to the surface for further use. Using geothermal energy from oil and gas wells increases the regional and local communities’ net product. It dismisses dependence on fossil fuels and helps preserve valuable resources for future generations. Abandoned wells supply thermal and electrical (converted thermal) energy, thus providing reliable base load energy for the future. This book offers a general overview of the various aspects of geothermal energy utilization extracted from abandoned oil and gas wells. We are looking forward to the further swift development of this attractive source of underground energy in the future. We wish all of us a reliable, safe, and environmentally friendly supply of thermal and electrical power. Geothermal energy extraction from abandoned oil and gas wells and its utilization are systematically offered. It contains the essential technical information required for developing and understanding this type of project for geothermal energy. We hope to contribute to the sustainable use of energy with the book. The book presents a historical overview of geothermal energy, the fundamentals of geothermal energy extraction, the optimal simulation of design and operation of geothermal systems, and harvesting geothermal energy from mature oil wells. Specific chapters of the book deal with productivity evaluation of geothermal energy production systems based on abandoned oil and gas wells, simulation and thermodynamic modeling of heat extraction, the main utilization forms, current developmental status of geothermal energy for building cooling/heating in developing countries, and

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Preface

electricity generation using heat extracted from abandoned wells using different technologies. Other topics are the integration of heat extraction from abandoned wells with renewables, thermodynamic modeling for ORC power plant for abandoned geothermal wells, and a Kalina cycle for low and medium enthalpy abandoned oil and gas reservoirs incorporated with solar technology power production. Abandoned oil and gas wells for geothermal energy: prospects for Pakistan, a case study on oil and gas well conversion to geothermal district heating systems for rural communities, geothermal energy from abandoned oil and gas wells in India, pragmatic steps to the revitalization of abandoned oil and gas wells for geothermal applications, exploration techniques for the identification of thermal potential zones, and comparative analysis and evaluations of the geothermal system potential to recover thermal resources of closed mines in Ukraine are the well-described case studies around the world. This book meets the demands of both groups of readers, students, and professionals. Students, researchers, and engineers will understand how to harvest energy from abandoned oil, gas, and geothermal wells; make sound thermodynamic and economic evaluations; and utilize numerical modeling and applications of such systems. System designers and others engaged in the energy sector will learn to design and choose the most appropriate technology, determine its efficiency, monitor the facility, and make informed physical and economic decisions for necessary improvements and environmental assessments. Associate Prof. Dr. Younes Noorollahi University of Tehran, Iran.

Acknowledgments

The editors acknowledge the extraordinary debt they owe to the reviewers for their continual support and vision that improved the quality of book chapters. Board of reviewers: Asad Ali Zaidi, Aminabbas Golshanfard, Cl
ement Rousseau, Davar Ebrahimi, Giti Nouri, Joe¨l M. Zinsalo, Justus Maithya, Mirmahdi SeyedrahimiNiaraq, Mohamad Hasan Ghodoosinejad, Mohammad Mohammadi, Muhammad Uzair, Pedram Bigdelou, Ralph B€aßler, Saeid Jalilinasrabadi, Shahab Eslami, and Tianshou Ma.

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Part I Introduction to geothermal energy

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Historical overview of geothermal energy

1

Muhammad Azhara, Asad A. Zaidia, Muhammad Nihal Naseera, Younes Noorollahib, and Muhammad Uzairc a National University of Sciences and Technology (NUST), Islamabad, Pakistan, bUniversity of Tehran, Tehran, Iran, cDepartment of Mechanical Engineering, NED University of Engineering and Technology, Karachi, Pakistan

1

Introduction

Geothermal energy is very old; it is available since the birth of this planet. However, humans found it difficult to explore geothermal energy. The oldest archeological finding shows that the use of geothermal energy from the volcanoes and hot springs dates back to the seventh millennium BCE. In the modern era, geothermal energy is considered as one of the very important resources for power production as it is renewable. Scientists and engineers are putting efforts to increase efficiency of power production plants that run on geothermal energy. The shift toward renewable resources and green energy to counter climate change especially in the potential places of this resource has grabbed an increased interest of scientific community toward geothermal energy.

2

First traces of usage of geothermal energy

The oldest literature related to man’s interest in geothermal energy can be dated back to seventh millennium BCE. It is a painting in which erupting volcano and dwelling structure of Neolithic settlement was shown [1]. The painting illustrates various morphological features of the volcano and its eruption. We can understand from the details of the painting how much advanced the ancient civilizations were in their period with respect to geothermal energy. The knowledge of eruptions of volcanoes and hot spring can be noticed in the painting. Those ancient civilizations created various by-products of geothermal energy such as hot bathing and cooking [2]. There were also many ancient constructions made around hot springs to make use of the geothermal energy, which shows the traces of man and geothermal energy relationship. The availability of such ancient construction is proved from the discovery of divine stones at Pantelleria Island in South Italy dating back to third millennium BCE [3]. The ancient knowledge from those civilizations has evolved with time and complex relationship between man and geothermal energy has formed with passing centuries [1,3].

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Geothermal energy and ancient Mediterranean civilizations

The geothermal energy attracted much attention in the Mediterranean era. There is presence of various tools made of lava and many other by-products of geothermal energy has been found on many nonvolcanic islands of Eastern Mediterranean [4]. The presence of such tools indicates the utilization of geothermal energy by the ancient people of the Mediterranean. These tools date back to fifth and third millennium BCE and are found in areas of Hattis, Himites, and Phoenicians in Anatolia, Minoans in Crete and Southern Cyclades, and Mycenaeans and peoples of Northeast Aegean [3]. In the Mediterranean people there were many myths, cults, and legends flourished regarding availability of the geothermal energy and its origins. In first half of the second millennium BCE lands full of hot springs, hydrothermal minerals, active manifestations, and by-products of geothermal heat utilized by ancient localities were discovered [5]. Mining and exportation of many by-products of geothermal energy and hydrothermal compounds began at this time by the people living in the Eastern Mediterranean. They used to explain the phenomena of geothermal energy by comparing with various legends as they had no idea of its origin. This rational thinking of people to explain the phenomena slowly evolved with new ideas and myths [6].

4

Etruscans and developments in geothermal energy

Ancient people of Etruria, Italy, who lived between Tiber and Arno rivers and west and south of the Apennines in 15th and 10th century BCE are called Etruscans [7]. These people were very advanced in their time, they were involved in the mining of metal and nonmetal ores, hydrothermal deposits, and evaporite minerals. They were also involved in various other advanced activities of science and utilizing geothermal energy is one of those [8]. The Etruscans developed various products from hydrothermal deposits for crafts and industries. Many manufacturing techniques such as grinding, processing, proportioning, pottery making, painting, fusing and coloring of glasses, preparing ointments, treating fabrics, and bleaching wool were developed by these people [9]. They were pioneers of various techniques used in geothermal sector and its by-products. Their various localities were situated near thermal manifestations, which show their interest in hydrothermal processing. Many archeological findings show how the Etruscans developed the industry using geothermal energy and sold their products to different parts of the world, which led to the urbanization of their civilization [10]. Their contribution in geothermal energy was so great that they are known as historical fathers of geothermal industry [1].

5

Geothermal energy and Roman period

The political and military pressures of the Roman Empire on the people were the main reason behind the development of interest in geothermal energy in their period. The strategic importance of the Etruscan localities was realized by the Romans [11].

Historical overview of geothermal energy

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In about fourth century BCE, the Romans started adapting the culture of the Etruscans and thermal bathing was one of those. Thus balneological culture in the Romans started developing, many public spas for bathing were built [1]. Thermal bathing culture was at its peak in 29 BCE and it was practiced at various thermal localities using hot springs. In the third century CE, there were about 1000 public baths in Rome. During first three centuries of Christian era, the practice of thermal bathing was made a custom, and places of thermal bathing were considered as meeting points. This culture was developed and other geothermal energy sources were also discovered until the fall of the empire in fifth century CE [4].

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Up to 1000 CE

With the passing of time balneological uses of geothermal energy extended to Larderello area. The poetry of the Greek poet Lycophron in third century BCE was inspired by geothermal thermal energy [12]. Glazes of Vasa Sigillata in the museum of Arezzo also prove the use of geothermal energy in ancient periods. The use of hydrothermal deposits and their mining continued from the Etruscans to the Romans, both communities advanced in their utilizations [13]. After the Romans, in the Christian era people used to sell small balls made of mud from hot water pools and these balls were used for healing purposes. After the decline of the Roman period, exploitation of hydrothermal minerals slowed down in the fourth century. Montecerboli “Devil’s Mountain” and Valle dell Infirno “Hell Valley” are names of local places that originated between 800 and 1000 CE, and these localities are clear indications of people’s belief in the origins of thermal manifestations [1]. In last two to three centuries of the millennium in Italy, social and economic growth retarded due to historical causes and widespread belief that end of the world would come in 1000 CE [3]. This retardation of the economic growth caused decline in the balneological practices and the use of hydrothermal products [1,14].

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Middle ages of geothermal energy (from 1000 CE)

After the beginning of the new era, conviction of the end of the world passed away. The reawakening spread over all Italy, relaunching of many new and old enterprises began to start. All activities of mining and exploitation of hydrothermal deposits were reborn [15]. The site known as Lumaie, which means “Bright Spot,” was the famous excavation site of that time where many hydrothermal deposits could be found [16]. The products excavated from the Lumaie included yellow sulfur for ointments and salves, Cyprian (green) and Roman (Red) vitriol (FeSO4.7H2 O) used by pharmacies, alum and nitro volterrano which may be boric acid. These products were considered so important commercially that many disputes and even wars broke out between various communities for the ownership of Lumaie [17]. The balneological and therapeutic uses of geothermal energy continued during different owners of the Lumaie. Many documents from middle ages written by Ristoro d’Arezzo (1282 CE), Ugolino da Montecatini (1420 CE), Savonarola (1460 CE), Agricola (1546 and 1556 CE),

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Fallopio (1560 CE), Merula (1605 CE), Cluverius (1624 CE), and Targioni Tozzetti (1769 CE) show the importance of thermal waters, gaseous inhalations, and mud for healing both internal and external injuries. Mascagni, a noted physiologist and chemist in 1779, discovered that boric acid is main the constituent of all thermal fluids [18]. He also published paper on the possibility of evaporating water using natural heat by burying metal boilers at sites of thermal manifestations [1,14].

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Developments of technology of chemical productions in 18th century

The growth in the production of chemicals from geothermal fluids started with the discovery of boric acid and various studies done by Hoefer and Mascagni [18,19]. There was a lot of importance given to boric acid all over Europe as it was produced using boron compound called Tincal, which was imported from Persia. Worth of boric acid can be estimated from its transportation from Persia which is far away, it makes us understand its importance in that period. Many powerful businesses were already set up in the Europe for selling boric acid [20]. At that time, Europe was going through many national movements, wars, and revolutions. It was difficult to bring up new product of boric acid that was produced from processing of hydrothermal manifestations and it clashed with established businesses in the Europe. In 1812 the first company for the exploitation of the boric acid from Larderello Area was established using the methodology of Mascagni [21]. The company failed for various economic and organizational reasons. A new company was created in 1815–16 for the evaporation of boric waters, it used wood from forest for heating purposes instead of heat exchangers proposed by Mascagni. The start-up was successful and produced 36 tons of boric acid in a period of 10 months [22]. Chemin-Prat-La Motte-Lardere a new boric acid production company came into being in 1818, lagoni of Montecerboli was leased by the company for 6 years. The company used the same technology for evaporating boric waters using metal boilers and wood and produced about 50 tons of boric acid per year for 10 years [23]. With the passing of time a new problem of forest depletion came up as firewood was used for evaporation, which crashed the profits of company. Thus the company started implementing innovative ideas from 1827 [24]. A new method of gathering steam was introduced by using covered lagoon, which helped in evaporating boron-bearing waters. In 1840 processing cycle— drainage of boric waters, vaporization, crystallization, and drying—was improved by new equipment and innovations [25]. One of those newly invented equipment was the boiler called Adriano boiler created by Adriano Larderel in which a series of brick conduits were lined internally with lead resulting in higher efficiency than previous boilers [24]. The Adriano boiler is the predecessor of the modern cross-flow heat exchangers [1,14].

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Geothermal energy in 19th century

With the start of new century, importance of geothermal fluids was recognized and multiple uses of fluids were introduced in the chemical industries. The drilling

Historical overview of geothermal energy

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technologies improved during this period. At first shallow hand-dug holes were used for the extraction of boron waters near geothermal manifestations [17]. In 1832 first geothermal wells were dug, which were about 10 cm in diameter and up to 8 m deep as ordered by Francesco Larderel. Those shallow wells produced greater amounts of fluids at higher pressures and temperatures as compared to covered lagoons [26]. In 1838 an engineer named Gazzeri discussed the possibilities of producing greater amounts of boric acid by drilling deep wells in his article. According to him the fluids containing boric acids are not isolated at different points but are concentrated at one point with large deposit which is unknown [27]. In 1848, Gazzeri’s concepts were developed further and using those concepts engineer Manteri invented new equipment for drilling. Three wells about 7 m deep were bored using this equipment at a site that was 100 m away from natural site, which was great distance in that time. Gazzeri’s theory was thus proved by the amount of production from those three wells, which were at such great distance away from natural manifestations site [28]. A newly established small company in 1841 drilled deep geothermal holes successfully using a new technique of rigs called artesian bar. In few years, many new technological advancements were introduced in drilling technology [29]. Four legged rigs, a winch, various drilling bits, and bailers are some of those technological advancements. With improving technology in drilling, depth of well increased with time. In 1842, geothermal wells could be dug up to 25–30 m. In the mid-19th century usually a large pit 5 or 6 m deep was dug first and then wells were drilled up to 35 m deep in that pit [30]. The beginning of new age of geothermal drilling started during the period 1856–70, many new drilling equipment and techniques were introduced and geothermal wells could be dug up to 200 m. The stimulation of geothermal wells was also introduced to encounter shallow cold aquifers that were created due to hydrostatic pressure and cooling by fresh water [31]. With the passing of time technology improved and geothermal wells were dug up to 300 m at end of the 19th century [1,14].

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Modernization period

Technological improvements for the extraction of geothermal fluids continued with passing years. The production of boric acid grew in the European market, amount of boric acid produced in 1850 was 1000 tons and in 1860 was 2000 tons [32]. In this period technological advancements were steam driven pumps, modern gathering system for boric brine and steam solutions, and the use of multitubular boilers. The idea of the production of power using geothermal steam as energy was first coined by Ginori Conti and it was his greatest achievement [33]. In 1904 for the first time geothermal power was used to light five bulbs. In the experiment a piston engine was used with 10-kW dynamo to light the bulbs. Successful results of the experiment led to the establishment of first prototype of geothermal power plant. In 1908 a small power station was installed which produced power from geothermal energy with 20-kW dynamo. The first commercial geothermal power plant capable of producing 250 kW started operating in 1913 and its energy was fed to chemical production plants [1,14]. Various achievements of 20th century regarding geothermal energy are summarized in Table 1.

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Table 1 Achievements of 20th century regarding geothermal energy. Year

Achievements

1906

Use of mechanical winches for drilling which were driven by geothermal heat Oxyacetylene welding in well castings Partly conversion of percussion into rotary system (Drilling) New type of Rigs were invented and were equipped into water circulation systems Trauzl Rigs were introduced Rotary Drilling was favored and percussion drilling abandoned Concept of space heating was introduced First commercial power plant operated Two 3.5 MW power stations were established First pilot turbine running by direct steam by wells was installed First large geothermal power plant with six 10 MW units was installed All geothermal power plants in Larderello region were bombed and destroyed due to war.

1907 1923

1929 1938–40 1845–1940 1913 1916 1923 1939 1944

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Summary

The first use of geothermal energy dates back to seventh millennium BCE in a painting that illustrates various morphological features of the volcano and its eruption. The presence of various tools made of lava and many other by-products of geothermal energy has been found on many nonvolcanic islands of Eastern Mediterranean, which indicates the utilization of geothermal energy by the ancient people of the Mediterranean. The Etruscans were pioneers of various techniques used in geothermal sector and its by-products. They developed the industry using geothermal energy and sold their products to different parts of world. The Romans started the balneological use of geothermal energy and hydrothermal deposits and built many public spas for bathing. In the Christian era small balls made of mud from hot water pools were sold, and these balls were used for healing purposes. The hydrothermal deposits excavated from the Lumaie included yellow sulfur for ointments and salves, Cyprian (green) and Roman (Red) vitriol (FeS04.7H2 O) used by pharmacies, alum and nitro volterrano which may be boric acid. In the 18th century, boric acid was produced by evaporating boric waters at thermal manifestations sites. Covered lagoons were introduced to increase production rates. In the 19th century, companies started digging geothermal wells for the production of boric acid by evaporating geothermal fluids. At first wells were 10 cm in diameter and 8 m deep. With improvements in drilling technology, geothermal wells could be dug up to 300 m at the end of 19th century. Geothermal power production started in the beginning of 20th century. Steam engines and dynamos were used to produce power.

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Many geothermal power stations were installed in the first half of 20th century, and the total power production by geothermal energy was about 900 MW until 1944. During the World War II, almost all geothermal power plants in Larderello region were bombed and destroyed.

References [1] P. Burgassi, R. Cataldi, Historical outline of geothermal technology in the Larderello region, 16 (3) (1987) 3–18. [2] R. Cataldi, Review of historiographic aspects of geothermal energy in the Mediterranean and Mesoamerican areas prior to the Modern Age, vol. 15, 1993. no. 1. [3] R. Cataldi, P. Chiellini, Geothermal energy in the Mediterranean area before the Middle Ages, in: Proceedings, 1995, pp. 373–380. [4] R. Cataldi, 11 Geothermal energy in the Mediterranean before the middle ages, a review, 1999. [5] J.M. Cook, Flames Over Atlantis-JV Luce: The End of Atlantis: New Light on an Old Legend, Thames and Hudson, London, 1969. Cloth, 63s, vol. 20, no. 2, pp. 224–225, 20 text-figs, 56 black and white plates, 8 col. plates, 1970. [6] F.H.J.A. Stubbings, JV Luce: The End of Atlantis: New Light on an Old Legend (New Aspects of Antiquity series.), Thames and Hudson, London, 1969, p. 303. inc. 64 pp. pls.(8 in colour). 63s," vol. 43, no. 172, pp. 324–326, 1969. [7] J. Mellaart, A Neolithic Town in Anatolia, Thames & Hudson, 1967. [8] M. Balter, The Goddess and the Bull: C ¸ atalh€oy€uk: An Archaeological Journey to the Dawn of Civilization, Routledge, 2016. [9] K. Lomas, (G.) Nenci and (G.) Vallet Bibliografia topografica della colonizzazione greca in Italia e nelle isole tirreniche. 8. Siti: Gargara-Lentini. Pisa: Scuola Normale Superiore  and Rome: Ecole Franc¸aise de Rome, 1990. Pp. xvii + 555,[94] maps and plans. Price not stated, vol. 112, 1992, pp. 221–222. [10] M. Pallottino, Etruscologia, Hoepli Editore, 1984. [11] N.M. Pasquinucci, Terme romane e vita quotidiana, 1987. [12] P.B.-R.C.-C. Donati, Scientific investigations and technological development in the Larderello region from XVI through XIX centuries, in: Proceedings of the World Geothermal Congress, 1995, pp. 433–440. [13] A. Greenberg, From Alchemy to Chemistry in Picture and Story, John Wiley & Sons, 2006. [14] P. Burgassi, Historical Outline of Geothermal Technology in the Larderello Region to the Middle of the 20th Century, 1999, pp. 195–219. [15] R. d’Arezzo, Della composizione del mondo di Ristoro d’Arezzo testo italiano del 1282 gia` pubblicato da Enrico Narducci ed ora in piu` comoda forma ridotto (Biblioteca rara vol. 54), G. Daelli, 1864. [16] P. Burgassi, Energia geotermica nelle colline metallifere, vol. 25, 1983, pp. 135–140. [17] M. Durand-Delga, E. Pandeli, G.J.G.A. Bertini, Le champ geothermique de Larderello (Toscane, Italie): situation geologique, utilisations industrelles, vol. 77, r^ ole de la famille de Larderel, 2001, pp. 9–21. [18] E. Barbier, Electricity from geothermal energy: 88 years of production, in: Renewable Energy, Technology and the Environment, Pergamon, 1992, pp. 2297–2305.

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[19] P.D. Burgassi, A. Bettini, Le manifestazioni geotermiche naturali nei comuni di Montieri e Radicondoli, 2011. [20] P. Mascagni, Ed., P. Siena, “Dei lagoni del senese e del volterrano,” 1779. [21] G.T. Tozzetti, Relazioni d’alcuni viaggi fatti in diverse parti della Toscana, per osservare le produzioni naturali, e gli antichi monumenti di essa, Stamperia imperiale, 1751. [22] R. Burgassi, P.J.I.M. Burgassi, I soffioni boraciferi della Toscana e le originali industrie a cui hanno dato luogo, vol. 2, 1981, pp. 13–23. [23] G. Celato, Per i rapporti di Camillo Pellegrino con il mondo culturale romano, 2019, pp. 293–312. [24] A. d’Achiardi, Bibliografia mineralogica, geologica e paleontologica della Toscana, Tipografia Barbe`ra, 1875. [25] G. Meneghini, Sulla produzione dell’acido borico dei conti de Larderel relazione, Tip. Nistri, 1867. [26] T. Boyns, F.J.A.H.R. Cerbioni, Accounting and performance monitoring in Tuscany, Larderello 29 (2) (1836–1858) 243–267. 2019. [27] B. Lotti, Sulla provenienza dell’acido Borico: nei soffioni della Toscana, G. Candeletti, 1907. [28] B. Lotti, I soffioni boraciferi della Toscana, vol. 47, Bollettino della Societa Geologica Italiana, 1928. [29] E. Repetti, Notizie e guida di Firenze e de’suoi contorni, G. Piatti, 1841. [30] R. Nasini, I soffioni ei lagoni della Toscana e la industria boracifera: storia, studi, ricerche chimiche e chimico-fisiche eseguite principalmente nell’ultimo venticinquennio, Tip. editrice Italia, 1930. [31] G. Terme, Montaione Montespertoli, 2012, p. 404. [32] R. Grassini, Sulla scoperta dell’acido borico nei vasi sigillati Aretini, Typographie Classique, 1932. [33] E. Fiumi, L’utilizzazione dei lagoni boraciferi della Toscana nell’industria medievale, [Casa Editrice del Dott. Carlo] Cya, 1943.

Fundamentals of geothermal energy extraction

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Hamdy Hassana,b a Energy Resources Engineering Department, Egypt-Japan University of Science and Technology (E-JUST), Alexandria, Egypt, bMechanical Engineering Department, Faculty of Engineering, Assiut University, Assiut, Egypt

1

Introduction

The word geothermal is derived from the Greek words geo (meaning Earth) and thermal (meaning heat). However, the term “geothermal energy” denotes the harnessing of heat or energy from underground resources ranging from the shallow subsurface to reservoirs of water, hot steam, and rock deep beneath the Earth. Geothermal energy (GE) is an original benign environmental resource of renewable energy contained in the interior of the Earth [1], which is generally associated with tectonic and volcanic activities. The geothermal heat is mainly stored in the hot rocks at higher depths from the surface of the Earth. Geothermal heat also exits at high temperatures in complicated structures of hydrothermal reservoirs [2,3]. Many scientists agree that geothermal energy is considered renewable energy resource. But, the speed of geothermal reservoir exploitation is generally quicker than the substitute of its heat depending on geothermal applications, geologic time scale, and ways of heat reinjection [4]. Techniques of using GE depend mainly on distributions of local heat. The parameters that have the greatest impact of using GE are availability, steam or water temperatures, and GE reservoir porosity and permeability. Geothermal sources of energy applications could be generally classified into three types: direct heating, power generation, and cooling and heating. The use of the GE by different techniques depends mainly on the GE source temperature [5]. Geothermal source of energy as an energy resource has different advantages as follows [6]: l

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Indigenous energy: it aids in the reduction of the dependence on fossil fuels. Clean energy: it aids in the reduction of combustion emissions from traditional and nonclean fuels. Variety of utilization: it can be utilized for heating and cooling, ground-coupled heat pumps, or power generation. Long-term energy resource: with an optimal development plan, geothermal energy can fill the requirements for more than 30–50 years. Flexible and variable system sizing: space heating systems based on geothermal energy vary from 30 kW to several megawatts. Also, power generation stations can vary from 200 kW to the maximum of 1200 MW as the geothermal power planet installed in Geysers in California, United States. Modularity: it can be utilized in simple small multiple easily transportable modules.

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Geothermal power stations’ longevity: they are designed for long life spans of 20–30 years. With the right geothermal resource management, its life span could exceed design values. High availability: availability of about 95%–99% is common for modern geothermal power plants compared to about 80%–85% of traditional plants. Combined utilization: geothermal plants could be utilized for electricity generation in addition to direct-use applications that result in cost savings and higher thermal efficiencies. Lower costs: annual electrical power cost is approximately 5%–8% of the capital cost which is about the same as the conventional plants. The recent cost of power generation from typical geothermal planet ranges from 0.05$ to 0.08$/kWh, which is competitive compared with conventional sources in some quarters of the world.

However, there are different parameters that in some cases limit the projects relied on geothermal energy to be commercially viable and influence the initial project costs which are l

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2

Geothermal source temperature: valuable geothermal temperatures varieties from 100°C for geothermal heat pumps to higher than 3000°C for power generation. Overall, the higher the temperature, the lower the cost for generating power. Rate of energy production: the value of power that can be economically generated from geothermal depends on the flow rate, fluid temperature, and the energy conversion technique. The useful energy extracted per well can range from lower values of kilowatts for shallow wells with low temperatures to higher values of megawatts for highly deep productive wells with high temperatures. Use factors: due to the substantial capital investment in power generation and drilling, power plants relying on geothermal energy are best suitable for baseload applications which usually supply higher economic incomes than applications with low use factors, as peaking plants. Well Depth: The deeper the geothermal well, the higher it costs. But sometimes wells having a depth of 3000 m could be drilled economically when it provides energy production at high rates. Energy transportation: Generated power could be transported over long distances. Therefore, geothermal power plants can serve distant customers. Extracted geothermal hot water could be transported through reasonable distances (normally 1–2 km, however up to 50 km if the transportation system capacity is very big), relying on terrain conditions, geothermal resource temperatures, and local climatic conditions. However, geothermal steam must be utilized in a short distance within 1–2 km of the production wells.

Geophysics of the Earth’s regions

The composition and structure of the Earth as shown in Fig. 1 is composed mainly of the core, the mantle, and the crust. Around the Earth, there are the mesosphere, asthenosphere, lithosphere, troposphere, stratosphere, mesosphere, exosphere, and ionosphere. The crust constitutes less than 1% of the Earth’s mass, which comprises the oceanic and the continental crust and it is more frequently found as felsic rock. Besides, the hot mantle represents approximately 68% of the Earth’s mass. Lastly, the Earth’s core, mostly composed of iron metal, constitutes about 31% of the Earth’s mass. The lithosphere is constructed from the crust and the upper mantle portion that acts as rigid and brittle solid. Whereas, the

Fundamentals of geothermal energy extraction

13

Fig. 1 Composition of the Earth [7].

asthenosphere is partly molten superior mantle layer material that acts like plastic and is able to flow [7].

2.1 Core The Earth’s core, found at the center of the planet is of high-density metallic material. Researchers discovered that the core is made up of metal for various causes. The density of the Earth’s surface layers is much less than the general planet density which is estimated from the rotation of the planet. If the density of individual Earth’s surface layers is less than the average value, then the interior layer of the Earth has a higher density than the average value. Estimations specify that the core density is approximately 85% iron and the remaining 15% is nickel. In addition, metallic meteorites show characteristics of the Earth’s core. If the Earth’s core was nonmetallic, the planet would not possess a magnetic field. Hence, metals such as iron, which is highly magnetic, are the constituent material in it. However, the rock, which constructs the crust and mantle regions, is not metals. Additionally, researchers discovered that the outer core of Earth is liquid, and its inner core is solid due to that S-waves stop at the interior core. The stronger magnetic field is aroused by convection currents in the Earth’s liquid exterior core. These currents are due to even heat from the Earth’s hotter interior core. The heat that retains the Earth’s exterior core from solidifying is formed by the breakdown of radioactive components in the interior core. The solid region is found at the center of the Earth’s interior core. Around the interior earth, the core is a solid zone where the pressure and temperature are accordingly balanced that the iron becomes molten and is found as a liquid. This is the Earth’s exterior core. The difference between the interior and exterior cores is not based on the structures (the structures are supposed to be the same). However, the difference happens in the physical states of the two cores: one is liquid and the other is solid.

14

Utilization of Thermal Potential of Abandoned Wells

2.2 Crust The crust layer that is the thinnest and most elementary layer comprises the Earth. It is a dynamic structure and one of the layers that constructs our pale blue dot. It is denoted as the chemical layer that has variable chemical compositions. It has two main types namely continental crust and oceanic crust, which are dissimilar from each other. The differences are because of plate tectonics, which then denotes plates and the movement of these plates up the asthenosphere, driving lithospheric processes including the formation and induction of natural phenomena such as ridges and earthquakes. Earth’s crust is one of the five chemical layers of the Earth and it is differentiated to display the diverse chemical properties happening at each layer. Earth’s crust with the superior mantle layer has its essential role in the dynamic destruction and creation of the crustal surface on which all living organisms thrive on. The Earth’s crust rocks can be classified into three main types. Sedimentary rocks: they are formed from the chemical precipitation, lithification of sediments, or by direct biogenic deposition. Some common types are shale, sandstone, coal, coral, and limestone. Igneous rocks: they are cool from magma. The two common types are basalt and granite. Metamorphic rocks: they have been changed by high temperatures, pressures, and/or chemical reaction when it is still in the solid state. The two known types are slate that originates from shale and marble that originates from limestone.

2.3 Mantle The mantle is formed from hot solid rock. Scientists discovered that it is formed from solid rock grounding on the proof from heat flow, seismic activity (waves), and meteorites. The mantle’s properties fit the ultramafic peridotite rock that is composed of magnesium-rich silicate and iron minerals. Peridotite seldom exits on the surface of the Earth. Moreover, scientists discovered that the region of the mantle is very hot due to heat flow outgoing from this region and due to the mantle’s physical properties. The heat flows from the mantle region in two different methods inside the Earth: convection and conduction. Heat transfer by conduction happens through vast collisions of atoms, solid material. The mantle region is mostly hot because of heat conducted from the Earth’s core. The heat convective process in the mantle region is similar to the convection heat transfer in a jar of water on the stove. Convectional flow within the Earth’s mantle region forms as material beneath the core heats up. For instance, when the lowest layer of the mantle region’s material is heated by the core, particles flow more rapidly, reducing the mantle density and making it go up. The increase of material starts the convection flow. As hot material arrives at the surface, it then expands horizontally. It, thereafter, cools down since it is now farther from the core. The material is ultimately enough dense as it cools to descend to the mantle. At the bottommost of this mantle region, the material spreads horizontally and then Earth’s core heats it. When it arrives back at that location where the hot material of mantle goes up, the convective cell of the mantle is completed.

Fundamentals of geothermal energy extraction

15

2.4 Mesosphere The strength of solid material is measured by both pressure and temperature. When a solid material is heated, it loses some of its strength. However, it gains strength when it is compressed. The differences in pressure and temperature divide the crust and mantle into three strength regions. In the inferior region of the mantle, there is a highly compressed rock that has substantial strength despite its temperature is very high hence, it is a solid region having high temperatures. However, also reasonably high strength is found within the mantle region from the core-mantle boundary (at about 2883 km depth) to a depth of approximately 350 km which is called the mesosphere.

2.5 Asthenosphere In the uppermost mantle layer, from 350 km to between 100 and 200 km under the Earth’s surface, is a region named the asthenosphere (“weak sphere”). In this region, the balance of pressure and temperature is such that the occurring rocks have petite strength. Instead of being as strong as the rocks in the mesosphere layer, the asthenosphere rocks layers are easily deformed and are as weak, as warm tar or butter. Geologists asserted that asthenosphere and mesosphere compositions are similar, while the dissimilarity between them is their strength.

2.6 Lithosphere Outside the asthenosphere occurs the outermost strength region, another section where rocks are stronger, cooler, and firmer than those found in the plastic asthenosphere. This hard outer region, including the uppermost mantle layer and all of the crust layer, is named the lithosphere (“rock sphere”). It is essentially noted that despite the reality that the mantle and crust regions differ in construction, it is only the rock strength, not rock composition, that distinguishes the asthenosphere from the lithosphere. The dissimilarity in the strength between rocks in the lithosphere and those in the asthenosphere is a function of pressure and temperature. At a pressure found at a depth of 100 km and temperature 1300°C, rocks of all types lose hardness and become readily deformable. This is the lithosphere-base beside the oceans, or as it is utmost termed the oceanic lithosphere. The continental lithosphere base is about 200 km deep.

2.7 Troposphere This is the lowermost layer of the atmosphere. Beginning at ground level, the troposphere prolongs upward to around 10 km above sea level. Animals and human beings live in this troposphere zone, and approximately all weather happens in this lowest layer. Moreover, the majority of clouds form in the troposphere layer, essentially due to 99% of the water vapor which is found in this troposphere layer. Temperatures get colder and air pressure drops when we go higher in this zone.

16

Utilization of Thermal Potential of Abandoned Wells

2.8 Stratosphere The following layer up is named the stratosphere. This layer extends from the troposphere’s top to approximately 50 km above the ground. Within the stratosphere, the infamous ozone layer exists. Ozone molecules in this layer absorb high-energy ultraviolet light from the sun, transforming the ultraviolet energy to heat. The stratosphere essentially gets warmer as one goes higher, unlike the troposphere. That tendency of increasing temperatures with altitude signifies that the air in this layer lacks the updrafts and turbulence of the beneath troposphere.

2.9 Mesosphere The mesosphere is located above the stratosphere. It prolongs upward to a height of around 85 km up our planet. Majority of meteors burn up in this layer. Temperatures become colder as we move up the mesosphere, unlike the stratosphere. The coldest temperature in the Earth’s atmosphere is around
90°C and is found beneath the top of this mesosphere layer. The mesosphere air is also way too thin to breathe. Moreover, the pressure of the air at the bottom of the mesosphere layer is well under 1% of the sea level pressure and it continues to decrease when you go up.

2.10 Thermosphere The thermosphere is the layer of very rare air found above the mesosphere. Ultraviolet radiation from the sun and high-energy X-rays are absorbed in this layer, increasing its temperature to 100 or at times 1000°C. However, the air in the thermosphere layer is very thin so much so that it will feel freezing cold to human beings. In many ways, this layer is taken more as outer space than a portion of the atmosphere zone. Many satellites orbit the Earth within this layer. Differences in the magnitude of the energy coming from the sun exert a powerful influence on both the temperature within this layer and that of its top. Due to this, the thermosphere’s top can be anywhere between 500 and 1000 km above the ground. Temperatures can vary from around 500°C to 2000°C or higher in the upper thermosphere. The Southern Lights, the Northern Lights, and the aurora occur in this layer.

2.11 Exosphere Despite some scientists considering the thermosphere layer to be the uppermost atmospheric layer, other experts consider this layer to be the real “final frontier” of the gaseous envelope of the Earth. It might be imagined that the “air” in this layer is extremely thin making the exosphere layer even greater space than the thermosphere. In reality, however, the air in this exosphere layer is very gradually but constantly “leaking” out of the atmosphere of the Earth into outer space. Various definitions put the top of this exosphere layer somewhere between about 100,000 and 190,000 km up the Earth’s surface. The latter value is nearby halfway to the Moon.

Fundamentals of geothermal energy extraction

17

2.12 Ionosphere The ionosphere layer is not as distinct as the other layers stated above. The ionosphere layer is instead a series of regions in parts of the thermosphere and mesosphere where high-energy radiation from the sun has knocked electrons loose from their parent molecules and atoms. The electrically charged molecules and atoms that are formed in this way are named ions, hence the name ionosphere and the special properties that are endowed in this zone.

3

Sources of Earth’s internal energy

Most of the Earth’s interior energy is created approximately 4.5 billion years ago when our planet was formed. Other planets and the Earth in the solar system first started to take form as smaller countless bodies collided and clumped together. The energy of the violent collisions was converted to heat energy. As the initial Earth grew larger, gravity started pulling substance to the center. The intense material compression deep inside the Earth augmented inner heat even further. As soon as temperatures were high enough, the element iron started to melt and go down to the Earth’s center, and less dense materials went up toward the Earth’s surface. The iron friction moving down through the other materials creates more heat. Layers were created inside the Earth as denser material went down: A core is primarily formed of iron, the smaller dense mantle, and even smaller dense crust. Meanwhile its creation, the Earth was losing heat energy to space. Some elements, recognized as radioactive elements as uranium, potassium, and thorium, break down through a procedure recognized as radioactive decay and discharge energy. This radioactive decay in the Earth’s mantle and crust adds heat continuously and reduces the Earth’s cooling. After 4.5 billion years, the Earth inside is still very hot (in the core, about 3800– 6000°C), and with the experience phenomena created by this heat energy including volcanoes, earthquakes, and mountain building. The composition of the different temperatures of Earth layers is illustrated in Fig. 2. Though Earth’s interior heat is the energy resource for processes such as plate tectonics and portions of the rock cycle, it supplies only a portion of a percent to the average atmospheric temperature of the Earth. Generally, the Earth’s interior participates heat energy to the atmosphere at a rate of around 0.05 W/m2; however, incoming solar energy radiation adds approximately 341.3 W/m2.

4

Classes of global geothermal regions

1. Normal: Temperature gradient less than 40°C per kilometer. These regions are accompanied by the average conductive heat energy flow of geothermal at 0.06 W/m2. It is doubtful that these areas are always able to provide geothermal energy at reasonable prices to the present renewable energy supplies. 2. Semithermal: Temperature gradient varies from 40°C to 80°C per kilometer. In these regions, there are accompanying anomalies far away from the boundaries of the plate. Heat

18

Utilization of Thermal Potential of Abandoned Wells

Crust 1-100 km thick

Lithosphere (crust uppermost solid mantle) Upper mantle 2,000°C Lower mantle 3,800°C

Athenosphere

Mantle 2,900 km

Crust

Liquid Outer core

5,100 km

Solid

Inner core

Outer core 3,800°C Inner core 6,000°C (11,000 °F)

Not to scale 6,378 km To scale

Fig. 2 Composition of the Earth’s heat energy. is extracted from fracturing dry rock or through harnessing natural aquifers. A well-known example of a district heating system is the geothermal system for heating houses located in Paris. 3. Hyperthermal: The temperature gradient is more than 80°C per kilometer. These regions are normally on the boundaries of the tectonic plate.

5

Harvesting the geothermal heat

1. Natural hydrothermal circulation, a technique in which water is percolated to deep hot aquifers that are heated to hot water, mix of vapor/liquid, or dry steam, is one way of harvesting geothermal heat. 2. Hot igneous systems are accompanied by heat produced from semimolten magma which solidifies to lava. The first geothermal power plant that used this geothermal energy resource was a 3-MW station located in Hawaii that is finalized in 1982. 3. Dry rock fracturing. A low conductive dry rock (e.g., granite) reserves up heat energy with a consequent temperature rise over millions of years. Artificial fracturing from boreholes assists water to be injected through the rock, Hence, (in principle) the heat energy is extracted.

5.1 Heat extracted from dry rock Assume that the geothermal heat energy is stored in a large quantity of dry hot material starting from the surface of the Earth and prolonging inside the Earth’s crust as stated in Fig. 3. Assume that the temperature through the Earth’s depth varies linearly with

Fundamentals of geothermal energy extraction

19

Fig. 3 Rock region temperature.

the Earth’s depth from the surface of the Earth. Then, the temperature distribution through the Earth’s depth is governed by [8,9] dT z dz

T ¼ Ts +

(1)

where dT dz is the temperature gradient through the Earth’s depth z and Ts is the Earth’s surface temperature. By applying Eq. (1) on the minimum temperature at level zl, it is found that Tl ¼ Ts +

dT zl dz

(2)

Then, the temperature gradient G ¼ dT dz , is determined by G¼

Tl
Ts zl

(3)

The thermal energy stored dE inside an Earth element dz at a depth z is governed by dE ¼ ρr Acr GT

(4)

where A represents the cross-sectional area of the geothermal well in m2, cr is the specific heat of the hot rock in J/kg K, and ρr is the rock density in kg/m3. Then, the useful thermal energy stored E inside the Earth’s region from the depth zl of the temperature Tl to the depth zh of the temperature Th is governed by Z

zh

E¼

ρr Acr dzT

zl

From Eqs. (3) and (5), the thermal energy stored E is governed by

(5)

20

Utilization of Thermal Potential of Abandoned Wells

Z

zh

E¼

ρr Acr ðTs + GzÞdz ¼

zl

ρr Acr ðzh
zl Þ2 2

(6)

If it assumed that the rocks thermal stored heat is extracted by a constant volume flow 

rate of water of V , then the spent time τ in extracting the stored thermal energy is governed by ρr Acr ðzh
zl Þ τ¼ 2 V ρw c w 

(7)

5.2 Heat extracted from the hot aquifer Within a hot aquifer system, the heat source is found in a layer of water deep within the ground as shown in Fig. 4. If it is assumed that, the aquifer thickness (h) is very much less compared to the depth (zq) below the ground level, and that therefore, all the water is uniformly at temperature Tq. The porosity, p0 , is the portion of the aquifer comprising water, proposing the remaining space to be the rock of density ρr. The minimum useful temperature is Tq. The characteristics of the geothermal resource are estimated equally to those of dry rock [8]. The difference between the properties of the hot water inside the aquifer compared with the hot rock discussed previously is that the thermal properties of the hot water include the properties of a porous material of the hot water and the hot rocks. Then, the specific heat Cq of the hot porous media inside the aquifer is governed by [10] Cq ¼ Ah½ρr ð1
φÞcr + ρw φcw  Hence the stored energy inside the aquifer is governed by

Fig. 4 Hot water inside aquifer.

(8)

Fundamentals of geothermal energy extraction

E¼

Acq 2 h 2

21

(9)

Therefore, the time required to extract this stored heat energy is calculated by Acq h τ¼ 2 V ρw c w 

6

(10)

Geothermal heat extraction techniques

The geothermal energy heat is extracted mostly by pumping out hot water from the deep subsoil and a heat exchanger is used to extract the heat. After that, the cooled water will be pumped back to the Earth and ultimately heats up again due to the heat energy in the Earth. Therefore, a geothermal installation composes of at minimum two geothermal wells, one for the yield of hot water which is the production well while the other well is for injection of the cooled water which is called the injection well. It is noted that the distance between the two wells is around 1–2 km in the deep subsoil, and hence they are partially drilled at an angle. However, some geothermal sources do not include sufficient fluid and they are dry and, hence, water should be injected at various spaces into the Earth’s geothermal heat formation (Fig. 5). The gain of the injected water is heated from the formed rock and after that be yielded from the other wells. Approximately 50% of the injected water in the well is lost to the formation, and hence, the water lost will be added to the price of the produced energy. In an area without access to purified water, heat extraction could not be economic due to these expenses. Another technique of geothermal heat extraction is the closed-loop circuit extraction heat with zero withdrawal mass. The essential idea behind this technique is pumping a working fluid of low boiling in a closed loop instead of producing geofluid as shown in Fig. 6. The working fluid, as an example, isopentane, is preferred to have a smaller boiling temperature compared with water for the similar pressure, which yields a more thermal efficiency. From another point of view, in the previous closed-loop technique, transfer of heat from the geothermal heat source to the fluid is mainly limited to conduction due to that the fluid formation does not have a sensible movement in the wellbore vicinity; hence the transfer of heat will be essentially restricted to the surface of the well. To reduce this drawback, fractures hydraulically could be placed in different stages in every well. But instead of yielding fluid from these induced fractures, they are filled with high conductive materials as high conductive cement or metal particles in the proppants form. A schematic image of this technique for vertical wellbore is illustrated in Fig. 7. Hence, the technology for injecting particles within fracturing fluids is already accessible for formations of fracturing shale gas, therefore it does not need additional

22

Utilization of Thermal Potential of Abandoned Wells

Fig. 5 Typical injection and production heat extraction technique [11].

investment to create new pumping units or equipment. The producing fracture network places the wellbore casing in contact with a higher volume of bedrock. Furthermore, a horizontal well with many fractures can be utilized to raise the rate of heat production with greater surface contact area within the formation as stated in Fig. 8. Highly conductive fractures increase formation-wellbore contact surface for

Fundamentals of geothermal energy extraction

23

Fig. 6 Closed-loop circuit extraction heat with zero withdrawal mass [11].

Fig. 7 A wellbore coupled to a double-wing fracture propped and filled with proppants [11].

24

Utilization of Thermal Potential of Abandoned Wells

Fig. 8 Horizontal wellbore with several fractures propped proppants [11].

manifolds. Therefore, these filled fractures supply a shortcut pathway for the heat to be transported to the wellbore, or in other meaning, the reservoir’s greater volume remains in connection with the wellbore. Fluid productivity is continuously associated with sand yield in soft unconsolidated formations. Furthermore, in formations soft, sustaining induced fractures to stand a high enough yield rate is very complex, however, the cement filled fractures reinforce in some way formations soft and stop possible deformations produced by the thermal stresses.

7

Applications of geothermal energy

The extracted geothermal energy can be used in different applications as electricity generation, solar water heating, building heating and cooling, and many other applications depending on the geothermal energy source temperature and properties. Fig. 9 illustrates the different applications of the geothermal energy source for the different available source temperatures and depths. As an example, electricity productivity will possibly be desirable if the temperature of the geothermal source is greater than 300°C, and it may be unattractive if the geothermal source temperature is lesser than 150°C. However, when the geothermal energy is lesser than 100°C, it is used for heating applications, and so the utilization of the available GE as heat is effective, even though when the geothermal source is not “high enough” for power generation. It is known that the efficiency of the electricity generation reduces by reducing the temperature of the geothermal source and by increasing the geothermal well depth.

Fig. 9 Geothermal heat energy applications.

26

Utilization of Thermal Potential of Abandoned Wells

7.1 Geothermal power generation Power generation based on available geothermal heat energy needs source temperatures greater than approximately 150°C. GE is a consistent and reliable resource of heat energy with an average availability of the system of 95% unlike intermittent power sources such as wind and solar. Geothermal power generations are classified into three main categories, namely, direct steam, flash plants, and binary plants. Direct steam power plants need geothermal resources at very high temperatures greater than 235°C. These kinds of plants are both the most and rarest valuable due to what they have entry to such high geothermal temperatures. The GE plants utilize steam of high temperature from the productive wells that are 1 km to 2.5 miles deep inside the Earth. The produced steam is processed in these systems so that nonessential fluids and particulates are detached and therefore, it is piped to run turbines that produce electricity. Power plants of flash steam type are more commercial and need geothermal resource temperatures varying from 150°C to 370°C. These geothermal power planets principally utilize highly pressurized hot water that is transferred to the surface through production wells arriving 2.5 miles depth. This extracted water pressure is decreased through transportation, a portion of the water explosively boils “flashes” to steam, and after that this generated steam is moved to generate electricity in the turbine, while water that is not flashed into steam is returned to the hot water reservoir to fix productivity and pressure. One of the applications of geothermal energy in power generation is Huka geothermal power station commissioned in 2010 in New Zealand. Huka geothermal station gives nearly 28 MW to the general grid. Besides, the Huka power station generates electricity throughout a binary cycle (organic Rankine cycle). It was the first station that was built on the Tauhara geothermal steam. The geothermal power station of Te Huka, which is known as Tauhara station is located in New Zealand near Taupo. It is run by fluid and steam from field of Tauhara steam, and all its utilized geothermal fluid is at some point which is reinjected back to the edge of the steam field. The plant is connected via 33 kV line to Transpower’s and injects its output electricity to both the national grid and Unison’s Taupo distribution network (Fig. 10).

7.2 Geothermal direct heating Even in spaces with GE resources that are inadequate for electricity and power generation, such geothermal resources can also be utilized for applications in heating and supplying heating requirements. Direct heating using of geothermal heat includes using low-to-moderate geothermal temperature resources (20–150°C) to supply heat to a wide diversity of residential, industrial, commercial applications, etc. Direct geothermal heating can provide cost savings up to 80% over traditional fossil fuels and oils. Examples of geothermal direct heating include [12]: l

l

l

l

l

Greenhouse heating Space and district heating (e.g., homes, offices) Ground source heating and cooling Crop drying Snow melting (e.g., melting snow on sidewalks)

Fundamentals of geothermal energy extraction

27

Fig. 10 Huka geothermal power station. l

l

l

Aquacultural heating Industrial process heat (e.g., food processing) Others

Fig. 11 illustrates the worldwide utilization of geothermal energy indirect heating for different applications from the year 2015 till the year 2020 in TJ per year.

TJ/Yr 600,000 550,000

1. Geothermal Heat Pumps 2. Bathing &Swimming 3. Space Heating 4. Greenhouse Heating 5. Aqua culture Pond Heating 6. Industrial

500,000 450,000 400,000 350,000

2020 2015 2010 2005 2000 1995

300,000 250,000 200,000 150,000 100,000 50,000 0 1

2

3

4

5

6

Fig. 11 Worldwide direct use of geothermal energy in TJ/yr from 1995 to 2020 [13].

28

Utilization of Thermal Potential of Abandoned Wells

7.2.1 Greenhouse heating GE can be an economical energy supply, covering requirements of greenhouse heating through the year, and only a few cold days will use fossil fuel, oil, or similar traditional energy resources to supply the necessary heating requirements. Geothermal energy has been verified to be very useful for agriculture requirements heating and other related activities. It is found that worldwide utilization of GE for ground and greenhouses heating raised by about 19% in constructed capacity and about 16% in yearly energy utilization. The leading countries in geothermal annual energy utilization in greenhouse heating are China, Turkey, Hungary, Russia, and the Netherlands.

7.2.2 Space and district heating The heating of residential structures and individual commercial from a downhole heat exchanger or pumped well is by far the simplest type of direct heating of geothermal. In the pumped well case, the hot water of geothermal sources is pumped to the structure from the well where a heat exchanger transports the heat energy from the geothermal hot source to the in-building system as stated in Fig. 12 [8]. The geothermal used hot water is then disposed to the surface or injected into the aquifer by an injection well. The utilization of geothermal heat resources for direct space heating governs the direct utilization industry with about 37% of all direct utilization development. In reality, the initial known commercial utilization of geothermal heat energy was constructed in Chaudes-Aigues Cantal, France, which was constructed in the 14th century. Despite geothermal resources temperatures in surplus of 50°C are generally advised for space heating, but resources as low as 40°C could be utilized in certain space heating requirements and circumstances. Moreover, if geothermal heat pumps are comprised, space heating will be a valuable substitute to other types of area heating at temperatures under 10°C. Elghamry and Hassan [5,14,15] experimentally utilized the geothermal energy system shown in Fig. 13 for cooling and ventilation of a room building during the summer times and also in heating and ventilation in wintertimes. During, summer, the soil Heat exchanger

From production well

Peaking backup unit

User apartment

To injection well

Geothermal reservoir

Geothermal reservoir water Working fluid

Fig. 12 Space and district heating [8].

Fundamentals of geothermal energy extraction

rg

y

e En

rc

a ol

S

hi

(in si

m

S

de )

ey

m

PV

r

a ol

29

Computer Data Logger

2m

Thermocouples

0.

7

m

2m

0.5 m

1.5 1.5 m m

PV

(o

ut

si d

e)

Room

Geothermal tube

Fig. 13 Utilization of GE in building cooling and ventilation [14].

temperature occurs lower than the ambient, such that the ambient air is dragged by utilizing the chimney impact in the geothermal tube where it is cooled before entering the building room. Contrarily through the wintertime, the cold ambient air is heated before entering the room building by the hot soil. At the measured climate conditions of Alexandria, Egypt, they reached during a summertime an increase of the room temperature of 3.5°C and changed the room diurnal air 42 times. Moreover, the lowest of the ventilated air occurs in a natural geothermal tube-chimney system with an angle of 30 degrees. However, during summertimes, a natural geothermal tube-solar chimney system of angle 45 degrees raised the room temperature by 6.4°C while its diurnal air was changed 46 times, which represented 55.5% of the ventilated air through forced airflow at 0.0184 m3/s.

7.2.3 Ground source heating and cooling It is unfortunate that there is limited potential for geothermal systems’ utilization for direct use applications and power generation due to low heat-flow temperatures. However, geothermal heat technologies can also be efficiently utilized through other means. The most practical method of accessing geothermal energy resources in the United States is by the use of geothermal heat pumps (GHPs). A GHP transfers free cooling and heating from within the ground to adjust the internal air temperature in a

30

Utilization of Thermal Potential of Abandoned Wells

building. The utilization of ground source HPs has varied the economic norms. The Earth’s heat is the source of heat for the heating or/and the sink of heat for cooling in this case, depending on the climate conditions. This GHP’s utilization makes it possible for people all over the world to use the Earth’s energy sources for cooling or/and heating applications. It should be stated that HPs can be utilized essentially anywhere. Chief among the merits of using GHPs is that the resource is only a few meters from the surface of the Earth, and the temperature of the ground remains reasonably constant (10–15°C), while, that of the surface can change significantly. A sensibly stable ground temperature signifies that GHPs can be constructed from anywhere in the United States, attaining efficiencies of 300%–600% during hot summers and cold winters. These system efficiency levels are several times more than found in other applied heating systems. In the winter season, GHPs work by using the geothermal temperature warmer than the air above the ground to be used in for heating buildings; however, in the summer season, the opposite is utilized for cooling buildings where the heat from the air in the building is removed and is taken down into the cooler Earth. Essentially, the ground is used as a heat sink through hot summer seasons and during the cold winter seasons as a heat source. Air conditioning (space cooling and heating) is utilized in different states starting with Bulgaria and followed by Brazil, Albania, Slovenia, Australia, India, and Algeria.

7.2.4 Crop drying Air in the drying process has different functions as drying fluid, such as porting the heat required for moisture evaporation, transportation of the evaporated water to the exterior of the plant and then, upon completion of the drying process, it works as the coolant to the dried product. The warm air temperature has a limit value dependent on the products that are to be dried. Temperatures higher than the optimal in the drying process may cause chemical and physical damage to the crop and product. Industrial drying techniques consume electricity and heat to drive the attaching equipment. Essential energy needs are associated with the heating of the crop and product to an appropriate temperature which in turn initiates and supports the evaporation process (of the crop moisture) until a certain percentage of crop moisture is achieved. Hence, geothermal resources of low temperature can be used as energy sources to heat up the air for agricultural products drying. Applications for geothermal drying of fruits and vegetables rise from year to year; some drying applications apply for cereals, onions, wheat, meat, coconut, etc., from different world regions.

7.2.5 Snow melting Comprehensive winter maintenance is an important aspect to ensure desired mobility on the roads. Traffic obstructions due to ice and snow may also constrain the utilization of emergency and maintenance vehicles. Subsequently, the length and number of the hold-ups would rise as opposed to the intended reduction instead. The icing problem may even lead to an increased frequency of vehicle breakdowns. Geothermally heated external surfaces normally rely on hydronic heat exchanger fixings in

Fundamentals of geothermal energy extraction

31

the road pavement. The constructed heating capacity will depend on the system’s specifications and climatic conditions of the area. Melting of snow requires higher operating temperatures compared to the prevention of ice and snow formation. However, lower operating temperatures require a proactive system control. Argentina and Iceland have snow melting of sidewalks, roads, and streets in some places, where about 2.5 million square meters of the area is unfrozen. Iceland also primes other countries in terms of geothermal ice and snow-melting applications. These applications are also available on sidewalks and in the streets of Japan, Slovenia, and the United States and to limited places in Norway and Poland which all add to the list with Iceland and Argentina.

7.2.6 Aquacultural heating In aquaculture, the goal is to heat water to the optimal temperature for aquatic species. Aquaculture involves a controlled environment of the nurturing of marine organisms to improve their productivity rates. Different biological organisms arrive the sexual maturity in different durations, weeks to months below controlled environmental conditions. In 2010, a total of 22 countries stated geothermal utilization in aquaculture. The United States, China, Iceland, Israel, and Italy were the leading countries. There are approximately 70 fish farms in Iceland, of which 15–20 utilize geothermally heated water.

7.2.7 Industrial process heat Several countries have applications of geothermal energy in this category. The industrial operations often tend to be sizeable with high-energy demand and also often operating year-round. Examples of such include pasteurization of milk, concrete curing, leather processing/tannery, pulp and paper processing, CO2 extraction, carbonated drink production, bottling of water, extraction of salt and iodine, and finally boric and borate acid production. The leading countries in geothermal energy usage (TJ/yr) are China, Iceland, New Zealand, Hungary, and Russia, which account for nearly 98% of the world’s geothermal energy use in industrial processes.

7.2.8 Other uses Besides the previously illustrated applications of geothermal heating, there are many other geothermal heating applications, which incorporate animal husbandry, spirulina cultivation, desalination, and sterilization of bottles. New Zealand has the leading utilization of geothermal energy, where the energy is used in frost protection, irrigation, and for recreational purposes in the form of a geothermal tourist park, followed by Japan (with cooking as the major use), and Kenya (for boiling water). It is to be noted that direct geothermal heat is also used for bathing, swimming, process heating, and several other geothermal heat applications.

32

8

Utilization of Thermal Potential of Abandoned Wells

Conclusions

The fundamentals of geothermal energy are presented in this chapter. Geothermal energy has a number of advantages such as it is an indigenous energy, clean energy, has a variety of utilization, is a long-term energy resource, flexible and allows for variable system sizing, modularity, geothermal power stations longevity, high availability, combined utilization, and lower costs. However, some parameters may limit its use such as the geothermal source temperature, rate of energy production, energy transportation, and use factors. The Earth is made up of different layers which include the core, crust, mantle, mesosphere, asthenosphere, lithosphere, troposphere, stratosphere, mesosphere, thermosphere, exosphere, and ionosphere. It is within some of these layers that geothermal resources are found. Global geothermal regions are classified into normal, semithermal, and hyperthermal. The energy sources inside the Earth include hot rocks and porous media of hot liquid with hot rocks. There are several techniques that can be used to extract geothermal heat energy such as injecting water inside the geothermal hot well, closed-loop circuit extraction of heat with zero mass withdrawal, using a wellbore coupled to a double-wing fracture that is filled and propped with proppants, and use of a horizontal well with several fractures propped with proppants. Geothermal heat energy can be utilized in many other different applications than just electricity generation. For high-temperature geothermal sources such as geothermal heat pumps, uses may include space heating/district heating, aquacultural heating, agro-drying, greenhouse heating, industrial processes heating, bathing, and/or swimming, cooling, and snow melting among others.

References [1] J.W. Tester, S.L. Milora, Geothermal Energy as a Source of Electric Power Thermodynamics and Economic Design Criteria, Amazon, 1976. [2] M. Bauer, W. Freeden, Handbuch Tiefe Geothermie, 2014, https://doi.org/10.1007/978-3642-54511-5. [3] S.Y. Yang, H. Der Yeh, Modeling heat extraction from hot dry rock in a multi-well system, Appl. Therm. Eng. 29 (8–9) (2009) 1676–1681, https://doi.org/10.1016/j.applthermaleng. 2008.07.020. Elsevier Ltd. [4] G.W. Braun, H.K. Pete Mccluer, Geothermal power generation in United States, Proc. IEEE 81 (3) (1993) 434–448, https://doi.org/10.1109/5.241485. [5] R. Elghamry, H. Hassan, Impact a combination of geothermal and solar energy systems on building ventilation, heating and output power: experimental study, Renew. Energy (2020), https://doi.org/10.1016/j.renene.2020.01.107. Elsevier B.V. [6] Advanced Technology Group, Geothermal Energy for Power Generation, 2021, Available at: https://geothermalcommunities.eu/assets/elearning/7.21.geothermalscan.pdf. [7] S. Earle, Physical Geography: 5.3: The Composition and Structure of Earth, Lumen, 2021. Available at: https://geo.libretexts.org/@go/page/12745. [8] G. O’Brien, N. Pearsall, P. O’Keefe, Renewable energy resources, in: The Future of Energy Use, 2020, https://doi.org/10.4324/9781849774819-14. [9] E. Huenges, Geothermal Energy Systems, Expolration, Devleompent and Utlization, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2010.

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[10] H. Hassan, S. Harmand, 3D transient model of vapour chamber: effect of nanofluids on its performance, Appl. Therm. Eng. 51 (1–2) (2013) 1191–1201, https://doi.org/10.1016/ j.applthermaleng.2012.10.047. Elsevier Ltd. [11] A. Dahi Taleghani, An improved closed-loop heat extraction method from geothermal resources, J. Energy Resour. Technol. 135 (4) (2013) 1–7, https://doi.org/10.1115/ 1.4023175. [12] I. Dincer, M. Ozturk, Geothermal energy utilization, in: Geothermal Energy Systems, 2021, pp. 85–136, https://doi.org/10.1016/b978-0-12-820775-8.00003-9. [13] J.W. Lund, A.N. Toth, Direct utilization of geothermal energy 2020 worldwide review, Geothermics 90 (November) (2021), https://doi.org/10.1016/j.geothermics.2020.101915. [14] R. Elghamry, H. Hassan, An experimental work on the impact of new combinations of solar chimney, photovoltaic and geothermal air tube on building cooling and ventilation, Sol. Energy 205 (May) (2020) 142–153, https://doi.org/10.1016/j.solener.2020.05.049. Elsevier. [15] R. Elghamry, H. Hassan, Experimental investigation of building heating and ventilation by using Trombe wall coupled with renewable energy system under semi-arid climate conditions, Sol. Energy 201 (December 2019) (2020) 63–74, https://doi.org/10.1016/ j.solener.2020.02.087. Elsevier.

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Optimal simulation of design and operation of geothermal systems

3

Mikhail Yu. Filimonova,b and Nataliia A. Vaganovaa,b a Ural Federal University, Yekaterinburg, Russia, bKrasovskii Institute of Mathematics and Mechanics UrB RAS, Yekaterinburg, Russia

1

Introduction

The last decades in human history have been characterized by a significant acceleration in the use of renewable energy sources as the era of cheap traditional energy sources has ended [1]. A large role in the preference for energy sources such as geothermal energy is also associated with rising prices for fossil fuels, as well as emissions of harmful gases and the greenhouse effect [2–6]. Unlike solar or wind energy, which creates interruptions in production during cloudy or calm weather, the heat of the Earth can be used constantly. The total Earth’s flow of heat (conduction, radiation, and convection) is estimated as 42
1012 W and 8
1012 W [7]. The Earth contains enormous thermal energy, but only geothermal resources can be used by humanity with the help of geothermal systems. Geothermal systems are systems that use the Earth as a heater and are of two main types [8]. Geothermal systems of the first type are closed-loop geothermal systems that deal with fluid circulating in pipes through the ground and back through a heat pump. Geothermal systems of the second type are open-circuit geothermal systems that use a water pump to supply water and return the used water back to the geothermal reservoirs (GR). For today, the geothermal system may serve for thermal energy delivery from the deep layers of the earth [2,3,5,9–13] and is a production facility, which uses a geothermal reservoir (aquifer) as a geological element. This system is considered throughout the whole service life with changing characteristics during operation. The temperature of the GR is an important parameter of the water utilization. For example, in Russia many regions have low-temperature and medium-temperature (50–150°C) GR, lying at the depth of 200–3000 m. In the central part of Iran, the Mahallat Geothermal Region is known as one of the largest low-temperature geothermal fields, at about 90°C [14]. The low-enthalpy geothermal system of Pismanta, in the Central Andes of Argentina, is operated with a geothermal reservoir with a temperature of 95°C [15]. Thermal energy may be used in different ways in view of the temperature of the fluid. It may produce electricity by steam machines with overheated (more than 150°C) water. In general, such GR are located in areas with seismic events or Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00003-8 Copyright © 2022 Elsevier Inc. All rights reserved.

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Utilization of Thermal Potential of Abandoned Wells

volcanism. Temperatures from 50°C to 150°C can be used for various industrial processes or for heating residential buildings or greenhouses. Water with lower temperatures may be heated by pumps to increase the temperature. Let us consider an open geothermal loop with PW and IW. The wells are drilled directly to the aquifer and equipped with indoor pumps. The hot water from PW is used and returned to the aquifer [16]. This method allows keeping the water layers filled. The effectiveness of the open geothermal loop system may be estimated by the time when the produced water is hot enough. To estimate the lifetime of the system, it is necessary to describe cold-water filtration in GR from the IW to the PW. The wells in the open-loop system may be grouped or arranged in different ways. For example, in the Paris countryside, there are 37 pairs (doublets) of wells that, due to geothermal sources, supply more than 0.5 million people and enterprises with heat and hot water for more than 30 years [17]. The optimization of multiple-doublet layout can improve energy recovery in GR [18,19]. The paper [20] provides an overview of the literature on the relationship between geothermal energy for power generation and sustainable development, as well as an overview of currently available sustainability assessment systems. Many countries are developing different methods of using geothermal energy [21]. Long-term prediction of the performance of a geothermal heat exchanger can improve the efficiency of geothermal systems [22,23]. A review of the study of existing methodologies and practices for resource assessment in quantifying the energy potential of geothermal fields is contained in Ciriaco et al. [24]. Quantifying the parameters of GR is a challenging task; therefore, various approaches are being developed to solve this problem Liu et al. [25]. Mathematical modeling methods for sustainable development of geothermal energy, along with methods of exploration for geothermal resources [26] and the use of machine learning methods [27–29], are important. In Refs. [16,30,31], a model of an open geothermal system with multiple wells is considered. The presented model considers the parameters of the characteristics of the geothermal reservoir, i.e., the soil, the location of the wells, and their most significant technical parameters. The space between the wells in an open geothermal system and the pressure drop are the main parameters of a doublet, which is a system of two wells [32]. To solve the described problems in a complex three-dimensional area for a long period of time, significant computing resources are required. The computation time for one variant can often exceed several hours of computer time on a supercomputer since it is necessary to consider a large computational area and a detailed computational grid [33,34]. To describe the functioning of the geothermal cyclic system (GCS), a threedimensional model is proposed, based on the work on underground hydrodynamics of fluid flow in porous soil [35], but considering the geothermal flow. Heat transfer in such a system is described in two processes: convective and diffusion. For the design and operation of the GCS, a new three-dimensional nonstationary mathematical model has been developed that considers the most important parameters of wells and a geothermal reservoir. The algorithms and programs developed based on this model describe the processes of heat transfer and filtration of water in a thermal reservoir, considering Darcy’s law and the law of conservation of mass, which in the

Optimal simulation of design and operation of geothermal systems

37

general case form a system of equations for finding the pressure distribution and the filtration velocity field. For the numerical implementation of the described model, a technology was developed for constructing grids with millions of nodes and an algorithm for their thickening in a three-dimensional region with a complex geometry that arises after considering the structural and geometric features of the GCS and the lithological structure of the GR. The numerical methodology was based on the ideas used in authors’ works. The results of numerical calculations based on data from a specific geothermal field in Russia in the North Caucasus are presented. Computer modeling of various options for placing wells in the GCS has been performed to increase the lifetime of such systems (there are options for such well arrangements in which the life of the GCS is practically unlimited). In particular, taking into account the seasonal decrease in the demand for hot water in the summer from production wells also makes it possible to increase the lifetime of the GCS, since due to a decrease in the pressure drop between the wells, the filtration rate of cold-water pumped into injection wells also decreases. The introduction of seasonal consumption of hot water in a particular one depends on the geographic characteristics of the region and on the purposes for which the GCS is used (e.g., for heating buildings).

2

Mathematical model and numerical algorithm

We will assume that the GCS consists of two wells: injection, with water temperature T1 ¼ T1(t), and production, with water temperature T2 ¼ T2(t) (T1(t) < T2(0)), t  0. Let the start of the GCS operation be t ¼ 0. Heat transfer in the GCS is described by two processes: convective and diffusion. To provide the convective method and select a mathematical model, consider the equation of fluid motion in porous soil. In general, an aquifer should be considered with the surroundings such as waterproof layers, underground creeks or lakes; however, it is sufficient to investigate the porous productive layer properties (Fig. 1). In Fig. 1 are the following notations: R1(R2) is the upper (bottom) waterproof layer, Ω is a geothermal reservoir area, bounded by surfaces S1 and S2; P1 ¼ P1(t) (P2 ¼ P2(t)) is the reservoir pressure at the bottom of the injection (production) well with the pumps running; a is the space between production and injection wells; T ¼ T(t,x,y,z) is the temperature at time t at a point (x,y,z) Ω; Γ 1, Γ 2 are geothermal flows on the upper (z ¼ Z1) and lower (z ¼ Z2) surfaces, respectively, typical for the given area. Let us consider a geothermal reservoir (productive layer), which is a porous soil layer in which water moves from an injection well to a production well by the flow created by the pressure gap in the pumps available in these wells. Note that the temperature of the investigated area is often determined by geographic location as well as the geothermal gradient. The average temperature increase with depth is 2.5–3°C for every 100 m (the average heat flux is 0.03–0.05 W/m2). The effectiveness of geothermal systems is largely dependent on the magnitude of the geothermal gradient. Areas with a high value of this gradient (usual areas with high seismic activity) are more

38

Utilization of Thermal Potential of Abandoned Wells

W2

W1 G1

G2

Fig. 1 A vertical slice of an aquifer with injection and producing wells.

promising for the development of geothermal energy. However, old and quiet mountainous regions also provide a sufficient level of geothermal energy. The water flow in the productive layer Ω is described by the Navier–Stokes equations, which are simplified for underground hydrodynamics [35]. It is assumed that the components of the fluid velocity V ¼ (u,v,w) and the derivatives with respect to the spatial (x, y, z) are small quantities. In this case, we get the system. ∂u 1 ∂p gσu ∂v 1 ∂p gσv ∂w 1 ∂p gσw ¼  , ¼  , ¼  g ∂t ρ ∂x k ∂t ρ ∂y k ∂t ρ ∂z k

(1)

where ϭ and k are porosity in the aquifer and average filtration coefficient, p ¼ p(t,x,y,z) is the pressure, and g is the standard gravity. We assume the fluid in the aquifer is at rest at the initial time moment, i.e., uð0, x, y, zÞ ¼ vð0, x, y, zÞ ¼ wð0, x, y, zÞ ¼ 0:

(2)

Under the assumption that the quadratic terms are sufficiently small, system (1) results from the Navier–Stokes equations and this linearization is justified in PolubarinovaCochina [35].

Optimal simulation of design and operation of geothermal systems

39

Fig. 2 A scheme of two-wells (doublet) geothermal open-loop system.

Let us suppose the porous layer Ω (Fig. 2) is included between two waterproof layers at the horizontal planes z ¼ Z1 and z ¼ Z2 (the floor and the ceiling). We set the boundary conditions at these planes as ∂p ∂p ¼ ¼ 0: ∂z z¼Z1 ∂z z¼Z2

(3)

The lateral vertical slices of the computational domain (the walls) give the similar conditions: ∂p ∂p ¼ ¼ 0: ∂x x¼X1 ∂x x¼X2

(4)

The wells are the vertical cylinders noted by γ 1 and γ 2. The surface of the production (injection) well has the radius r1(r2). On these surfaces, we set the hydrostatic pressure and the pressures of indoor pumps Pðt, x, y, zÞjγ 1 ¼ P1  ρgz, Pðt, x, y, zÞjγ 2 ¼ P2  ρgz:

(5)

In the productive layer, we have the hydrostatic pressure, which is considered as an initial pressure P(0,x,y,z) in the aquifer: Pð0, x, y, zÞ ¼ ρgz:

(6)

The heat transfer in the GR is described by convection and diffusion. In the computational domain Ω for the pressure of the water in the porous layer p(t,x,y,z), we consider the piezoconductivity equation [36,37] ∂p ¼ ωΔp, ∂t

(7)

40

Utilization of Thermal Potential of Abandoned Wells

where ω is a piezoconductivity coefficient. System (1), Eq. (7), conditions (2), (3)–(6) should be considered together. The solution of the problems (1)–(7) generates the pressure field in the aquifer Ω and in the following the pressure in the productive layer is used to get the velocity field (u,v,w). The pressure p(t,x,y,z) is found by an iterative method. The equation for the temperature T ¼ T(t,x,y,z) in the aquifer Ω has the form [35,38].   ∂T ∂T ∂T ∂T +b u + v + w ¼ λ0 ΔT: ∂t ∂x ∂y ∂z

(8)

The components of the fluid filtration velocity V ¼ (u, v, w) are found from Eqs. (1) σρcf κ0 and (2) and, λ0 ¼ ρ c0 ð1σ Þ + ρcf σ , b ¼ ρ0 c0 ð1σ Þ + ρcf σ , where ρ0(ρ) is the soil(water) density 0 in the aquifer, c0(cf) is the specific heat of the soil(water), σ is porosity, and κ0 is the heat conductivity of the soil. The GR has an initial temperature T ð0, x, y, zÞ ¼ T0 ðx, y, zÞ:

(9)

On the surfaces γ ,1 and γ 2 of the injection Ω1 and production Ω2 wells, the temperature is T ðt, x, y, zÞjγ i ¼ Ti ,i ¼ 1, 2:

(10)

The temperature Т 1 ¼ Т 0(x,y,z). The temperature in the production well T2(t) will be obtained as the result of numerical calculations and its value will be influenced by the temperature of the injected fluid. Geothermal heat flow is given on the planes z ¼ Zj, (j ¼ 1,2) ∂T ¼ Γ j , j ¼ 1, 2: ∂z z¼Zj

(11)

The following conditions are set on the lateral boundaries: ∂T ∂T ¼ ¼ 0, j ¼ 1, 2: ∂x x¼Xj ∂y y¼Yj

(12)

Thus, to find the temperature T ¼ T(t,x,y,z) at any point in the geothermal reservoir, it is required to solve Eq. (8) with conditions (9)–(12). The following basic parameters of optimization are suggested to be considered: the distance between the wells and the pressure of indoor pumps. As a rule, the time period of GCS exploitation is supposed as 30 years or more. The producing temperatures have to be high enough during the life period of GCS. The indicated economic needs must be satisfied, which should be ensured by choosing the parameters of the GCS, and at the same time, it is necessary to ensure the longest period of effective

Optimal simulation of design and operation of geothermal systems

41

operation of this system [30,31,39,40]. These parameters of the GCS are determined during numerical calculations to determine the water temperature in the production well. Problem (1)–(12) in GR is solved by the finite difference method based on the approach of works [41,42] using the method of splitting in spatial variables. An orthogonal computational grid to solve the problems (1)–(12) is used, which is thickened near the wells [32,43,44]. The computational domain Ω should be chosen large enough to avoid artificial influence of the lateral boundary conditions. The general scheme of the numerical algorithm is as follows: first, the pressure is found by the settling method, and then the velocity field in the productive layer Ω. The results of such calculations for one of the typical options are presented in Figs. 3 and 4 in the plane (x,y) after 5 years of operation of the GCS. After obtaining the velocity field, we solve problems (8)–(12) [16,32,38,40,45,46]. The GCS can consist of several wells. Fig. 5 shows the scheme of the GCS operation, consisting of two IWs (blue) and one PW (red). Fig. 6 shows the different ways of filtering water (the streamlines in a horizontal plane) in the GR depending on the location of the wells.

Fig. 3 Reservoir pressure field for two wells.

42

Utilization of Thermal Potential of Abandoned Wells

Fig. 4 Velocity field in the GR.

W

Fig. 5 Geothermal open-loop system with 2 IWs and 1 PW.

Fig. 6 The streamlines of the water filtration from the IW to the producing well in the GR.

Optimal simulation of design and operation of geothermal systems

3

43

Numerical simulation of GCS exploitation

Let a computational domain be a parallelepiped Ω with the injection and producing wells. We choose the box 6000 m
6000 m
50 m. The reservoir parameters correspond to geothermal stations of the North Caucasus. The soil thermal parameters are given from Hankal GR in the North Caucasus. The aquifer is supposed at the depth of 950–1000 m, and the temperature is 95°C, while the temperature of the injected water is 55°C. The following parameters are used in the calculations: seam thickness is 50 m; porosity ratio is 24.1% (average); filtration coefficient is 1.41–2.3 m/day; velocity of filtration is 1.7
105 m/s; piezo conductivity coefficient is (2.5–4.75)
105 m2/day; water conductivity coefficient is 59.2–135.0 m2/day; permeability is up to 2.8
10–12 m2; permeability is 1.04–2.85 Darcy parallel to sandstone bedding; 1.24–4.18 Darcy perpendicular; coefficient of thermal conductivity of sandstone is 2.06–2.6 W/m K; thermal conductivity coefficient of clay (boundary layers) is 1.23–1.7 W/m K. Radii of the wells are 0.12 m. The numerical solution of the problem (1)–(12) is based on the splitting method by the spatial variables. The numerical solution of the problems (1)–(12) is based on the splitting method by the spatial variables. A rectilinear grid condensing in the wells zones is constructed. A finite difference with an implicit central-difference upwind scheme and a three-point sweep pattern are used. The filtration processes are slow and may be considered in a quasi-steady-state approach, so we use a sequence of steps: pressure calculation (steady-state)—velocity field (steady-state)—temperature changes. We can use the pressure and the temperature fields in the aquifer, and the average temperature in the production well for different time moments to describe the results. Fig. 7 shows the temperature field [solution of problem (1)–(12)] in a geothermal reservoir Ω for GCS of two wells (Fig. 2) in a horizontal plane after 5 years of operation (Fig. 7A) and after 30 years (Fig. 7B). The distance between the wells is 800 m (a ¼ 800). Consider this GCS with parameters from Table 1.

Fig. 7 The temperature field in a geothermal reservoir.

44

Utilization of Thermal Potential of Abandoned Wells

Table 1 Pressure in the injection and production wells. Number of variants

P1 (injection well pressure), kPa

P2 (production well pressure), kPa

The indoor pumps pressure difference, kPa

Var 1 Var 2 Var 3 Var 4 Var 5

200 230 250 250 275

170 190 170 210 195

370 420 420 460 470

95 94 93 92 91

T

90 89 88 87 86 85 84 83 82 81 80 79 78

Var 1 Var 2 Var 3 Var 4 Var 5

0

5

10

15

20

25

30

35

40

45

50

55

Years Fig. 8 Profile of the average temperature in the production well.

Fig. 8 shows the dynamics of temperature changes in the production well for various options for the operation of the GCS, depending on the pressure drop between the wells (Var 1–Var 5). The size of the numerical grid is 201
201
51 ¼ 22,060,451 nodes, the time step in numerical calculations is 86,400 s (1 day). In Fig. 9 we also consider the distance between two wells. The injection well is the Points 1. Distance between the injection and production wells is 500 and 1000 m in Fig. 9A and B, respectively. The pressure difference at the wells is 2400 and 1200 kPa. The blue spot of cold water reached the closer well and the temperature of producing water is 75°C. If the pump pressure is less, the produced temperature also changes. However, the distance between the wells seems to be more effective rather than the pressure reduction for the GCS lifetime. Fig. 9C shows the profiles of changes of temperature in the producing well during 15 years of exploitation of the geothermal system.

Optimal simulation of design and operation of geothermal systems

45

Fig. 9 Horizontal slice of the temperature field in 15th year of exploitation (A and B).

4

Different seasonal regimes

Approaches of optimization and the facilities lifetime increasing are actual problems. The distance and arrangement of the wells are considered, as a rule, at the design stage. The option of the hot water utilization is the debit of the water, which is regulated by the indoor pumps of the wells. Let us consider the GCS with the given parameters of the productive layer. We will also consider various options for operating such a system in the warm period of the year (the summer) and the cold period (the winter) when the demand for hot water is different. It is reasonable to assume that such an approach for the considering operation of geothermal systems with a decrease in the demand for hot water in summer will increase the lifetime τ of the GCS [46]. Figs. 10A and B and 11A and B show the temperature in the production well for various variants of the GCS operation in the summer, in which the demand for hot water decreases. In Figs. 10 and 11, the following designations are used for summer (S) and winter (W): SJ/WI, where J(I) is the number of months in the summer

46

Utilization of Thermal Potential of Abandoned Wells

Fig. 10 Temperature during GCS exploitation with 75% (A) and 50% (B) decreasing power in the summer season.

Fig. 11 Temperature during GCS exploitation with 25% (A) and 0.01% (B) decreasing of power during the warm season.

(winter) season. For example, S6/W6 means 6 months is the warm season and 6 months is the cold season. In summer, the capacity of the GCS is reduced by a certain percentage of the power of the GCS in the cold season. Temperature changes in the production well show that considering the seasonal decrease in hot water production in summer helps to extend the lifetime of the GCS. This effect can significantly increase the cost savings and efficiency of the GCS use. To assess the construction of the GCS, it is necessary to consider not only the technical characteristics of the wells and the GR but also the possibility of using various modes of hot water.

Optimal simulation of design and operation of geothermal systems

5

47

Multiple productive well systems

It is possible to get not only one point of that produces hot water, and we should also take into account the arrangement of the wells. Now we will consider GCS including several PW and IW, which may deliver hot water from the GR or may pump the waste cold water into the GR (e.g., Fig. 12A and B). The pressure in the injection well is 1200 kPa, in the PW is 300 kPa. For this case, the temperature fields are shown in Fig. 13.

6

Two injection well systems

Let us consider the GCS [16] with two IWs (Points 1, 2) and one PC (Point 3). The distance between these points is 500 m. The temperature fields are presented in Fig. 14A (symmetrical case). The pump pressure in well 3 is 1200 kPa and in wells 1 and 2 it is 600 kPa. For the case shown in Fig. 14B the IW 1 does not influence the PW. This case better conserves the temperature in the aquifer. In Fig. 14B, wells 1 and 2 are located on the left side of well 3 (nonsymmetric case). The temperature change in well 3 over 15 years of operation of geothermal systems for two options for the location of injection wells 1 and 2, Fig. 14A (blue line) and B (red line) is shown in Fig. 14C. The nonsymmetrical case allows for a higher water temperature in the production well 3.

7

Multiple injection well systems

In the case of a multiple injection well system, the pressure of the injecting pumps may be distributed to return the waste cold water. Fig. 15 shows various options for the location of the wells in the GCS. The space between PW and IW of 500 m (variant Na) and

Fig. 12 GCS with one injection well and several PW: (A) symmetrical case, (B) asymmetrical case.

Utilization of Thermal Potential of Abandoned Wells y

48

T 95 90 85 80 75 70 65 60 55

y 3500

10 years

3000

2500

3000

3500

4000

x

T 95 90 85 80 75 70 65 60 55

3500

20 years

20 years

3000

2500

2000

nonsymmetrical case

2500

y

symmetrical case

3000

2000

3500

2500

3000

3500

4000

x

2500

2000

2500

3000

3500

4000

x

y

10 years

T 95 90 85 80 75 70 65 60 55

T 95 90 85 80 75 70 65 60 55

3500

3000

2500

2000

2500

3000

3500

4000

x

Fig. 13 Temperature fields in the (x, y)-plane for GCSs for 10 and 20 years of operation.

700 m (variant Nb), N ¼ 1,2,3,4. In Fig. 15 the blue and red points correspond to the positions of injection well and PW, respectively. The PW is in the center of the area. The pressure in the PW will be proposed as 1200 kPa and will be distributed between the IWs. Fig. 16 shows the pressure fields in the (x,y) plane for Variants 1a, 1b, 2a, and 2b. In Fig. 17 the pressure fields in the (x,y) plane are shown for Variants 3a, 3b, 4a, and 4b. The pressure fields allow estimating the zones of influence of the pumps. In the case of two wells the pressure interference in the aquifer is more massive (Fig. 16); for 5 and 9 wells system it is more localized (Figs. 17 and 18). Fig. 18 shows pressure fields in the horizontal plane for variant 8. Figs. 19 and 20 show the thermal fields for 25 years of modeling. Cold spots around IWs depend on the pressure in the IWs and PW. In the case of the GCS consisting of three wells, the injection of cold water into the GR is more intensive comparing with the nine wells system (Fig. 21). Fig. 22 shows the dynamics of temperature change in the production well over 25 years of operation of the GCS consisting of a different number of wells: with two (Fig. 22A), three (Fig. 22B), and four wells (Fig. 22C). If we consider a geothermal system of nine wells (eight IWs and one PW in Fig. 22D, green line) in

Optimal simulation of design and operation of geothermal systems

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comparison with the geothermal system of five wells (Fig. 22D, blue and red lines), it turns out that the lower cold-water pressure in the IWs gives a higher temperature in the PW.

8

Future prospects

For modeling open loop geothermal systems in the future, it is planned to consider the perforated injecting parts of the wells that may be located in the productive layer (geothermal reservoir) not necessarily perpendicular to the boundaries. It should also be considered that the perforated parts of the wells can only partially be immersed in the productive layer. These assumptions will allow simulating the operation of the GCS more accurately.

Fig. 15 The variants of the location of the wells in GCS. 2 WELLS 9.1712E+06 9.0712E+06 8.9712E+06 8.8712E+06 8.7712E+06 8.6712E+06 8.5712E+06 8.4712E+06 8.3712E+06 8.2712E+06 8.1712E+06 8.0712E+06 7.9712E+06 7.8712E+06

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Fig. 18 Pressure distribution in GSC with 9 wells in the (x, y) plane.

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9

Utilization of Thermal Potential of Abandoned Wells

Conclusions

A 3D model of an open geothermal cyclic system (GCS) is considered. The investigations deal with the system of the producing and injection wells drilled into an aquifer and considering the filtration of the water in the porous soil as a result of the impact of the pressure of the indoor pumps in the production and injection wells. The space between these wells and their location are also very important and influence the producing temperature of the water and the lifetime of the system. Numerical simulations showed that if the cold utilized water is pumped into the productive layer with slower pressure and the wells are spaced in the system layout to reheat the water, then the produced temperature is provided, and the GCS is more effective. The preferable strategy in GCS exploitation seems to be choosing appropriate modes of exploitation. In particular, due to the seasonal changes in need of hot water during the warm or the cold period of a year, it is possible to elongate the lifetime of the GCS. Therefore, designing and justification of GCS effectiveness are based not only on the technical parameters of the wells, pumps, and the thermal reservoir but also on the rationale for using strategy of the GCS exploitation. Numerical simulations allow the creation of a model of real GCS systems and to estimate the different parameters and modes to choose the optimal.

Conflicts of interest The authors declare no conflict of interest.

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Part II Abandoned wells and its global thermal potential

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Harvesting geothermal energy from mature oil reservoirs using downhole thermoelectric generation technology

4

Xingru Wu and Kai Wang The University of Oklahoma, Sarkeys Energy Center, Norman, OK, United States

1

Executive summary

At temperatures 50°C or above, thermal energy stored in a hydrocarbon reservoir is enormous. This thermal energy is currently wasted at rates of million BTU from any hydrocarbon producing well at 100 barrels per day or more. To enhance the revenue from an oil field, operators have been searching for options to recover the thermal energy from oil fields. Geothermal energy production from oil fields can benefit the oil field by offsetting the operation expenditure and extending the oil well’s economic life span, especially the mature wells with high water cuts. Even though many advantages are obvious, the choices are often limited because technical requirements for these choices disqualify most oil wells. This chapter presents a technology for power generation by harvesting the thermal energy from an oil well using downhole thermoelectric generation (TEG) devices. This could enable aging oil wells to produce electric power with no further footprint on the surface by using thermoelectric technology. In this chapter, we present how to retrofit, both horizontal and vertical wells for power generation using the TEG devices. This technology can also be applied to thousands of stripper wells producing less than 100 STB/D of liquid. Subsequently, we learn the current status of producing thermal energy from hydrocarbon fields. Then the mechanism of TEG technology and material selection protocols will be discussed with well designs and configurations of TEG for vertical and horizontal wells.

2

Review of geothermal energy development in oil fields

Geothermal energy is renewable and sustainable energy featuring operational reliability and environmental friendliness [1]. For decades geothermal energy was mainly utilized in regions with a high geothermal gradient with intense volcanic or hydrothermal activities such as the Geysers in the United States and Iceland in Europe. However, the development of geothermal energy is hindered by risky and costly geothermal drilling operations and low power generation efficiency. Geothermal formations are usually hot, hard, abrasive, highly fractured, and underpressured, which leads to frequent Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00004-X Copyright © 2022 Elsevier Inc. All rights reserved.

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severe drilling problems, reduced drilling efficiency, and increased drilling cost. Typically, the drilling cost of a traditional geothermal well could run as high as 50% of the total cost [2]. It is also reported that drilling geothermal wells will be an average of 56.4 days longer than drilling comparable oil and gas wells [3]. Moreover, the energy conversion efficiency of geothermal power generation is relatively lower than other thermal power plants. The worldwide average conversion efficiency of geothermal plants is 12% lower than coal, natural gas, oil, and nuclear power stations [4]. Thermal energy in the hydrocarbon reservoir is substantial and technically ready for use [5] as there are thousands of well with bottom hole temperatures above 150°C [6]. Developing thermal energy from oil fields has several advantages over classical geothermal fields, and Wang et al. [7] detailed these advantages. In summary, for a mature hydrocarbon that has potential for thermal recovery, the protracted production history and the abundant reservoir characterization minimize the development risks, especially for subsurface ones. The additional environmental footprint of developing mature hydrocarbon reservoirs is very likely to be much smaller than that of geothermal reservoirs since many processing facilities and equipment have been installed for oil wells [8]. More importantly, developing thermal energy from a mature oil well is much more cost-effective as it saves the cost of drilling a new well, and developing thermal energy from oil reservoirs could save millions of dollars in drilling and completions alone [8]. These benefits could make the thermal development from oil reservoirs an attractive option. It is hard to ignore the fact that the large thermal energy storage in hydrocarbon fields is due to the fact that cumulative sizes of these reservoirs and the temperatures of most reservoirs are below 150°C. When the temperature is low, the energy quality is poor, and hence the recovery efficiency will be low and recovery options will be limited. Despite the large quantity of thermal energy in the oil reservoir and the advantages of developing them, the current practice of producing electric power from the thermal energy in the oil reservoirs is still in the pilot testing stage. These preliminary efforts failed to be upscaled for regional geothermal utilization. Possible reasons are multifolded [7], but the main technical reason is low heat exchange effectiveness and efficiency. There are two common ways to produce power from reservoirs. The first one is to use a binary cycle power plant, and discussion of this technology with applications is available in the literature [9–12]. For example, the Teapot Dome Oil field in Wyoming was reported to generate power using produced water at temperatures between 90.6°C and 98.9°C at a liquid production rate of 40,000 STB/D [13–15]. The main problem with this method is that it requires at least 15,000 barrels of water per day with a minimum temperature of 98.7°C on the surface for efficient and economical power generation [16,17]. This will rule out most oil reservoirs and wells. However, we cannot ignore thousands of those striper wells producing at rates below 100 STB/D or wells with temperatures less than 150°C. Another method that is often used is using a downhole flow loop by injecting water as a working fluid to extract the heat through the reservoir [18]. This method is usually used in abandoned wells using a heat exchanger system. The mechanism is based on heat conduction between formation and reservoir media [19,20]. The thermal energy

Harvesting geothermal energy from mature oil reservoirs

63

produced in this way is often used for spacing heating and other nonpower generation purposes. This method is not suitable for power generation mainly due to low efficiency and low temperature in the working fluid on the surface. The saturated formation rocks have a thermal conductivity of less than 3 J/(s -m -k) and thermal diffusion coefficient of 1 mm2/s. This means once the rock surrounding the wellbore is cooled down, it would take a long time to warm back and the heat flux conducted from the surrounding formations would be less. Some applications are available in the literature [5]. Recent research has proposed encouraging solutions to unlock the oil field geothermal potential, and here we would like to present the downhole direct power generation from a producing oil well. The thermoelectric device that is installed downhole converts the conducted thermal flux to electric power directly based on the Seebeck effect. Thermoelectric power generation is a mature technology with proven technical and economic visibility [21,22]. Secondly, it does not interfere with hydrocarbon production as the device does not contact the producing fluids. Since there is no injection into formation, little to no concern about causing seismic activities which are usually concerns for traditional injection-involved operations [23]. Furthermore, the wide temperature range could enable thousands of stripper wells to become the candidates for thermoelectric power generation.

3

Introduction of thermoelectric technology

Thermoelectric power generation converts thermal energy to electric power based on the Seebeck effect. When there is a temperature difference across a thermoelectric generator (TEG), it would generate an electric current if a loop is established [22]. The technology has been used in multiple industries to meet a wide range of power requirements [21,22,24,25]. As shown in Fig. 1, TEG consists of a series of thermoelectric modules electrically connected in series. A unit of the thermoelectric module is made of a pair of N-type and P-type thermoelectric materials. When the high temperature is applied to one side of the TEG and the other side is kept at a lower temperature, then a voltage is produced and can be modeled by V ¼ αðTH  TC Þ

(1)

where V is the voltage of the thermoelement, TH is the hot side temperature of thermoelement, TC is the cold side temperature of the thermoelement, and the α is the absolute Seebeck coefficient of the thermoelectric module. From the Seebeck effect, the electrical power is proportional to the temperature difference across the device surfaces [25]. The figure of merit (Z) is the material nature property, and it stands for the energy conversion efficiency of a material to generate electric power. It is often evaluated in terms of a dimensionless figure of merit (ZT), which is a function of temperature, Seebeck coefficient, electrical resistivity, and thermal conductivity of the thermoelectric material [26]. Mathematically it can be expressed as

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Utilization of Thermal Potential of Abandoned Wells

Fig. 1 Schematic representation of a typical TEG. Modified from G.J. Snyder, E.S. Toberer, Complex thermoelectric materials, Materials for Sustainable Energy: A Collection of Peer-Reviewed Research and Review Articles from Nature Publishing Group, 2011, pp. 101–110.

ZT ¼

α2 T α2 ðTH + TC Þ ¼ kσ 2kσ

(2)

where k is the thermal conductivity and σ is the electrical resistivity of thermoelectric material. Therefore, to maximize the dimensionless figure of merit for a given temperature system, materials with a high Seebeck coefficient and low thermal conductivity are preferred [21]. A general expression of efficiency is net power output over the total heat input. For an ideal power generation, the Carnot efficiency is the maximum efficiency possible for any power generation. From thermodynamics, we know that energy efficiency could reflect the quality of energy by the temperature. The efficiency of a TEG using thermoelectric material can be written as pffiffiffiffiffiffiffiffiffiffiffiffiffi TH  TC 1 + ZT  1 η¼ TH pffiffiffiffiffiffiffiffiffiffiffiffiffi TC 1 + ZT + TH

(3)

Eq. (3) shows that the efficiency of TEG is a function of the ratio of cold side temperature (TC) to hot side temperature (TH), and the thermoelectric material properties

Harvesting geothermal energy from mature oil reservoirs

65

40% 35%

Efficiency

30% 25% ZT=1.5

20% 15%

ZT=1

10%

ZT=0.5

5% 0% 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Tc/TH

Fig. 2 Relationships of efficiency with temperature ratio and ZT.

(the value of ZT). A graphic description of such a relationship using an example of three types of thermoelectric materials can be seen in Fig. 2. For the same temperature ratio, higher efficiency thermoelectric material (higher ZT value) could lead to higher power generation efficiency; for a given material, a lower temperature ratio will result in higher power generation efficiency. Such a relationship will help guide the design of downhole power generation to achieve optimal efficiency. By far, the most widely used thermoelectric material on the market is alloys of Bi2Te3 and Sb2Te3, which take up 19% of the entire thermoelectric materials market as shown in Fig. 3 [27]. Technically, the popularity of Bi2Te3-based alloys is due to their high performance in low to medium temperature ranges. Bi2Te3-based alloys made thermoelectric generator exhibits the highest ZT value when the temperature ranges from 0°C to 150°C [28].

8%

4%

17%

PbTe Bi2Te3 SiGe Skutterudite 19% 18% Clathrate Half heusler alloy Other emerging inorganic materials Conducting polymers CNT/graphene- polymer composite

Fig. 3 Thermoelectric materials in the current industry [27].

12%

18%

2% 2%

66

4

Utilization of Thermal Potential of Abandoned Wells

Downhole power generation in oil wells

Downhole power generation is the design of the thermoelectric generator installed in the lower part of a wellbore to convert thermal energy to electric power. Thermometric generators are exposed to the highest temperature location in a wellbore to maximize the heat extraction, and direct thermal-electricity conversion eliminates the dependence and technical constraints of a binary power plant, largely increasing the number of wells competent for thermal energy production from oil wells.

4.1 Design for a vertical well To fit the need of downhole geothermal power generation, TEGs are designed as an annual ring shape and attached to the outer surface of production tubing (Fig. 4), without any interference with fluids flow in the tubing. In a vertical well, the hot side is maintained by continuous fluid flow in the tubing. At the bottom hole of the tubing, the temperature of the hot side of the TEG device should be close to the reservoir temperature. Therefore, the design of this type of well is mainly about how to create a cold side on the TEG devices. We propose to inject working fluids that should have a high heat capacity, low viscosity for easy pumping, and no corrective effect. Freshwater treated with friction-reducing surfactants would be a good choice as a working fluid [29,30]. Fig. 5 demonstrates the schematic representation of downhole power generation design in the vertical wellbore of an actively producing well [8]. In this design, a production packer is installed at the top of the production interval to prevent the mixing of injected water and reservoir fluids. The packer should be coated to lower the heat flux from below. TEG devices are mounted on the tubing. The annulus is installed with small size tubes for cold fluid circulation. To maintain the low temperature in the tubing/casing annulus, the remaining part of the tubing without TEG encapsulation should be coated with insulation materials [31,32]. Fig. 6 shows the diagram of high temperature and low temperature across the tubing and TEG devices [8].

Tubing wall P-type thermoelectric element N-type thermoelectric element Series connection

(i)

(ii)

TEG Hot Fluid Cold Fluid

Fig. 4 Schematic representation of designed TEG installation on downhole pipes.

Harvesting geothermal energy from mature oil reservoirs

67

Tubing

Wellbore

High Temperature

Thermoelectric Generator (TEG)

Low Temperature

Packer Production Zone

Fig. 5 Schematic representation of downhole power generation in a producing well [8].

Fig. 6 Detailed drawing of TEG attached on the tubing wall [8].

N P

N P Hot fluid

TEG

Cold fluid

Tubing Wall

The power for pumping water down the annulus is not expected to be very high since the water will flow down the annulus under gravity. The power for the cold water injection mainly needs to overcome the head loss due to friction. At a low injection rate, the power is expected to be low and can be easily calculated using fundamental hydraulics.

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Utilization of Thermal Potential of Abandoned Wells

Fig. 7 Mathematical model of downhole power generation in a vertical well [8].

To evaluate the capacity and efficiency of power generation using TEG technology, Wang and Wu [8] developed mathematical models to calculate the temperature distributions of tubing and casing/tubing annulus along a vertical wellbore using the diagram as shown in Fig. 7. In the mathematical development, the following assumptions were made: (1) neglect the compressibility of fluid; (2) constant production and injection rates; (3) constant geothermal gradient; (4) steady-state temperature field in the wellbore; (5) temperature drop across both the tubing and casing walls are neglected due to high thermal conductivity of metals as well as the small thickness of the walls; (6) temperature drop across the fluid film is ignored; and (7) cold fluid injection pipe is thermally insulated. Wang and Wu [8] used reservoir and well parameters from Shengli Oil Field where the geothermal gradient is 3.5°C/100 m and the bottom hole temperature is around 120°C. The tubing is insulated with a coating with thermal conductivity of 0.068 W/(m K). The material of the TEG device was Bi2Te3 based on a dimensionless figure of merit of 0.97. Fig. 8 shows the calculated temperature distributions in tubing and the annulus. The calculated efficiency of thermal to electricity was about 4.7% with a power output of 9.8 kW. Detailed input parameters and simulation results are available in the literature for the case study [33].

4.2 Design for a horizontal well One constraint for vertical well power generation is the effective length suitable for TEG installation as the temperature gradient decreases from the bottom of the well upward. A horizontal usually has an extensive horizontal segment in the oil-bearing reservoir with the reservoir temperature for the entire length. With more than four

Harvesting geothermal energy from mature oil reservoirs

69

Temperature, ∞C 0

20

40

60

80

100

120

500

Depth, m

1000

140

Fig. 8 Temperature distribution along the wellbore in this case study. The dash lines represent the temperature profile in tubing and annuls without TEG installation, and the gap between the dashed line and full line demonstrate the temperature changes caused by the geothermal energy conversion to electricity.

1500

2000

2500

3000 Tubing

Annulus

Formation

decades of technology advancement, the horizontal well drilling and completion technologies have been increasingly more mature, and the horizontal segment length is becoming longer and longer [34,35]. Recently the horizontal extension up to 2000 m or longer is very common [36]. Since the whole horizontal segment penetrates the formation, the temperature along the wellbore is almost constant from toe to heel [34]. With the boom of unconventional reservoir development for tight formations such as shale gas formation, many horizontal wells have been drilled. The unconventional wells are usually completed with multiple stages and fluids come into the wellbore from these stages at the reservoir temperature [37]. One feature of unconventional development is the quick decline in the production rate after the well comes online, which indicates the revenue from hydrocarbon decreases. Therefore, we propose to install TEG devices on a horizontal well to capture the thermal energy and arrest the revenue decline. Fig. 8 shows the prototype of our proposed TEG installation on part of the horizontal segment as an illustration [33,38]. Different from the vertical counterpart, we propose to inject cold water through a small ID tube into the production tubing. The injected water flows out and circulates back to the surface through the annulus between the injection tube and production tubing. The tubing end should be sealed to establish U-tube flow. The TEG devices are still installed on the outside tubing wall.

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Utilization of Thermal Potential of Abandoned Wells

Casing Tubing TEG Cold Fluid

Annulus Inner pipe Hydraulic fracture Produced Fluid

Fig. 9 Schematic representation of downhole power generation in unconventional horizontal wells [38].

The hot fluids from the formation will flow out to the surface through the production tubing and production casing annulus. This design does not interfere with current production except changing the flow path of the reservoir fluid from tubing to the tubing/ casing annulus. When the injected working fluid flows back to the surface, its temperature will increase due to the heat conduction through tubing and TEG devices. The magnitude of temperature change in the production tubing/injection tube is determined by the circulation rate. At a high circulation rate, the temperature is expected to maintain low, which will yield an ideal situation for TEG power generation. Overall, the temperature profiles in the annulus of the production tubing/production casing and the annulus of production tubing/injection tube are much more complex than its counterpart in vertical wells. A numerical simulator is needed to calculate the temperature profiles and power generation. The simulation capability has been developed at the University of Oklahoma by Dr. Wu’s research group. Fig. 9 demonstrates the temperature distribution along three stages as a prototype case study [33]. In this study, the dimensionless figure of merit was determined to be 0.99, and the energy conversion efficiency was up to 7.2%. This gave the output electric power up to 128 kW (Fig. 10).

5

Summary

The huge thermal energy stored in oil and gas fields should be produced in an environmentally conscious way. Even though developing the thermal energy from oil fields has significant advantages over developing geothermal reservoirs by capitalizing on the existing infrastructure and subsurface knowledge, current extracting methods have either high rate and temperature requirements or low efficiency. To materialize the energy extraction from oil wells, even for stripper wells that produce at low rates, we proposed the TEG technology which is based on the Seebeck effect. The hypothesis of TEG technology for power generation is that the TEG technology can be applied downhole by retrofitting current oil-producing wells and generate a

Harvesting geothermal energy from mature oil reservoirs

71

Stage 2

Stage 1

Stage 3

Temperature (∞C)

180 176∞c

140

Produced Fluid Temperature TEG

100

100∞c

40∞c

60 Injected Fluid Temperature 20 3500

3600

3700 3800 Measured Depth (m)

3900

Fig. 10 Temperature of produced fluid and injected fluid in three stages showing three pairs of temperature changes, representing the decrease of produced fluid temperature and increase temperature injected fluid in three stages as circled in gray [33].

positive economic return. This hypothesis will be tested by conducting tasks including (1) the feasibility study of the proposed pilot test site and characterizing the geothermal resources, (2) designing and engineering the equipment and TEG technology to implement the test, (3) evaluating well conditions and wellbore/site workover for pilot tests, and install TEG equipment to the pilot well and commission it to work, (4) making a surveillance plan to monitor well performance and power generation, and (5) establishing an economic model to evaluate the project performance. This chapter reviewed the advantages, opportunities, and challenges of geothermal energy development from oil wells, and presented a promising solution, downhole power generation, to harvest geothermal energy from mature oil wells. Designs for vertical and horizontal wells are demonstrated with a mathematical model and case studies. Key points can be summarized as follows: l

l

l

l

The storage of thermal energy in hydrocarbon fields is large in quantity, but the quality of thermal energy is not always high due to relatively low temperatures compared with geothermal fields. Therefore, its recovery options are limited with a few demonstrated pilot tests. We proposed two prototypes of TEG configurations in the vertical and horizontal wells. These prototypes can be engineered and optimized based on temperature and rate of producing fluids, injection rate, temperature, and TEG materials. The tools for engineering and optimization are mathematical models and numerical simulation as published in the literature. Currently, these configurations are still in the design stage and need field tests to validate their economic feasibility and engineering design constraints.

References [1] X. Wu, An Investigation of Partitioning Tracers for Characterizing Geothermal Reservoirs and Predicting Enthalpy Production, University of Texas Libraries, Austin, TX, 2006. http://repositories.lib.utexas.edu/bitstream/handle/2152/2672/wud58017.pdf.

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[2] E. Barbier, Geothermal energy technology and current status: an overview, Renew. Sustain. Energy Rev. 6 (1–2) (2002) 3–65. [3] J. Tilley, J. Evans, S. Ravndal, Activated reamer at-bit system reduces rathole to 3 ft in RSS hole-enlargement applications, in: SPE/IADC Drilling Conference and Exhibition, OnePetro, 2015. [4] S.J. Zarrouk, H. Moon, Efficiency of geothermal power plants: a worldwide review, Geothermics 51 (2014) 142–153. [5] S. Wang, J. Yan, F. Li, J. Hu, K. Li, Exploitation and utilization of oilfield geothermal resources in China, Energies 9 (10) (2016) 798. [6] R. Erdlac Jr., L. Armour, R. Lee, S. Snyder, M. Sorensen, M. Matteucci, J. Horton, Ongoing resource assessment of geothermal energy from sedimentary basins in Texas, in: Proceedings of Thirty-Second Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA, 2007. [7] K. Wang, B. Yuan, G. Ji, X. Wu, A comprehensive review of geothermal energy extraction and utilization in oilfields, J. Pet. Sci. Eng. 168 (2018) 465–477. [8] K. Wang, J. Liu, X. Wu, Downhole geothermal power generation in oil and gas wells, Geothermics 76 (2018) 141–148. [9] A. Franco, M. Villani, Optimal design of binary cycle power plants for water-dominated, medium-temperature geothermal fields, Geothermics 38 (4) (2009) 379–391. [10] A.F.M. Parada, Geothermal Binary Cycle Power Plant Principles, Operation and Maintenance, Geothermal training programme, Reykjavik, 2013. [11] T.-L. Li, J.-L. Zhu, W. Zhang, Performance analysis and improvement of geothermal binary cycle power plant in oilfield, J. Cent. South Univ. 20 (2) (2013) 457–465. [12] N. Nasruddin, I.D. Saputra, T. Mentari, A. Bardow, O. Marcelina, S. Berlin, Exergy, exergoeconomic, and exergoenvironmental optimization of the geothermal binary cycle power plant at Ampallas, West Sulawesi, Indonesia, Therm. Sci. Eng. Prog. 19 (2020) 100625. [13] J. Nordquist, L. Johnson, Production of power from the co-produced water of oil wells, 3.5 years of operation, in: Geothermal Resources Council Transactions, Geothermal Resources Council 2012 Annual Meeting, 2012, pp. 207–210. [14] L. Johnson, D.L. Simon, Electrical power from an oil production waste stream, in: Proceedings of Thirty-Forth Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA, 2009. [15] M. Milliken, Geothermal resources at Naval petroleum reserve-3 (NPR-3), Wyoming, in: Proceedings of Thirty-Second Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA, 2007. [16] X. Liu, K. Gluesenkamp, A. Momen, Overview of available low-temperature, in: Coproduced Geothermal Resources in the United States and the State of the Art in Utilizing Geothermal Resources for Space Conditioning in Commercial Buildings, 2015. [17] W. Gosnold, Electric Power Generation from Low to Intermediate Temperature Resources Executive, Technical Report, 2017. [18] Y. Noorollahi, R. Saeidi, M. Mohammadi, A. Amiri, M. Hosseinzadeh, The effects of ground heat exchanger parameters changes on geothermal heat pump performance—a review, Appl. Therm. Eng. 129 (2018) 1645–1658. [19] R. Fan, Y. Jiang, Y. Yao, D. Shiming, Z. Ma, A study on the performance of a geothermal heat exchanger under coupled heat conduction and groundwater advection, Energy 32 (11) (2007) 2199–2209. [20] P. Cui, X. Li, Y. Man, Z. Fang, Heat transfer analysis of pile geothermal heat exchangers with spiral coils, Appl. Energy 88 (11) (2011) 4113–4119.

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[21] G.J. Snyder, E.S. Toberer, Complex thermoelectric materials, in: Materials for Sustainable Energy: A Collection of Peer-Reviewed Research and Review Articles from Nature Publishing Group, 2011, pp. 101–110. [22] S. Twaha, J. Zhu, Y. Yan, B. Li, A comprehensive review of thermoelectric technology: materials, applications, modelling and performance improvement, Renew. Sustain. Energy Rev. 65 (2016) 698–726. [23] M.W. Hitzman, D.D. Clarke, E. Detournay, J. Dieterich, D. Dillon, S. Green, Induced seismicity potential in energy technologies, in: GSA Meeting, 4–7 Nov 2012, Charlotte, NC, USA, 2012. [24] X. Liu, G. Falcone, C. Alimonti, A systematic study of harnessing low-temperature geothermal energy from oil and gas reservoirs, Energy 142 (2018) 346–355. [25] W. He, G. Zhang, X. Zhang, J. Ji, G. Li, X. Zhao, Recent development and application of thermoelectric generator and cooler, Appl. Energy 143 (2015) 1–25. [26] H. Ohta, S. Kim, Y. Mune, T. Mizoguchi, K. Nomura, S. Ohta, T. Nomura, Y. Nakanishi, Y. Ikuhara, M. Hirano, Giant thermoelectric Seebeck coefficient of a two-dimensional electron gas in SrTiO3, Nat. Mater. 6 (2) (2007) 129–134. [27] C. Gayner, K.K. Kar, Recent advances in thermoelectric materials, Prog. Mater. Sci. 83 (2016) 330–382. [28] F. Cheng, Y. Hong, B. Zhang, W. Tang, Experimental optimization of the area-specific power for thermoelectric modules, Spacecr. Environ. Eng. 33 (2016). [29] N. Le Brun, I. Zadrazil, L. Norman, A. Bismarck, C.N. Markides, On the drag reduction effect and shear stability of improved acrylamide copolymers for enhanced hydraulic fracturing, Chem. Eng. Sci. 146 (2016) 135–143. [30] Z.-Y. Liu, F.-J. Zhou, H.-Y. Qu, Z. Yang, Y.-S. Zou, D.-B. Wang, Impact of the microstructure of polymer drag reducer on slick-water fracturing, Geofluids 2017 (2017). [31] M.S. Al-Homoud, Performance characteristics and practical applications of common building thermal insulation materials, Build. Environ. 40 (3) (2005) 353–366. [32] P.L. Simona, P. Spiru, I.V. Ion, Increasing the energy efficiency of buildings by thermal insulation, Energy Procedia 128 (2017) 393–399. [33] K. Wang, X. Wu, Downhole thermoelectric generation in unconventional horizontal wells, Fuel 254 (2019) 115530. [34] K. Yoshioka, D. Zhu, A.D. Hill, P. Dawkrajai, L.W. Lake, A comprehensive model of temperature behavior in a horizontal well, in: SPE Annual Technical Conference and Exhibition, OnePetro, 2005. [35] J. Thompson, L. Fan, D. Grant, R.B. Martin, K.T. Kanneganti, G.J. Lindsay, An overview of horizontal-well completions in the Haynesville Shale, J. Can. Pet. Technol. 50 (06) (2011) 22–35. [36] L.K. Britt, M.B. Smith, Horizontal well completion, stimulation optimization, and risk mitigation, in: SPE Eastern Regional Meeting, OnePetro, 2009. [37] R.A. Seale, J. Donaldson, J. Athans, Multistage fracturing system: improving operational efficiency and production, in: SPE Eastern Regional Meeting, OnePetro, 2006. [38] K. Wang, X. Wu, Transient thermoelectric generation in oil wells under transient production, in: 44th Stanford Geothermal Workshop, 2019.

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A brief survey on case studies in geothermal energy extraction from abandoned wells

5

Davar Ebrahimia, Mohammad-Reza Kolahib, Mohamad-Hasan Javadia, Javad Nouralieea, and Majid Amidpourc a Renewable Energy Research Department, Niroo Research Institute (NRI), Tehran, Iran, b Energy & Environment Research Center, Niroo Research Institute (NRI), Tehran, Iran, c Faculty of Mechanical Engineering, Department of Energy System Engineering, K.N. Toosi University of Technology, Tehran, Iran

1

Introduction

Geothermal energy is a renewable resource stored in subsurface layers, and its power increases by depth. In spite of the other renewables, the weather conditions and geographical location cannot restrict its advantages, which make it more reliable. Geothermal energy utilization has increased in recent decades to reduce greenhouse emissions and global warming impacts [1]. Therefore, it can play an essential role in global electricity generation by the equity of approximately 3.5% in 2050 [2]. Geothermal resources are categorized based on temperature (or enthalpy) into hightemperature (>150°C), intermediate-temperature (90–150°C), and low-temperature (30–90°C) reservoirs to indicate the power of geothermal resources and their applications [3]. There are two methods of geothermal utilization: direct and indirect, which depend on the temperature of resources. However, electricity generation by binary and steam power plants are considered conventional utilization methods for high-temperature resources located near volcanoes in general [4]. Recently, organic Rankine cycles (ORCs) have provided power generation for low-temperature reservoirs which are more available globally, and where the typical power generation methods are not appreciated options from an economic point of view [5]. Altogether, the installed capacity of geothermal power generation has been increased by about 3.649 GW between 2015 and 2020, and it has achieved 15,950.46 MWe, which produced 95,098.40 GWh/year in 2020 [6]. Direct geothermal utilization could be implemented in different industries such as space heating, food, agriculture, aquaculture, space heating, water desalination; due to this variety, this method has experienced a noticeable growth of 52.0% installed capacities over 2015–19 (8.73%/yr), equal to 107,727 MWt. According to the present data, 283,580 GWh/yr of the thermal energy consumption shows a 72.3% growth compared to the 2015 status, indicating a growth rate of 11.5% annually [7]. Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00005-1 Copyright © 2022 Elsevier Inc. All rights reserved.

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This diversity of applications has also attracted researchers and investors to implement the direct utilization of low- and intermediate temperature resources, such as hydrocarbon fields, and facilitator infrastructures, such as wells, surface equipment, access road, valuable data [8–10]. Conventional fossil reservoirs usually contain a very compressed and hightemperature deep aquifer under the hydrocarbon layers, which drives oil and gas toward the production wells. Over time, constant production leads to reservoirs becoming depleted, and a large amount of water is produced as a by-product of hydrocarbons called “coproduced water.” As well as the aquifers, unconventional reservoirs such as shale or coal reservoirs and production scenarios like water flooding, steam injection, hydraulic fracturing, and other methods could affect the volume and quality of produced water at the surface [11]. This extracted water has been known as waste in oil industries since it makes reservoir management difficult, increasing operational costs seriously, and finally causing the abandonment of wells or even fields [12,13]. In a hydrocarbon production process, we can find many abandoned wells which have an enormous amount of water extractions. Also, the dry exploratory wells could be abandoned. In addition to the abandoned wells, there are suspended wells in oil fields that are mainly influenced by oil and profit. Along with these issues [14], Table 1 presents data gathered about the different wells in Alberta province of Canada after price plunging in 2014. It is reported that only a few wells are operational, and a large number of the 63,411 wells have been abandoned in Alberta province. Reports also show that 10,730 and 76,844 wells have been abandoned in Texas and China, respectively [10,15]. It should be noted that before the water extractions, they are suspended by operator companies for 6–12 months till finding infrastructures or another profitable instrument that forces them to reactive the wells. After this, the wells must be abandoned carefully under local policies to minimize other surface and subsurface contaminations [14]. Dissolved methane, ethane, propane, and salinity in oil and gas products are known as the possible hazardous compositions which could emit into the atmosphere like methane or leak into the groundwater resources [16–18]. In order to measure the methane emission into the atmosphere, studies across the United States indicated that the suspended and abandoned wells emit a significant amount of methane every hour, which could also be found in groundwater [19–21]. Results showed that gross methane

Table 1 Number and type of wells in Alberta [14]. Well type

Number of wells

Total oil and gas wells (%)

Active Inactive but not suspended Suspended Abandoned Reclaimed Orphaned Total number of wells

143,984 17,527 75,479 42,571 17,723 3117 300,401

47.93 5.83 25.13 14.17 5.90 1.04

A brief survey on case studies in geothermal energy extraction

77

emissions from unplugged and plugged wells in the United States are about 1.0
104 and 2 (mg/h), respectively [22]. Recently, Kang et al. [23] showed that completed methane protection plugging costs equal $37,000 per well, which could be justified and confirmed by air quality, climate change, and social consideration costs. As mentioned, a large volume of the coproduced water management and abandonment of the suspended wells imposes environmental and economic issues for production companies, besides the water management challenges such as providing the necessary injection facilities for disposing of water extraction such as well, pump, and transportation [24,25]. Environmental policies must be considered to prevent groundwater and subsurface layers from getting contaminated [26–28]. Therefore, oil and gas companies initiate the use of accessible geothermal energy in the subsurface to find solutions for economic problems such as reservoirs shrinkage or rising production cost and inconstant oil price [29–32]. Furthermore, harnessing the stored geothermal energy in oil fields allows them to take steps in renewable energy to reduce the operational costs, increase profits of the rich field, attain benefits, environmental protection and global warming mitigation [33]. In recent decades, researchers have been attracted to study the feasibility of harnessing the geothermal energy in oil fields which could be extracted at lower prices than conventional geothermal resources since the surface facilities exist there, such as pump and piping system, infrastructures. The developed oil and gas fields have produced hydrocarbons for more than a decade; therefore, there are also comprehensive data and studies about the geology, geophysics, and production history. Besides reducing the cost of exploration surveys, these features could enhance the risk management of harnessing the stored geothermal energy in oil fields more than conventional geothermal resources [10]. Along with the mentioned features, both direct and indirect utilization have been studied and even practiced in oil fields to extend the fields’ economic life [34,35]. This paper intends to introduce the possible methods of geothermal harnessing and utilization in oil field by reviewing the previous and recent studies. After examining the potential geothermal feasibility in oil fields, utilization and extraction methods are introduced. Then the installed capacity, advanced research, challenges, and opportunities of retorting oil field for geothermal power production are evaluated in continue.

2

Features of the stored geothermal energy in oil fields

Regarding the geothermal gradient of the region, the potential of stored geothermal energy in the subsurface is accumulated by increasing the depth. Along with this theory, conventional hydrocarbon reservoirs located at a depth of more than 1 km could strengthen the geothermal energy. It was demonstrated that the temperature meets the range of 60–150°C in conventional petroleum reservoirs, while natural gas reservoirs usually have more temperature than oil reservoirs at the same level [34]. Globally, researchers have studied the abandoned geothermal resources in oil and gas fields. A GIS-based temperature study has investigated the retorting of existing oil wells for UK geothermal energy production (Fig. 1). It showed 2242 onshore

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Utilization of Thermal Potential of Abandoned Wells

Fig. 1 Regional temperature variation at 1 km depth across the UK [36].

hydrocarbon wells, in which 560 wells are suitable to be repurposed, and 292 are currently operating. Similarly, using aggregated water production data for all operating wells in each field, the Wytch Farm and Wareham fields has been selected as the one with the most significant potential for geothermal repurposing. The Wytch Farm is the largest onshore oil field in western Europe which produces coproduced water at 65°C that might result in a feasible thermal power output of 90 MW [36]. Augustine and Falkenstern [37] demonstrated the distribution of temperature of 48 states in the United States at a depth of 3500 m, illustrating the intermediate to high temperature in the regions with enriched oil and gas activities, such as Oklahoma, Texas, North Dakota, and Louisiana. As approved by the study [38], some wells in Oklahoma, Louisiana, and Texas have relatively high temperatures (150–200°C) at the bottom hole depths. It is only in Texas that there are tens of thousands of wells whose bottom hole temperatures are 121–204°C [39]. Such wells are also found in other regions, such as in the Turkey and Italy enriched oil fields [33,40]. China’s geothermal resources, such as the Huabei Oil field, the Liaohe Oil field, and the Daqing Oil field, have total reserves of up to 424 EJ (1EJ ¼ 1018 J) (Table 2) [13].

Table 2 Value of Stored and recoverable geothermal energy in Great Chinese oil field [13]. Oil field

Recoverable geothermal energy, EJ

Total geothermal energy, EJ

Hubaei Liaohe Daqing Total

306 29 89 424

7099 1008 2905 11,012

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79

The water-to-oil (WOR) and water-to-gas (WGR) ratios are indicators used to quantify the volume of produced water compared to the volume of produced fossil fuel. Globally, the average WOR was about 3:1 in the 2000s [41] and is recently closer to 4:1, but based on factors such as field history, the type of hydrocarbon, and the technologies employed, it can range between 0.4 and 36 locally [42]. At the global scale, the WOR index has been increasing because conventional hydrocarbon reservoirs are maturing. Therefore, they produce fewer hydrocarbons but a higher volume of water [43,44]. The estimated volume of coproduced water worldwide has increased by more than 78% between 1990 and 2015 from about 10.6 billion m3 to 18.9 billion m3 compared to 38% growth of oil production from 3.7 billion m3 to 5.1 billion m3, respectively. This growing trend is expected to continue as the predictions say that the volume of global produce water will be between 29 and 54 billion m3 in 2020 [45]. Although little information is available from the oil and gas industry, reports said that a significant volume of coproduced water from hydrocarbon reservoirs is located in arid regions suffering from water shortages [30,45]. The rock and fluid characteristics of reservoirs could affect the volume of coproduced water and its progress over time. For instance, the higher porosity, permeability, and lower compressibility of oil are the reasons why oil reservoirs produce a larger volume of water than gas reservoirs commonly [30]. As shown in the study of Echchelh et al. [45], the coproduced water contains various chemical contaminants, which routinely have high total dissolved solids (TDS), high electrical conductivity (EC), a high sodium adsorption ratio, and acidic to alkaline PH. Coproduced water also contains moderate to high amounts of different heavy metals such as B, Cd, Cr, Cu, Pb, Ni, and Zn [46–49]. The type of hydrocarbon affects the chemical composition and physical characteristics of coproduced water. Produced water from oil reservoirs has higher TDS, oil, and grease components than coproduced water from gas reservoirs. The geology of formation, age of the producing well, operation conditions, and chemical contents used in process facilities also affect the quality of coproduced water [27,44,48,50,51]. Like the volume, the composition of coproduced water might vary over time within the same well or reservoir [44]. This water contains lots of pollution such as organic matter, scales, bacteria, and dissolved salts which must be eliminated to provide high-quality water for different applications. Therefore, it needs essential treatments for disposal, or it is possible to be desalinated for different industrial applications. In addition to the deep wells and large volume of coproduced water, undeveloped geopressurized formations containing water with soluble methane and mature oil fields will play an essential role in the future in the enlargement of oil field renewable energies (geothermal, solar, and wind) [52–54].

3

Utilizations of the stored geothermal energy in oil fields

The history of geothermal energy utilization worldwide is traced back to many years ago when Native Americans, Icelanders, Japanese, and other ancients used the thermal energy of hot springs for cooking, bathing, and heating. By technology expansion in the 19th century, both direct utilization and power generation of geothermal energy were introduced on an industrial scale [55]. As Fig. 2 shows, the produced heat from

Direct use Low-temperature resources 0

10

20

30

40

Indirect use High-temperature resources

Intermediate-temperature resources 50

60

70

80

90

100

110

120

130

140

150

160

170

180 190.... 300 °C

Aquaculture

Greenhouse heating Food processing. Equipment sterilization in meat processing

Mushroom culture Pickling

Fishmeal and timber drying

Beet sugar extraction Fruit wine making Pasteurization Soil warming

Sterilizing Malt bewerage

Personal hygiene /laundry in meat processing

Distilled liqours Sugar evaporation

Milk evaporation

Boiling

'Fruit and vegetables drying

Whey condensing Beeswax melting

Grains and fish drying

Washing

Pre-heating and heating Peeling and blanching Evaporation and distillation °C

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

Fig. 2 Linda diagram for appropriate usages based on the temperature of geothermal resources [56].

160

170

180

190.... 300

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81

geothermal resources typically provides the required energy to generate electricity or be used directly as the heat source for different purposes, which strictly depends on the temperature of geothermal resources [57]. Geothermal energy is also used for power production; single flash and double flash cycles are the well-known technologies for power generation from high enthalpy reservoirs with more than 150°C [4,58]. As mentioned before, since the oil fields have a low to intermediate temperature, there are case studies and research that offered binary power plants such as organic Rankine cycles (ORCs) to convert the produced heat from the stored geothermal energy in oil fields as an appropriate option [57,59,60]. In this section, the case studies which used the oil field geothermal energy for power generation and provided the required heat for direct applications are reviewed.

3.1 Direct utilizations Nonelectricity purposes of geothermal utilization take advantage of the produced heat for applications requiring temperatures between 10°C and 150°C, as shown in Fig. 2. Worldwide, oil field geothermal utilization has a long history, when in European countries such as Austria the produced heat from abandoned oil exploration wells has been utilized for spa resorts. Likewise, in Albania, the required heat for greenhouses is supplied from abandoned wells with more than 65°C temperatures. In Hungary, water flooding as the secondary oil production method and heating the gathering pipes in heavy oil production have been implemented to use geothermal water [61]. Since 2002, China has utilized its geothermal potentials of the Shengli oil field as the principal source for house heating and oil gathering heat tracing systems. This oil field had 55 geothermal and abandoned oil wells whose total water production was 703
104 m3 in 2012. The total saved energy is up to 10.3 GJ, which prevents from burning 3
104 tons of coal or 2
104 tons of oil. Therefore, 9.8
108 and 500 tons reduction of carbon dioxide and sulfur dioxide resulted respectively [62,63]. Wang et al. [13] reviewed the other Chinese oil field which utilizes the stored geothermal energy there. In the Huabei oil field, the gathering of heat-trace oil and the transportation of crude oil have been utilized by retrofitting two abandoned wells which provide the thermal water at 600 m3/day and 100–110°C and result in conserving approximately 3500 m3 of gas and 5 ton of oil daily. Also, the Daqing, Liaohe, and Zhongyuan oil fields extract geothermal energy from the coproduced water for transportation of crude oil and space heating purposes [13].

3.2 Indirect utilization method and power generation Organic Rankin cycle power plants provide electricity generation for intermediate and low-temperature geothermal resources like oil fields [5,59,64,65]. Although several studies have investigated the performance of ORC power plants at oil fields (abandoned wells and coproduced water) [60,66–68], there are three implemented examples worldwide to get the application from this technology to generate electricity from high-temperature coproduced water at oil fields [10]. There are two implemented projects in the United States: the first exists in the Wyoming oil field where an ORC

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Utilization of Thermal Potential of Abandoned Wells

power plant generates electricity at 180 kW from coproduced water with a temperature and flow rate of 90.6–98.9°C and 40,000 bbl/day, respectively [35]. The second is the first commercial project located in North Dakota; available water with a temperature of 98°C and flow rate of 30,000 bbl/day provide the net power generation equal to 250 kW [69]. Another project for power generation from oil field geothermal power is located in Huabei oil field of China. The net power generation of geothermal water (temperature of 110°C) with a flow rate of 18.114 bbl/day has reached 310 kW [70]. Table 3 summarizes the research both in the direct and indirect types of utilization of oil wells.

4

Methods of harnessing geothermal energy from oil fields

In this section, the two main methods used in previous studies are reviewed. The first type converts the oil wells to Borehole heat exchangers (BHEX), and the second uses the heated coproduced water. The equations for predicting the future of system performance are also discussed.

4.1 Converting oil wells (active and abandoned) to borehole heat exchangers When the production of fossil fuels from a well becomes inadequate and when the cost of managing and disposing of the water outweighs the profits from oil production, the well is abandoned. Water flooding results in higher water cut wells that lose their commercial value. This type of well could be repurposed for geothermal energy exploitation, and many researchers have investigated converting abandoned wells to borehole heat exchangers (BHEXs) [68,71]. The most used type of BHEX is coaxial, which has an injection annulus and a production tubing or vice versa, as shown in Fig. 3. Table 3 Summarization of both in direct and indirect types of the utilization of oil wells Type

Region

Energy

References

Direct Utilizations Direct Utilizations Direct Utilizations Indirect Utilization Indirect Utilization Indirect Utilization

Shengli Oil field, China

Heat: 10.3 GJ

[62,63]

Huabei Oil field, China

Heat: 7099
109 GJ Heat: 2905
109 GJ Power: 180 kW Power: 250 kW Power: 310 kW

[13]

Daqing, Liaohe and Zhongyuan Oil fields, China Wyoming Oil field, USA North Dakota, USA Huabei Oil field, China

[13] [35] [69] [70]

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AZ-I & DQ-I

83

AZ-II & DQ-II

Flow in outer pipe Flow in inner pipe Insulation

Fig. 3 Converting abandoned oil wells to coaxial borehole heat exchangers [68].

The configuration of the coaxial BHEX contains well casing as an outer boundary of the well and a concentric installed tubing which is thermally insulated to reduce or prevent heat loss from the inside high-temperature fluid to the low-temperature ground [72–74]. Globally, many candidate wells can be used for geothermal energy extraction. However, for repurposing the abandoned wells to geothermal heat exchangers, the depth, temperature, regional geothermal gradient, and well integrity will play key roles in sustainable energy production in an economical manner. Noorollahi et al. [68] simulated two deep abandoned wells numerically with a downhole temperature of 138.7°C and 159.8°C in the southern oil fields of Iran which can produce heat by the extractable values of 967 and 1842 kWt. The considered binary geothermal power plant (Fig. 4) generates electricity by the net values of 138 and 364 kWe, respectively. Recently, Wang et al. [75] studied the heat transfer phenomena through the coaxial BHEX and provided a semianalytical equation to predict the fluid temperature in two scenarios of fluid flowing into the internal or external pipe (Fig. 5) based on the energy equation as follows: h

i ∂T
2  ∂Ti Ta  Ti i πrii2 ðρcÞt + π rio ¼  V ðρcÞt +  rii2 ðρcÞip ∂t ∂z Ria 



where rii , rio , ðρcÞf , ðρcÞip ,Ti , V , z,Ta ,t, and Ria are the inner radius of the internal pipe (m), the outer radius of the internal pipe (m), the Volumetric heat capacity of the fluid [J/(m3 K)], the Volumetric heat capacity of the internal pipe [J/(m3 K)], the temperature of the internal fluid (°C), the volumetric flow rate of the fluid (m3/s), the depth

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Utilization of Thermal Potential of Abandoned Wells

Turbine

Injection pump

Generator

Air sink Condenser

Valve

Cooling tower Air source

Injection-Production well

Heat exchanger pump pump

Fig. 4 Designed binary geothermal power plant to generate electricity from abandoned wells [68]. Grout

Annular fluid

Internal fluid

Internal pipe

External pipe

Fig. 5 Cross section of the considered BHEX [75].

(m), the temperature of the annular fluid (°C), the time (s) and the thermal resistance between the internal fluid and the annular fluid [(m K)/W], respectively. As is shown in Fig. 6, another type of BHEX is the U-tube heat exchanger, which has a well-known history in the ground-source heat pump systems (GSHPs). It also could be applied in abandoned or active wells [76]. Usually, a working fluid that flows into the u-tube heat exchanger gives the geothermal heat from the reservoir and moves back to the surface [10]. The existing abandoned oil and gas wells which are converted into a geothermal well by implementing a U-tube heat exchanger in a single well can result in reducing the risk of corrosion, scaling, and reinjection; therefore, it is a much-advanced technique, as compared to the U-tube heat exchanger [77]. Nevertheless, the benefits of a coaxial heat exchanger are the high surface area for heat exchange and high volume of fluid through which heat exchange occurs [78].

Fig. 6 Application of a U-tube system in (A) abandoned [10] and (B) producing wells [76].

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Utilization of Thermal Potential of Abandoned Wells

4.2 Geothermal energy extraction from the coproduced water As mentioned earlier, the high temperature of coproduced water could be used in both direct and indirect (power generation) usage methods. For the exploitation of stored heat directly, it is adequate to put a heat exchanger between the coproduced water stream and the considered application. However, there are two well-known power generation purposes: the organic Rankin cycle and the second direct steam cycle [79]. The direct steam cycle is used when its high temperature could boil the water after the separator. So water is transported to the expansion chamber after exiting the separator, as shown in Fig. 7. The gas turbine station can be charged with more power, as is required. Therefore, electricity is generated by converting the rotation mechanical energy resulting from the steam flow. However, in ORC power plants, the coproduced water with a temperature lower than the boiling point is

(A)

Steam from production well

Turbine + – Generator

Water to injection well

Condenser

4

(B)

Turbine Cooled water to reinjection well

+ HE

– 3

Qin

Hot water from the separator

Generator Qout

1 2

Pump

Air driven condenser

Fig. 7 Schematic representation of power generation cycles on a coproduced water stream: (A) direct water (DW) and (B) organic Rankin cycle (ORC) [79].

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87

directed to the heat exchanger of the ORC power plant. So the binary fluid with boiling points lower than water expands in the turbine makes movement and generates electricity. Some factors, such as smaller size turbines, required a less expensive air-cooled system and adequate operation temperature to make the ORCs more suitable [79]. Liu et al. [34] investigated the power generation by simulating an installed capacity of 500 kW over a high water cut well. The results showed that a single well could generate approximately 25 GWh of electricity during 10 years of operation. They introduced a systematic study for repurposing the oil fields in extracting geothermal power. In this study, the wellhead temperature and temperature profile were determined under changing flow rates over the simulation time based on Hasan et al. [80] as follows: h   i Tf ¼ Teibh  gG sin α ðL  zÞ  1  eðzLÞLR =LR where   2π rto Uto ke LR ¼ cp W ke + ðrto Uto TD Þ TD ¼ 0:4063 +

1 ln td 2

td ¼ ke t=ρe ce rwb The variables of the above equation are shown in Table 4.

Table 4 The variables used in the model of [80]. Variable

Definition

Variable

Definition

Teibh

Static bottomhole temperature (°C) Geothermal gradient (°C/ 100 m) Wellbore inclination from horizontal (°) Total measure well depth (m)

rwb

Radius of wellbore (in.)

rto

Outer radius of tubing (in.)

Uto

t

Overall heat transfer coefficient (Btu/°F-day-ft2) Thermal conductivity of formation rocks (Btu/°F-dayft) Production time (day)

ρe

Formation density (lbm/ft3)

ce

Formation heat capacity (Btu/ (lbm-°F))

gG α L

z cp W

Variable well depth from surface (m) Coproduced fluid water heat capacity (Btu/(lbm-°F)) Mass flow rate (lbm/h)

ke

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Utilization of Thermal Potential of Abandoned Wells

They also found a correlation to relate the thermal efficiency and inlet coproduced water temperature of the ORC power plant as follows: η ¼ 0:0005Ti2  0:0577Ti + 8:2897 where η is the thermal efficiency in percent (%) and Ti is the inlet temperature of coproduced water [34].

5

Further studies

Hydrocarbon reservoirs lose their productivity over time, leading to enhanced oil recovery (EOR) methods which extend their lifetime and economic interest. One EOR method is thermal procedures containing high-temperature water flooding or steam injection to reduce the viscosity of crude oil and enhance the productivity of oil fields [81]. Regarding the temperature of coproduced water, renewable energies could be coupled to enhance oil recovery [82,83]. If geofluid temperature, which stored geothermal energy, is as high as the boiling point of water, the produced steam could be injected into the reservoir as a thermal EOR process. However, if the stored geothermal energy is not adequate, the concentrated solar power (CSP) could be integrated with geothermal energy to produce the required steam. Previously, the CSP system has been implemented in Oman with 1 GW of power, which has the capacity to produce 6000 tons of steam per day [84], and it is predicted that the geothermal power could be coupled more with the solar system to increase the power of steam production without environmental hazards in the future [81]. Coupled solar and geothermal energy has also been investigated in the study [85] as hybrid systems to produce more power from the designed ORC power plant over an abandoned oil BHEX. They compared two systems of solar photovoltaic (PV) with CSP. PV collectors are coupled with parallel systems, and CSP provides solar heat power for the superheating geothermal binary cycle. Results showed that combining CST with geothermal resulted in a 23.5% increase in power generation compared to the 15.7% performance increment of a solar PV system with geothermal. Global water shortage has become a concern for societies, and water desalination technology has experienced growth as a solution for water supplements. In recent decades, researchers have investigated the water desalination at oil fields because, as mentioned by Tiedeman et al. [86], oil fields are commonly located in arid regions suffering from water shortages. Massive amount of coproduced water is produced in oil fields which contains contaminants whose treatments are well known historically in the oil and gas industry [87]. Because they contain organic and mineral matters with high TDS and TOC, ordinary desalination methods (such as Reverse Osmosis) are not effective, and thermal desalination methods like MSF, MED, and MD are recommended for desalination and water supply for different purposes in oil fields which use the available geothermal power [88]. Since TDS of seawater is less than that of formation water, a new practical method has been investigated by Noorollahi et al. [89]. They coupled a BHEX resulting from converting an abandoned oil well with a multieffect distillation (MED) system to desalinate the seawater in an arid region.

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89

Fig. 8 Schematic representation of converting the abandoned horizontal wells to BHEXs [90].

Results showed that an abandoned well with a temperature of 114.35°C could produce fresh water with a flow rate of 565 m3/day. The methods of harnessing the stored geothermal energy from vertical wells were also discussed in the literature. Recently, researchers investigated and simulated the heat transfer potential of converting existing horizontal wells in oil fields, as shown in Fig. 8. Results showed that the injected fluid heated up more than vertical wells at the same flow rate due to the higher contact time with the hottest formation [10]. Along with using horizontal wells, Zhang et al. [91] investigated the geothermal production from fractured horizontal wells in the Daqing oil field of China, Cui et al. [90] simulated the heat extraction through a double pipe heat exchanger within horizontal wells, and Feng et al. [92] considered the two coaxial heat exchanger installed in a horizontal well that proved the enhanced efficiency of the heat transfer phenomena. Another progressive technology investigated for electricity generation in oil and abandoned wells is thermoelectric, as shown in Fig. 9. The thermoelectric devices could directly convert the temperature differences on surfaces to electrical energy without any mechanical movement [10]. Due to its low required temperature differences (as low as 30°C), this technology could be developed in generating electricity from geothermal resources, especially in harnessing geothermal energy from abandoned and active oil and gas wells [63,93].

6

Opportunities and challenges

Wang et al. [10] summarized the opportunities and challenges of harnessing geothermal energy from oil fields. Numerous existing wells (active and abandoned), surface infrastructures (Piping system and access roads), previous exploration activities,

Heat absorbed

Substrates

Heat absorption

h+ Heat flow

p e–

Thermoelectric Metal elemets interconnects

n

+Current External electrical connection

Heat rejected

Fig. 9 Schematic representation of thermoelectric devices [10].

Heat rejection

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geology, geophysics surveys, and reservoir studies could reduce the drilling cost of traditional geothermal wells by more than 50%, and they could also minimize the risk of drilling, exploitation, and decision-making. Another benefit of using geothermal power in oil fields is the abundant market using the produced geothermal power in the oil and gas industry. In addition to financial benefits for operation companies, geothermal power production leads to governments investing in green energy, a trend to reduce greenhouse gas emissions [68]. In addition to inadequate supportive laws in great oil-producing countries such as Iran [94], the low conversion efficiency of power generation, insufficient involvement, limited studies about the probable formation damages during geothermal energy extraction, and lack of integrity of old abandoned wells can be mentioned as the biggest challenges for geothermal development in oil fields [10].

7

Conclusions

This paper summarized the harnessing of stored geothermal energy in oil fields. Previous studies in assessing the available geothermal energy in hydrocarbon wells, probable types of geothermal extraction in hydrocarbon fields and utilization methods, as well as case studies, were reviewed. It is found that using the existing facilities and infrastructures in oil fields could reduce the initial cost of geothermal projects significantly. Geothermal power could be recoverable by repurposing the abandoned wells or by using the high-temperature coproduced water. The produced heat could be used directly for different purposes or indirectly to generate electricity. By reviewing the methods of power generation and case studies worldwide, it is found that harnessing the stored geothermal energy in oil fields offers environmental and economic benefits for governments and operation companies. Nevertheless, this procedure needs more involvement, supportive laws and regulations.

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[42] J. Veil, US Produced Water Volumes and Management Practices in 2012, Groundw. Prot. Counc, 2015. [43] R.W. Healy, W.M. Alley, M.A. Engle, P.B. McMahon, J.D. Bales, The Water-Energy Nexus—an Earth Science Perspective: US Geological Survey Circular 1407, USGS, Reston, 2015. [44] J.A. Veil, M.G. Puder, D. Elcock, R.J. Redweik Jr., A White Paper Describing Produced Water from Production of Crude Oil, Natural Gas, and Coal Bed Methane, Argonne National Lab, IL (US), 2004. [45] A. Echchelh, T. Hess, R. Sakrabani, Reusing oil and gas produced water for irrigation of food crops in drylands, Agric Water Manag 206 (2018) 124–134. [46] C.E. Clark, J.A. Veil, Produced Water Volumes and Management Practices in the United States, Argonne National Laboratory ANL. Environ. Sci. Div, 2009. [47] B.R. Hansen, S.R. Davies, Review of potential technologies for the removal of dissolved components from produced water, Chem. Eng. Res. Des. 72 (1994) 176–188. [48] J. Pichtel, Oil and gas production wastewater: soil contamination and pollution prevention, Appl. Environ. Soil Sci. 2016 (2016). [49] W.A. Van Voast, Geochemical signature of formation waters associated with coalbed methane, Am. Assoc. Pet. Geol. Bull. 87 (2003) 667–676. [50] R.M. Abousnina, L.D. Nghiem, J. Bundschuh, Comparison between oily and coal seam gas produced water with respect to quantity, characteristics and treatment technologies: a review, Desalin. Water Treat. 54 (2015) 1793–1808. [51] E.T. Igunnu, G.Z. Chen, Produced water treatment technologies, Int. J. Low-Carbon Technol. 9 (2014) 157–177. [52] Glassley, W.E., Brown, E., n.d. Geothermal Energy Potential Within the Los Angeles Basin and Its Co-Location With Solar and Wind Renewable Energy Resources. [53] X. Liu, G. Falcone, C. Alimonti, Harnessing the heat from a mature oil field, in: European Geothermal Congress, Pisa, Italy, 2013, pp. 3–7. June, 2013. [54] J.-D. Van Wees, L. Kramers, J. Juez-Larre, A. Kronimus, H. Mijnlieff, D. Bonte, S. van Gessel, A. Obdam, H. Verweij, Thermo GIS: an integrated web based information system for geothermal exploration and governmental decision support for mature oil and gas basins, in: Proceedings World Geothermal Congress 2010, 2010, p. 7. [55] J.W. Lund, World Status of Geothermal Energy Use Overview 1995–1999, 2000. [56] M. Van Nguyen, S. Arason, M. Gissurarson, P.G. Pa´lsson, Uses of Geothermal Energy in Food and Agriculture – Opportunities for Developing Countries, FAO, Rome, 2015. [57] M. Soltani, F. Moradi Kashkooli, A.R. Dehghani-Sanij, A. Nokhosteen, A. AhmadiJoughi, K. Gharali, S.B. Mahbaz, M.B. Dusseault, A comprehensive review of geothermal energy evolution and development, Int. J. Green Energy 16 (2019) 971–1009. [58] D. Moya, C. Alda´s, P. Kaparaju, Geothermal energy: power plant technology and direct heat applications, Renew. Sustain. Energy Rev. 94 (2018) 889–901. [59] T. Li, J. Zhu, W. Zhang, Cascade utilization of low temperature geothermal water in oilfield combined power generation, gathering heat tracing and oil recovery, Appl. Therm. Eng. 40 (2012) 27–35. [60] Y. Yang, Y. Huo, W. Xia, X. Wang, P. Zhao, Y. Dai, Construction and preliminary test of a geothermal ORC system using geothermal resource from abandoned oil wells in the Huabei oilfield of China, Energy 140 (2017) 633–645, https://doi.org/10.1016/j. energy.2017.09.013. [61] J.W. Lund, T.L. Boyd, Direct utilization of geothermal energy 2015 worldwide review, Geothermics 60 (2016), https://doi.org/10.1016/j.geothermics.2015.11.004.

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Part III Energy Extraction from abandoned wells

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Energy Extraction from abandoned wells

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Zachary Siagia and Charles Nzilab a Department of Production, Mechanical & Energy Engineering, Moi University School of Engineering, Kenya, bDepartment of Manufacturing, Industrial & Textile Engineering, Moi University School of Engineering, Kenya

List of acronyms CO2 EGS HCl HDR HEGF HF KCL NH4HF2 PAA PAC PPA RMA USD

1

carbon dioxide enhanced geothermal systems hydrochloric acid hot dry rock high-energy gas fracturing hydrogen fluoride potassium chloride ammonium bifluoride poly allylamine poly acrylamide/sodium acrylate power purchase agreement regular mud acid United States Dollar

Introduction

The key requirements in the production of geothermal energy include high formation temperature, adequate fluid to transport the heat from the reservoir to the surface as well as sufficient formation permeability to allow passage of the geothermal working fluid through the subsurface at a relatively high mass flow rate. The required high temperatures (>150°C) to produce geothermal electricity are normally present at a depth of about 5 km across a vast majority of the Earth’s surface. While conventional drilling is possible at these depths, most places lack adequate permeability which is necessary for the economic utilization of geothermal resources. Under these circumstances, the need for hydraulic fracturing to generate permeability arises. One common approach for resolving the permeability issue is through the concept of enhanced geothermal systems (EGS) which entails the use of hydraulic fracturing and fluid circulation in a closed loop between the injector and production geothermal wells. However, this necessitates the availability of sufficient surface geology and chemistry of thermal manifestation data. Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00006-3 Copyright © 2022 Elsevier Inc. All rights reserved.

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To validate the surface geology and thermal manifestation data, it is necessary to drill an exploration well and access the geothermal resource. However, at least two key difficulties are encountered at this stage thus leading to the abandonment of geothermal wells. Firstly, due to limited data, exploration wells are predisposed to miss the permeability targets thus causing them to fail. Secondly, since the permeability of geothermal reservoirs depends on lithologic contacts and fractures, transport of heatbearing geothermal fluids to the surface is hampered if the wellbore fails to intersect the networks of fractures and lithologic contacts [1].

2

Stimulation of abandoned geothermal wells

Application of EGS techniques is a leading option for the stimulation of abandoned geothermal wells. EGS was originally developed at the Fenton Hill project in the United States in the 1970s [2]. The economic success of the EGS largely relies on enlarging existing fractures or developing new ones while ensuring that the fracture network is kept open to allow geothermal working fluid circulation [3]. The various approaches for EGS are presented in the following sections.

2.1 Hydraulic fracturing Hydraulic fracturing is one of the leading techniques that have been used to create artificial fractures that aid in the extraction of heat from geothermal resources such as a hot dry rock (HDR) geothermal reservoir. The process entails the exertion of sufficient hydraulic pressure on the HDR formation until the formation fracturing pressure (breakdown pressure) is overcome. Hydraulic fracturing has also been widely used in the recovery of oil and gas resources from abandoned wells. In most settings, hydraulic fracturing is used to (i) improve the connection between a productive reservoir and a well and (ii) create or stimulate fractures in a low permeability matrix through the engineering of the reservoir [2]. Hydraulic fracturing, therefore, stimulates wells by cracking the formation’s plane of weakness (caused by unequal earth stress) with a hydraulic or fluid wedge. Sand is normally pumped with the fluid at a pressure above the frac gradient so that the crack grows to form a fracture void to hold the sand. After shutdown, the fluid is pumped out and the sand remains in the fracture to form a permeable pipeline from the formation to the wellbore. Stimulation ratios up to 10 are common with the average being from two to three times the prestimulation production value [4]. Hydraulic fracturing is usually conducted in two successive stages namely the pad stage and the slurry stage. During the pad stage the hydraulic fracturing fluid, usually water, is injected into the well to (i) breakdown the HDR formation, (ii) create fractures, and (iii) to ensure a sufficient reduction of fluid loss into the immediate wellbore formation in anticipation of the subsequent injection stage. During the slurry stage the slurry, usually a mixture of fracturing fluid and propping solid material (proppant) is injected into the wellbore as well as the fractures. The most widely used proppants include resin-coated sands, ceramic, silica sand, and bauxite spheres. Generally,

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Proppant

R Ep , vp

lpr lpr

d Er , vr Fracture surface

Fig. 1 The embedment of proppants in a hydraulic fracture (single layer). Adapted from Y. Chen, H. Wang, T. Li, Y. Wang, R. Ren, G. Ma, Evaluation of geothermal development considering proppant, Renew. Energy (2020) 985–997.

the proppants work by supporting the fracture walls and thus resulting in the creation of flow channels once the hydraulic pressure is removed [5]. However, a major drawback of this method is difficulty in the injection and transport of the proppant into the subsurface. During the hydraulic fracturing process, a significant fraction of the volume injected (typically 240–600 g/L of injected fluid) consist of the proppants account. Meanwhile, the large density difference between typical proppants (2.6 g/cm3) and the water (1–1.05 g/cm3) present mass flow challenges that have to be surmounted [6]. Consequently, the use of highly viscous fluids or gels to transport the proppants is necessitated but this, introduces high loads on injection pumps hence increasing pumping costs and energy requirements. The foregoing has been a subject of research whereby Childers et al. [6] investigated the functionalization of bare bauxite particles with polyacrylamide/sodium acrylate (PAC) and polyallylamine (PAA). The investigation resulted in proppants with higher dispersibility in aqueous solutions while the increased stability of the core/shell proppant aqueous dispersions eliminated the need for high viscosity carrier fluids for transporting the proppants down the borehole. Therefore, the use of proppants such as in Fig. 1 to maintain fracture conductivity can vastly improve reservoir-fracture creation and propagation by hydraulic fracturing in EGS. Fig. 1 presents a model of a single-layer pattern in the fracture for the derivation of proppant embedment and fracture conductivity [5]. In this study, the proppants are assumed to be evenly paved, and the distance between two adjacent proppants is given as lpr while the proppant distribution density ρpr is defined as ρpr ¼ 1=l2pr : In numerical analysis, the fractures are discretized into small elements and for each fracture element, an element area ae is defined. Therefore, the number of proppants npr in each fracture element can be computed as [5] npr ¼ ae =l2pr :

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Based on the proppant radius, the initial fracture width can also be calculated. For example, if the proppant radius is represented as R, then the initial fracture width, x0 is 2R. Furthermore, the effective stress for each fracture element can be calculated based on σ e,c ¼ σ e,n  αPe, f where σ e, n and Pe, f are the respective fracture element normal stress and fracture pressure. The maximum contact stress, σ max is related to the average contact stress σ ave, i.e., σ max ¼ 3σ ave/2. The average contact stress can therefore be expressed as σ ave ¼

Pe,c l2pr : πa2

The contact circle radius (r), the contact depth (δ), and the average contact stress can be expressed respectively as 3Pe,c l2pr R r¼ 4E∗

!1=3

3Pe, c l2pr R δ¼ 4E∗

!2=3

1 R

2 6Pe,c l2pr E∗2 σ ave ¼ 3π R2

!1=3 :

The elastic deformation of proppants is generally assumed for an evenly paved system. The proppant deformation can then be calculated from the expression Δxp ¼

Pave w0 : Ep

The variation of the fracture aperture is regarded to be composed of two parameters namely the contact depth and the proppant deformation hence it can therefore be expressed as Δxf ¼ Δxp + 2δ: Consequently, the final fracture aperture (w) can be expressed as x ¼ x0  Δxf :

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Meanwhile, the fracture porosity (Φf) and fracture permeability (kf) can be expressed, respectively, as Φf ¼ kf ¼

V e  Vp Ve Φf 3

CS2p ð1  Φ f Þ2

where Ve is the volume of the fracture element while VP is the embedded proppant volume in each element. The parameter VP can be derived as pffiffiffiffiffiffiffiffiffiffiffiffiffiffi   Vp ¼ 43 πR3  2πb2 ðR  b=3Þ npr and b ¼ R  R2  r 2 . C is the Kozeny–Carman constant and for uniform spherical packing, it has an assigned value of 5. Sp is the specific surface area, and it is defined as the total pore surface area per unit volume, i.e., Sp ¼ aw/Vp. The total pore surface area aw is composed of two parts namely (i) the contact area between fracture faces and fluid as, and (ii) the contact area between proppants and flowing fluid ap whereby   as ¼ 2 ae  npr πr 2 pffiffiffiffiffiffiffiffiffiffiffiffiffiffi ap ¼ 4πR R2  r 2 npr aw ¼ a s + ap : After obtaining the fracture aperture and permeability, the fracture conductivity can then be calculated as Fc ¼ kf :w:

2.2 Acidizing The most well-known well-stimulation technique is an acid injection and it was in use for over 50 years before the advent of hydraulic fracturing. Two acidizing treatment techniques are commonly used in the petroleum industry although they can also be used in the geothermal field: (a) matrix acidizing and (b) acid fracturing, or “fracture acidizing.” The pressure at which acid is pumped into the formation differentiates the two techniques.

2.2.1 Matrix acidizing In the matrix acidizing process, acids are used that react with the mineral phases restricting fluid flow and removing them. In the case of carbonate formations, matrix stimulation aims at creating new and free channels of flow between the wellbore and

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the formation. Thus the technique is commonly used in treating only the region near the wellbore [3]. In this method, acid is injected at pressures below the formation fracturing pressure in a manner that is calculated to eliminate the skin damage that results from the flow of mud cake and cement during drilling operations. It is also effective in healing any formation damage that can be observed during well operation. There are three main stages of matrix acidizing as applied in the stimulation of geothermal wells namely, preflush, main flush, and postflush. In the preflush stage, carbonate minerals in the formation are dissolved by the injection of hydrochloric acid (HCl) concentration with a concentration of 5%–15%. The preflush is followed by the main flush which is composed of HCl and HF (mud acid) having concentrations of 10% and 5% respectively. During the main flush, the HCl dissolves limestone and dolomites while the HF dissolves siliceous minerals such as silica sands, feldspar, and clays. The final stage is the postflush (or overflush) and this pushes the acid mixture from the main flush deeper into the formation and reduces any precipitation reactions near the wellbore. Freshwater is used in this stage during geothermal well stimulation. Based on Darcy’s equation of a steady-state liquid flow the production rate is given by the relation [1], q_ ¼

2πkh ð Pr  Pw Þ sμB

where q_ is the production rate, k is the permeability, s is the dimensionless skin, h is the thickness, pw is the well flowing pressure, pr is the reservoir pressure, μ is the fluid viscosity, and B is the formation volume factor. The skin and permeability are normally determined from pressure transient tests. The wellhead injection pressure during matrix acidizing is calculated from the following equation [7]: 

 141:2iμw pti ¼ pe  ph + pfr + kw h



rb ln + s rw



where pti is the wellhead injection pressure (kPa), pe is the average reservoir pressure (kPa), ph is the hydrostatic head (kPa), pfr is the total friction losses, i is the injection rate m3s1, μw is the water viscosity (cp), kw is the effective water permeability (md), h is the net pay thickness (m), rb is the radius of formation cylinder in which majority of pressure drop takes place (m), rw is the wellbore radius (m), and s is the skin factor appearing in Darcy’s equation (dimensionless). Among the factors that affect the acid stimulation of geothermal reinjection wells is the presence of mineral deposits around the near-wellbore formation and within the production liner. The acid dissolves the mineral deposits such as silica scales with the resultant effect of elimination of the plugging of the natural fractures that impede the flow of brine into the reservoir.

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2.2.2 Acid fracturing Acid fracturing is a kind of technique that provides conductive paths deeper into the formation. In this technique, undamaged formation is stimulated using a pressure higher than the formation fracturing pressure. In the method, acid fluid is injected into the formation at a rate higher than the reservoir matrix will accept and this produces a buildup in wellbore pressure that results in the fracturing of the rock. As the fluid injection continues, the fracture’s length and width are increased. Just like in matrix acidizing, HF and HCl mixtures are normally used in sandstone acidizing operations. The HCl treats any calcareous zones, while HF can dissolve silica and clay minerals. This method is also carried out in three main steps namely, preflush, main flush, and overflush. In the preflush, the main objective is to reduce the likelihood of the formation of insoluble precipitates using 10% concentration HCl acid. Brine formation is displaced away from the wellbore during this step and most of the calcareous material is dissolved. In the main flush, the damage is removed by pumping a mixture of 3% HF–12% HCl (regular mud acid) into the well. The procedure for the preparation of the regular mud acid (RMA) is to dissolve ammonium bifluoride (NH4HF2) in HCl. In the final stage of overflush, a fluid consisting of KCl, NH4Cl, HCl, or freshwater, is used to displace the mud acid reaction products and the nonreacted mud acid away from the wellbore into the formation [3]. Dissolution etching due to the passing acid results in the unevenness of the fracture surfaces and this leads to the retention of the fracture conductivity of the formation. There are relatively shorter conductive channels in geothermal formation due to their higher temperatures and consolidated nature thus the limited penetration of the live acid into the formation. Acid fracturing has not been widely used in geothermal reservoirs and, as a stimulation technique, it is still in its infancy.

2.3 Thermal fracturing In the normal case where injectate is cooler than the reservoir, injectivity of a geothermal well should be expected to increase with time at a rate like tn where n ¼ 0.4–0.7 [8]. Injectivity is also strongly temperature-dependent, increasing greatly with an increased temperature difference between injectate and reservoir. The increase in permeability with time can be up to two orders of magnitude. Well stimulation by thermal fracturing is similar to conventional hydraulic fracturing save for the way in which fractures are initiated. Thermal fracturing is based on the principle of thermal contraction due to the temperature difference between the hot rock formation and the cold fracturing fluid that results in the creation of new fractures. The technique thus can be used to enhance the productivity of geothermal wells through the creation of a system of permeable fractures in the rock formation by induced thermal gradients. Fluids at a lower temperature than the hot reservoir rock are injected in a cyclic manner and after each injection cycle, a period of thermal recovery is allowed. The resulting thermal shock causes the widening of existing channels or even the creation of completely

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new fluid channels with the attendant permeability enhancement of the reservoir. The presence of thermally induced fractures, increased permeability, and increased effective flow area, results in the acceleration of the heat transfer process [9]. In thermal fracturing, the pumping pressure is kept low so as not to cause hydraulic fracturing.

2.4 Casing perforation In conventional well drilling operations, the nonproductive zones of the well are cased off with solid casing and cemented. But at points where it is determined that the formation is productive, preperforated casings are inserted to tap the zone and allow the steam to flow into the well and to the surface. These casings are normally inserted at great depths (up to 3000 m deep). As a stimulation technique, casing perforation targets cased-off permeable zones by perforating the well casing. These zones are normally found at the shallow depths of the geothermal reservoir and are indicated by a high temperature that is observed during the operation or testing of the well. Suspected productive zones are confirmed by examining the drilling circulation loss records, pressure records, the geology as well as petrology of the formation. If all these show a possible productive zone, a perforation job is done. During the casing perforation job, deep-penetrating perforating charges are used. A temporary plug is used to ensure that the well is overbalanced at a pressure of about 1000 psig as the charges are detonated. For a successful connection to a permeable zone, the pressure will decline and not recover even if pumping is maintained [10].

2.5 High-energy gas fracturing (HEGF) or explosive stimulation he use of explosives (energetic materials) for the stimulation of oil wells has been extensively employed in enhancing the recovery of wellbore fluids although its use for geothermal wells is still new. To assure safety in the handling and transportation of the energetic materials that are used in HEGF, it is advisable to use binary materials which are subsequently mixed down the well to eliminate the risk of premature detonation. In most systems, a gradual increase in pressure is normally used in order to have multiple fractures and to reduce the chances of wellbore damage [11]. The principle of operation of high explosives is the production of a large number of short fractures that effectively shatter the wellbore in the near field. In the binary fuel and oxidizer method, gaseous reactants are injected into the formation where a reaction is subsequently initiated, and high pressures are generated that can improve the formation permeability. In explosive stimulation-controlled fracturing is achieved which eliminates the shortcomings and complications of conventional hydraulic fracturing and does not result in the production of wastewater, a common problem during hydraulic fracturing. An added advantage of high-energy gas fracturing (HEGF) is the improved cleanup of the perforations. Deflagration, which is the high gas wave that is generated during the vaporization of the propellant, leads to the collapse of the formation damage near the perforation channel. The gas surge back that results from the dissipation of the pressure carries back the fine particles from the formation.

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2.6 Acoustic stimulation (active cavitation and ultrasonic) Acoustic Stimulation operates on the principle of the ultrasonic wave to stimulate a matrix such as the rock structure in a geothermal well. This approach has been proven commercially viable as evidenced by the scale removal from equipment such as domestic water filters and dentist’s tools. The high-intensity vibrations that result from ultrasonic waves have also been shown to be an attractive tool in the refining of the grain structure of metals during casting [12]. The ultrasonic principle can therefore have a profound and positive effect in the enhancement of rock permeability. Therefore, in geothermal applications, the effect of acoustic stimulation is mainly based on the extent of the modification of well permeability [13]. The effect of the acoustic field on the saturated porous rock results in an improved rock permeability and a cleanup by the removal of plugging materials. Nevertheless, the use of ultrasonics in practical situations is faced with numerous problems such as (i) infancy of this technology, (ii) acoustic streaming and acoustic cavitation, and (iii) insufficient data necessary for the optimization of the treatment conditions during ultrasonic stimulation, especially those concerned with the cavitation zone characteristics.

2.7 Electric stimulation Electric stimulation makes use of electric current to stimulate the well. Electric stimulation has a strong potential to positively impact rock permeability. In geothermal applications, the effect of electric stimulation is achieved by either of two mechanisms; electrodynamic and electrothermal techniques. The electrothermal mechanism refers to the heating of the rock formation using an electric current. In this method microwaves or high frequency current are used to accomplish the heating. The resulting thermal stresses lead to fracturing of the rock near the wellbore zone and increased permeability of the formation. The electrodynamic mechanism removes clay particles from the bottom hole formation zone thus giving the formation an improved well permeability [14].

2.8 Enhanced geothermal systems (EGS) using CO2 as a working fluid The use of carbon dioxide (CO2) in place of the more commonly used water to transmit heat in a novel technique of enhancing the productivity of geothermal systems was first proposed by Brown. The method had an added advantage of achieving CO2 sequestration [15]. Some of the properties that make CO2 a particularly attractive media for Enhanced geothermal systems (EGS) operation are inability to dissolve most rock minerals which lead to limited or no scaling problems, larger compressibility and expansivity that would lead to increased density differences between the hot CO2 in the production well and the cold CO2 in the injection well with the resultant buoyancy force reducing the power consumption of the fluid circulation system. This is of great importance for an optimum operation of any CO2-driven EGS system when you consider the reservoir heat extraction, which, for a given pressure gradient, the

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CO2 with its lower viscosity would give higher flow velocities compared to water [16]. In the CO2 EGS, carbon dioxide is pumped into the reservoir and it displaces the mixture of water and brine that is present in the well, resulting in its flows out of the well. As more CO2 is injected, the percentage of CO2 in the outflow of water and brine from the reservoir also increases. The heat extraction from the reservoir fluid takes full effect once equilibrium is achieved between the CO2 flows into and out of the reservoir. The CO2 is pumped back into the reservoir, after the heat is extracted from the fluid, in a supercritical state. This cycle continues throughout the life cycle of the geothermal reservoir with a migrating cold front from the injection to the production well. The attendant subsurface fluid losses in the reservoir and its surroundings lead to CO2 sequestration. In water-based systems, fluid losses of up to 5% have been observed and equal percentages of CO2 are expected to be sequestered during this process. Thus for this technique, permanent storage of CO2 is realized [16].

3

Lessons for the reclamation of abandoned geothermal wells from reclamation of petroleum wells

The current understanding and developments in the reclamation of petroleum wells have been well documented ([13,17,18] among others). Indeed, there has been a growing concern over the number of abandoned oil and gas wells in Canada as well as in many other countries. The major issues include (i) majority of the abandoned wells are on forests, farms, or ranches and any leaks from the abandoned and aging wells risk contaminating the soil and water, (ii) the industry has largely operated with the premise that the polluter pays to cleanup the abandoned wells, however with the era of the oil boom behind us, many companies have gone bankrupt thus being unable to pay for the cleanup hence leaving behind the so-called “orphan” wells, and (iii) the costs to cleanup orphaned wells could be as high as $100 billion and there is a high likelihood that cleanup costs will most likely be passed to taxpayers. Basically, there are three basic steps to return a well site to its previous original state. The steps consist of abandonment, remediation, and reclamation. Abandonment entails removing the aboveground infrastructure (such as pumps and piping) prior to sealing the well at least 1 m below the ground so that it can no longer be used. The well site is thereafter backfilled and checked for any leakage (gas or liquid) which could pose a threat to the environment. Remediation entails decontamination of soil and groundwater. Remediation is regarded as the most expensive step which often takes years or decades to accomplish. During remediation, soil and groundwater are tested for contaminants (such as salts and hydrocarbons) and if found they are treated. Contaminated soil is either treated on-site or removed and replaced with clean soil (commonly referred to as dig and dump). Meanwhile, contaminated groundwater is typically removed and treated using conventional water treatment techniques or treated in situ by installing several temporary wells. Reclamation entails restoring the land to its original and acceptable state. Reclamation usually includes planting

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vegetation such as trees, grasses or reestablishing wetlands. The land is then monitored for a period of several years after which it is certified prior to being returned to the previous owners. The key lessons that energy generation from and reclamation of abandoned geothermal wells can therefore learn from the reclamation of petroleum wells include (i) Reclamation of geothermal wells for energy production should be brought to the forefront and factored for during the inception of geothermal wells instead of being relegated to the tail end with concomitant risks. This calls for a well-thought-out scheme and participation of the key stakeholders including the governments and the private actors. (ii) The threat of orphan geothermal wells is quite apparent and even likely to increase given the time capped structure of power purchase agreements (PPA’s) between the geothermal energy producers and the power off-takers. (iii) There is a need for increased attention on reclamation and energy generation from abandoned geothermal wells. This includes well stimulation as well as the development of liability management frameworks and regulation changes on licensing of new geothermal wells with a view to bringing reclamation of abandoned geothermal wells to the center stage of any well permit negotiations.

4

Potential environmental impacts of reclamation of abandoned geothermal wells

There are various components in a typical geothermal power plant. These include; production/reinjection boreholes, connecting/delivery pipelines, intermediate equipment like silencers/separators, powerhouse (including turbines/generators, controls) and cooling towers. Each of these components has its environmental effects hence contributes to either temporary or long-lasting life cycle impacts [19], e.g., during construction and silencer noise respectively. However, different studies have highlighted that under geothermal electricity generation, air emissions, water consumption, and land use will have less of an environmental impact than under the corresponding traditional fossil fuel-based electricity scenarios [20]. Pertaining to the geothermal scenarios, the water consumption for the EGS construction stage is particularly much higher than the case for the other geothermal scenarios. This is primarily attributed to the additional requirement of reservoir stimulation in EGS. Generally, the water required for stimulation contributes approximately 60%–80% of total upfront geothermal water requirements. However, the water requirements for stimulation can also vary according to (i) the required number of stimulations for successful circulation and (ii) the reuse of water for multiple stimulations [20]. For example, matrix acidizing necessitates the use of approximately 1000 m3 of water. The foregoing could significantly impact groundwater resources or potentially reduce the available groundwater, depending on the characteristics of the aquifer and the time of year (season) when the work is carried out [21]. The effect of chemical stimulation on the other hand depends largely on the sensitivity of the medium. For instance, when ascertaining the significance of impacts

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(e.g., on the vegetation) it is important to consider whether the areas are vegetated or not since chemical substances are bound to be deposited on the vegetation as well as on the soil but with different consequences. Analysis of matrix acidizing further indicates that wildlife can particularly be affected by noise, odors, and transport of materials, and equipment. In addition, during acid stimulation, the staff might also be exposed to harmful substances such as hydrochloric acid, ammonium bifluoride, and additives, especially during injection and mixing. Additionally, handling of acidizing additives and tanks as well as transportation of pumping and injection equipment by cranes and trucks present an extra risk of accidents, therefore, special care should be taken [21].

5

Conclusions

The development of geothermal wells is generally an expensive undertaking that can cost over several million dollars per typical high-temperature geothermal well necessary for electricity generation. The cost of drilling a well in Kenya is about half a billion Kenyan shillings (USD 5 million). In the eventuality that a geothermal well is abandoned as a result of not being productive after drilling, the investors can be faced with a major economic loss with the potential of being rendered bankrupt. The high costs associated with the development of geothermal wells are therefore a major barrier toward the entry and exploitation of geothermal resources, especially in developing economies that have proven the potential of geothermal resources. Recovery of abandoned geothermal wells for energy extraction is regarded as one of the promising circular economy approaches in the geothermal sector. Reclamation of the abandoned geothermal wells can rely on important reservoir parameters that determine the productivity of a geothermal well including porosity, permeability, transmissivity, temperature, and fluid saturation. Techniques for the recovery of the abandoned geothermal wells can therefore be designed to target the specific geothermal reservoir parameters while at the same time being engineered to largely remain self-sustaining. Stimulation of abandoned geothermal wells is one of the promising reclamation approaches. Meanwhile, while the different simulation techniques have varying levels of key strengths (Table 1) most of the novel stimulation techniques, however, are still in the infancy stage of development and requires more research before they can be tested on a wider scale. Among the various techniques discussed in this chapter, experimental studies on acoustic and electric stimulation on a laboratory scale are very scarce. Consequently, basic questions that need to be addressed are as follows: (i) What are the kinetic mechanisms of these stimulation techniques? (ii) What is the role of chemical reactions during the geothermal well stimulation process? (iii) Which geothermal well stimulation approach is most effective? (iv) How long should the process be undertaken for an effective simulation? (v) To what extent are the stimulation techniques sustainable? Obviously, there are far more pertinent additional questions that must also be well understood and resolved for an effective and scientific approach to these techniques especially for stimulating the abandoned

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Table 1 Comparative analysis of the different stimulation techniques. S. no Technique

Key strengths

1

l

Hydraulic fracturing

l

The technique is widely used and there is vast experience that has been amassed over time. Yields high simulation ratios (up to 10 times).

Key weaknesses l

l

l

l

l

2

Acidizing

l

l

Undissolved precipitates loosened or softened by the acid reaction are cleared when production recommences. Acid treatment can result in up to 90% improvement in well productivity.

l

l

l

l

l

3

Thermal fracturing

l

l

l

4

Casing perforation

l

Attractive for shallow reservoirs. Leads to increased well productivity of up to 75%. Cold water stimulation is fairly cheap, usually making it the most economic form of stimulation. Increases the production zone significantly.

l

l

l

l

l

Injection and transport of proppant into the subsurface can be challenging Water-based systems cause dissolution of most rock minerals hence causing scaling problems Generates a liquid waste stream hence necessitating wastewater treatment High energy consumption Risk of seismic activity Adversely affected by the presence of mineral deposits around the near-well bone formation and within the production liner Acids cause dissolution of most rock minerals hence causing scaling problems Generates a liquid waste stream hence necessitating wastewater treatment High power consumption Liable to corrosion problem that affects the well casings. The technique is still poorly understood to date Method requires large amounts of energy

Can lead to collapse of the cemented region. Lack of standard procedures for evaluation of well perforators at elevated temperature. Since it is done at low depths, it may hit a low temperature zone. Continued

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Table 1 Continued S. no Technique

Key strengths

5

l

High energy gas or explosive stimulation

l

l

l

6

Acoustic stimulation

l

Key weaknesses

Makes controlled fracturing possible without the limitations and complications of conventional hydraulic fracturing techniques Eliminates the wastewater produced with conventional hydraulic fracturing. Allows for multiple fractures to be produced, Can propagate existing fractures and increase well bore permeability.

l

The technique has strong potential to positively impact rock permeability

l

l

l

l

l

l

7

8

Electric stimulation

l

CO2 stimulation

l

l

l

Electric stimulation has a strong potential to positively impact rock permeability

l

Environmentally friendly due to geologic sequestration of CO2 CO2 is a poor solvent for most rock minerals hence reduces or eliminates scaling problems Low power consumption

l

l

Most explosives are unstable in the temperature environment encountered in geothermal wells. Use of liquid explosives requires the use of large pumping equipment and sophisticated controls. Military explosives suitable for the high temperatures are expensive

Although the technique has been proven commercially, it is still at its infancy There is lack of data needed to optimize the ultrasonic treatment conditions High power consumption Practical application of ultrasonics remains quite limited Concept still at its infancy High power consumption

Optimal operation of a CO2-driven EGS system involves complex trade-offs between reservoir heat extraction and power consumption in the fluid circulation system

geothermal wells. Based on the current work, future work can focus on (1) exploring the mechanisms of abandoned geothermal well stimulation techniques, (2) establishing unified evaluation criteria for selecting geothermal well stimulation techniques, and (3) developing the basis for identification of potential and determination of geothermal well reclamation.

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Acknowledgment This chapter is based on research supported by the Danish Ministry of Foreign Affairs Grant DFC 14-09AAU. We are grateful to our collaborators in the Innovation and Renewable Electrification in Kenya (IREK) project.

References [1] A. Aqui, S. Zarrouk, Permeability Enhancement of Conventional Geothermal Wells. New Zealand Geothermal Workshop, 2011, pp. 1–11. Auckland, New Zealand. [2] M.W. McClure, R.N. Horne, An investigation of stimulation mechanisms in enhanced geothermal systems, Int. J. Rock Mech. Min. Sci. (2014) 242–260. [3] S. Portier, F.D. Vuataz, P. Nami, B. Sanjuan, A. Gerard, Chemical stimulation techniques for geothermal wells: experiments on the three-well EGS system at Soultz-sous-For^ets, France, Geothermics (2009) 349–359. [4] U.S., D. G., Geothermol Reservoir Well Stimulation Program: Technology Transfer, Republic Geothermal, Inc., Santa Fe Springs California, 1980. Maurer Engineering, Inc. [5] Y. Chen, H. Wang, T. Li, Y. Wang, F. Ren, G. Ma, Evaluation of geothermal development considering proppant, Renew. Energy (2020) 985–997. [6] M.I. Childers, M. Endres, C. Burns, J.B. Garcia, J. Liu, W.T. Wietsma, A.C. Fernandez, Novel highly dispersible, thermally stable core/shell proppants for geothermal applications, Geothermics (2017) 98–109. [7] G. Paccalonl, M. Tambini, Advances in matrix stimulation technology, J. Pet. Technol. (1993) 256–263. [8] A.M. Grant, J. Clearwater, J. Quina˜o, F.P. Bixley, L.M. Brun, Thermal Stimulation of Geothermal Wells: A Review of Field Data. Thirty-Eighth Workshop on Geothermal Reservoir Engineering, SGP, Stanford, California, 2013, pp. 1–7. [9] W. Kumari, P. Ranjith, M. Perera, B. Chen, Experimental investigation of quenching effect on mechanical,microstructural and flow characteristics of reservoir rocks: thermal stimulation method for geothermal energy extraction, J. Pet. Sci. Eng. (2018) 419–433. [10] C.M.M. Ramonchito, C.B. Balbino, O.M. Patricia, D.M. Yglopaz, A.M. Lacanilao, A case history on geothermal wellbore enhancement, Mindanao Geothermal Production Field, Philippines. in: Proceedings World Geothermal Congress. Kyushu – Tohoku, Japan, May 28–June 10, 2000. [11] C.M. Grubelich, D. King, S. Knudsen, D. Blankenship, S. Bane, P. Venkatesh, An Overview of a High Energy Stimulation Technique for Geothermal Applications. Proceedings World Geothermal Congress, Sandia National Laboratories, Melbourne, Australia, 2015, pp. 1–6. [12] S. Komarov, K. Oda, Y. Ishiwata, N. Dezhkunov, Characterization of acoustic cavitation in water and molten aluminum alloy, Ultrason. Sonochem. 20 (2) (2013) 754–761, https:// doi.org/10.1016/j.ultsonch.2012.10.006. Epub 2012 Oct 23. PMID: 23141190. [13] M.F. Pedrotti, M.S.P. Enders, L.S.F. Pereira, M.F. Mesko, E.M.M. Flores, C.A. Bizzi, Intensification of ultrasonic-assisted crude oil demulsification based on acoustic field distribution data, Ultrason. Sonochem. 40 (Part B) (2018) 53–59. ISSN 1350-4177. https:// doi.org/10.1016/j.ultsonch.2017.03.056. [14] M.D. Baterbaev, V.D. Bulavin, V.I. Seljakov, A.F. Savchenko, Application of technology of electroinfluence for intensification of an oil recovery in Russia and abroad, Oil Industry 2002 (11) (2002) 92–95.

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[15] K. Pruess, Enhanced geothermal systems (EGS) using CO2 as working fluid—a novel approach for generating renewable energy with simultaneous sequestration of carbon, Geothermics (2006) 351–367. [16] J. Biagi, R. Agarwal, Z. Zhang, Simulation and optimization of enhanced geothermal systems using CO2 as a working fluid, Energy (2015) 627–637. [17] K.A. Khajehesamedini, A. Sadatshojaie, P. Parvasi, M.R. Rahimpour, M.M. Naserimojarad, Experimental and theoretical study of crude oil pretreatment using lowfrequency ultrasonic waves, Ultrasonics Sonochemistry 48 (2018) 383–395. ISSN 1350–4177. https://doi.org/10.1016/j.ultsonch.2018.05.032. [18] X. Luo, J. Cao, H. Gong, H. Yan, L. He, Phase separation technology based on ultrasonic standing waves: a review, Ultrason. Sonochem. 48 (2018) 287–298, https://doi.org/ 10.1016/j.ultsonch.2018.06.006. Epub 2018 Jun 20. PMID: 30080553. [19] P. Bayer, L. Rybach, P. Blum, R. Brauchler, Review on life cycle environmental effects of geothermal power generation, Renew. Sust. Energ. Rev. (2013) 446–463. [20] C. Clark, J. Sullivan, C. Harto, J. Han, M. Wang, Life Cycle Environmental Impacts of Geothermal Systems. Thirty-Seventh Workshop on Geothermal Reservoir Engineering, SGP-TR, Stanford, California, 2012, pp. 1–8. [21] B.A. Marroquı´n, Environmental Considerations in Production Tests and Geothermal Well Stimulation, United Nations University-Geothermal Training Programme (UNU-GTP), Reykjavik, Iceland, 2016.

Productivity evaluation of geothermal energy production system based on abandoned oil and gas wells

7

Jie Zhanga,b and Xiaohua Zhua,b a School of Mechatronic Engineering, Southwest Petroleum University, Chengdu, China, b Geothermal Energy Research Center, Southwest Petroleum University, Chengdu, China

Geothermal resources development of abandoned oil and gas wells was studied. It is very significant to reduce the cost of geothermal development and improve the efficiency of oil field utilization.

1

Introduction

Abandoned wells are the products in the late stage of oil and gas development. About 20–30 million abandoned wells have been produced worldwide [1]. Improper disposal of abandoned oil/gas wells may lead to safety hazards or leakage and damage the environment [2]. In some bare and abandoned oil and gas well areas, there is no effective ecological restoration, which will lead to loose soil quality, water and soil erosion, bad weather, and other phenomena [3]. If the wellhead sealing of many abandoned oil/gas wells is not stringent, a large number of harmful flammable gases will enter the atmosphere, which causing harm to people, animals, and plants nearby [4]. At the same time, there are safety risks such as fire and explosion. In the process of exploitation, untreated fallen crude oil or spillover oil caused by loose sealing of wellhead enters the soil and river after precipitation, which causing serious harm to the soil and water environment [5]. However, many abandoned oil/gas wells are located in regions with rich geothermal resources, which store a large amount of heat energy [6,7]. At present, the development and utilization of geothermal energy are in a period of rapid development. Geothermal energy is a green, recyclable, low-carbon, and renewable resource [8], which is a widely distributed, clean, stable, and reliable clean energy with a large reserves [9,10]. Geothermal well drilling has always been the main mean of geothermal resources development [11]. However, it has higher risks and costs. If rich experience in oil and gas exploration and development could be fully utilized, geothermal resources in middle and deep strata can be exploited. It can not only solve the problems of corrosion and blockage of abandoned oil/gas Wells, but also solve the

Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00007-5 Copyright © 2022 Elsevier Inc. All rights reserved.

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Utilization of Thermal Potential of Abandoned Wells

difficulties of geothermal mining recharge [12,13]. Geothermal energy is obtained based on the comprehensive treatment of abandoned oil/wells, which has huge economic and environmental benefits [14,15]. Many scholars have researched abandoned wells. Bu et al. [6] studied the influence of working parameters on the heat extraction rate of spent oil/gas wells. Davis et al. [16] studied the effect of well temperature, injection pressure, and flow rate of organic working fluid on well’s power generation. A transient 3D model of heat transfer of rock and wellbore fluids was established by Greishi-Madiseh et al. [17]. Ebrahimi et al. [18] used organic carbon to generate geothermal energy from abandoned wells. Templeton et al. [19] simulated the transient heat transfer coupled of geothermal system. Kujawa et al. [20] found that flow rate and heat insulation affect the heat exchange of deep wells. Kharseh et al. [21] researched the geothermal energy used in oil extraction, transportation, and power supply. Nian and Yang [22,23] found that the data from oil/gas drilling, completion, and exploitation is very important for geothermal development. In this chapter, two schemes of well pattern are proposed for abandoned oil/gas wells. A two-dimensional heat fluid–structure coupled model was established. Heat production was simulated by combining the injection and production, well patterns commonly used in the oil field. The temperature distribution, pressure distribution, production temperature, and thermal extraction performance were compared. Then, the parameters of the injection-production model with a better heat recovery performance were analyzed.

2

Mathematical model

2.1 Model assumption The THM coupling process in the heat extraction process of the geothermal system has a macro effect on the production capacity of the rock matrix and the whole system [24]. A local thermal nonequilibrium method can be established when the heat reservoir is heated or cooled rapidly [25,26]. The working fluid in the whole process is water, as described by Darcy’s law.

2.2 Governing equations For the fluid flow in porous matrix, the mass conservation equation is: ρw Sm

∂p ∂e + r  ρw u ¼ ρw αB  Qw ∂t ∂t

u¼

κm ðrp + ρw grzÞ μw

(1) (2)

where the subscripts w is the water matrix. m is the rock matrix. p, u, ρw, and Sm denote the fluid pressure, the velocity vector of rock matrix, water density, and linearized

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storage of porous media. αB is the Biot coefficient. t is the time. e is the volume strain, e ¼ exx + eyy + ezz. κ m is the rock matrix permeability. Qw is the mass transfer between fractures and rock matrix. g is gravity acceleration. μw is the water dynamic viscosity. r represents the divergence operator. z is the depth direction. Mass conservation equations of fluid flow in discrete fracture network and artificial fracture are: df Sf

∂ef ∂p + rτ  uf ¼ df + Qw ∂t ∂t

(3)

κf ðrτ p + ρw grτ zÞ μw

(4)

uf ¼ df

where df is the fracture aperture. ef is the fracture volume strain. Sf is the fracturespecific storage. uf is the kinetic energy conservation equation. rτ is the gradient operator of fracture’s tangential plane. κf is the fracture permeability. Energy conservation equation in water: φm ρw cp,w

∂Tw + ρw cp,w r  ðu  Tw Þ ¼ r  ðφm λw  rTw Þ + hcon ðTm  Tw Þ ∂t

(5)

Energy conservation equation in rock matrix: ð1  φm Þρcp,m

∂Tm ¼ rðð1  φm Þλm rT Þ + hcon ðTw  Tm Þ ∂t

(6)

Energy conservation equation in fracture: df ρw cp,w


∂Tw + df ρw cp,w uf rτ Tw ¼ rτ  df λw rτ Tf + hcon ðTw  Tm Þ ∂t

(7)

where φm is the rock matrix porosity. cp,w is the water’s specific heat capacity. cp,m is the rock matrix specific heat capacity. Tw is the water matrix temperature. Tm is the rock matrix temperature. λw is the water heat conductivity. λm is the rock matrix heat conductivity. hcon is the convective heat-transfer coefficient for fractures. The simulation results using the thermal equilibrium model were larger than those using the local thermal nonequilibrium model. Accordingly, hcon is assumed as 100 W/(m2 K). The rock matrix is a linearly elastic material, its deformation satisfies Hooke’s law. The governing geomechanical equation is:
3ð1  υÞ 2 2ð1  2υÞ r σm + r  F  αB r2 p + 3βKr2 Tm ¼ 0 1+υ 1+υ

(8)

where β is the thermal expansion coefficient. K is the bulk module of the rock matrix. rF is the external body force. υ is the Poisson’s ratio. σ m is the mean total stress.

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2.3 Coupling process The relationship between effective stress and mean total stress in the thermal reservoir is [27]: σ 0 ¼ σ m + αB p

(9)

In [28,29], empirical formula of the porosity-permeability relationship of thermal reservoir is: φm ¼ φr + ðφm0 + φr Þeγσ

0

κ m ¼ κ m0 eζðφm =φ0 1Þ

(10) (11)

where κm0 is the rock matrix permeability and porosity at zero stress. φm0 is the rock matrix porosity. φr is the residual porosity at high stress. Fracture deformation can describe the fracture permeability when the porosities are constant. The relationships between total normal stress and effective normal stress of fractures are [30]: σ 0n ¼ σ n  αB p σ 0n ¼

σ 1 + σ 3  2p cos 2θ 2

(12)

0 ∗ κf ¼ κf 0 eðσn =σ Þ

where κf0 is the baseline permeability. θ is the intersection angle between fractures and principal stress. σ* is taken as 10 MPa.

2.4 Models with different wells According to the well pattern layout, two models are established. Case1 is a model with one-injection and one-production, and Case2 is a model with two-injection and one-production as shown in Fig. 1. The correctness of the computational model has been verified in reference [31]. For the two models, a randomly generated fracture grid serves as a key heat extraction channel between each injection and production well. The fracture grid is distributed randomly in the rock mass reservoir, and the distributions of the fracture grid are the same for the two models. Fig. 2 shows two different computational models. Table 1 shows the model parameters. In the injection well, the water temperature is 293.15 K. Initial temperature of the rock mass and water in the reservoir is 473.15 K. Injection pressure of the water is 19 MPa, and water pressure in the production well is 6 MPa. The initial reservoir pressure is 6 MPa.

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Fig. 1 Schematic diagram of two models.

Fig. 2 The two calculation models. Table 1 Material parameter of the model. Parameter Rock matrix Density Permeability Porosity Specific heat capacity Thermal conductivity Fracture Permeability Thermal conductivity Aperture

Value 2700 kg/m3 8  1015 m2 0.0001 J/(kg K) 3 W/(m K) 1  1010 m2 2 W/(m K) 0.0005 m

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Utilization of Thermal Potential of Abandoned Wells

Capacity analysis

Fig. 3 shows the temperature distribution of Case1 for 1a, 3a, 5a, 10a, 20a, and 40a. Fig. 4 shows the temperature distribution of Case2. Fluid flows mainly along the fracture when the fracture permeability is higher than that of the rock mass. The random 1a

3a

5a

T/K 460 440 420 400

10a

20a

40a

380 360 340 320 300

Fig. 3 Temperature distribution of Case1.

1a

3a

5a

T/K 460 440 420 400

10a

20a

40a

380 360 340 320 300

Fig. 4 Temperature distribution of Case2.

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fracture grid becomes the main water channel of EGS, so the temperature change of rock mass near the densely distributed fracture channel is faster. The heat exchange range between rock mass and fracture water gradually increases with time. The fracturing zone temperature around the injection well drops rapidly, which creating a cryogenic zone. In Case1, the low-temperature tip begins to appear after 20 years of system operation. In Case2, the low-temperature tip appears after 5 years of system operation. When the injection well number increases, the interval between injection and production wells decreases, and the time of low-temperature tip appears earlier. In Case2, the EGS experienced a thermal breakthrough when the cryogenic surface approached the producing well at 40 years. Figs. 5 and 6 show the system pressure distributions of Case1 and Case2 under different working conditions. The common characteristic of pressure changes in both cases is that as high-pressure water is injected, pressure increases throughout the reservoir, especially around the injection well. The pressure of the injection well is constant at 19 MPa and that of the production well is constant at 6 MPa. The linear distribution of pressure near the injection-production well is much denser than in other areas, which indicating a higher-pressure gradient that occurs near the injectionproduction well. The pressure isolines are concentric circles which indicate that the injection and production wells are essentially uniform pressure boundaries. When the system runs for 40a in Case1, the high-pressure area of the injection well does not completely reach the low-pressure area of the production well for the long distance between them. At the operation end, the system pressure is obviously less than that in Case2. In Case2, the high-temperature zone of the injection well gradually diffused to the low-temperature zone of production well. Fig. 7 shows the production temperature and heat extraction rate after 40 years. The long injector production distance of Case1 resulted in the slowest production temperature drop, and the maximum stable operation time in the early stage is 10.5a. The stable running time of Case2 is about 2a. At the operation end, the production temperatures of the two systems are 454.54 K and 376.49 K, respectively. When the production temperature is greater than 378.15 K and 358.15 K, respectively, the power generation and heating requirements can be met. For power generation demand, the heat recovery rates of Case1 and Case2 are 37.09% and 41.66%. Their life spans are 40.0a and 37.9a, respectively. For heating demand, the heat recovery rate of Case1 and Case2 are 37.09% and 42.68%, respectively, and their service lifes are 40.0a. Therefore, Case2 is superior to Case1 in both power generation and heating demand.

4

Parameter analysis

4.1 Effect of rock mass parameters 4.1.1 Thermal conductivity and specific heat capacity of rock mass The production temperature and heat extraction rate of the system are shown in Fig. 8. The rock mass’s thermal conductivity influences the seepage and stress fields by temperature change. The rock mass’s thermal conductivity has little effect on the temperature distribution and heat extraction rate. The results are consistent with that of

Fig. 5 Pressure distributions of Case1.

Fig. 6 Pressure distributions of Case2.

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Fig. 7 Production temperature and heat extraction rate with different injection and production well patterns.

Fig. 8 Temperature and heat extraction rate under different thermal conductivities of rock mass.

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Fig. 9 Temperature and heat extraction rate under different specific heat capacities of rock mass.

Sun et al. [32]. Fig. 9 shows the heat extraction rate and production temperature with different rock mass heat capacities over time. The rock mass’s specific heat capacity has little effect on them.

4.1.2 Rock mass permeability The increasing of rock mass permeability leads to the seepage field change, and more low-temperature heat-carrying fluids flow from fractures to rock mass. The hightemperature rock mass shrinks sharply when it encounters the low-temperature fluid. Therefore, the stress field is affected when the rock mass permeability increases. As the rock mass permeability increases, the heat extraction rate from the reservoir accelerates (Fig. 11). In Fig. 10, the early thermal breakthrough results in a drop in the temperature of the produced fluid. The preproduction temperature is stable during the 40a operation. The decreasing trend of production temperature is obvious when the permeability of rock mass increases. Under different reservoir permeabilities, the thermal extraction rate is obviously different, and it increases with the increasing of reservoir permeability. The rock mass permeability increases from 6  1015 to 9  1015 m2 resulted in a decreasing of production temperature from 384.05 K to 373.6 K. The permeability of rock mass increased from 6  1015 to 9  1015 m2, and the heat extraction rate also increased from 38.39% to 44.59%.

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Fig. 10 Production temperature curves with different rock mass permeabilities.

Fig. 11 Heat extraction ratio curves with different rock mass permeabilities.

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127

4.1.3 Rock mass porosity Figs. 12 and 13 show the production temperature and heat extraction rate under different rock mass porosities. Production temperature at the termination time increases from 376.49 K to 376.62 K when the rock mass porosity increases from 0.1% to 1%. This is because the greater the porosity, the larger the working medium carrying heat, the higher the production temperature. The porosity had little effect on the thermal extraction rate, and the thermal extraction rate decreases from 42.67% to 42.64% at the end of the operation. Therefore, rock mass porosity has little effect on the production temperature and heat extraction.

4.2 Effect of fracture parameters 4.2.1 Fracture permeability Figs. 14 and 15 show the production temperature and heat extraction rate under different fracture permeabilities. There is a difference between 1  1010 m2 and the other three parameters. When the permeability is 1  1010 m2, the production temperature has a stable period in the early stage of system operation. Fracture permeability from 1  1010 to 7  1010 m2 can decrease the production temperature at termination from 376.49 K to 352.93 K. This is because the fluid flow velocity increases with the increasing of fracture permeability, and the heat transfer time is greatly reduced. 480 Production temperature(K)

Production temperature(K)

379

460

440

378

377

40

38

420

Time(year)

jm=0.1%

400

jm=0.3% jm=0.5%

380

360

jm=1% 0

10

20

30

Time (year) Fig. 12 Production temperature curves with different rock mass porosities.

40

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Utilization of Thermal Potential of Abandoned Wells

jm=0.1% jm=0.3% jm=0.5% jm=1%

Fig. 13 Heat extraction ratio curves with different rock mass porosities.

Fig. 14 Production temperature curves with different fracture permeabilities.

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Fig. 15 Heat extraction ratio curves with different fracture permeabilities.

4.2.2 Fracture aperture Production temperature and heat extraction rate under different fracture apertures are shown in Figs. 16 and 17. The production temperature decreases with the increasing of crack aperture. Production temperature at the termination moment decreases from 377.61 to 374.16 K when the fracture aperture increases from 0.3 to 0.9 mm, and the heat extraction rate at the termination time increases from 40.97% to 44.68%. The reason is that the heat exchange and heat transfer area between the lowtemperature fluid and high-temperature rock increases with the increasing of fracture aperture, which leads to the decreasing of production temperature at the outlet. In addition, when the fracture aperture is large, the flow velocity of cryogenic fluid decreases, and heat transfer can be fully carried out with the high-temperature rock mass.

4.2.3 Fracture thermal conductivity Fig. 18 shows the production temperature and heat extraction rate under different fracture thermal conductivities. The thermal conductivity of fracture is the same as the rock mass’s thermal conductivity and specific heat capacity, and its variation has little effect on production temperature and heat extraction rate.

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Fig. 16 Production temperature curves with different fracture apertures.

Fig. 17 Heat extraction ratio curves with different fracture apertures.

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Fig. 18 Temperature and heat extraction rate under different fracture thermal conductivities.

4.3 Effect of injection temperature Fig. 19 shows the production temperature at different injection temperatures. The injection temperature increases from 283.15 to 313.15 K, and the production temperature at termination decreases from 387.01 to 371.43 K. The production temperature has a fast decreasing trend when the injection temperature is 313.15 K in the early stage of system operation. The reason is that cryogenic water’s flow rate in the reservoir is low and there is a better chance of heat transfer with the rock mass matrix. That is consistent with the results of Zhang et al. [33]. Fig. 20 shows the change of heat extraction rate at different injection temperatures. With an increasing of injection temperature, the heat extraction rate in the hot extraction process increases. This is because a higher injection temperature results in a smaller thermal stress by cryogenic fluid, which is conducive to fluid flow. When the system was closed, the heat extraction rate increases from 40.22% to 45.03%.

5

Conclusions

(1) The one-injection and one-production model and two-injection and one-production model are proposed for the utilization of abandoned wells. With the increasing of the operating life, the low-temperature area converges from the injection well to the production well, and the low-temperature area gradually increases. (2) Under the same conditions, the enhanced geothermal system with two injection-production is better than that with one injection-production. For power generation demand, the heat recovery rates of Case1 and Case2 are 37.09% and 41.66%. Their life spans are 40.0a and 37.9a, respectively. For heating demand, the heat recovery rate of Case1 and Case2 are 37.09% and 42.68%. And their service lifes are 40.0a.

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Fig. 19 Production temperature curves with different injection temperatures.

Fig. 20 Heat extraction ratio curves with different injection temperatures.

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(3) The higher the permeability of rock mass, the lower the system production temperature is, but higher is the heat extraction rate. With an increase in fracture permeability, the system production temperature decreases but the heat extraction rate increases. Rock mass’s thermal conductivity, specific heat capacity, and fracture thermal conductivity have little effect on system productivity. The production temperature decreases and the heat extraction rate increases with the fracture aperture increases. (4) The increasing of injection temperature leads to the production temperature decreases, but the thermal extraction increases. When the injection temperature is appropriate, the system can obtain a higher heat extraction rate and a longer life.

References [1] E. Barbier, Geothermal energy technology and current status: an overview, Renew. Sustain. Energy Rev. 6 (2002) 3–65. [2] Z. Chen, Environment damage by deserted oil and gas wells and concerning legal liability, J. Southwest Pet. Univ. 5 (2011) 1–9. [3] J. Liu, Study on Enhanced Geothermal Utilization System of Abandoned Oil and Gas Wells, University of Science and Technology of China, 2018. [4] G. Jiang, Transformation and Heat Transfer Study on Utilizing Abandoned Oil Well for Extracting Deep Geothermal Energy, Shandong Jianzhu University, 2020. [5] J. Guo, On the ecological environment problems and countermeasures of the deserted oil wells in Shanbei hilly region, J. Lanzhou Inst. Technol. 4 (2013) 85–87. [6] X. Bu, W. Ma, H. Li, Geothermal energy production utilizing abandoned oil and gas wells, Renew. Energy 41 (2012) 80–85. [7] C. Robert, Reuse of abandoned oil and gas wells for geothermal energy production, Renew. Energy 112 (2017) 388–397. [8] X. Zhou, Pilot test of transforming abandoned wells into geothermal wells in Dongpu Depression, Well Test. 4 (27) (2018) 27–34. [9] P. Liu, T. Liu, Development and utilization of geothermal resources in oil regions, Contemp. Chem. Ind. 11 (43) (2014) 2370–2373. [10] W. Ma, Y. Gong, D. Zhao, et al., Geothermal energy exploitation, utilization, and its development trend in China, Bull. Chin. Acad. Sci. 2 (31) (2016) 199–207. [11] Y. Li, C. Duan, X. Zheng, Best practices for high-temperature geothermal drilling, Geol. Explor. 1 (2016) 173–181. [12] X. Pu, W. Ma, Y. Huang, Geothermal energy obtained from obsolete oil and gas production wells, J. Eng. Therm. Energy Power 5 (2011) 621–625. [13] T. Li, Study on Geothermal Power Generation Using Abandoned Oil Wells, University of Science and Technology of China, 2014. [14] L. Liu, Study on Comprehensive Utilization Technology of Geothermal Resources in Oil Field, China University of Petroleum (East China), 2010. [15] X. Liu, Study on thermal resources in camp, Geotherm. Energy 4 (2001) 8–12. [16] A.P. Davis, E.E. Michaelides, Geothermal power production from abandoned oil wells, Energy 34 (2009) 866–872. [17] S.A. Ghoreishi-Madiseh, F.P. Hassani, M.J. Al-Khawaja, A novel technique for extraction of geothermal energy from abandoned oil wells, World Renew. Energy 3 (2012) 1873– 1878. [18] M. Ebrahimi, S.E.M. Torshizi, Optimization of power generation from a set of low temperature abandoned gas wells, J. Renew. Sustain. Energy 4 (2012) 063133.

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[19] J.D. Templeton, S.A. Ghoreishi-Madiseh, F. Hassani, et al., Abandoned petroleum wells as sustainable sources of geothermal, Energy 70 (2014) 366–373. [20] T. Kujawa, W. Nowak, A.A. Stachel, Utilization of existing deep geological wells for acquisitions of geothermal energy, Energy 31 (2006) 650–664. [21] M. Kharseh, M. Al-Khawaja, F. Hassani, Optimal utilization of geothermal heat from abandoned oil wells for power generation, Appl. Therm. Eng. 153 (2019) 536–542. [22] Y. Nian, W. Cheng, Evaluation of geothermal heating from abandoned oil wells, Energy 142 (2018) 592–607. [23] Y. Yang, Y. Huo, W. Xia, et al., Construction and preliminary test of a geothermal ORC system using geothermal resource from abandoned oil wells in the Huabei oilfield of China, Energy 140 (2017) 633–645. [24] S. Salimzadeh, H.M. Nick, R.W. Zimmerman, Thermoporoelastic effects during heat extraction from low-permeability reservoirs, Energy 142 (2018) 546–558. [25] Y. Chen, G. Ma, H. Wang, et al., Evaluation of geothermal development in fractured hot dry rock based on three dimensional unified pipe-network method, Appl. Therm. Eng. 136 (2018) 219–228. [26] L.-W. He, Z.-H. Jin, Effects of local thermal non-equilibrium on the pore pressure and thermal stresses around a spherical cavity in a porous medium, Int. J. Eng. Sci. 49 (2011) 240–252. [27] Y. Zhao, Z. Feng, Z. Feng, et al., THM (thermo-hydro-mechanical) coupled mathematical model of fractured media and numerical simulation of a 3D enhanced geothermal system at 573 K and buried depth 6000-7000 M, Energy 82 (2015) 193–205. [28] W. Cao, W. Huang, F. Jiang, A novel thermal-hydraulic-mechanical model for the enhanced geothermal system heat extraction, Int. J. Heat Mass Transf. 100 (2016) 661–671. [29] J. Rutqvist, Y.S. Wu, C.F. Tsang, et al., A modeling approach for analysis of coupled multiphase fluid flow, heat transfer, and deformation in fractured porous rock, Int. J. Rock Mech. Min. Sci. 39 (2002) 429–442. [30] S.A. Miller, Modeling enhanced geothermal systems and the essential nature of large-scale changes in permeability at the onset of slip, Geofluids 15 (2015) 338–349. [31] J. Zhang, M. Zhao, G. Wang, Effects of heat transfer fluid and boundary conditions on temperature field of enhanced geothermal system, Petroleum (2021) 2405–6561. [32] Z. Sun, X. Zhang, Y. Xu, et al., Numerical simulation of the heat extraction in EGS with thermal hydraulic mechanical coupling method based on discrete fractures model, Energy 120 (2017) 20–33. [33] J. Zhang, J. Xie, X. Liu, Numerical evaluation of heat extraction for EGS with tree-shaped wells, Int. J. Heat Mass Transf. 134 (2019) 296–310.

Simulation and thermodynamic modeling of heat extraction from abandoned wells

8

Ali Sohania, Ardeshir Mohammadiana, Nima Asgarib, Saman Samiezadeha, Mohammad Hossein Doranehgardc, Erfan Goodarzia, Benedetto Nastasid, and Davide Astiaso Garciad a Lab of Optimization of Thermal Systems’ Installations, Faculty of Mechanical EngineeringEnergy Division, K.N. Toosi University of Technology, Tehran, Iran, bSahand University of Technology, Tabriz, Iran, cDepartment of Civil and Environmental Engineering, School of Mining and Petroleum Engineering, University of Alberta, Edmonton, AB, Canada, d Department of Planning, Design, and Technology of Architecture, Sapienza University of Rome, Rome, Italy

Nomenclature Variables A a Ad Aup b E CW cp const dh !

F f f(t) g h hl I ! Jj

k Keff m_ P

the auxiliary parameter for wellbore temperature equation (m) coefficient of the well and fluid temperature equation (°C m
1 or K m
1) area of the downward stream (m2) area of the upward stream (m2) coefficient of the well temperature equation (°C or K) the total energy (kJ) the specific heat capacity of water at a constant pressure (kJ kg
1 K
1) the specific heat capacity at a constant pressure (kJ kg
1 K
1) a constant value hydraulic diameter (m) external forces (N) friction factor dimensionless time function gravity (m s
2) enthalpy (kJ kg
1) head loss (m) turbulence intensity the diffusion flux in energy equation thermal conductivity (W m
1 K
1) effective conductivity (W m
1 K
1) mass flow rate (kg s
1) pressure (kPa)

Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00008-7 Copyright © 2022 Elsevier Inc. All rights reserved.

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Utilization of Thermal Potential of Abandoned Wells

p R Re r rW Sm Sh t T V ! v v0 Yj Z

pressure (kPa) bigger radius (m) Reynolds number smaller radius (m) well radius (m) the source term for the continuity equation (kg m
3 s
1) the source term for the energy equation time (s) or thickness (m) temperature (°C or K) velocity (m s
1) overall velocity (m s
1) the root mean square of the fluctuations in velocity (m s
1) percentage of the jth species depth (m)

Greek symbols α β ρ τ Δ ε μ ∂

thermal diffusivity (m2 s
1) coefficient of the heat capacity equation (kJ kg
1 K
2) density (kg m
3) stress tensor (N m
2) difference roughness (m) kinematic viscosity (m2 s
1) partial derivative

Subscripts AZ DQ fluid i inj

r ref

name of one of the investigated wells in the studies name of one of the investigated wells in the studies fluid initial injection rock the reference condition

Abbreviations AOGW AZ DQ EPA GHG LCOE ORC U.S.

abandoned oil and gas well name of one of the investigated wells in the studies name of one of the investigated wells in the studies Environmental Protection Agency greenhouse gas emissions levelized cost of electricity organic Rankine cycle the United States

Simulation and thermodynamic modeling

1

137

Introduction

An abandoned well is defined as a well that is no longer used for producing oil and gas. Abandoned wells are also known between territories as temporarily inactive, orphaned, inoperative, and idle. An abandoned well is filled with concrete in order to prevent movement of liquids or gas. This procedure is called abandonment. During this process, isolation between gas and fluid is needed. The pipes utilized for extracting also should be eliminated. A portion of the methane emitted through the atmosphere belongs to abandoned oil and gas wells (AOGWs) which have not come to the attention of researchers considerably because measuring the respective CH4 emissions was next to impossible. However, attempts have recently uncovered that AOGWs are responsible for CH4 emissions; the contribution of CH4 emissions from AOGWs is assumed to be the second largest of the total CH4 emitted in the United States, where it has an estimated 3 million AWOGs [1]. Accordingly, the US Environmental Protection Agency (EPA) embodied the AOGWs in the US greenhouse gas emission (GHG) inventories since 2018 but not the accounting strategies to reduce them. A proper strategy to adopt is pertained to how much CH4 emissions does an abandoned well emit and how can reliably measure the CH4 emitted from the AOGWs. Before clarifying these questions, the types of wells should be classified and defined in the first place, depending on which state or territory is regarded. All AOGWs have had no recent production, either have not been plugged, named an idle well, or have no operator, named a deserted or long-term idle well [2]. Also, there exists other wells that have been plugged to inhibit migration of fluids. In order to return to the mentioned questions, some studies should be reviewed that directly measured the methane emissions at the ground surface during various timescales, ranging from minutes to hours. Based on the results obtained, the flow rates of methane emission produced from AOGWs vary from 1.8 g h
1  10
3 to 1.8 g h
1  10
3 to 48 g h
1 according to the status of the well, type of well, and province. Regarding the type of well, unplugged wells account for the highest flow rate of methane emission, approximately 11 g h
1, while plugged wells account for around 1.6 g h
1. In relation to the type of well, abandoned gas wells produce around 12 g h
1, which is two times more than that of oil and gas wells. The region of wells is also considered as an important factor for methane emissions. For instance, plugged wells located in Utah emit around 4.1  10
3 18 g h
1, compared to 18 g h
1 in Pennsylvania. It was estimated that about 4 million AOGWs are located in different parts of the United States. In Canada there are around 313,000 AOGWs. Also, results showed that 0.36 and 0.027 MMt of methane emissions are produced annually in the United States and Canada, respectively [3]. Regarding reducing emission from wells, the available ways are plugging the abandoned wells with and without gas flaring and capturing and using gas emissions. The options with plugging have the potential to protect groundwater resources. The cost of mitigation approaches as an important issue should also be investigated. The cost of plugging changes according to the location of the well, type of well, well depth, and well accessibility. The maximum cost of plugging is around 3565$ per ton of methane

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Utilization of Thermal Potential of Abandoned Wells

for a 50-year life span of plugging. Capturing the gas costs varies from 20$ to 200$ per well. Moreover, it was reported that flaring costs are between 32$ and 640$ per ton of methane [4]. Considering the points mentioned, in addition to the high thermal potential of abandoned wells, and energy and environmental issues, heat extraction from abandoned wells is gaining more and more attention, and this chapter provides details about modeling and simulation of the heat extraction process. The chapter is composed of six sections. The first section is the introduction, i.e., the current part. The second section gives the definition of modeling. The third section shows the ways to model different parameters. The fourth and fifth sections are different possibilities for used mesh in numerical simulation and literature review, respectively. The last and final part is conclusions.

2

Definition of modeling

Modeling means finding a “way” to determine the quantity or quality of something (called the output) based on the parameters which have effect on (known as inputs) [5]. For example, the temperature of a well has a direct relationship with the depth. Therefore, in this example, the goal is to find the value of temperature, while the effective parameter is depth. There are a variety of potential methods or “ways” that are used for modeling in engineering applications. The output could be determined based on analytical methods. In the analytical approach, a number of governing equations are written, and a mathematical function is introduced for obtaining the output based on the input parameters. If an analytical solution could not be found, the governing equations could be solved by numerical methods, and the name numerical solution refers to that [6]. Moreover, using the data-driven approaches like correlations is another way of modeling. Artificial intelligence methods, including the artificial neural network, genetic programming, response surface methodology, etc., could be also implemented. In the last two methods mentioned above, a number of available data from the system performance, usually extracted from the experiments, are used, and the way for prediction is found in such a way that an error-related criterion is minimized. Therefore, the last two methods mentioned are also known as statistical approaches [7].

3

The ways for modeling different parameters

Having provided the modeling definition, in this part the ways for modeling the parameters related to heat extraction from abandoned wells are introduced.

3.1 Well temperature In order to evaluate the potential of each well correctly, knowing the temperature of that well plays an essential role. According to the information presented in references

Simulation and thermodynamic modeling

139

like Wight and Bennett [8] and Hagoort [9], well temperature is a linear function of depth, and it could be expressed in the form of Eq. (1): T ðZ Þ ¼ aZ + b

(1)

In Eq. (1), T and Z stand for temperature and depth, respectively, a and b are also the coefficient of the correlation, which should be determined based on the available data. In fact, a is the geothermal gradient, while b shows the temperature on the ground level. For example, in the study of Hu et al. [10], the data of 14 petroleum wells in the Hinton region, which is located in Alberta, Canada (Fig. 1), was used, and Eq. (2) was found: T ðZ Þ ¼ 0:035Z + 2:29

(2)

In Eq. (2), Z should be given in meters, while T is in °C. Based on the information provided in Hu et al. [10], the average value for a is around 20–30°C (km)
1, or 0.020–0.030°C (m)
1. However, the temperature gradient for the case of Hu et al. [10] is 0.035°C (m)
1, which shows that the investigated region has a high potential for heat utilization from abandoned wells. Similar equations were also provided for the well temperature in the work done by Noorollahi et al. [11]. The correlations in Fig. 2 obtain the oil well depth as a function

150 y=0.035x+2.29 R2=0.792

140

Temperature (°C)

130 120 110 100 90 80 70 2800

3000

3200

3400

3600

Depth (m) Fig. 1 The relation between the well temperature and depth [10].

3800

4000

140

Utilization of Thermal Potential of Abandoned Wells

Fig. 2 Well depth as a function of well temperature as reported in Noorollahi et al. [11].

of well temperature. If we write them in the form of Eq. (1), Eqs. (3) and (4) are found for AZ and DQ wells, respectively: TAZ ðZÞ ¼ 0:032Z + 14:72 TDQ ðZ Þ ¼ 0:034Z + 9:34

(3) (4)

However, all the reported data for well temperature in the literature has not manifested the linear relationship between the well temperature and depth. As indicated in Fig. 3 from reference [12], for the investigated case, which was a dry abandoned well, from the top of the well to around 700 m, because of a suitable heat conduction process, temperature has an upward trend, where it reaches around 145°C. In that range, the temperature gradient is around 1.85°C (m)
1. Next, from the depth of 700–1900 m, the temperature almost stays constant. After that, however, another temperature increase could be seen from the depth of 1900 m to the well bottom.

3.2 Properties of materials Despite having several designs, a system for heat extraction from abandoned wells works similarly. In general, in a technology to exploit the heat from abandoned wells, a liquid (like water) enters the well, gains the energy from the well, and finally exits from the system for a heat consumer. A schematic picture showing the general working principle of a heat recovery system from an abandoned well is illustrated in Fig. 4. Accurate estimation of properties of materials in different technologies to exploit heat from abandoned wells, such as borehole heat exchangers, is also taken into account as an important requirement for the simulation and thermodynamic modeling of abandoned wells. In order to understand better, two different designs for the case considered in Noorollahi et al. [11] are shown in Fig. 5.

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141

Fig. 3 Different classifications of thermal storage systems [12].

Fig. 4 A schematic picture showing the general working principle of a heat recovery system from an abandoned well [13].

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Utilization of Thermal Potential of Abandoned Wells

((AZ))

((DQ)) 24”-96m

270m 730m

320m

20”-1125m

18 5/8”-730m 810m

1220m 16”-1405m

1180m 13 3/8”-1650m

13 3/8”-2175m 2270m

2060m 9 5/8”-2750m

3400m

9 5/8”-3685m

3140m 7”-3861m cement coat casing pipe

sandstone wet-sandstone

7 5/8”-4423m marl dolomite

limestone calcite

Fig. 5 Two different designs for the case considered in Noorollahi et al. [11] in which different materials are shown.

As indicated in several references, including Wight and Bennett [8], Sui et al. [14], Nian and Cheng [15], the properties of some parts such as steel and casing are usually considered to be constant. On the other hand, for other properties, usually working fluid and rock, two approaches have been implemented. One is taking them constant. The references such as Noorollahi et al. [11] could be given as an example of such a group. Another approach is to consider the temperature dependency of the mentioned group of properties, as Hu et al. [10] did. Table 1 introduces the properties of materials based on the reference [11]. As mentioned, the properties of some materials like rock could be also considered as a function of temperature. For heat capacity, like the well temperature and depth, Table 1 The specification of materials needed for simulation and thermodynamic modeling [11]. No.

Material

cp (kJ kg21 K21)

k (W m21 K21)

ρ (kg m23)

1 2 3 4 5 6 7 8 9 10

Stainless steel Cement coat Dolomite Calcite Sand Polystyrene Bentonite Marl Lime-stone Sand-stone

0.480 0.840 0.911 0.920 0.935 1.210 0.650 0.880 0.908 0.920

13.8 2.9 3.7 2.8 2.3 0.027 2.05 2.6 2.8 3.1

8055 2510 2900 2730 2600 55 2620 2650 2700 2720

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143

the relationship is linear. Eq. (5) describes the temperature dependency in this case [16–18]: CðT Þ ¼ CðTi Þ + βðΤ
Ti Þ

(5)

where C and T are the heat capacity and temperature, respectively. The subscript “i” represents the initial. β is also a coefficient. By substituting values for the case investigated in Hu et al. [10], C(T) could be found through Eq. (6) in J kg
1 K
1: CðT Þ ¼ 824:8 + 0:9343ðT
21Þ

(6)

For heat conductivity of the rock, the temperature dependent function suggested by Haenel et al. [19] could be used: kðT Þ ¼

770 + 0:7 Bð350 + T Þ

(7)

where k and T are thermal conductivity and temperature, respectively. B also represents a coefficient similar to β in the previous case. β for the investigated case of Hu et al. [10] was found to be 0.929. Therefore, the equation which shows the temperature dependency of rock thermal conductivity for that is kðT Þ ¼

770 + 0:7 0:929ð350 + T Þ

(8)

3.3 Temperature distribution in the wellbore In order to determine temperature distribution in the wellbore, an analytical method is proposed by Ramey [20]. As explained in Hu et al. [10], this method has been extensively used in the literature to obtain temperature distribution in the wellbore, as a function of depth and temperature gradient:
 Z Tfluid ðZ, tÞ ¼ aZ + b
aA + Tinj
b + aA eA

(9)

where T, Z, and t are the temperature, depth, and time, respectively. Moreover, a and b are coefficients, while the subscripts “fluid” and “inj” denote the wellbore fluid and injection, respectively. A is also an auxiliary parameter which is calculated using the following equation: A¼

mCW f ðtÞ 2πkr

(10)

_ CW, and kr are the mass flow rate, isobaric heat capacity of water, and In Eq. (10), m, thermal conductivity of rock, respectively. f(t) is also a parameter which is called the dimensionless time function. It is computed from Eq. (11):

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Utilization of Thermal Potential of Abandoned Wells



 rW f ðtÞ ¼ In pffiffiffiffi
0:29 2 αt

(11)

where rW is the well radius, α is rock thermal diffusivity, and t is time.

3.4 Continuity (mass conversion) equations In this part, the continuity governing equations are provided for two cases. One is the case studied by Noorollahi et al. [11] (Fig. 5, which is called case #1). Another is the system investigated in the study of Davis and Michaelides [21], which is schematically presented in Fig. 6. (This is considered as case #2 in the rest of this book chapter.)

3.4.1 Case #1: Ahwaz oil field in southern Iran For this case, Eq. (12) is initially written [11] as   ∂ρ ! + r  ρ v ¼ Sm ∂t

(12)

!

where ρ, t, and v are the density, time, and overall velocity vector, respectively. Moreover, Sm stands for the added or removed mass, which might come from changing the phase, or any other possibilities.

3.4.2 Case #2: South Texas oil wells in the United States The continuity equation for this case is [21] m ¼ ρVA ¼ const

(13)

_ ρ, V, and A denote the mass flow rate, density, velocity, and area, respecwhere m, tively. For the system studied in this case, Eqs. (14), (15) calculate the area of the downward and upward streams, respectively [21]:   Ad ¼ π R2
ðr + tÞ2

(14)

Aup ¼ πr 2

(15)

It is worth mentioning that the parameters appearing in Eqs. (14), (15) have been introduced in Fig. 6.

3.5 Momentum equation Following the same fashion as continuity, here, the equations for cases #1 and #2 are introduced.

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145

Fig. 6 The investigated design in the reference [21]; (A) general description; (B) flow direction and view from the top.

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Utilization of Thermal Potential of Abandoned Wells

3.5.1 Case #1: Ahwaz oil field in southern Iran Eq. (16) expresses the momentum equation for this case [11]:   ! ∂  ! ! !! ρ v + r  ρ v v ¼
rp + r  τ + ρ g + F ∂t

(16)

In addition to the parameters that have been introduced so far, the stress tensor and !

!

gravitational and external forces are indicated by τ, ρ g , and F , respectively. p shows the pressure as well.

3.5.2 Case #2: South Texas oil wells in the United States In this case, Eq. (17) could be utilized [21]: P 1 V1 P2 V2 + + z1 ¼ + + z 2 + h1 ρ1 g 2g ρ2 g 2g

(17)

where the static pressure, density, gravity, and height are indicated by P, ρ, g, and z, respectively. Head loss is also shown by hl, which is determined using Eq. (18) [21]: 1 V 2 Δz h1 ¼ f 1 2 2g dh

(18)

In Eq. (18), f is the friction factor. It is computed by Eq. (19) [22]: 20 ε 11:11 3 1 6:97 6B d C pffiffiffi ¼
1:8 log 10 4@ h A + 5 Re 3:7 f

(19)

where ε stands for the equivalent roughness, which could be considered to be 0.06 mm for cast iron [23]. Re in Eq. (19) is also the Reynolds number, which is determined based on Eq. (20): Re ¼

ρVdh μ

(20)

where μ is the kinematic viscosity. In addition, dh in Eq. (18) stands for the hydraulic diameter. For the downward and upward streams, it is calculated according to Eqs. (21) and (22), respectively [21]: dh ¼ 2

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi R2
ðr + tÞ2

dh ¼ 2r

(21) (22)

Simulation and thermodynamic modeling

147

3.6 Energy equations The energy equations are also introduced for cases #1 and #2.

3.6.1 Case #1: Ahwaz oil field in southern Iran The energy equation for case #1 is [11] !    X !  ∂ ! ! ðρΕÞ + r  v ðρΕ + pÞ ¼ r  Keff rT
hj J j + τeff  v + Sh ∂t j

(23) !

where the diffusion flux, heat source, and effective conductivity are shown by J j , Sh, and Keff, respectively. E also represents the total energy, which is determined via Eq. (24) [11]: p v2 E ¼h
+ ρ 2

(24)

h for the streams which are not compressible is obtained from Eq. (25) [11]: h¼

X j

Yj hj +

p ρ

(25)

where Yj denotes the percentage of the jth species. hj is also computed by Eq. (26) [11]: ZT hj ¼

Cp, j dT

(26)

Tref

where Cp, j is the isobaric heat capacity of the jth species, while Tref is usually considered to be 298.15 K. In addition, we have   ∂ ! ðρhÞ + r  v ρh ¼ r  ðKrT Þ + Sh ∂t

(27)

In Eq. (27), r  (K r T) is heat flux comes from the conduction heat transfer. Consid! ering the fact that in the solid area, v is 0, Eq. (27) could be expressed in the form of Eq. (28):   ∂ ! ðρhÞ + r  v ρh ¼ Sh ∂t

(28)

148

Utilization of Thermal Potential of Abandoned Wells

3.6.2 Case #2: South Texas oil wells in the United States As Fig. 6 shows, the change in the temperature of working fluid, which is isobutane, in the outer pipe is due to: (1) heat transfer between the rock and working fluid in the outer pipe and (2) heat transfer between the fluid in the inner pipe and the fluid in the outer pipe.

The energy transferred from the rock to the outer pipe could be obtained using Eq. (29) [21]: Q ¼ 2πRh½TW ðzÞ
T1 Δz

(29)

In Eq. (29), Δz is the height of the considered air volume, while T1 is the average temperature of the rock. h is also the heat transfer coefficient. It is determined from Eq. (30) [21]: h ¼ 0:023k

Re0:8 Pr0:4 dh

(30)

where Pr is the Prandtl number. In addition, the heat transfer rate between the fluid in the inner pipe and the fluid in the outer pipe (section 3–4 of Fig. 6) is determined from Davis and Michaelides [21]: _ p ðT3
T4 Þ Q34 ¼ 2πrU ðT3
Tout ÞΔz ¼ m_ ðh3
h4 Þ ¼ mc

(31)

where h is enthalpy and Uis the overall heat transfer coefficient. U is calculated by Eq. (32) [21]: U¼

1 r+t 1 r+t t 1  +  + r hi r + t k h0 2

(32)

In Davis and Michaelides [21], polystyrene was selected as the insulation. It has the thermal conductivity of 0.027 W m
1 K
1. Furthermore, hi and ho, which are the convective heat transfer coefficients of the inner and outer surfaces of the pipe, could be determined using the corresponding Nusselt numbers. They are computed via Eqs. (33), (34) [21]: Nu3 ¼

hi 2r 0:4 ¼ 0:023 Re0:8 3 Pr3 k

(33)

Nu4 ¼

h0 2ðr + tÞ 0:4 ¼ 0:023 Re0:8 4 Pr4 k

(34)

Simulation and thermodynamic modeling

149

Therefore, the amount of heat transferred to the downward stream, which flows in the outer pipe, is the summation of the two introduced heat transfer rates. In other words, and in the mathematical form Q_ 12total ¼ Q_ + Q_ 34

(35)

3.7 Turbulence intensity Based on the definition, turbulence intensity is the ratio of the root mean square of the fluctuations in velocity (v’) to the average velocity [24]. This parameter could be determined using Eq. (36) [12]: I¼

4


1 v0 ¼ 0:16ð Redh Þ 8 vave

(36)

Different possibilities for used mesh in numerical simulation

When solving the governing equations, selection of the mesh type is of great importance. However, there are several alternatives for this purpose based on the investigated system. Quadrilateral and cylindrical types of mesh have been utilized in different studies. Fig. 7 shows an example of a quadrilateral mesh, while in Fig. 8 a sample of cylindrical type is illustrated.

5

Literature review

Geothermal energy is one of the worldwide sustainable energy sources, meeting industrial and residential sectors’ power and thermal demands. However, considering the high investment costs of geothermal wells, the abandoned petroleum wells have drawn scientists’ and researchers’ attention to their economic plus points [14]. In this regard, heat transfer analysis and thermodynamic investigations of heat extraction from the abandoned wells have been conducted in recent studies, the most important of which are discussed here. The first type of geothermal energy exploitation from existing wells is known as the open-loop system, in which geothermal fluid is injected through an injection well into the reservoir in order to capture thermal energy, and then it is pumped out via an extraction well. The economic and feasibility analyses have been widely carried out on this type of geothermal system. Da´vid et al. [26] introduced a geothermal well-triplet system as the most feasible alternative among 14 examined abandoned wells, considering the geologic, hydrodynamic, and thermal limitations. Heat transfer modeling reveals that this system is feasible for at least 30 years without considering resting periods.

150

Utilization of Thermal Potential of Abandoned Wells

1500 m 40 m

Inner tube Inner casting Insulation layer Insulation casing

Annulus

Outer casing Cement Strata rock

Fig. 7 An example of a quadrilateral mesh [25].

Simulation and thermodynamic modeling

0.00

35.00

151

70.00 (m) 52.50

17.50

0.00

500.00 250.00

1000.00 (m) 750.00

Fig. 8 An example of a cylindrical mesh [11].

Comparing the influences of different well patterns (one injector and two producers, one injector and three producers, one injector and four producers) on the outcomes of the thermo-hydromechanical model of an abandoned oil reservoir in the North China Oilfield, Guo et al. [27] determined the elliptical, triangular, and square temperature fields for the mentioned well patterns, respectively. The last well pattern provides the highest output heat and the largest heat transfer area, so that is the best geothermal development model. The second alternative plan in utilizing abandoned wells’ thermal energy is converting these wells to heat exchangers through closed-loop systems. The first approach in closed-loop systems is to install the U-type heat exchangers in wells. The second and more popular approach is to use double-pipe or wellbore heat exchangers to sufficiently enhance the heat transfer rate [14]. To some extent, Hu et al. [10] developed a numerical model of a borehole heat exchanger to study the feasibility of producing geothermal energy from abandoned petroleum wells in Hinton, Alberta. Their conclusions demonstrate that the long-term performance of the heat exchanger could be notably affected owing to the temperature dependence of thermodynamic properties of both the water and the rock. Also, under the circumstances considered, the temperature drawdown extends to 80 m from the wellbore after 25 years.

152

Utilization of Thermal Potential of Abandoned Wells

Bu et al. [28] concluded that in addition to the capability of existing wells in deeper drillings, they could offer a considerable amount of reduction in expensed costs. Moreover, they found an optimal flow rate for the maximum net power and heat extraction, along with an allowed distance for the two wells proposed. The optimization results of Alimonti and Soldo’s work [29] indicated that water with a flow rate of 15 m3 h
1 is the best working fluid in terms of heat and power production compared with diathermic oil. Hydrodynamic and heat transfer modeling of the abandoned horizontal wells with CO2 as circulating medium is conducted in the article of Sun et al. [30]. Considering a decrease in the temperature and enthalpy and an increase in the cost and heat production rate, a small amount of the mass injection rate is recommended to achieve better economic performance. Moreover, taking an increase in cost and temperature into account and considering a decrease in the heat production rate, the small injection pressure is suggested to acquire better economic performance. By simulating the heat transfer process in an abandoned dry well in Sabalan Field, Northwest Iran, Noorollahi et al. [12] observed that the temperature profile of the well, the injection velocity, and the fluid mass flow rate ascertain the obtained heat from the well. They could also achieve the highest temperature of the returned fluid, varying the inlet injection velocity and fluid flow rate. Maceni and Kurevija [31], in their established numerical model of a deep dry well in the Drava subbasin, could determine the maximum heat extraction potential of 1750 MW year
1 with 1.5 MW of peak heating load in winter under the variable outside conditions. Additional horizontal branch wells are proposed by Li et al. [32] with the aim of enhancing the thermal output of borehole heat exchangers for geothermalbased building heating sectors. The produced heat could rise by 630 kW for every 1 m2 increase in the heat transfer area of horizontal branch wells, with respect to an increment in heat loss from the extraction channel to the injection channel. The power generation potentials of abandoned wells have been studied extensively by researchers. Davis and Michaelides [21] predicted the range of 2–3 MW of electric power generation potential for the typical wells in the South Texas region. Needless to say, variation in the values of different factors such as the downhole temperature, the injection pressure, the injection velocity, and the geometric characteristics of the pipe alters the amount of generated power. The feasibility analysis of power generation utilizing the downhole heat exchanger in a deep abandoned well was implemented in Yildirim et al.’s work [33]. It was observed that in order to obtain the maximum output power of 2511 kW, utilizing R134a in the organic Rankine cycle (ORC) was highly recommended. Moreover, based on the results of the economic assessment, the payback period and electricity generation cost are calculated as 2.25 years and 0.46$ MWh
1, respectively. Using ORC for power production with the heat extracted from abandoned oil wells, Kharseh et al. [13] maximized the electricity generation capacity and second law efficiency at a temperature difference, geofluid flow rate, and extraction rate of 15–17°C, 3.7–4.4 kg s
1, and 275 kW, respectively. Noorollahi et al. [11] improved the simulation of power production from two abandoned wells in southern Iran by considering a higher mass flow rate in the larger outer pipe diameter, higher temperature of the

Simulation and thermodynamic modeling

153

outlet fluid with lower thermal resistance and larger insulation thickness, and lower fluid pressure in the injection. As a result, they could generate 138 and 364 kW of electrical power, respectively, through the first and the second wells. Using the thermal reservoirs, Cheng et al. [34] could enhance the heat and electric power output by about 4 times. The techno-economic analysis conducted by Kurnia et al. [25] indicated that since the Malaysian wells have relatively low-temperature profiles, the levelized cost of electricity (LCOE) of the ORC was almost two time more than the conventional geothermal systems. Thus, in order to reduce the LCOE, it is necessary to exploit at least four other abandoned wells in the vicinity of the first well.

6

Conclusions

This chapter gave an insight into the simulation and thermodynamic modeling of heat extraction from abandoned wells. The ways for determination of a variety of important performance criteria in the design of technologies for heat recovery, including well temperature, properties of materials, temperature distribution in the wellbore, as well as continuity, momentum, and energy equations, were introduced and discussed. In addition, the common types of used mesh were introduced, and it was seen that both quadrilateral and cylindrical types of mesh have been widely used in the literature. Additionally, it was found that both analytical and numerical simulation approaches have been employed in the studies based on the investigated case.

Acknowledgment The first (corresponding) author of this book chapter sincerely thanks Dr. Muhammad Nihal Naseer, the editor of the book, for all his kind help and support during the preparation of the chapter, and wishes him the best.

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[6] A. Sohani, H. Sayyaadi, M.H. Doranehgard, S. Nizetic, L.K.B. Li, A method for improving the accuracy of numerical simulations of a photovoltaic panel, Sustainable Energy Technol. Assess. 47 (2021) 101433. [7] A. Sohani, M. Zabihigivi, M.H. Moradi, H. Sayyaadi, H. Hasani Balyani, A comprehensive performance investigation of cellulose evaporative cooling pad systems using predictive approaches, Appl. Therm. Eng. 110 (2017) 1589–1608. [8] N.M. Wight, N.S. Bennett, Geothermal energy from abandoned oil and gas wells using water in combination with a closed wellbore, Appl. Therm. Eng. 89 (2015) 908–915. [9] J. Hagoort, Ramey’s wellbore heat transmission revisited, SPE J. 9 (2004) 465–474. [10] X. Hu, J. Banks, L. Wu, W.V. Liu, Numerical modeling of a coaxial borehole heat exchanger to exploit geothermal energy from abandoned petroleum wells in Hinton, Alberta, Renew. Energy 148 (2020) 1110–1123. [11] Y. Noorollahi, M. Pourarshad, S. Jalilinasrabady, H. Yousefi, Numerical simulation of power production from abandoned oil wells in Ahwaz oil field in southern Iran, Geothermics 55 (2015) 16–23. [12] Y. Noorollahi, S.M. Bina, H. Yousefi, Simulation of power production from dry geothermal well using down-hole heat exchanger in Sabalan field, Northwest Iran, Nat. Resour. Res. 25 (2016) 227–239. [13] M. Kharseh, M. Al-Khawaja, F. Hassani, Optimal utilization of geothermal heat from abandoned oil wells for power generation, Appl. Therm. Eng. 153 (2019) 536–542. [14] D. Sui, E. Wiktorski, M. Røksland, T.A. Basmoen, Review and investigations on geothermal energy extraction from abandoned petroleum wells, J. Pet. Explor. Prod. Technol. 9 (2019) 1135–1147. [15] Y.-L. Nian, W.-L. Cheng, Evaluation of geothermal heating from abandoned oil wells, Energy 142 (2018) 592–607. [16] L. Eppelbaum, I. Kutasov, A. Pilchin, Thermal properties of rocks and density of fluids, in: Applied Geothermics, Springer, 2014. [17] W.H. Somerton, Thermal Properties and Temperature-Related Behavior of Rock/Fluid Systems, Elsevier, 1992. [18] D.W. Waples, J.S. Waples, A review and evaluation of specific heat capacities of rocks, minerals, and subsurface fluids. Part 1: minerals and nonporous rocks, Nat. Resour. Res. 13 (2004) 97–122. [19] R. Haenel, L. Stegena, L. Rybach, Handbook of Terrestrial Heat-Flow Density Determination: With Guidelines and Recommendations of the International Heat Flow Commission, Springer Science & Business Media, 2012. [20] H. Ramey Jr., Wellbore heat transmission, J. Petrol. Tech. 14 (1962) 427–435. [21] A.P. Davis, E.E. Michaelides, Geothermal power production from abandoned oil wells, Energy 34 (2009) 866–872. [22] J.A. Schetz, A.E. Fuhs, Fundamentals of Fluid Mechanics, John Wiley & Sons, 1999. [23] B.R. Munson, D.F. Young, T.H. Okiishi, Fundamentals of Fluid Mechanics, Wiley, 1998. [24] S. Hoseinzadeh, A. Sohani, S. Heyns, Comprehensive analysis of the effect of air injection on the wake development of an airfoil, Ocean Eng. 220 (2021) 108455. [25] J.C. Kurnia, Z.A. Putra, O. Muraza, S.A. Ghoreishi-Madiseh, A.P. Sasmito, Numerical evaluation, process design and techno-economic analysis of geothermal energy extraction from abandoned oil wells in Malaysia, Renew. Energy 175 (2021) 868–879. [26] B. Da´vid, S. Peter, M. Rita, I. Csaba, Feasibility of repurposing existing and abandoned hydrocarbon wells in the form of a geothermal well-triplet system, Multidiszciplina´ris Tudoma´nyok 11 (2021) 2–8.

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[27] T. Guo, Y. Zhang, J. He, F. Gong, M. Chen, X. Liu, Research on geothermal development model of abandoned high temperature oil reservoir in North China oilfield, Renew. Energy 177 (2021) 1–12. [28] X. Bu, W. Ma, H. Li, Geothermal energy production utilizing abandoned oil and gas wells, Renew. Energy 41 (2012) 80–85. [29] C. Alimonti, E. Soldo, Study of geothermal power generation from a very deep oil well with a wellbore heat exchanger, Renew. Energy 86 (2016) 292–301. [30] F. Sun, Y. Yao, G. Li, X. Li, Geothermal energy extraction in CO2 rich basin using abandoned horizontal wells, Energy 158 (2018) 760–773. [31] R. Club, S.C.O. Lukic, Measurements of radon, CO2 and hydrocarbon concentrations in soil gas and gamma dose rate for the purpose of geological model improvement. https:// www.rgn.unizg.hr/en/component/content/article/225-blog-en/2883-measurements-ofradon-co2-and-hydrocarbon-concentrations-in-soil-gas-and-gamma-dose-rate-for-thepurpose-of-geological-model-improvement?Itemid¼109 (Accessed 29 December 2021). [32] H. Li, S. Huang, X. Bu, L. Wang, Analysis of deep borehole heat exchanger with horizontal branch wells for building heating, Int. J. Low Carbon Technol. (2021). [33] N. Yildirim, S. Parmanto, G.G. Akkurt, Thermodynamic assessment of downhole heat exchangers for geothermal power generation, Renew. Energy 141 (2019) 1080–1091. [34] W.-L. Cheng, J. Liu, Y.-L. Nian, C.-L. Wang, Enhancing geothermal power generation from abandoned oil wells with thermal reservoirs, Energy 109 (2016) 537–545.

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Part IV Feasibility, economic, and environmental analysis

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The main utilization forms and current developmental status of geothermal energy for building cooling/heating in developing countries

9

Zhengxuan Liua,b, Chao Zengc, Yuekuan Zhoud,e, and Chaojie Xinga a College of Civil Engineering, National Center for International Research Collaboration in Building Safety and Environment, Hunan University, Changsha, Hunan, China, bFaculty of Architecture and the Built Environment, Delft University of Technology, Delft, Netherlands, c School of Mechanical Engineering, Southwest Jiaotong University, Chengdu, China, d Sustainable Energy and Environment Thrust, Function Hub, The Hong Kong University of Science and Technology, Guangzhou, China, eDepartment of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China

1

Introduction

In the past decade, with the improvement of people’s indoor environment demand, the energy consumption of buildings for cooling/heating has increased significantly [1]. The increasing energy consumption caused by using traditional air-conditioning systems not only exacerbates the global energy crisis but also has an important effect on the environment, especially in terms of ozone depletion and global warming [2,3]. To decrease the cooling/heating energy consumption of buildings, various renewable energy technologies (e.g., wind energy, solar energy, and geothermal energy) are utilized to reduce the application of traditional air-conditioning systems. Different from wind energy and solar energy, geothermal energy has the advantages of being consistently stable and highly efficient due to the soil’s thermal inertia [4]. In addition, geothermal energy is not limited to specific countries; it can supply energy continuously and reliably everywhere in the world. As one of the most used renewable energy, geothermal energy has attracted more and more attention [5,6]. Due to the large latent heat of the underground soil, when the outdoor environment temperature changes periodically, the soil temperature is basically constant at a certain depth. That is to say, the soil temperature at a certain depth is lower/higher than the atmospheric environment in summer/winter. Therefore, geothermal energy can be effectively utilized to provide the cooling/heating capacity for buildings in summer/winter [7]. Geothermal energy is important renewable energy with the characteristics of environmental protection, green, reliable, and sustainable, which is mainly the heat Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00009-9 Copyright © 2022 Elsevier Inc. All rights reserved.

160

Utilization of Thermal Potential of Abandoned Wells

generated and stored under the crust when the earth was formed [8]. However, the commonly mentioned geothermal energy generally refers to the fraction of the Earth’s heat that can be found in the shallow strata for space heating/cooling, power generation and domestic hot water, etc. Plenty of studies show that there are many ways to utilize the geothermal energy potential, and the basic idea is to use shallow geothermal and deep geothermal energy to develop the energy resources stored within the earth [9]. In the past decades, the importance of geothermal energy exploitation has increased on both political and social agendas all around the world [10]. A lot of research works have been carried out on the utilization of various geothermal energy technologies in buildings. Almost all the results show that making full rational use of geothermal energy technology can effectively decrease building energy consumption and improve the indoor thermal environment, which are also conducive to the improvement of the outdoor environment and carbon dioxide emission reduction [11]. In recent years, more than 30 review papers on geothermal energy utilization have been published on the website of ScienceDirect, which is a well-known database of academic journals in the world. Researchers have summarized the research status of geothermal energy in various fields and countries from different aspects. For instance, Lebbihiat et al. [12] comprehensively reviewed the historical development, current status, research practices, utilization opportunities, and barriers of geothermal energy in Algeria. Sayed et al. [13] summarized the environmental impacts of geothermal energy systems considering all the stages as well as the whole service life. Lund et al. [14] presented some review works of geothermal energy for direct utilization based on the country update papers of more than 60 countries and regions in 2020. Similar comprehensive review works were carried out in their other published papers in 2015 [15] and 2010 [16]. However, in the existing studies, there appears to be no comprehensive review of geothermal energy utilization for building cooling/heating in developing countries. The main objective of this chapter is to present the main utilization forms, current application, developmental status, and existing issues in the practical application of different geothermal energy technologies for building cooling/heating in developing countries.

2

Literature review and categories of geothermal energy utilization

2.1 Literature review on geothermal energy development for building cooling/heating in the developing countries In recent years, the application of geothermal energy in buildings in developing countries has received increasing attention. Many researchers have analyzed the important role of geothermal energy in improving the indoor thermal environment and reducing building energy consumption from different aspects. To conduct a more comprehensive understanding of the application and development trends of geothermal energy in

The main utilization forms and current developmental status of geothermal energy

161

the field of building energy-saving in developing countries in recent years, this paper summarizes the research publications of geothermal energy application in the field of building energy-saving in the developing countries during the past 20 years. The annually published papers on the application of geothermal energy in some representative developing countries from 2000 to 2021 are summarized to further analyze and predict the research tendency for building cooling/heating in summer/winter. These published papers were retrieved on the website of https://www.sciencedirect. com/, which was one of the most used literature search websites in academia. The main keywords of “Geothermal energy, China,” “Geothermal energy, Mexico,” “Geothermal energy, India,” “Geothermal energy, Iran,” “Geothermal energy, Indonesia,” “Geothermal energy, Brazil,” and “Geothermal energy, Pakistan” were selected and input in the search box of title, abstract, or author-specified keywords using the advanced search function. Table 1 and Fig. 1 show the search results of the academic publications about the application of geothermal energy in buildings in some representative developing countries. Based on the above statistical data in Table 1, a total of 371 papers have been published for the application of building cooling/heating in some representative developing countries during the past two decades. In China, the existing studies on the improvement of building thermal performance are the most extensive with a total number of 156 published papers from 2000 to 2021, which indicates that the geothermal energy system has been widely recognized and applied in the field of building energy saving in China. In addition, these statistical data also show that geothermal energy has received more and more attention in Brazil and Mexico. As shown in Fig. 1, the number of published papers on the application of geothermal energy for building cooling/heating presents an overall upward trend in the considered developing countries. It should be noted that the deadline for data statistics of the number of published papers is May 2nd, 2021. The increasing numbers of the published paper data also indicate that geothermal energy has received increasing attention for reducing building energy consumption and improving the indoor thermal environment in developing countries.

2.2 Categories of geothermal energy utilization for building cooling/heating Based on the above analysis, plenty of existing studies have shown that geothermal energy is one of the most promising energy-saving technologies for building cooling/heating, and thus it has an important role in decreasing building energy consumption and reducing carbon dioxide emissions in practical application [17]. According to different classification standards, geothermal energy can be divided into many types, such as high-, medium-, and low-temperature geothermal energy system based on the soil temperature, vertical buried-pipe and horizontal buried-pipe geothermal energy system based on the buried pipe form, open and closed cycle geothermal energy system based on heat exchange medium circulation form, etc. In this section, based on the type of heat-exchange medium and source form of pile hole, the most

Table 1 The statistics of published papers on the application of geothermal energy in some representative developing countries from 2000 to 2021. Input keywords

Year

Geothermal energy, China

Geothermal energy, Mexico

Geothermal energy, India

Geothermal energy, Iran

Geothermal energy, Indonesia

Geothermal energy, Brazil

Geothermal energy, Pakistan

2021 2020 2019 2018 2017 2016 2015 2014 2013 2012 2011 2010 2009 2008 2007 2006 2005 2004 2003 2002 2001 2000 Total

14 32 23 16 8 13 10 10 7 6 4 5 2 2 1 1 0 0 1 1 0 0 156

4 9 7 4 6 4 4 6 3 1 3 1 0 1 0 3 1 2 2 3 2 3 69

1 8 3 3 3 5 0 2 1 1 1 2 1 0 1 1 0 0 0 1 0 0 34

6 7 6 6 5 4 5 0 3 2 2 3 4 0 0 1 0 1 0 0 0 1 56

1 4 1 4 2 4 3 3 1 2 0 2 0 1 0 0 1 0 0 0 1 0 30

1 5 1 1 0 0 0 0 0 1 0 0 0 0 1 1 0 1 0 0 1 0 13

1 1 0 1 1 2 1 1 0 0 1 1 3 0 0 0 0 0 0 0 0 0 13

The main utilization forms and current developmental status of geothermal energy

163

Fig. 1 Number variation of yearly published papers from 2000 to 2021. Source: ScienceDirect.

common geothermal energy utilization can be classified into three categories: ground source heat pump (GSHP) system, underground duct system (UDS), and abandoned wells energy (AWE) system. The GSHP system is a high-efficiency heat pump using shallow geothermal energy (the general design depth is 50–200 m), which collects and transmits the heat from the underground soil through a series of buried pipes filled with liquid heat transfer medium [18]. The generated geothermal energy is sent to air-conditioning equipment units for the improvement of operating energy efficiency or directly supplied to the buildings for cooling/heating in summer/winter. According to the different heat sources, the GSHP system can be divided into the ground coupled heat pump (GCHP) system and groundwater heat pump (GWHP) system [19]. The typical GSHP systems including the GCHP system and GWHP system are illustrated in Fig. 2. From the available literature, it can be seen that these GSHP systems have been paid attention to by various countries, and a large number of studies on their application in buildings are being carried out in the world. In some developing countries, e.g., China, Mexico, and Iran, the GSHP systems have been widely used in many practical projects, which has become an important measure to reduce building energy consumption, decrease carbon emissions, and improve the indoor thermal environment. The UDS system, as one of the most common utilization forms of geothermal energy, has been considered a highly promising shallow geothermal ventilation technology in developing countries. The UDS system mainly utilizes the shallow soil with a stable and appropriate temperature to cool/heat outdoor hot/cold air in summer/

164

Utilization of Thermal Potential of Abandoned Wells

Fig. 2 The schematic design of the typical GSHP systems.

winter. Then the cooled/heated air is sent directly to the buildings through the fan, to regulate the indoor thermal environment [20]. Compared to the conventional GSHP system, the UDS system does not require outdoor unit equipment, and the fresh hot and cold air produced by the UDS system directly provides the cooling/heating capacity for the buildings only through one draught fan. Therefore, the construction cost and operation energy consumption of the UDS system is relatively low in the practical application for building cooling/heating. In recent years, the UDS system has been widely used to reduce the building energy consumption and improve the indoor thermal environment by using underground soil to cool/heat the outdoor air in summer/ winter [10]. In academia, the UDS system can also be called the underground tunnel ventilation (UTV) system [21], earth air tunnel heat exchanger (EATHE) system [22], ground-air heat exchanger (GAHE) system [23], earth to air heat exchanger (EAHE) system [24], etc. The operation principle diagram of the typical UDS system is illustrated in Fig. 3. The AWE system is a promising environmentally friendly energy-saving technology, which utilizes the middle-deep interval geothermal energy from the abandoned oil/gas wells to provide the ideal hot source for satisfying the energy demands of heating and power generation in developing countries. In the past decades, more and more oil/gas wells in the world have been abandoned due to the depletion of oil/gas reservoirs. Statistics show about 20–30 million abandoned wells all over the world, with an average well depth of more than 1000 m. The bottom temperature of these abandoned wells can reach 125–175°C [25]. Therefore, if the abandoned well energy can be fully utilized in the form of geothermal transformation, the energy consumption for building cooling/heating will be greatly reduced. In addition, it can also

The main utilization forms and current developmental status of geothermal energy

165

Fig. 3 The operation principle diagram of the typical UDS system.

reduce or avoid the serious pollution problems caused by abandoned wells, such as greenhouse gases and methane gases [26,27]. Compared to the conventional GSHP system, the abandoned oil and gas wells only need appropriate modification for the existing wells without considering new drilling, and thus the high cost of drilling can be saved, which makes the utilization of middle-deep geothermal energy more economical and feasible. At present, many researchers have carried out various studies on the application of abandoned oil/gas wells in the field of heating and power generation [28]. The schematic diagram of the typical AWE system is illustrated in Fig. 4.

3

Common utilization of the GSHP system and its current application and development

In the past few decades, plenty of GSHP systems have been widely utilized for the cooling/heating demands of various buildings in developing countries due to the attractive advantages of low environmental impact and high energy efficiency. The common GSHP system is mainly composed of the ground heat exchanger, heat pump unit, and secondary unit. The ground heat exchanger is the system’s energy source, also known as the main unit, which is commonly made by high-density polyethylene (HDPE) loops in different combinations. The common underground buried tube forms mainly include the U-shape tube, double U-shape tube, W-shape tube, 3-U-shape tube in parallel, 3-U-shape tube in series, and spiral shape tube [29], as shown in Fig. 5. The heat pump unit is a power supply equipment that uses geothermal energy to provide the cold and heat capacity for buildings. The secondary unit mainly transports the heat generated by the heat pump to the buildings, to satisfy the cold/heat requirements of the residents. In this section, the common utilization of the GCHP system and GWHP

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Fig. 4 The schematic diagram of the typical AWE system.

system and their current developments are summarized to comprehensively analyze the application potential of the GSHP system for building cooling/heating in developing countries.

3.1 GCHP system The GCHP system uses the underground soil as a heat source/sink to provide the cooling/heating capacity for various buildings, which can provide a higher-energy efficiency compared with the conventional air-source heat pump (ASHP) due to the more stable and appropriate soil temperature at a certain depth. According to the form of buried tubes, the GCHP system could be divided into a horizontal buried tube system and a vertical buried tube system [30]. In the horizontal GCHP system, the

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Fig. 5 The common underground buried tube forms of the GSHP system.

buried tubes are usually composed of a series of parallel tubes, and the buried depth is about 1–2 m. The main disadvantage of the horizontal GCHP system is that the soils around the buried tube are more susceptible to the fluctuations of ambient air temperature because they are close to the ground surface. In addition, the installation of the horizontal GCHP system requires more floor space. For the vertical GCHP system, the underground buried tubes consist of a single, tens, or even hundreds of boreholes with the diameter ranging from 100 to 200 mm based on the building areas. The common buried tube forms are one and double U-tubes with a diameter of about 19–38 mm and a buried depth of 20–200 m [31]. The typical GCHP systems with horizontal and vertical buried tubes are illustrated in Fig. 6. With the increasing awareness of the geothermal energy application and the strengthening of energy conservation in many developing countries (e.g., China), relevant policies have been promulgated, which could greatly promote the development of both horizontal and vertical GCHP systems for building cooling/heating. In practical application, the vertical GCHP system is the most commonly used technology, which has attracted the greatest attention in the research field due to its advantages of less land occupation and wide applicable scope [32]. Plenty of studies on the application of vertical GCHP systems in the various buildings have been conducted to explore their cooling/heating capacity potentials in some developing countries [33]. These studies have shown that the application of vertical GCHP systems in various buildings can greatly reduce building energy consumption and improve the indoor thermal environment [30].

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Fig. 6 The typical GCHP systems: (A) Horizontal buried tubes; (B) Vertical buried tubes.

During the long-term operation of the GCHP system, the soil around the buried tubes continuously provides the energy for the heat exchange medium in the tube, which easily leads to the heat imbalance of the soil around the buried tubes, and thus reduces the heat exchange efficiency of the GCHP system. To decrease this issue, it is necessary to achieve the intermittent operation of the GCHP system or input the heat into the soil regularly. Thus, the GCHP system needs to be combined with other energy-saving technologies, to maximize the efficient use of renewable clean energy. At present, the common coupling technologies that can achieve good application effect with the GCHP system include the solar photovoltaic/photothermal system [34], solar heat pump system [35], ASHP system [36], distributed energy system [37], energy storage system [38], etc. Almost all the studies show that the various hybrid GCHP systems have a great energy-saving potential for building cooling/ heating. In addition, it is possible to improve the application feasibility of the GCHP system for unbalanced climates in developing countries.

3.2 GWHP system The GWHP system is a highly efficient shallow geothermal utilization technology which uses the groundwater extracted from the wells or abandoned mines as a lowlevel heat source, through a small amount of electric energy input based on the heat pump technology, to achieve the heating or cooling supply in buildings [39,40]. Specifically, in summer, the GWHP system absorbs the cooling capacity from underground water through a heat pump unit and converts it into a high-grade cooling capacity to reduce the indoor temperature of buildings, to achieve the purpose of indoor cooling. In winter, the heat pump unit absorbs heat from the underground water provided by the water intake well to heat the buildings, and the heated underground water returns to the ground through the return well. If the groundwater quality is good,

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it can directly enter the heat pump for heat exchange; such a system is called the open loop GWHP system. In practical engineering, the closed-loop heat pump circulating water system is commonly used. The main reason is that the plate heat exchanger is used to separate the groundwater from the circulating water through the heat pump, to prevent the influence of sediment and corrosive impurities in the groundwater on the performance of the heat pump unit [41]. The operation principle diagram of a typical GWHP system is illustrated in Fig. 7. In the existing studies, the typical GWHP system can be classified as three types based on the different intake and return water modes, and the specific structure is shown in Fig. 8. For a single well, the utilized water is discharged to the surface water (Fig. 8A) or recharged to the extracting well (Fig. 8B). As shown in Fig. 8A, this mode is suitable for the ground with good permeability, and the surface water is close to the extracting well. Besides, it still has a risk of recharging water pollution. The mode in Fig. 8B extracts and recharges water in the aquifer to save the land occupation and investment. However, with the operation time increasing, the temperature difference between the extracting and recharging water will be reduced, and the system cannot operate under the design conditions. The GWHP system with double wells is the most common form of utilization in developing countries, as shown in Fig. 8B. The water is extracted from the extracting well and recharged into the recharging wells after heat exchange. The extracting well is usually placed upstream of the recharging well. The distance between two adjacent wells should be designed to prohibit heat interference between them [42].

Fig. 7 The operation principle diagram of a typical GWHP system.

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Fig. 8 The typical GWHP systems with different intake and return water modes: (A) Recharge to surface water; (B) Recharge to same well; (C) Recharge to different wells.

In recent years, as an environmental protection, energy-saving, and advanced airconditioning mode, the GWHP system for building cooling/heating has been developed rapidly in developing countries [43]. However, the system is suitable for the situation where groundwater resources are abundant and the local resource management department allows the exploitation and utilization of groundwater. In addition, the GWHP system requires abundant and stable groundwater resources as a prerequisite. Since the cost of well drilling is not directly proportional to the water intake, the investment benefit of a larger system may be higher. The economy of the groundwater source heat pump system is also closely related to the depth of groundwater. Therefore, before using the GWHP system, it is necessary to make a detailed hydrogeological survey and drill a survey well to obtain the data of underground temperature, underground water temperature, water quality, and water yield, so as to reasonably configure the whole system [44].

4

Common utilization of the UDS system and its current application and development

The UDS system, as an environmentally friendly geothermal energy technology, has been widely used for space cooling/heating in developing countries [45]. The soil can provide a cold/heat source in summer/winter for the flowing air in the buried tube of the UDS system due to the stable soil temperature below a certain depth all the year round. After heat exchange, the air is sent into the building by the fan, to improve the indoor thermal environment and provide fresh air for buildings. In recent years, plenty of researchers have investigated the energy-saving potential of UDS systems for building cooling/heating, which has accelerated the practical application and development of the UDS system in developing countries [46,47]. At present, the UDS system is mainly focused on the theoretical research and practical application research. The theoretical research is aimed at the establishment and

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calculation of the heat exchange model of the UDS system, and the practical application research is mainly focused on the analysis of influencing factors of the heat exchange capacity of the UDS system and its energy-saving effect in engineering applications. Almost all the results show that the UDS system could effectively reduce building energy consumption and improve the indoor thermal environment. In current studies, the common utilization of UDS systems includes the horizontal UDS system, vertical UDS system, UDS-PCM system, and UDS system-advanced energy-saving technologies. Based on these categories, the application and development of the UDG system for building cooling/heating in developing countries will be investigated and analyzed in the following chapter.

4.1 Horizontal UDS system The horizontal UDS system is designed with one or more rows of horizontal buried tubes, which is one of the most common shallow geothermal ventilation systems for building cooling/heating. It is commonly known that the buried tube depth of the horizontal UDS system is generally less than 5 m, and the most common buried depth is in the range of 2–4 m [24,48]. The common horizontal UDS system for building cooling/ heating is shown in Fig. 9A and B. The existing studies show that the UDS system with the horizontal buried tubes commonly occupies a large area because of its buried tube structure characteristics. In order to decrease the occupancy area of the horizontal UDS system, Khabbaz et al. [49] proposed a UDS system with three parallel PVC pipes for a residential building cooling in Morocco, which belonged to the hot semiarid climate areas. The horizontal single buried pipe was designed with a 72 m length, 0.15 m diameter, and 2.2–3.2 m buried depth. The schematic diagram of the horizontal UDS system with three parallel PVC pipes is presented in Fig. 10. The results showed that the UDS system was a good semipassive system for building cooling based on the experimental

Fig. 9 The common SGV system: (A) cooling in summer and (B) heating in winter.

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Fig. 10 Schematic diagram of the horizontal UDS system with three parallel PVC pipes. Reprinted from M. Khabbaz, B. Benhamou, K. Limam, P. Hollmuller, H. Hamdi, A. Bennouna, Experimental and numerical study of an earth-to-air heat exchanger for air cooling in a residential building in hot semi-arid climate, Energ. Buildings 125 (2016) 109–121. Copyright with permission from Elsevier.

results. As the outside temperature exceeded 40°C, the indoor environment temperature could still be maintained at about 25°C. The simulation results showed that the UDS system could perform a maximum outlet air temperature drop of around 19.5°C and 18.3°C for the SGV system with one and three buried pipes. When the inlet air temperature was 44.6°C, the achieved specific cooling capacity was 58 and 55 W/m2 for one pipe and three pipes, and the corresponding outlet air temperatures were 25°C and 26°C. In the practice application, the multilayer configuration of buried tubes of the horizontal UDS system has also been investigated for building cooling/heating in developing countries. The multilayer configuration is one in which the buried tubes of the UDS system are set one on the other at different depths with an obvious height difference. To explore its thermal performance, Li et al. [50] proposed a novel UDS with double-layer buried tubes, which could be an effective solution to save land occupation. The structure chart of the UDS system is shown in Fig. 11. This UDS system was designed with a buried depth of 2.5 m for the upper tube and 5.0 m for the lower tube. The total buried length was 36 m including the vertical tube, and the corresponding upper and lower tubes were 15.0 and 16.0 m, respectively. Results showed that the maximum indoor temperature and maximum heating capacity using the UDS system were 22.2°C and 7718 W, respectively, and the corresponding average temperature drop was 13.6°C during the cooling operation. In addition, the average annual COP of this proposed system could be calculated as 8.5. In addition to the efficient application of the UDS system, the current research trend of UDF system is possible to be focused on the development of some simple and accurate models, which makes the simulation calculation of the UDS system more easy to operate and its integrated design with various buildings more feasible.

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Fig. 11 Structure chart of the UDS system with double-layer buried tubes. Reprinted from H. Li, L. Ni, Y. Yao, C. Sun, Annual performance experiments of an earth-air heat exchanger fresh air-handling unit in severe cold regions: operation, economic and greenhouse gas emission analyses, Renew. Energy 146 (2020) 25–37. Copyright with permission from Elsevier.

Minaei et al. [51] developed a new transient model based on a thermal resistance capacity circuit to evaluate the system’s performance and assess the transient heat transfer of flowing air in the tube. The calculated results of the model were compared with the experimental and numerical results with good agreement between them. Using this model, the effects of buried depth, air velocity, and system operation strategy (continuous or intermittent) on the cooling/heating potential of the UDS system were studied further. Compared to the continuous operation mode, the intermittent operation mode can restore the system’s cooling capacity in summer and heating capacity in winter, which indicates that shortening the daily operation time would be instrumental in improving the heat recovery rate of the system, so as to improve the system’s thermal performance.

4.2 Vertical UDS system The vertical UDS system is not a new concept which has been mentioned in previous studies. Its main feature is that all the underground buried tubes are set vertically with a falling gradient of 90°. The depth of buried tubes is generally more than 10 m; the soil temperature at this depth is basically stable at 18–20° all the year round in various areas due to its not being commonly affected by the outdoor climate conditions and weather variations [52]. However, the research on the application of vertical buried pipe systems in buildings is rarely involved in the previous literature; the possible reason is that the UDS system with vertical buried tubes owns a relatively high construction cost in its practical application. Based on the existing literature, Zhengxuan Liu and his research team may be the first to attempt to carry out the experimental and numerical research on the application of the UDS system with vertical buried tubes in developing countries [52,53]. Their study concluded that the vertical UDS system had several apparent advantages of small land occupation, high energy efficiency, and

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timely discharge of condensate, compared to the conventional UDS system with the horizontal buried tubes [54,55]. These advantages can effectively increase the application scope of the UDS system and the application effect under different working conditions in buildings. Concerning the practical application effect of the vertical UDS system, Liu et al. [53] conducted a series of studies to investigate its temperature regulation capacity, cooling/heating potential, and economic feasibility. The schematic diagrams and construction pictures of the vertical UDS system are presented in Fig. 12. Results show that the vertical UDS system had a great energy-saving potential in the practical

Fan

Air valve

Filter

Indoor air

15.5m

A

16.5m

A Insulation layer

7.5m

Outdoor air

Bypass structure

Fig. 12 The schematic diagrams and construction pictures of the vertical UDS system. Reprinted from Z. Liu, Z. Yu, T. Yang, L. Roccamena, P. Sun, S. Li, et al., Numerical modeling and parametric study of a vertical earth-to-air heat exchanger system, Energy 172 (2019) 220– 231. Copyright with permission from Elsevier.

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application of buildings, which could provide a quite good cooling effect in summer and preheating capacity in winter for the various buildings. Specifically, as the outside air temperature exceeded 39°C, the outlet air temperature of the proposed system was still in the range from 22.4°C to 24.4°C at the air velocity of 1 m/s in summer. In winter, the outlet air temperature would remain from 16.0°C to 18.0°C. For the proposed system, for a given economic life span of 20 years, its energy payback time and carbon dioxide emission mitigation potential were calculated as 8.2 years and 7170.42 kg, respectively. In addition, the monetary payback period of the proposed system was calculated as 17.5 years. The above results demonstrate the thermal performance feasibility and economic viability of the vertical UDS system for building cooling/ heating in summer/winter.

4.3 UDS-PCM system Phase change material (PCM) absorbs and releases huge latent heat during its phase change process, which has been widely used in various systems to improve the overall performance [2]. Therefore, the UDS integrated PCM (UDS-PCM) system is suggested to be a meaningful attempt to effectively improve the performance of the UDS system for building cooling/heating in developing countries. For nearly 2 years, some researchers had explored the effects of phase change energy storage on the thermal performance of UDS systems [55,56]. These works are mainly divided into two types: one is that reducing the outlet air temperature fluctuation of the UDS system by integrating the PCM in the ventilation system, to improve the thermal comfort of the buildings. Another is that the PCM was installed around the buried tubes to improve the energy storage capacity of the surrounding medium and the supplied cooling/heating capacity of the UDS system. Liu et al. [57] explored the vertical UDS system integrating the annular PCM component to evaluate its thermal performance in hot summer and cold winter areas in China. In this coupled system, the annular PCM component was installed from the outlet to 3.6 m depth inside the vertical buried tube. The schematic diagram and site construction pictures of the vertical UDS-PCM system are presented in Fig. 13. Results showed that the annular PCM could effectively decrease the air temperature fluctuation at the outlet of the UDS-PCM system. Specifically, compared to the UDS system without PCM, the annular PCM component used around the outlet of the UDS system could decrease the outlet air temperature fluctuation by 31% and 29% under air velocities of 1 and 2 m/s. In addition, the static payback period of the UDS-PCM system was calculated as 20.8 years. For the application of another layout of the phase change energy component, Zhou et al. [58] proposed a UDS system integrating the PCM set around the buried tube to explore its effects on the energy consumption and cooling/heating potential in buildings. In this coupled system, the PCM was filled between the tube and soil, and the schematic diagram of the UDS-PCM system is shown in Fig. 14. Results showed that the UDS-PCM system had a better performance for building cooling with an improvement of about 20.24% in summer, compared to the conventional UDS system. A similar PCM structure was discussed by Liu et al. [59] to investigate the impacts of design

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Fig. 13 The schematic diagram and site construction pictures of the vertical UDS-PCM system. Reprinted from Z. Liu, Z. Yu, T. Yang, M. El Mankibi, L. Roccamena, Y. Sun, et al., Experimental and numerical study of a vertical earth-to-air heat exchanger system integrated with annular phase change material, Energy Convers. Manag. 186 (2019) 433–449. Copyright with permission from Elsevier.

Fig. 14 The schematic diagram of the UDS-PCM system. Reprinted from Q. Liu, Y. Huang, Y. Ma, Y. Peng, Y. Wang, Parametric study on the thermal performance of phase change material-assisted earth-to-air heat exchanger, Energ. Buildings 238 (2021) 110811. Copyright with permission from Elsevier.

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and operation parameters on the system’s thermal performance. The results indicated that the most suitable air velocities for improving the heat transfer performance of the UDS-PCM system were 4.5 and 6.8 m/s for the charging and discharging processes. In addition, the authors recommended applying the UDS-PCM system to some new and existing buildings in China.

4.4 UDS-advanced energy-saving technology system At present, some research works on the UDS system integrating solar chimney and solar photovoltaic/thermal (PV/T) have been conducted to broaden the application scope and energy efficiency of UDS systems in buildings. The research on the coupling technology of the UDS system and the solar chimney system has been conducted in some studies. The common operational principle of the UDS-solar chimney system can be seen in Fig. 15. In this system, the solar chimney could provide the power for the UDS system [60]. Specifically, when solar radiation irradiates the glass cavity of the solar chimney, the air in the cavity will be heated. The density of hot air is lower than that of cold air, and thus the hot air with low density can be promoted from the bottom to the top in the cavity. The migration of hot air will lead to the wind pulling effect in the solar cavity, which will drive the UDS system to inhale outdoor air and maintain the indoor air pressure balance. When the outdoor hot air is sent to the underground buried tubes of the UDS system, heat exchange between the flowing air and underground soil occurs to provide fresh cold air for the indoor environment of the building [61].

Fig. 15 Schematic diagram of the UDS system integrating solar chimney system. Reprinted from H. Li, Y. Yu, F. Niu, M. Shafik, B. Chen, Performance of a coupled cooling system with earth-to-air heat exchanger and solar chimney, Renew. Energy 62 (2014) 468–477. Copyright with permission from Elsevier.

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Maerefat et al. [61] investigated the coupled system between the UDS and solar chimney to analyze its thermal performance under the different solar radiations, outdoor air temperatures, and design configurations. Results showed that the solar chimney could supply enough power for the UDS system in the daytime without any power. In addition, the reasonable design of the coupled system could provide the indoor thermal comfort environment for several hours in hot summer. Serageldin al. [62] proposed a passive cooling/heating and ventilation system between the UDS system and solar chimney to investigate the indoor temperature and thermal energy performance in Egyptian conditions. Results showed that the proposed coupled system could attain a temperature drop of around 9 °C for indoor environments in summer. The total annual electrical energy was 42.9 kWh/m2 and the corresponding carbon dioxide emission saving was 4.545 tons/year. In recent years, the coupled technology of the UDS system and solar photovoltaic has been applied for improving the thermal environment of buildings in developing countries, especially for greenhouse buildings [63]. Nayak et al. [64] developed a simplified numerical model to explore the year-round effectiveness of the coupled system between the UDS system and solar photovoltaic/thermal (PV/T) for cooling/heating of the greenhouse in New Delhi, India. Results showed that the indoor temperature could be increased by 7–8°C using the UDS system coupling with the PV/T system in winter. The generated effective heat energy of the coupled system was 33 and 24.5 MJ in daytime and nighttime. In addition, the year-round heating capacity and net electrical energy saving of the coupled system were calculated as 24,728.8 and 805.9 kWh, respectively.

5

Common utilization of the abandoned wells energy system and its current application and development

With the progress of industrial development, emerging natural resource extraction wells have appeared all over the world. When petroleum or natural gas reservoirs are depleted beyond an economically feasible point, the wells are abandoned, decommissioned, and reclaimed. When the petroleum/gas wells are estimated to be economically unfeasible, they would be abandoned and would be referred to as “dry” wells. Abandoned petroleum/gas wells are an enduring liability to the companies that drill them, as the specific company is responsible for the possible environmental contamination and litigation in the case of a failed decommissioning of a well [65]. Generally, petroleum and gas wells are abandoned once they become depleted or unprofitable. According to the research of Caulk et al. [66], there were about 147, 127 wells indicated as abandoned, plugged, and buried in the United States. The number of abandoned wells produced in developing countries cannot be ignored. According to the research of Mehmood et al. [67], approximately 60% of total abandoned oil wells (AOWs)/abandoned gas wells (AGWs) dried in Pakistan were nonproducing. Therefore, there is great potential to utilize the geothermal energy of the AOWs /AGWs. The cost of decommissioning a well is high. If an AOW/AGW is treated improperly, it will adversely contaminate the surrounding environment [68]. One effective

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and environmental way to mitigate this problem is integrating the heat exchangers in the AOW/AGW to extract geothermal energy. Compared to the conventional vertical pipes, utilization of the drilled wells could improve the energy utilization by utilizing the high ground temperatures at deeper depth, which reaches up to 5000 m below the ground surface. According to Augustine et al. [69], the wells were drilled to 5000 m in 2003 at a cost of $ 5 million per well. As the drilling costs account for 42%–95% of the total enhanced geothermal system power plant costs, it is extremely valuable to take advantage of the predrilled and extendable abandoned wells.

5.1 Application of the AWE system This section presents the current situation and the prospects of using AOW/AGW all around the world for harvesting geothermal energy. Investigations on the suitability of utilizing the abandoned wells all around the world for enhanced geothermal systems are presented. Specifically, there are three categories, i.e., geothermal heat pump system, electric generation, and indirect heating for desalinating produced water.

5.1.1 Geothermal heat pump system The AOWs/AGWs have rich geothermal energy due to the relatively higher bottomhole temperatures; thus, they can be retrofitted to be the ground heat exchangers integrated with the geothermal heat pump systems. Compared with the conventional vertical pipes, the energy extracted from a single drilled well would be significantly improved and maximized by exchanging energy with high ground temperatures. Nian et al. [70] numerically explored the thermal performance of a 3000 m AOW, heating a

Fig. 16 Schematic diagram of geothermal heating from an abandoned oil well. Reprinted from Y.-L. Nian, W.-L. Cheng, Evaluation of geothermal heating from abandoned oil wells, Energy 142 (2018) 592–607. Copyright with permission from Elsevier.

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building with an area of 10,000 m2. Fig. 16 shows the schematic diagram of the system. By utilizing the novel system, the building’s indoor temperature of around 26°C is achieved when the HTF flow rate is set as 20 m3/h. Moreover, the system could heat a maximum area of 11,000 m2 and the bottom-hole temperature could recover to a steady-state 1 year apart. Annual heating production is about 5.5  1012 J during the entire heating period. Moreover, it has a reduction of 457 tons as the carbon dioxide emission is considered. It is delighted to find that the largest annualized cost of the novel system was approximately 50% of that of a conventional heating system. Sun et al. [71] numerically explored the carbon dioxide circulating in a geothermal horizontal well, with the diagram shown in Fig. 17. Based on the parametric study of the injection parameters on the geothermal productivity, it is concluded that the standard of choosing parameters for measuring the rate of geothermal production was related to the parameter reflecting the heat transfer rate or fluid temperature rise. Moreover, a small mass injection rate and pressure are recommended to achieve better economic performance. Moreover, Gharibi et al. [72] demonstrated the feasibility of utilizing the AOW as a geothermal resource. Based on the parameters of a real AOW in southern Iran, a 3-D numerical model of a U-tube heat exchanger was developed and simulated. In addition, an optimization study was conducted based on the parametric study of mass heat flow, fluid inlet temperature, insulation length, and pipe diameter. Results showed that

Fig. 17 Heat transfer fluid circulating in the full-length horizontal geothermal well. Reprinted from F. Sun, Y. Yao, G. Li, X. Li, Geothermal energy extraction in CO2 rich basin using abandoned horizontal wells, Energy 158 (2018) 760–773. Copyright with permission from Elsevier.

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the proposed heat exchanger worked steadily in a long-term operating period. In the case with 288.16 K inlet temperature and 0.03 m/s inlet velocity, the outlet temperature reached 324.73 K in the first year and the temperature rise declined 0.6 K after 5 years.

5.1.2 Geothermal power generation system (GPGS) Besides the direct utilization of geothermal energy for building heating, research on the utilization of power generation has been carried out based on the principle of the organic Rankine cycle. Cheng et al. [73] enhanced the geothermal utilization efficiency by developing thermal reservoirs. The structure diagram of the geothermal power system cycle is shown in Fig. 18. Results showed that the thermal reservoirs could enhance the geothermal utilization efficiency of the AOWs and steadily maintain the comprehensive power generation efficiency at about 13%. Cheng et al. [74] explored the feasibility of applying the AOW for GPGS by using the organic Rankine cycle. Results showed that the geothermal energy from the AOWs with a well deeper than 3000 m and a geothermal gradient higher than 0.04 K/m would be worth exploring. Similar works were conducted by Bu et al. [75], where the AOW, serving as a heat exchanger, was utilized to extract geothermal energy. In addition, parametric studies were conducted to reveal the regulation of the recommended values of the main parameters. They pointed out that the flow rate of the fluid and the geothermal gradient have an ignorable impact on the geothermal energy extracted from the abandoned wells. Moreover, a distance between adjacent wells of 40 m is recommended to avoid thermal interference. With an optimal setting, there is 36,833.26 US $/year saving, taking the electricity cost into account. Recovery Well 1

Injection Well A

Turbine

Generator

Evaporator 2 Stratum

Stratum

Condenser

B

Cooling Water

3

Thermal Protective coating

4

Pump

Thermal reservoirs

Stratum

Fig. 18 Schematic diagram of geothermal power generation using AOW/AGW. Reprinted from W.-L. Cheng, J. Liu, Y.-L. Nian, C.-L. Wang, Enhancing geothermal power generation from abandoned oil wells with thermal reservoirs, Energy 109 (2016) 537–545. Copyright with permission from Elsevier.

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Wight and Bennett [76] proposed and evaluated an approach using water as the wellbore fluid in combination with abandoned wells and a closed wellbore. The wellbore was therefore used as a coaxial borehole heat exchanger. A total of 2500 wells in Texas are set as the research object, using the geothermal gradient and surface temperature. By using the binary cycle power plant with a multistage heat exchanger, a net power figure of 109–630 kW was obtained. Harris et al. [68] numerically explored the outlet temperatures and heat extraction rates from the system based on a given geometry organically Rankine cycle. It specifically pointed out that 2 MW of thermal energy and 200 kW of power could be generated with 4000 m deep vertical wells and a 4800 m horizontal section. In addition, these wells could function as the heat source for GPGS for several decades. To give a wide range of power generation rates in different scenarios, Table 2 summarizes the studies conducted in previous research.

5.1.3 Desalinating produced water system Another notable function of the abandoned wells is the desalinating produced water system. By retrofitting the AOW into geothermal wells, low-temperature geothermal resources in the abandoned wells could be used to desalinate produced water. A schematic diagram of the system is shown in Amin et al.’s [83] research, as shown in Fig. 19. The produced water stream was treated on the ground surface and would no longer be injected back into the retrofitted geothermal well or the closed-loop flow system. The extracted hot water from the abandoned wells provided the powers for the desalination unit. It was positively proposed that the generated clean water represents a constant and resilient source of freshwater, which could be used for continued oil/gas operations, agriculture and to meet the nonpotable municipal demands. Table 2 Classical GPGS application integrated with AWs in previous literature. Author

Net power

Depth

Geo. gradient

Study length

Kujawa et al. [77] Davis and Michaelides [78] Cheng et al. [74] Noorollahi et al. [79] Wight and Bennett [76] Feng et al. [80] Alimonti and Soldo [81]

140 kW 3.4 MW

3950 m 3000 m

25°C/km 42°C/km

1 year –

239 kW 133 kW 217 kW 350 kW 121 kW

50°C/km 29.6°C/km 50°C/km – 23°C/km

300 days Not listed 300 days 30 years 1 year

Harris et al. [68]

2 MW

6000 m 3861 m 6000 m – 5800– 6100 m 4000 m

–

Kharseh et al. [82]

11 kW

4000– 7000 m

11–30°C / km

Several decades 25 years

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Fig. 19 Schematic diagram of a retrofitted geothermal well and its associated closed-loop flow system. Reprinted from A. Kiaghadi, R.S. Sobel, H.S. Rifai, Modeling geothermal energy efficiency from abandoned oil and gas wells to desalinate produced water, Desalination 414 (2017) 51–62. Copyright with permission from Elsevier.

5.2 Influential of geothermal utilization efficiency The benefits are ubiquitous, and the only drawback is the challenging optimization of design and operating parameters [66]. Therefore, parametrical or optimization studies should be carried out to guarantee the maximum utilization of geothermal energy. According to previous research, parameters affecting the heat transfer rate are generally summarized in Fig. 20. The influential parameters include three categories, namely geometry parameters, geothermal parameters, and working parameters. In the research of Caulk et al. [66], it was found that the flow rate has a negative impact on the temperature rise but a positive effect on the COP. Specifically, it shows that the COP was larger with moderate flow rates and greater depth. Operating parameters such as the geo-flow rate, heat extraction rate, the temperature difference

Fig. 20 Influential parameters of AW energy.

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between the HTF inlet and outlet are the main parameters when exploiting the geothermal resource. Nian and Cheng [25] specifically explored the optimal working parameters to make maximum utilization of the geothermal resource for power generation. Especially, the maximum electricity generation during 25 years in Qatar could be achieved based on the heat extraction rate of 275 kW, the geofluid flow rate of 3.7– 4.4 kg/s, and the temperature difference between the well’s inlet and outlet of 15– 17°C. Similarly, Hu et al. [28] found that the performance of heat exchangers can be controlled by varying the injected flow rate, temperature, and thermal conductivity of the pipe container. Based on their investigation, it was concluded that there was great potential for utilizing the energy using the coaxial borehole heat exchangers.

6

The existing issues and in-depth analysis on the practical application of geothermal energy for building cooling/heating

In recent years, the GCHP system is one of the fastest-growing and most popular forms of the heat pump industry in developing countries, because it is relatively less restricted by some conditions. The difficulties in the development of the GCHP system mainly focus on the thermal response experiment as well as the unbalanced cold and heat extraction. In terms of the thermal response experiment, many countries necessitate it when the application area exceeds a particular threshold (e.g., more than 5000 m2 in China), although there are currently few GCHP projects that have been executed according to the standards [84,85]. In some developed countries such as Europe and the United States, GCHP system is mainly used in commercial buildings and single residential projects. The thermal response test is required if the GCHP system is utilized in commercial buildings. Single residential projects, on the other hand, are not subject to any required standards. Furthermore, in the practical use of the GCHP system, the heat and cold balance is a critical concern. Some existing projects in diverse developing countries do not conduct yearly load calculations or balance calculations of annual heat emission and absorption during the system design stage. As a result, after 2 or 3 years of system operation, some flaws began to appear in many projects [86]. For the GWHP system, if there is no reliable recharge measure, it will cause serious consequences. The geological problems such as ground subsidence, ground fissure, and ground collapse caused by large-scale exploitation of groundwater are becoming increasingly prominent [87]. For the GWHP system, if 100% groundwater recharge to the original aquifer is implemented in strict accordance with the requirements of the government, the supply and supplement of groundwater is balanced overall, so the ground subsidence will not be caused by pumping and irrigating groundwater. However, in the practical application, because the plugging problem of recharge has not been fundamentally solved, the groundwater may be directly discharged from the

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surface. Once the geological environment problems appear, they are often catastrophic and irreparable. It can be seen from the above review that the UDS system with horizontal buried tubes is still the most common form of shallow geothermal ventilation for effectively reducing building energy consumption and improving the indoor thermal environment in developing countries. However, the most controversial problem in the practical application of the UDS system is how to solve the condensation water produced on tube walls in summer [20]. If the condensate on the tube wall for a long time cannot be solved in time, it will lead to the problem of mold breeding in the tube, thus affecting the air supply quality of the UDS system. At present, many researchers propose to increase the gradient of buried tubes so that the condensate can be concentrated in a certain position of the pipeline for centralized treatment. In practical application, some scholars set the gradient of the buried pipeline as 1–5°. Obviously, the gradient of the buried tube is relatively small, so it is still difficult to drain the condensate on the tube wall timely. However, the increase of the buried tube slope will greatly increase the construction cost and difficulty. In addition, the commonly used UDS system with horizontal buried tubes covers a large area, especially for the single row buried tube system. The foundation pit area of the UDS system with horizontal buried tubes is usually more than 50 m2, which will greatly limit the use of the horizontal buried pipe system in areas with high building density [88,89]. Although some researchers have proposed using the multirow or multilayer buried tube system to solve this problem, its land occupation area is still large, and the construction cost will also increase greatly. To solve the issue of the UDS system with horizontal buried tubes, Liu et al. [52,54] proposed the UDS system with vertical buried tubes to reduce the energy consumption and improve the indoor thermal environment of buildings in China. The UDS system with vertical buried tubes has a relatively small floor area (the foundation pit area is usually less than 1 m2) and a large buried tube slope of 90°, which is conducive to condensing timely centralized treatment. However, the practical application has proved that the construction cost of a UDS system with vertical buried tubes is relatively high. Therefore, the following studies should be carried out, mainly on how to solve the condensate treatment problem of the UDS system with horizontal buried tubes timely and how to reduce the construction cost of the UDS system with vertical buried tubes. Many abandoned wells in developing countries present an opportunity for the development of low-cost renewable geothermal energy. However, according to the previous literature, it remains several challenges for further utilization [25]. The prediction of hydraulic fractures in various stress regimes remains to be solved. Moreover, continuous effort is required to estimate the influence of thermal gradient and lithology on heat force and heat exchange rate per unit length. In addition, the benefits of utilizing the AWE were ubiquitous with the prerequisites that the designing parameters are optimized. Therefore, more studies should be carried out to optimize the design and working parameters to take the largest advantages of geothermal energy. Specifically, for the application of power generation, economic optimization should be carried out for the power plants using AOW due to its high cost.

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Nima Norouzi, Maryam Fani, and Saeed Talebi Department of Energy Engineering and Physics, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran

1

Introduction

Freshwater supply requires energy. Unfortunately, in many countries where freshwater resources are scarce, energy resources are also scarce [1–7]. As an example, Iran is a country with a dry and desert climate in a worrying situation, and while only 2.5% of the water in the world is considered fresh, Iran has a smaller share of this small amount. Only by modifying the pattern of water consumption can part of this problem be compensated. The general situation in Iran is more worrying than in the world, and the per capita share of water in Iran concerning the country’s total population is also unfavorable. According to the UN index, annual rainfall and evaporation in different parts of the world in millimeters and the water crisis in Iran indicate water scarcity in different parts [5]. Meanwhile, the average annual growth of electricity consumption in Iran is twice the world average. Therefore, it is necessary to increase electricity and water production capacities [6–9]. In addition, if we review the world’s conventional methods in this field, it is shown that according to global experience, the most widely used and main methods of desalination of seawater in medium and high volume are the RO system (reverse osmosis), MED (multistage distillation), and MSF (multistage sudden evaporation). However, the RO process has a larger share in the global desalination industry and these units are extremely feasible when the source of power is thermal. Also when the plant has access to seawater and the required volume of water and its temperature is high the thermal systems such as MSF and MED are more suitable. Another advantage of the MSF and MED is when the concentration of sea salt and total solids if the solution (TDS) is high. The technology of manufacturing RO consumables in the country has not been localized yet [10], but because there is a surplus of electricity in the network at certain times of the year, the RO method can be employed to make optimal use of the planned capacities that provide the baseload. Therefore, experts recommend a general hybrid system package (Hybrid MED +RO). Although MSF technology has a greater share in global desalination industry, due to the recent advances in MED technology and the natural advantages of this method, its share in the market is expanding rapidly [11], so that in many new and massive Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00010-5 Copyright © 2022 Elsevier Inc. All rights reserved.

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projects of cogeneration of electricity and water on the southern shores of the Persian Gulf, the MED method has been used instead of MSF in combination with thermal power plants [12]. In today’s times, in which there is an ongoing discussion about global warming, carbon emissions, and nuclear energy waste, geothermal energy could represent the hope for a radical turnaround on global energy. However, although favorable geological conditions exist, high drilling costs generally limit many useful geothermal projects. This is true for projects outside the obvious high enthalpy areas, which are often only promising prospects. On the other hand, there are hundreds and even thousands of abandoned oil and gas wells around the world that, at least in some cases, could be converted for geothermal use [13,14]. In principle, it may be feasible to use an abandoned oil or gas well for geothermal purposes due to the available facilities (well, pipes, pumps, etc.). Also, locating a nearby reception structure is necessary so that the recovered energy can be accessible [15]. The preferred development will depend on the depth or rather the temperature of the well, analysis of the heat flow, and the availability of thermal water in the reservoir. If these characteristics are present, several parameters should be monitored: type of fluids (hydrochemistry), reservoir pressure, the number of remaining hydrocarbons, porosity and permeability, sustainability of the production rate, and extent of the reservoir rock (aquifer) [16]. Under favorable circumstances, the aquifer has a regional extent that ensures constant flow and long-term production spanning several decades. Additionally, the hydrochemistry of the hot spring water should have minimal mineralization to allow for an uncomplicated operation of the geothermal plant concerning scaling (or dimensions) and corrosion [17,18]. However, in many cases, the relevant parameters for an efficient system, such as hydrothermal doublets, do not apply; therefore, their use should be considered an alternative. The most direct application would be to convert an abandoned well into a deep heat exchanger (geothermal probe). Consequently, a second well would not be necessary for reinjection, and the scaling problems due to chemical mineralization and corrosion—so frequently seen in hydrothermal systems related to the chemical composition of brines—do not occur. To carry out a deep geothermal probe, the gas or oil must be removed, and, if necessary, the remaining influx of water or oil-gas formation must be sealed employing cement plugs [19,20]. Furthermore, with the recent progress in membrane distillation technology, the utilization of direct geothermal brine with temperatures up to 60°C has shown a new technical horizon [21]. This chapter aims to provide a critical overview of seawater and wastewater water desalination using geothermal resources. Specific case studies are presented as well as an assessment of environmental risks and market potentials. The availability and suitability of geothermal energy compared to other renewable energy resources for desalination are also discussed.

1.1 Desalination using renewable energies Undoubtedly, in the short-term future, renewable energy will play an important role in human energy supply, and the crises caused by the excessive consumption of fossil

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fuels will make it more and more important to pay attention to this issue [22]. On the other hand, given the compulsion of human beings to move toward new energies, this compulsion can be made an opportunity because renewable energies create suitable employment and investment environments. According to statistics, oil resources with this use rate will be depleted in the next 50 years [23]. Therefore, to have a sustainable future, renewable energy applications must be replaced more seriously. Fig. 1 shows possible ways to use renewable energy to launch desalination technology [24]. Each of the ways involves different technologies that have their particular efficiency. Today, the use of renewable energies such as wind, water, and solar energy is very important due to their compatibility with the environment [25].

1.2 Geothermal energy and desalination The source of heat in the Earth’s crust and mantle is mainly the decomposition of radioactive materials. This internal heat is produced slowly, and is stored and trapped inside the Earth during the Earth’s life [26]. Geothermal energy comes from the natural heat of molten material inside the Earth, so it is deliberately concentrated around volcanic mountains and active areas and on the global seismic belt. One of the obvious signs of geothermal energy on Earth is hot springs [27]. Earth temperature is widely used, and geothermal energy has a temperature of more than 140°C. Geothermal energy pools are divided into low temperature (less than 150°C) and high temperature (more than 150°C) [28]. High-temperature ponds are suitable for commercial electricity generation. This energy is affordable home energy, with renewability and environmental benefits. Due to the renewable nature of geothermal energy and the low cost of environmental pollution compared to fossil fuels, more research is needed on this energy [29,30]. When using geothermal energy to power systems such as desalination plants, we avoid the need for thermal storage. In addition, this supply’s energy output is generally stable than other renewable resources such as solar and wind power [31]. Kalogirou [16] has shown that the ground temperature below a certain depth remains constant throughout the year. Popiel et al. [32] reported that one could distinguish three ground zones—surface, shallow and deep—with geothermal energy sources being classified in terms of their measured temperatures as low (150°C), respectively. Geothermal wells deeper than 100 m can reasonably be used to power desalination plants [16]. The utilization of geothermal power directly as a stream power in thermal desalination plants can also be envisaged. Furthermore, with the recent progress on membrane distillation technology, the utilization of direct geothermal brine with temperatures up to 60°C has become a promising solution [22]. Improved heat exploitation technologies, which are still at the trial stage, have huge potential for primary energy recovery of the Earth’s stored thermal energy [11,16]. Direct use of geothermal energy for heating is also commercially competitive with conventional energy sources. An exponential increase is foreseen in the geothermal heat pump sector for heating and cooling. There is an environmental advantage in that geothermal heat pumps compared to those driven by fossil fuel-fuel electricity. Using

Renewable energy source

Hydro

Sea wave

Wind

Tidal

Geotherm

Biomass

Solar

Thermal energy

Electrical energy

Mechanical vapor compression

Reverse osmosis

Multistage Flash

Multieffect distillation

Hydration

Nano filtration

Solar chimney

Thermal vapor compression

Ion-exchange resin

Electro-dialysis

Humidification dehumidification

Forward osmosis

Secondary refrigerant freezing

Capacitive deionization

Solar still distillation

Membrane distillation

Fig. 1 Classification of desalination technologies [2].

Desalination design using geothermal energy of abandoned oil wells

195

geothermal energy source reduces CO2 emissions by at least 50% compared to the fossil fuel-fired boilers. Furthermore, we support Bertani’s [33] view that renewable energy sources can significantly mitigate climate change by reducing the use of fossil fuels. Geothermal energy is accessible every day and night of the year, and can thus serve as an add-on to energy sources that are only available intermittently. An MIT study indicates a potential of more than 100 GW for the USA and 35 GW for Germany [34,35]. Up to 8% of the world’s electricity may likely be produced with geothermal resources, serving 17% of the global population [36]. Thirty-nine countries, situated by and large in Africa, Central/South America, and the Pacific, can obtain 100% of their electricity from geothermal resources [37].

1.3 Desalination and abandoned Wells Global concerns about declining water resources are growing. According to the number of water resources and per capita consumption, Iran faces physical water shortages [38]. In general, water desalination methods are divided into two main categories. Thermal water is converted to freshwater by evaporating water and then condensing [39]. This method is suitable for high-salinity waters such as seawater and oceans [40]. Among renewable energies, geothermal energy can easily be used to desalinate seawater [41]. However, geothermal energy has not yet been economically viable due to the need for expensive drilling, but the nonproduction of environmental pollution is one of the most important benefits of this energy [42]. Abandoned oil wells are a feasible source of geothermal energy in which drilling has been carried out to extract oil, and there is no need for further drilling for heat recovery purposes. The geothermal energy in these wells and the extracted heat were used to desalinate water [43]. This method reduces the overall cost of geothermal energy and uses a renewable energy source in the desalination system. Given the water crisis in Iran and the depletion of fossil fuels, renewable energy in the desalination process seems necessary [44]. In this research, geothermal desalination is evaluated using the heat of abandoned oil wells, and the appropriate water desalination method is selected. This type of freshwater is then designed, and then the process is optimized. This research includes three main steps: Step 1: Collect oil well information, desalination methods and select the appropriate method. Step 2: Model the selected method and software simulation. Step 3: Model methods to increase freshwater production.

According to the method or technology used, freshwater processes are divided into two groups [45]. l

l

membrane process, thermal processes.

The main thermal methods include: – – –

multistage sudden evaporation (MSF), multistage desalination (MED), condensed steam distillation (VCD).

196

2

Utilization of Thermal Potential of Abandoned Wells

Multistep desalination method

According to Fig. 2, the multistage desalination method’s basis is that the output of steam or steam power plants, obtained by a rock or fossil fuels or any other type of heat, enters the first Mishu stage [46]. This vapor has a low temperature and pressure and is referred to as the primary vapor [47]. The feed water is sprayed on the evaporator tubes in which the primary steam flows, and thus part of the feed water evaporates into the second stage [48]. This vapor is called secondary vapor. The saline water in the first stage enters the second stage by a pump, and the secondary steam, which was obtained from the evaporation of the feed water, condenses in the second stage by transferring its latent heat to the saline water and evaporates part of the saline water. Thus, condensed steam is collected from the second stage as freshwater, and final purification is performed [49]. Water reclassifiers were classified according to their energy source as follows [51]: – – –

3

solar desalination system, wind water desalination, geothermal water desalination.

Methods and materials

According to Table 1 and the well’s outlet temperature, which is about 114–120°C, the multistage desalination method, due to higher thermodynamic efficiency and the highest outlet temperature of this process, seems more logical. Therefore, a multistage desalination method was selected to design the geothermal desalination process using abandoned oil and gas wells. The mass and energy survival equations for the first stage are shown in Eqs. (1)–(3) [52]. brin stout stout Q + mbrin h1 + mbrout hbrout 1 h1 ¼ m1 1 1

(1)

stout mbrin + mbrout 1 ¼ m1 1

(2)

brin brout brout xbrin m1 1 m 1 ¼ x1

(3)

In these equations, Q, m, h, and x, are the heat absorbed from the oil well, flow rate, enthalpy, and salt concentration, respectively. In these equations, dis stands for desalination represents freshwater, br represents the effluent flow, and st represents steam. Energy balance for T1 to T2 can be expressed using Eqs. (4)–(6): brin stin brout brout dis + mstin hi + mstout hstout + mdis mbrin i hi i hi ¼ m i i i i hi

(4)

¼ mbrout + mstout mbrin i i i

(5)

brin ¼ xbrout mbrout xbrin i mi i i

(6)

Boiler

Steam Supply

S

Dr

Ts

TF

TF

S+Dr F1

F2 D1

D2

F5

F4

F3 D3

D4

R

F

D5

Discharge T2

T1

T3

T4

T5 Condenser

Saline Mc Tsw

1

2

B1

3

4

B3

B2

5

B4

DF D4

S+Dr

D1

Boiler

D2

D3

D1+D2+D3+Dr Product

Brine water B5

Fig. 2 Schematic of multistage desalination process [50].

198

Utilization of Thermal Potential of Abandoned Wells

Table 1 Design parameters. Parameter

Unit

Value

Water flow supply Feeding water temperature Feeding water pressure Depth of oil well Temperature of the water entering the oil well Hot water temperature coming out of the well Hot water flow coming out of the well Number of desalination process steps

kg/s °C bar m °C °C kg/s –

13.4 25 1 3860 25 114.5 9.05 12

The equations of energy and mass conservation for the last stage are given in Eqs. (7) and (8). stin dis dis fdout fdout h m fdin h fdin + mstin N1 hN1 ¼ mN hN + m

(7)

dis fdout m fdin + mstin N1 ¼ mN + m

(8)

In this equation, fd represents feeding water.

4

Results

4.1 Scenario 1: Conventional multistage geothermal desalination process According to Fig. 4, water is first injected into the well at a temperature of 25°C by a pump and exits the well at 114.5°C. This water enters the first stage of the desalination process, a heat exchanger with an operating temperature of 66°C. Hot water transfers its heat to cold water flow in this heat exchanger, the sea’s saltwater. Due to the vacuum conditions, this water starts to boil at less than 100°C and produces steam. This steam enters the next stage and plays the hot flow role in the next stage’s heat exchanger [53]. In the second stage, the steam produced in the first stage enters the second stage and condenses while giving its heat to the sea’s saltwater [54]. At this stage, some of the saltwater in the sea turns to steam. This steam enters the third stage, and the same process continues until the last stage. Fig. 3 shows a schematic of the conventional multistage geothermal desalination process.

4.2 Scenario 2: Multistage geothermal desalination process with secondary preheating The water coming out of the oil well converts some of its heat into saltwater in the heat exchanger, but this water still has enough temperature to preheat the feed water. Due to

13.4 kg/s

36.6 kg/s Preheater

Steam

Steam

Steam

Tseawater_in=25C Pseawater_in=1bar Mseawater_in=50kg/s

Steam

Cold Water outlet

Steam

Hot water inlet Desalinated water

Brine

Oil well

Desalinated water

Desalinated water

Brine

Brine

Brine

Brine

Oil well

Effect 1

Effect 2

Effect 3

Effect 4

Effect 12

Tcoldwater_in=25C Pcoldwater_in=57bar Well depth=3860m Thotwater_out=114.35C Photwater_out=3.5bar Mhotwater_out=9.05kg/s

T_op1=66C Pstage1=0.2616bar

T_op2=63.55C Pstage2=0.2344bar

T_op3=61.09C Pstage3=0.2096bar

T_op4=58.64C Pstage4=0.1871bar

T_op12=39C Pstage12=0.06971bar

Fig. 3 Schematic of a conventional multistage geothermal desalination process.

Desalinated water

Desalinated water Saline water

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Utilization of Thermal Potential of Abandoned Wells

this issue, by installing another heat exchanger, before reinjecting water into the well, its heat is used to preheat the feed water. Using this method, the temperature of feed water increases significantly and greatly impacts the freshwater produced. Fig. 4 shows the geothermal desalination process using oil wells and secondary preheating.

4.3 Scenario 3: Geothermal desalination process with secondary preheating and external flash box The basis of flash box work is that water enters the system with a certain temperature and pressure. Water starts to boil when it enters the flash box [55]. This idea can produce steam in a desalination system and increase the thermal energy in the cycle. Fig. 5 illustrates the multistage geothermal desalination process with secondary preheating and shows the external flash box [56].

4.4 Scenario 4: Geothermal desalination process with secondary preheating, external flash box, and internal flash box Each stage of the desalination stage has a lower temperature than the previous stages. Due to the secondary preheating [57], the feed water temperature in some cases reaches 45°C [58]. This temperature is higher than the operating temperature of stages 11, 10, and 12. For this reason, some of this water can be evaporated by placing a flash box in the feed water inlet [59]. Fig. 6 shows the geothermal desalination process with secondary preheating, external flash box, and internal flash box [60]. In this design, the results of the simulation of all four processes using Engineering Equation Solving (EES) software are presented [61].

4.5 Conventional multistep desalination process simulation results (Scenario 1) According to the simulation results, water production in Scenario 1 equals 316,645 L per day. The TDS of water in the first stage is higher than the later stages (in the later stages, the TDS is below the technical standard level) [62,63]. In the first stage, we have the highest amount of steam production, and this issue has caused the salt to increase above the allowable amount. Fig. 7 shows that the amount of freshwater production in the first stage is higher than all stages [64]. This is due to the higher heat recovery reached to the first stage from the geothermal heat source (Table 2).

4.6 Multistage desalination simulation results with secondary preheating (Scenario 2) According to Scenario 2, the amount of freshwater production is equal to 580,428 L per day. In this method, due to secondary preheating placement, freshwater production increases significantly (Table 3).

13.4 kg/s

36.6 kg/s Preheater

Cold Water outlet

Steam

Steam

Steam

Tseawater_in=25C Pseawater_in=1bar Mseawater_in=50kg/s

Steam Steam

Hot water inlet Desalinated water

Brine

Oil well

Desalinated water

Desalinated water

Brine

Brine

Brine

Brine

Oil well

Effect 1

Effect 2

Effect 3

Effect 4

Effect 12

Tcoldwater_in=25C Pcoldwater_in=57bar Well depth=3860m Thotwater_out=114.35C Photwater_out=3.5bar Mhotwater_out=9.05kg/s

T_op1=64C Pstage1=0.2614bar

T_op2=63.55C Pstage2=0.2344bar

T_op3=61.09C Pstage3=0.2094bar

T_op4=58.64C Pstage4=0.1871bar

T_op12=39C Pstage12=0.06971bar

Fig. 4 Schematic of multistage geothermal desalination process with secondary preheating.

Desalinated water

Desalinated water Saline water

13.4 kg/s

36.6 kg/s Preheater

Cold Water outlet

Steam

Steam

Steam

Tseawater_in=25C Pseawater_in=1bar Mseawater_in=50kg/s

Steam Steam

Hot water inlet

Steam Desalinated water

Brine

Desalinated water

Desalinated water

Brine

Brine

Desalinated water

Brine F.B

Product

Product

Oil well

Effect 1 T_op1=64C Pstage1=0.2614bar

Effect 2 T_op2=63.55C Pstage2=0.2344bar

F.B

Product

Oil well Tcoldwater_in=25C Pcoldwater_in=57bar Well depth=3860m Thotwater_out=114.35C Photwater_out=3.5bar Mhotwater_out=9.05kg/s

Brine

F.B

F.B

Effect 3 T_op3=61.09C Pstage3=0.2094bar

Product

Effect 4

Effect 12

T_op4=58.64C Pstage4=0.1871bar

T_op12=39C Pstage12=0.06997bar

Fig. 5 Geothermal desalination process with secondary preheating, external flash box.

Desalinated water

Desalinated water Saline water

13.4 kg/s

36.6 kg/s F.B

Steam

Cold Water outlet

Steam

Steam

Steam

F.B

Steam

Tseawater_in=25C Pseawater_in=1bar Mseawater_in=50kg/s

Steam

Steam

Preheater

Steam

Hot water inlet Desalinated water Brine

Desalinated water

Brine

Steam Desalinated water

Desalinated water

Brine

Brine

Brine Desalinated water

F.B

F.B

Brine

F.B F.B Product

Product

Product

Product

Oil well

Oil well

Tcoldwater_in=25C Pcoldwater_in=57bar Well depth=3860m Thotwater_out=114.35C Photwater_out=3.5bar Mhotwater_out=9.05kg/s

Effect 1

Effect 2

Effect 3

Effect 4

Effect 11

Effect 12

T_op1=64C Pstage1=0.2614bar

T_op2=63.55C Pstage2=0.2344bar

T_op3=61.09C Pstage3=0.2094bar

T_op4=58.64C Pstage4=0.1871bar

T_op11=41.45C Pstage11=0.07971bar

T_op12=39C Pstage12=0.06997bar

Fig. 6 Geothermal desalination process with secondary preheating, external flash box, internal flash box.

Desalinated water Saline water

204

Utilization of Thermal Potential of Abandoned Wells

Freshwater(L/day)

60000 50000 40000 30000 20000 10000 0 1

2

3

4

5

6 Stage

7

8

9

10

11

12

Fig. 7 The amount of freshwater production in each of the stages of Scenario 2. Table 2 Production of freshwater, saltwater, and salt related to Scenario 1.

Level

Saltwater output (l/day)

Freshwater (l/day)

1 2 3 4 5 6 7 8 9 10 11 12

40,768 47,596 53,968 59,886 65,354 70,376 74,956 79,096 82,800 86,074 88,914 91,330 Freshwater production

55,712 48,884 42,512 36,594 31,126 26,104 21,524 17,384 13,680 10,408 7566 5150 3,16,645

Output water salt (g/l) 82.83 70.95 62.57 56.39 51.67 47.98 45.05 42.69 40.78 39.23 37.98 36.7

According to this figure, the amount of freshwater production in the first stage is the highest; the reason for this is that in the first stage, the hot water out of the oil well has the most heat to produce freshwater, so this step produces the most steam. For this reason, the amount of steam production decreases with increasing phases. Fig. 8 also shows the amount of saline water production in each stage in liters per day. As expected, when we have the highest steam production amount in the first stage, the amount of output saline water is also at its lowest. This amount increases until the steam production decreases; then, with the increase of the amount of steam production, this amount also decreases in the last stages.

Desalination design using geothermal energy of abandoned oil wells

205

Table 3 Production of freshwater, saltwater, and salt related to Scenario 2.

Level

Saltwater output (l/day)

Freshwater (l/day)

1 2 3 4 5 6 7 8 9 10 11 12

37,323 40,725 43,687 46,212 48,305 49,969 51,206 52,021 52,416 52,395 51,960 51,114 Freshwater production

59,157 55,755 52,793 50,268 48,175 46,511 45,274 44,459 44,064 44,085 44,520 45,366 5,80,428

Output water salt (g/l) 90.48 82.92 77.3 73.07 69.91 67.58 65.95 64.91 64.42 64.45 64.99 66.06

70000

Freshwater (L/day)

60000 50000 40000 30000 20000 10000 0 1

2

3

4

5

6

7

8

9

10

11

12

Stages

Fig. 8 The amount of freshwater production in each of the stages of Scenario 2.

4.7 Multistage desalination simulation results with secondary preheating and external flash box (Scenario 3) Some other steam is produced from the flash box’s desalinated water by adding an external flash box to the previous process and the steam produced in each converter. This steam enters the next stage together with the steam produced in the converter. The amount of freshwater production, in this case, has increased to 590,014 L per day (Table 4).

206

Utilization of Thermal Potential of Abandoned Wells

Table 4 Production of freshwater, saltwater, and salt related to Scenario 3.

Level 1 2 3 4 5 6 7 8 9 10 11 12

Saltwater output (l/day)

Freshwater (l/day)

37,323 40,725 43,428 45,711 45,774 49.19 50,047 50,659 50,857 50,829 50,801 50,772 Freshwater production

59,157 55,770 53,064 50,799 48,915 47,468 46,438 45,824 45,624 45,651 45,679 45,904 5,90,014

Output water salt (g/l) 90.48 82.92 77.76 73.87 70.98 68.89 67.48 66.66 66.4 66.43 66.47 66.51

70000

Freshwater (L/day)

60000 50000 40000 30000 20000 10000 0 1

2

3

4

5

6 7 Stage

8

9

10

11

12

Fig. 9 The amount of freshwater production in each of the stages of Scenario 3.

Fig. 9 also shows the amount of desalinated water production at each stage. As expected, this diagram’s process is similar to the secondary preheating method, except that in the stages in which the flash box is used, the amount of saline water production is less; in other words, more steam is produced. Fig. 8 shows the amount of freshwater production in liters per day for each method’s steps. According to the previous methods, in this method, the stage has the largest water production share. The water production process in this method is the same as the secondary preheating method, with the difference that in this method, the amount of production has increased compared to the previous method in the stages in which external flush boxes are used. The amount of freshwater production, in this case, has increased to 590,014 L per day.

Desalination design using geothermal energy of abandoned oil wells

207

4.8 Multistage desalination simulation results with secondary preheating, external flash box, and internal flash box (Scenario 4) With the increase of internal flash boxes to the process, the amount of freshwater production in steps 10 and later increases due to internal flash boxes. The steam produced in stages 10, 11, and 12 is injected into the inlet steam to each of those stages to increase their heat load. It should be noted that the steam produced in the internal flash box is added to the total freshwater in the process because it is produced from saltwater fed to this steam (Table 5). Fig. 10 shows the amount of saline water output at each stage. The process of this shape is the same as the process of the previous method. The saline water output had decreased with the difference in the last three stages when the internal flash box was added. Fig. 9 shows the amount of freshwater production in each stage of this process. As shown in the figure, the freshwater production in this initial stage up to stage 10 is equal to the previous method without an internal flash box. In stages 10, 11, and 12, with the addition of the internal flash box, freshwater production equals 592,779 L per day.

5

Economic analysis

The process is analyzed economically using the net present value method. It should be noted that this chapter examines the rate of inflation for several different cases. In addition, the lifespan of the power plant is assumed to be equal to 20 years. For better analysis, the results of all four inflation rates are plotted in one figure. Figs. 11 and 12 Table 5 Production of freshwater, saltwater, and salt related to Scenario 4.

Level 1 2 3 4 5 6 7 8 9 10 11 12

Saltwater output (l/day)

Freshwater (l/day)

37,323 40,725 43,428 45,711 45,774 49,019 50,047 50,659 50,857 50,642 50,016 48,979 Freshwater production

59,157 55,770 53,064 50,779 48,915 47,468 46,438 48,524 45,624 45,837 46,462 47,700 5,92,779

Output water salt (g/l) 90.48 82.92 77.76 73.87 70.98 68.89 67.47 66.66 66.4 66.68 67.51 68.94

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Utilization of Thermal Potential of Abandoned Wells

Freshwater (L/day)

70000 60000 50000 40000 30000 20000 10000 0 1

2

3

4

5

6

7 Stage

8

9

10

11

12

Fig. 10 The salinity of effluent water in each of the steps of Scenario 4.

Fig. 11 Comparison of return on investment (ROI) for different inflation rates.

illustrate the results of the “return rate on investment” and “net present value” calculations for five different inflation rates. These figures show a general comparison of the plan’s economic performance regarding inflation and different interest rates. As shown in Fig. 11, the higher net present value is calculated for higher inflation rates.

6

Conclusion

According to modeling and simulation, the oil well selected in this research can produce 9.05 kg/s of fluid at a temperature of 114.5°C. This study’s calculations showed that a well with this temperature and flow rate could produce 316 cubic meters of

Desalination design using geothermal energy of abandoned oil wells

209

Fig. 12 Comparison of net present value for the different inflation rate.

freshwater per day. This study showed that the use of secondary preheating and raising the feeding water temperature impact water production in the each of desalination stages. The amount of freshwater production was calculated using secondary preheating of 580 cubic meters per day. In this plan, by placing the flash box in the freshwater path, the amount of freshwater production reached 590 cubic meters per day, which, when compared to the previous case, shows that water production has increased by 10 cubic meters. The use of flash boxes in the feed water path can also help produce more freshwater, and the amount of freshwater production reached 592 cubic meters per day. This research’s economic analysis results are presented based on 10%, 15%, 20%, and 25% inflation rates. The results showed that for the stated inflation rates, the net present value is equal to zero for the interest rates of 29%, 44%, 49%, and 54%, respectively. In other words, the net present value becomes zero when the plan is not economically viable, and the fact that the plan is zero at this interest rate indicates that the economic plan is economical at a lower interest rate.

References € ur, 2010 Present status of geothermal energy in Turkey, in: [1] U. Serpen, N. Aksoy, T. Ong€ Proceedings of Thirty-fifth Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA, USA, 1–3 February 2010, 2010. SGP-TR-188. [2] H. Mahmoudi, N. Spahis, M.F.A. Goosen, N. Ghaffour, N. Drouiche, A. Ouagued, Application of geothermal energy for heating and fresh water production in a brackish water

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[11]

[12] [13]

[14]

[15]

[16] [17] [18]

[19]

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Utilization of Thermal Potential of Abandoned Wells

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Part V Applications and case studies

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Electricity generation using heat extracted from abandoned wells

11

Hamdy Hassana,b a Energy Resources Engineering Department, Egypt-Japan University of Science and Technology (E-JUST), Alexandria, Egypt, bMechanical Engineering Department, Faculty of Engineering, Assiut University, Assiut, Egypt

1

Introduction

All nations over the world have shown great interest in the resources of geothermal energy (GE). It is one of the renewable energy types that is generated inside the Earth and could be transformed into electrical energy or be directly utilized for heating purposes. It is found that the amount of geothermal heat available within 104 m2 of the Earth’s surface is estimated to contain 5  104 times greater energy than all gas resources and oil worldwide. Since the extracted heat is little compared to the content of Earth’s heat, geothermal generated power is considered a renewable and reliable energy source. Geothermal heat energy is generated from the Earth’s internal heat which is available under the surface of the Earth. It is obvious that geothermal heat energy in most world parts has a huge potential for heat. However, it has been created and existed for more than a century, their investment rate was primarily slow. In the last decades, the available energy sources were essentially utilized for heating purposes all over the world, which are involved in extreme weather conditions. For example, in Africa, Kenya is considered a leader in its GE investment. Around 37% of the energy supply of this country was from geothermal heat energy. Joining geothermal heat energy with other resources of renewable energy would significantly decrease the reliance on other resources of nonrenewable energy and fossil fuels. Some cities, in the case of Iceland, are slowly substituting their powered heating systems of fossil fuel with geothermal heating systems. Still, there is further to do to effectively use the available resources of geothermal energy. Despite the heat extracted being less compared to the heat content of the Earth, the geothermal generated power is considered a renewable source of energy and a reliable source. The emission of the geothermal power plants represents 45 g of CO2 per kWh of electricity, or about 5% smaller than conventional-fired coal plants. Geothermal wells are drilled into the crust of the Earth at 3–10 km depth to abstract the geothermal stored energy [1]. Different techniques are utilized to extract heat from inside the Earth’s deep layer, however the most known is the utilization of steam and water. Heated water from the geothermal hot reservoir can be directly pumped and channeled to heat buildings and homes. This is carried out by either pumping heated water through a heat exchanger that dissipates heat through the buildings’ structure or by circulating the heated water around the homes or Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00011-7 Copyright © 2022 Elsevier Inc. All rights reserved.

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buildings. Also, the heated water can be transferred to steam which is used to run a turbine that generates electrical power. Geothermal energy sources have different advantages as a renewable energy source including: l

GE source does not have bad impact on the environment

First, the heat of GE is subtracted from the earth by not including burning fossil fuels, besides geothermal sources don’t yield practical emissions. In addition, the heat of GE can be highly worth, where it can save more than 80% of traditional energy use. l

GE is a reliable energy reserve

The heat of GE also has different merits by comparing to other renewable sources such as wind, biomass, or solar energy. It is considered a special continuous energy source, which means that it depends on neither wind nor sun, and it is obtainable throughout the year. l

GE systems have high efficiency

Systems of heat pumps relying on geothermal energy utilize from 25% to 50% lower electricity than traditional energy systems for heating and cooling, and with an adaptable design, these systems can be adjusted to various conditions, needing less space for hardware as compared to traditional energy systems. l

GE systems require small to no maintenance

Because geothermal energy systems have only few removable parts that are protected inside a building, the life span of the system of heat pumps relying on GE is reasonably high. Pipes of this heat pump have warranties of 25–50 years; however, the heat pump can generally last for at least 20 years. l

From the point of view of the availability factor

GE is a constant and reliable energy source and is ranking on the top as shown in Fig. 1.

AVAILABILITY FACTOR

80 60 40 20 0 Solar PV

Wind

Fig. 1 Availability factor of geothermal energy [2].

Biomass

Geothermal

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Nevertheless, sometimes negative sides of the GE exist, so let us see them in the following: l

Land requirements for the installation of geothermal system:

In the case of geothermal systems a piece of land beside the home is needed to install a geothermal system. That makes GE systems difficult to be applied for home possessors in large towns, except in the vertical ground resource, the heat pump is utilized. l

High investment costs for GE system:

Another drawback is the elevated initial cost for individual house owners. The requirement for drilling and establishing quite a complicated system into one’s house makes the price climbs relatively high. However, the outcome of such GE investment is very promising, which can earn the investment back within 2–10 years. l

Partially environmental matters concerning emissions:

No matter the reputation of GE to be a friendly alternative resource to the environment, inopportunely, GE causes some slight concerns related to the environmental impact. The GE extraction from the Earth leads to the release of some greenhouse gases such as hydrogen sulfide, carbon dioxide, ammonia, and methane. Nevertheless, the quantity of greenhouse gas emitted is considerably smaller than that of the fossil fuels. l

Possibility of depletion of geothermal sources:

Besides, in spite of geothermal sources are considered renewable and sustainable energy, particular sites of GE maybe cool down after time, and it is not possible to harvest additional GE in the future. The only choice is sourcing GE well from magma but it is still in progress. This choice adds value to the investment essentially because hot magma will remain for billions of years.

2

Geothermal energy resources

The total stored thermal energy inside the Earth is of order 12.6  106 million EJ whereas that of the Earth’s crust is of order 5.4  103 million EJ in the depth of 50 km. The essential sources of GE are generated by continuous decaying of radioactive isotopes in the Earth’s crust itself and the heat generating from the Earth’s core and mantle. Heat is transported mostly by conduction from the inside to the surface at 0.065 W/m average value on continents and 0.101 W/m2 throughout the floor of the ocean. The outcome is a total terrestrial heat flow rate of about 1400 EJ per year. Seeing that continents include approximately 30% of the surface of the Earth and their average energy flow is less, which is assessed at 315 EJ per year. Various kinds of resources of geothermal heat energy can be classified into [3]: Vapor-dominated resources Liquid/hot water resources Geo-pressurized resources Hot dry rock resources Molten rock or magma resources Radiogenic resources

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2.1 Vapor-dominated resources Nearly all of the currently exploited GE resources comprise water at a high temperature of 100°C and high pressures. As this water is transported to the surface of the Earth, its pressure level is significantly decreased, producing great amounts of steam, and also a mix of saturated steam and liquid water is generated. The yielded steam to water ratio diverges from one place to another place. Some of the finest famous GE resources, such as Wairakei (New Zealand), Cerro Prieto in Mexico, Salton Sea in United States, Otake in Japan, and Reykjavik (Iceland). Hence steam accompanying with water is formed in these resources, these yielded steam and water are recognized as reservoirs of wet steam. There are restricted other significant GE fields such as The Geysers in the United States and Larderello (Italy) which yield steam of superheated condition with no supplementary fluids. Reservoirs of the last sort are recognized as reservoirs of dry steam. The main prerequisites of the vapor-dominated GE reservoirs whether of wet steam or dry steam type, comprise sufficient deliveries of water besides the prerequisites stated previously. The fact that some of these vapordominated geothermal reservoirs are situated on or beneath volcanoes, or are sited in the zones of the latest volcanism has proved that magma is considered their resource. Young (high temperature ranging from 500°C to 1000°C) magma disturbances within a depth of a few to many kilometers from the surface of the Earth permit the essential heat to be collected in inexpensive quantities. Good geothermal fields can also be constructed at the formation and unconventionality boundaries signified that they have good hydraulic water supply and continuity and are permeable (Fig. 2).

Higher than average heatflow

Hot Spring

Steam Well

Fumarole

Geyser

rainfall recharges aquifer water table

F F

F

Impermeable Cap Rock or Seal

Steam

Confined Aquifer

Unconfined Aquifer

Confined Aquifer Vapor

Boiling surface water table

Recharge

Impermeable Crystalline Rocks Heat Source (e.g. Crysatilline Granite)

Fig. 2 Vapor-dominated geothermal energy resources [4].

F indicates fault

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2.2 Liquid/hot water resources Some of the hot liquid geothermal water is formed by underground water distributing to profound and rising from buoyancy in porous geothermal reservoirs which are at a regular temperature on a larger volume. It exists naturally on an upper flowing region at the middle of each convective hot cell, an outgoing flowing area or plume of hot water going sideways departure from the system center, and a downward flowing region where recharge is occurring. Surface indicators comprise fumaroles, geysers, hot springs, chemically modified rocks, travertine deposits, or occasionally, no surface signs or blind source. The phase of liquid is the steady, pressure-defining phase in these GE reservoirs. The available water contained by these GE systems is assumed as a chemical solution comprising chloride, sodium, calcium, potassium, bicarbonate, lithium, sulfate, silica, and borate. Kızıldere in Turkey, Wairakei in Cerro Prieto in Mexico, and also in New Zealand could be cited as cases of these worm liquid water-dominated GE reservoirs. Moreover, the heat recuperated from these hot water-dominated GE reservoirs is higher than that from vapor GE-dominated resources. The principal reason for the greater heat recuperation of hot water in the reservoir is the boiling of GE or reinjection of the exit fluid. Yield difficulties faced in these hot water GE reservoirs are poorer than that of GE vapor reservoirs. Fig. 3

Permeable

Rock C F

Crystalline

H

E

A

Rock

T

G

Convecting magma

Fig. 3 Liquid/hot water geothermal heat energy resource [5].

Y HD EN SIT

LD

NSIT Y LOW DE

WAT ER HOT

Rock of low permeability

WA TER

D

Boiling begins

B

Hot Spring Geysers

E

HIG

10°C Surface

CO

A

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Utilization of Thermal Potential of Abandoned Wells

indicates the essential features of hot liquid or hot water-dominated GE sources that contain the resource of heat basically surface manifestations and magma that involve hot springs, and geysers and high-density rocks, porous rock formation layers, and low porousness rock.

2.3 Geo-pressurized resources Geo-pressurized GE resources are methane which is rich fluids frequently under 4500 m depth below the surface of the Earth, which are included in geothermal reservoirs within up to 150°C temperature and 70 MPa pressure [6]. This geothermal resource earns the form of geothermal heat and the flammable exploited ordinary gas. These resources found in basin environments where deeply buried hot fluids included in permeable sedimentary solid rocks are heated in an enhanced or ordinary gradient of geothermal under their high underground burial depth. The fluids are strongly restricted by their neighboring impermeable rocks and hydrostatic pressure is much smaller than bear pressure. The pressure slope of the entrapped geothermal fluid is able to rise with extra sedimentation and could arrive up to 22.6 kPa/m (regular hydrostatic gradient is between 9.8 and 11.3 kPa/m). These geothermal systems’ temperature rises with high-specific heat and low heat conductivity of the fluids. Thermal hot waters in sand aquifers at high pressure are the drilling target, essentially as they comprise dissolved methane that is able to harvest. Geo-pressurized GE resources are composed of methane gas, mechanical energy, and thermal energy. Karytsas and Mendrinos [7] stated that geo-pressured geothermal reservoirs are estimated to be 70 times of the total world conserve of fossil fuel or 355.93 billion TOE. Geopressured GE reservoirs are like creations to gas reservoirs and geo-pressured oil. In these GE resources, fluid is caught in a permeable solid rock structure by crustal motion around millions of years accompanied with pressure increase to lithostatic pressure. Geothermal geo-pressurized resources are commonly quite deep from 2 km and profounder with over 100°C/km thermal gradient. These geothermal reservoirs have often been created during petroleum harvesting. They are linked with petroleum in some cases, the hot water that is extracted with CH4 gas, which could be exploited as a more essential energy resource than the water heat. Geothermal well of such system is more as a petroleum well than groundwater aquifer or hydrothermal basin. Hence, despite of having important potential of geo-pressurized geothermal sources, difficulty exist how to retain high CO2 contents, high content of fluid and salts minerals, and high great pressures linked with the GE resource which lasts to utilize these important GE resources [5].

2.4 Hot dry rock resources These GE resources form in the state of storage geothermal heat in rocks at a depth nearly 10 km from the Earth’s surface in which it cannot economically be extracted by ordinary steam or heated water. These indicated that hot dry rocks possess limited fractures or pore spaces and hence have no or little water, or no unified rock porousness. To harvest these geothermal heats, dry rocks are fractured affectedly by cold

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water liquid circulating and hydraulic pressure, and down one well to harvest the heat from these fractured dry rocks and hence heated water extracted from an additional geothermal well in a locked system. These systems do not include any fluid to harvest and transform the geothermal heat to the Earth’s surface for utilization. The only method of using these systems is to harvest the geothermal rock’s heat energy by water flow along a nonnatural fracture among two wells. Tosha et al. [8] stated that seismic monitoring technology help in creating fractures in the dry rock, where high temperature is predictable. Then, a yield well is drilled in and it is linked to the well of injection via the artificial fractures. The injected water into the well of injection that flows through these nonnatural fractures absorbs geothermal heat from the hotter dry rocks and returns to the Earth’s surface through the yield well that extracts geothermal heat. It is expected that geothermal extracting will be significant in its magnitude all over the world if extraction technology of the geothermal heat from the dry rocks becomes commercially viable. The main challenges of the extraction technology from the hot dry rocks are control of water loss, drilling costs, and better mapping techniques and fracture stimulation. Fig. 4 reveals heat corruption for hot dry rock resources.

Fig. 4 Hot dry rock geothermal energy resource [4].

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2.5 Magma resources or molten rock In magma GE sources, geothermal heat is directly extracted from the Earth’s crust with high heat on active volcanoes from cooled magma. For such geothermal resources, surface manifestations are hot fumaroles and springs. Nonetheless, it is likely that several magmatic GE systems have not surface indicators that are difficult to be determined and found [6]. The drilling process inside magma is considered a massive challenge for engineering but the achievement of this process might initiate a new stage of power generation from geothermal. However, available GE projects throughout the world utilize steam or hot water less than 300°C, magma is able to produce steam at very high temperatures or in the critical temperature. Water is available in a phase described as “supercritical,” at the most extreme temperatures where it behaves as not a true gas or true liquid and is able to recollect a phenomenal quantity of heat energy. Besides, supercritical water saturated with corrosive chemicals and with a temperature up to 1000°C has a greater capacity and can produce up to 10 times greater power than traditional GE resources. The accidental discovery of magma as a GE resource was great. This occurred in the year 2009 when the researchers team drilled a geothermal well of 15,000-ft depth in Iceland of Krafla where a volcano floundered upon magma that was flowing through the well at 6900 ft depth, which was only the second time that magma has slipped through the geothermal well through the process of drilling. Magma’s available resources or available molten rock includes considerable heat energy that can be separated or extracted. This has been experimentally carried out in Hawaii city by drilling process to and inside the molten rock to extract directly the geothermal heat energy via a heat exchanger. This has also been utilized effectively following the 1973 volcanic eruption at Heimaey city. In such case, the construction of a heat exchanger was performed on the lave flow surface to retrieve heat energy from the boiling water that penetrated from the surface. In this indicated geothermal project, the obtained heat was employed for space heating procedure for more than 10 years but then was shut down when the hot lava is cooled down. Consequently, this GE magma resource could not be considered sustainable because this resource could not be permanent, and larger research works and developments are required to enhance the energy transformation efficiency and also sustain geothermal heat extraction from magma or lava. The magmatic GE resources include roughly 327,360 billion tons of oil equivalent that is considered nearly 400 times the total reserves of fossil fuel. Fig. 5 demonstrates the power plant of molten rock and magma resource in Iceland, In this deep drilling project in Iceland, it was drilled to depths under 4 km in the Icelandic crust. Through their initial drilling leg in 2009, they hit by accident a magma pocket and stabilized eventually the drilling system to generate the hottest steam with temperature of 450°C ever yielded in GE exploration [5].

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Fig. 5 Molten rock/magma geothermal energy resource [4].

2.6 Radiogenic resources GE resources exist in areas where beneath the ground surface existing of granitic intrusions resulted in heating up of the local groundwater because of decaying radioactive materials such as uranium, potassium, and thorium. This local heating rises the regular geothermal grade yielding at inexpensive drilling depths, hot water for requests from low-to-medium temperature, and space heating. These GE resources are shown in Fig. 6.

Geothermal well

Vertical recharge thru leaky aquifers

Aquitards Aquifer

30°C 60°C Basement Crystalline Rocks

Radiogenic intrusive rocks

Fig. 6 Radiogenic geothermal energy resource [5].

Sediments of low thermal conductivity

Recharge at outcrop area

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Utilization of Thermal Potential of Abandoned Wells

Electricity generation

Deep geothermal energy resources with temperatures more than 100°C have been demonstrated to be viable sources for electrical power generation frequently demanding deep drilling among 1500 and 4500 m or as deep as 2 miles underground [9]. According to EIA [9] for the production of geothermal electricity, GE resources in the phase of steam, water, or both phases with a high temperature of 150–370°C. The GE fluid from deep underground runs a turbine that yields electrical power. Power plants or geothermal operators generate electrical power either by utilizing hot pressurized geothermal fluid or by utilizing the steam subtracted directly from GE reservoirs in a turbine or to evaporate a low-temperature boiling fluid for utilizing in a cycle of the binary turbine. Moreover, steam turbines are usually utilized in geothermal sources of higher temperature while binary geothermal plants are utilized in geothermal systems of midway temperature. In both of these production geothermal systems, pressurized working fluid vapor flows via a turbine and hence is condensed successively in a condenser. The water vapor runs as it expands inside the turbine stages running the turbine which spins a generator directly linked to the turbine shaft to yield electricity [10]. Power plants running on geothermal energy have many advantages as follows: Sustainable and renewable: GE will be dissimilar nonrenewable sources of energy. As long as we live on the Earth, geothermal heat will be presented, and geothermal power based on geothermal energy will be produced. Large capacity: power plants can seriously aid in realizing the required energy that increases per annum, both in developing and developed countries. Comparatively ecologically clean: Geothermal power plants utilize a renewable heat resource with a fixed supply of dissimilar coal-fired ones. Works have displayed that only 6.5% of the total potential energy of the world is included in the industry, which signifies that energy will continue for various years in advance. Additionally, the quantity of greenhouse gases from power plants of GE is only 5% contrary to coalfired power plants. Stable price: Conventional power plants depend on fossil fuel, so the output electrical power cost varies with the fuel price market. However, geothermal power plants do not utilize fuel, hence the fuel cost is not considered here, and then, they offer nearly fixed electrical power costs. Small operating costs: Geothermal power constructions need lower reparation costs as compared to traditional fuel power plants. Hence, these plants are cheap in operation and reliable. Permanent power supply: Geothermal power stations can supply a fixed source of energy 24 h a day all over the year regardless of exterior factors dissimilar to other renewable energy resources. As an example, solar power stations can yield electrical power only during the daytime, and also wind turbines yield only energy with enough wind speed. Little noise work: Small noise occurs during geothermal energy yielding. It is the sound of the fan for the systems cooling. To decrease the level of noise, generator shop

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materials with high damping characteristics can be installed. It aids to decrease noise pollution. Small area: Geothermal power plants occupy a smaller space than that equivalent of oil, coal, and gas. Despite they will arrive far distance below the surface of the Earth, their area will be negligible. Security of energy: Utilizing local GE resources reduces the requirement to provide sources from other nations, which diminishes dependence on outside effects and aids to reduce energy security. Sometimes, some benefits can be returned to disadvantages, and also it is difficult to find the issue without negative side effects. Therefore, the drawbacks of power plants of GE may include: Seismic instability: There are reasons to think that the structures of the Earth have produced underground vibrations in various places of the Earth. Even though seismic action isn’t frequently significant, it can result in some building destruction, harm, and maybe death. For example, in the year 2006, some researchers thought that the exploration of GE project in Switzerland caused earthquakes series of points 3.4 on a Richter scale. Ecological problem: Geothermal energy harvesting requires high freshwater consumption, which will eventually result in its deficit. In addition, liquids removed from the ground via drilling include some chemicals that are toxic (such as mercury or arsenic), besides hothouse gases (such as methane, carbon dioxide, hydrogen sulfide, radon, and ammonia). If they are wrongly treated or disposed of, then they will go to the environment or seep into the water in the ground and can cause damage to the environment and then human health. Costly installation: Geothermal plants need some considerable investments. Their construction cost may be much higher than that of oil, gas, and coal plants despite they have low running costs. Much of these costs are due to the drilling and exploration of geothermal energy resources. Possible exhaustion: Researchers display that devoid of wary managing, GE tanks may be exhausted. In these conditions, the power plants of GE will be shutting down till the tank is reconstructed. The only acceptable choice is to get GE from the magma directly. Geographical limits: Geothermal action is the biggest along the tectonic fault lines in the crust of the Earth. Precisely in these areas, GE has the highest capability. The negative point is that only a low number of countries can utilize geothermal resources. Fig. 7 illustrates the top countries that harvest geothermal energy in MW. There are different techniques or power plant types that are used to generate electricity from geothermal resources including: Dry steam power plant Flashed-steam power plant Binary cycle power plant Combined-cycle or hybrid plants

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Fig. 7 Top countries harvesting the geothermal energy in MW [11].

3.1 Dry steam power plant Power plant working on dry steam was the first built type of geothermal power plants. They utilize steam from the geothermal field as it originates from wells and goes directly through the turbine/generator unit to yield electrical energy. This electricity generation technology was firstly commercially utilized for electrical power generation from a geothermal field. High-energy geothermal reservoirs (its temperature is more than 200°C) are the resources of dry steam. The common characteristics of the dry steam resource are that it includes porous rock with fractures, either connected, that are full with steam. The steam seems to have either magmatic or meteoric origins. The first possibility includes the slow progress of vapor from magma chambers situated at high depth and very high temperatures beneath the molten rock. The second one includes the percolation of rainwater through fractures and faults at a large depth where it meets great temperature rock. Fundamentally, this is called vapor-dominated system. Dry steam could be directly utilized to run the turbine. Fig. 8 shows a layout diagram of the power plant of dry steam. Darajat geothermal power station uses a geothermal steam power plant as stated in Fig. 9. It is situated at Garut (Pasirwangi District) and produces 271 MW electrical power. Darajat energy plant was formerly created by a union of companies including Union Oil Company and Chevron Global Energy. This geothermal power plant includes three plants that serve up the Bali and Java provinces. These plants were custom-built in the year 1994, year 2000, and year 2007. The constructed second and third plants of these stations are shared in some facilities by the steam collecting technique.

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Dry Steam Plant Generator TB

CT

CD Air WP HGF

CDS lP

EP

Injection Well

Production Well

SR GR

TB: Turbine CD: Condenser WP: Cooling Water Pump CT: Cooling Tower CDS: Condensate EP: Extraction Pump lP: lnjection Pump GR: Geothermal Reservoir HGF: Hot Geothermal Fluid BR: Bedrock

Fig. 8 Dry steam power plant [12].

Fig. 9 Darajat power station [13].

Air Water

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3.2 Flashed-steam power plants Flash steam ones are the utmost known kind of GE power generation stations in working today. They utilize hot water at temperatures more than 182°C that is pumped under higher pressure to the generation plant at the Earth’s surface. Upon attaining the generation plant, the pressure is suddenly decreased, permitting some of the heated water to transfer or “flash” it into steam. After that, this steam is utilized to run the turbine-generator units to yield electricity. The rest of the hot water that is not flashed into steam, and also the condensation of heated water yield from steam, is commonly injected back into the well. Flash steam plants are classified into single and double flash steam plants.

3.2.1 Single flash steam plants Plants of single flash are usually constructed in geothermal regions of high temperatures. The geothermal wells yield a mix of hot water and steam. The plant of singleflash steam is a reasonably simple technique to transform the geothermal heat energy supported by the hot fluid in electric power. At the flash separator chamber, the mixture is split into distinct liquid and steam phases with the lowest pressure loss. The arrangement of the flash separator is part of the overall design of the flash plant and different possible arrangements can be used. After the separation of steam and hot water in the flash separator, the removed liquid water is not utilized to yield extra steam at lower pressure but is directly injected into injection wells. However, separated steam goes directly to the steam turbine. Fig. 10 demonstrates a layout diagram of the cycle of the single flash GE plant.

Fig. 10 Single flash steam plants [12].

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Fig. 11 Olkaria II power station.

One of the geothermal plants that utilize the single flash steam power plant is the Olkaria II power plant. It yields about 105 MW where it is initially started by a power generation of 70 MW from two units producing each 35 MW. While another unit was accomplished in 2010, bringing 105 MW power generation of the total plant capacity. The drilling of the well was performed between 1986 and 1993, but plant construction was postponed until the year 2000 because of the unavailability of funds. The plant operates on the cycle of a single flash but with newer technology and consumes steam of 7.5 t/h/MW. The used turbines are single flow six condensing stages with directly contact condenser of type spray jet (Fig. 11).

3.2.2 Double flash steam plants Double flash ones are also mounted at geothermal zones of high temperature. This flash plant is a development on the design of the single flash plant. It can produce from about 15% to 25% more electrical power output for similar geothermal fluid properties as compared with the single flash one. However, this plant type is more costly, more complex, and needs more repairing, additional power production rises its utility. The main fundamental characteristic of the double flash plant is that the separated liquid from the flash chamber is utilized to yield extra steam at a smaller pressure flashing process. The additional separated steam also enters the turbine to produce the extra additional electricity. Fig. 12 reveals a layout of the plant of double flash steam. Krafla GE plant is a double flash power plant situated in Iceland near Lake Mvatn and Krafla Volcano. It has 33 boreholes and an output power capacity of 60 MW, can produce annually 500 GWh electricity, and obtains its thermal energy from 29

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Fig. 12 Double flash steam plants [12].

geothermal wells. Its construction started in 1974 and was opened officially in early 1977, and its second turbine was installed by the year 1996 to produce its maximum power of 60-MW output. It has two 30 MW units, each with a dual flow turbine of five steps on each turbine side and a double pressure inlet. It obtains its hot water from 17 high-pressure production wells at a rate of 110 kg/s and 7.7 bar and 5 low-pressure production wells at a level of 36 kg/s and 2.2 bar. While the remaining seven wells are inactive now. Each steam turbine utilizes 52.5 kg/s at high pressure and 17.8 kg/s at low pressure (Fig. 13). Generated electricity

Water and steam Steam Hot water Cooling Water Gasses

11 kV

High voltage substation

Transmission line 132 kV

Transformer Separator Dry Steam Second flasher Silencer

Moisture separator

Turbine 30 MW Generator 37,5 MVA

Ejector Condenser

Well

Silencer Brine Low injection pressure

Geothermal High Steam pressure

Fig. 13 Krafla geothermal power plant.

Pump

Waste overflow water

Cooling Tower

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3.3 Binary cycle power plant The binary cycle differs from flash steam systems or dry steam plants because the steam or hot water from the geothermal wells will be never in direct connection with the units of the turbine generator. If the produced geothermal fluid of temperature is less than about 150°C. Then, it becomes difficult to produce power utilizing a flash steam geothermal plant, which can economically and efficiently deliver power. However, in the binary cycle system, the hot water coming from the Earth well is utilized to heat up an additional “working fluid,” of low boiling temperature, which is evaporated and utilized to operate the units of the turbine generator. Geothermal heat carried by the hot geothermal fluid is transferred to the “working fluid” as through a heat exchanger of closed-loop type. The heating geothermal fluids remain single phase; however, its temperature gradually decreases between the outlet and inlet of the heat exchanger because its heat is transmitted to an additional “working fluid.” The latter is heated up to saturation temperature and rests isothermal until it is completely evaporated. The working fluid and geothermal water are each passing in distinct circulating systems or “not open loops” and they never become in direct connection with each other. The merit of the plant of the GE binary cycle is that it can run at a lesser temperature of hot water (100–180°C) thanks to the lower boiling temperature of the working fluids compared to water. It also produces no air emissions. Hot water fluid coming out from the geothermal well will pass directly through the separator, heat exchanger, preheater, and finally again is injected back to the GE reservoir via the injection well. Fig. 14 shows the layout diagram of binary geothermal cycle operation. Different cycles are utilized to generate electricity in the binary cycle power plant. One of these cycles is the Rankine cycle that can be categorized into different

Turbine

Generator

Air& Water Vapor

Condenser Cooling Tower

Steam Air Separator

Waste Water Water

Air Water

Water

Steam

Condensate Direct Heat Users

Production Well

Geothermal Reservoir

Fig. 14 Binary cycle power plant [5].

Injection Well

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categories such as organic Rankine, water Rankine, and other multifluids cycles. In addition, the Rankine working fluids are comprised of organic fluids of various kinds, water, or binary fluids, or a mixture of multifluids. Organic Rankine uses as a working fluid in refrigerants or any other organic working fluids with lower boiling temperatures are broadly utilized in the production technique of electrical power from a wide range of medium- and low-temperature heat sources including not only geothermal but also ocean thermal, solar thermal, and industrial waste heat. The choice of binary cycle “working fluid” is determined based on the heat sources’ temperature. Binary power units are clean, ecologically as the direct contact of the geothermal hot fluid comprising contaminants and harmful gas. Moreover, low-used fluid temperatures aids to decrease the produced thermal pollution of the atmosphere. The scalability and geography of geothermal binary power technologies application are widely specified by the potential and location of the geothermal energy resource. If the geothermal reservoir of a type of low enthalpy is always preferred to utilize the Kalina cycle [14] based on a binary power plant to produce electric power. In the Kalina cycle, as shown in Fig. 15, organic fluid, the mixture of ammonia/water is utilized as working fluid in the binary Kalina cycle. Kalina cycle as illustrated in Fig. 15 is the thermodynamic cycle that runs on the identical Rankine cycle but employs a mix of ammonia and water as the cycle working fluid. Because of the particular thermodynamic properties of the operating fluid, the form of the Kalina cycle diagram differs from the organic Rankine cycle diagram. The Kalina cycle geothermal binary plant relied on an ammonia/water mix to provide a higher cycle efficiency with varying operating conditions and terms. By using special fluids mixture and modifications,

Generator

Turbine

Separator

Vapor Liquid Pump

Condenser

Kalina Fluid (Liquid)

Water or Air Vaporizer Heated Brine

Cooled brine

Geothermal Zone Production Well

Fig. 15 Kalina cycle [15].

Injection Well

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it is possible to organize condensation and vaporization heat exchange more efficiently at a lower temperature difference. Solution concentration differs and can be adjusted at different points of the cycle arrangement to perform the efficiency of optimum thermal cycle. Kamchatka binary geothermal power plant was constructed in Russia at Paratunsky in 1967 using hot water at 90°C for electricity generation with a rating electric power of 750 kW. It uses Freon R12 as the “working fluid” for this unit. Geothermal hot water at 90°C and a flow rate of approximately 200 m3/h is used to run a Freon cycle with a superheater, an evaporator, and three heaters in series. Liquid Freon R12 was boiled and superheated by hot water at a pressure of 1.4 MPa. The produced superheated Freon R12 vapor was then employed to run the turbine, which rotates the turbo-generator to produce electrical power. Freon steam with low-pressure (0.5 MPa) output from the turbine was routed to two condensers, where it condensed and transferred its heat to the cooling water. The highest flow rate of the cooling hot water is 1500 m3/h and the condenser inlet temperature is 5°C. Liquid refrigerant from the condenser is drained into a condensate storage tank from which it is sent to the steam generator by two centrifugal pumps.

3.4 Combined cycle or hybrid plants Some geothermal power plants utilize a combined cycle that adds a conventional Rankine cycle to yield electricity from the waste heat from a binary cycle. A combination of combined cycle technologies could as well be applied dependent on the characteristics and the geothermal energy source quality. This technology can use binary and flash dry steam, dry steam, and flash, or binary and flash combined. In this flash/ binary-type geothermal plant, the hot fluid inside the Earth is flushed to produce steam that is supplied to the steam turbine whereas the detached liquid from the flashing process in the flashing chamber is oriented to the binary cycle to produce additional electrical power. Hence, it is possible to call the combined plant as a hybrid plant as illustrated in Fig. 16. The main features of the power plant of the combined cycle comprise a production well, a reinjection well, a separator, steam turbine heat exchanger, electricity generator, another working fluid, and maybe other components depending on the technologies that are combined for the used plant. The combined cycle efficiency depends on geothermal fluids that are available in a large range of chemical and physical properties comprising pressure, temperature, gases, noncondensable, corrosion potential, and scaling. The basic systems of power generation in this combined cycle can be joined in a suitable way to realize better or more power generation with lower losses. Examples of combination cycles are systems of hybrid fossil/geothermal, single type flash/binary, direct steam/binary, etc. An accurately designed combined system will provide greater efficiency. One of the geothermal power plants that working on the combined cycle is the Blue mountain geothermal power plant as shown in Fig. 17. It was commissioned in October 2009 which located in Humboldt County in northern Nevada, United States. It is a binary geothermal power plant having six turbines each rated at 8.25 MW. The gross

Fig. 16 Combined geothermal power plant [5].

Fig. 17 Blue mountain geothermal power plant.

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power production of Nevada plant is 49.5 MW; however, the net power production of this plant is 39.5 MW. Nevada plant is a blind geothermal area without visible hydrothermal features. For this cause, the geothermal energy resource was not known till hot water in drill holes in the early 1990s made for mineral exploration was discovered. After discovering the hot water, drilling started with a thin hole observation well called Deep Blue No. 1 in 2002, followed by a second in the year 2004. This plant covers an area of 11,120 acres and is located 33 km away from the electrical transmission grid. This geothermal plant utilizes three energy converters, each producing 16.5 MW and depending on six geothermal wells. The plant includes a water-cooling tower, fire protection systems, control buildings, and safety systems. It utilizes organic Rankine cycle technology as a binary cycle. The main used fluid (hot water here) reaching the plant is through the stated drilled wells, which are about 1220 and 2440 m deep. Heat is transmitted to a secondary fluid from the hot water with a lower boiling point in the heat exchanger. Vapor coming of the secondary fluid is utilized to run the Rankine turbine, which produces the generated electrical power. The plant started with an initial output power of 38 MW before reaching 49.5 MW. Studies performed on the geothermal site indicated that its geothermal resource potential is about 100 MW.

4

Conclusion

The different electricity production techniques from geothermal energy wells are discussed in this chapter for different geothermal energy resources. These geothermal energy resources include vapor-dominated resources, liquid/hot water resources, geo-pressurized resources, hot dry rock resources, molten rock or magma resources, and radiogenic resources, which are discussed. The geothermal electrical generation techniques involve power plant of dry steam, flashed-steam power plant, binary cycle power plant, and combined-cycle or hybrid plants. In the case of geothermal energy resources that are sufficient to yield steam, the steam power plant is used to generate electricity from produced steam and from the geothermal wells. However, in the case of the production wells is hot water, the flash steam techniques are used to produce electricity from these wells. In the single flash technique, the hot water is flashed into steam and liquid where the steam is employed to run the turbine to yield electrical power. While the flashed hot liquid water is injected back to the wells. However, in the double flash geothermal power plant, the output hot water from the first flash chamber is pumped to the second flash chamber. The produced steam from the second flash chamber is used to run the low-pressure turbine to produce excess electrical power. The efficiency of the power plant of double flash type is higher than that of the single flash one but its cost is higher. The binary cycle power plant is used in the case of a geothermal reservoir of low temperature. The power of the binary cycle is produced from the Rankine cycle of working fluid having a low boiling temperature compared to that of water. The combined cycle adds a conventional Rankine cycle to yield electricity from the waste heat from a binary cycle.

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References [1] R. Wolfson, Energy from Earth and Moon, in: Energy, Environment, and Climate, second ed., W.W. Norton & Company, New York, 2012, pp. 204–224. [2] S.B.A. Kashem, M. Hasan-Zia, M. Nashbat, A. Kunju, A.E.S.B.A. Kashem, M. HasanZia, M. Nashbat, A. Kunju, A. Esmaeili, A. Ashraf, M.A. Odud, M.E. Majid, E.H. Muhammad, M.E.H.C. Chowdhurymaeili, A review and feasibility study of geothermal energy in Indonesia, Int. J. Technol. 2 (2021). [3] H.K. Gupta, Geothermal Resources: An Energy Alternative, Elsevier Scientific Publishing Company, 1980. [4] A. Kundu, Geo-thermal energy—a green-lane towards, in: National Conference on Waste to Energy, Carbon Capture and Storage, NIT Rourkela, 2017. [5] M.J. Barasa Kabeyi, Geothermal electricity generation, challenges, opportunities and recommendations, Int. J. Adv. Sci. Res. Eng. 5 (2019) 53–95, https://doi.org/10.31695/ ijasre.2019.33408. [6] E. Tzen, R. Morris, Renewable energy sources for desalination, Sol. Energy 75 (2003) 375–379, https://doi.org/10.1016/j.solener.2003.07.010. [7] C. Karytsas, D. Mendrinos, Global geothermal power market, in: European Geothermal Congress, Pisa, Italy, 2013. [8] T. Tosha, T. Shimada, H. Nakashima, The research and development for the geothermal energy in Jogmec, Japan, in: Proceedings World Geothermal Congress, Melbourne, Australia, 2015, pp. 19–25. [9] US Energy Information Admistration (EIA), 2017, https://www.eia.gov/. [10] World Energy Council, 2016. https://www.worldenergy.org/. [11] H. Aydin, S. Akin, E. Senturk, Evaluation of production capacity of geothermal power plants in Turkey, Trans. Geotherm. Resour. Counc. 44 (2020) 163–174. [12] R. Das, R.K. Gupta, T. Gupta, C. Maji, Study on geothermal power generation techniques related to Bakreswar-Tantloi geothermal area, in: International Conference on Renewable Energy—Extension & Outreach, Santiniketan, India, 2016. [13] Thorndoncook, Project, n.d. https://www.thorndoncook.com/projects/darajat-iiigeothermal. [14] Nasruddin, R. Usvika, M. Rifaldi, A. Noor, Energy and exergy analysis of Kalina cycle system (KCS) 34 with mass fraction ammonia-water mixture variation, J. Mech. Sci. Technol. 23 (2009) 1871–1876. [15] J.G. Boghossian, Dual-Temperature Kalina Cycle for Geothermal-Solar Hybrid Power Systems, Massachusetts Institute of Technology, 2011.

Thermodynamic modeling of an ORC power plant for abandoned geothermal well

12

Saeid Mohammadzadeh Binaa, Hikari Fujiia, Shunsuke Tsuyaa, and Younes Noorollahib a Graduate School of Engineering and Resource Science, Akita University, Akita, Japan, b University of Tehran, Tehran, Iran

1

Introduction

Geothermal energy, as renewable energy, is a clean and sustainable energy, which is trapped between Earth’s surfaces [1]. Furthermore, among other renewable sources, this energy is the most reliable source of electricity production regardless of climate condition or time of the day. Regarding energy sources such as wind or solar, their availability depends on weather condition but in the case of geothermal, if a reservoir exists in a region, it is available consistently for many years [2]. The uses of geothermal energy can be divided into two main categories of electricity production and direct use depending on the various physical and chemical features of the geofluid in the reservoir [3,4]. Direct use application of geothermal energy is for space heating and cooling, greenhouses, aquaculture, snow melting, and other industrial facilities [5]. On the other hand, the heat content of this energy source can be converted to electricity using different energy conversion technologies such as flash cycle. Geofluid temperature and flow rate are the determining factors for geothermal system application. However, chemical factors such as dissolved elements’ concentration limits the geofluid usage due to the potential concerns such as corrosion, scaling, etc. Despite being an unlimited and consistent energy source of electricity without intermittency issues, the development is limited due to the high cost of drilling associated with geothermal power plant projects. Abandoned oil and geothermal wells are the best alternative solution to mitigate this cost and make this energy more accessible with other energy sources. There are many oil wells and thousands of geothermal wells that are abandoned. Currently, it is estimated that in the United States only there are around 2.3 million abandoned wells that became depleted or in other words, extracting oil is not profitable anymore [6]. These wells are dry holes without any oil or hot fluid production while they have a large amount of stored heat. On the other hand, the management of these wells is costly since serious pollution problems are

Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00012-9 Copyright © 2022 Elsevier Inc. All rights reserved.

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caused by leaking if they are left unsealed. Repurposing abandoned petroleum wells for a geothermal heat extraction project will not only solve the pollution problems but also reduce the cost of drilling by up to 50%. This approach may become a novel way to utilize geothermal energy and obtain more renewable energy. Moreover, the additional merit of retrofitting of abandoned wells is the availability of large amounts of thermos-physical logged data on the existing wells. Data is a useful tool for energy policymakers to analyze which wells provide the highest bottom-hole temperature and consequently generate higher energy. Abandoned wells offer a profitable opportunity to be retrofitted as a heat extraction system since they are generally deep enough to access the higher temperature strata of the Earth. Heat extraction from these wells through closed-loop heat exchangers is an opportunity to reuse them for heating or power generation. Geothermal energy obtained from abandoned wells is a low-to-moderate temperature resource that can be used for electricity generation using the organic Rankine cycle (ORC). In this chapter, a numerical model of an abandoned well was simulated in FEFLOW software for heat extraction from an abandoned geothermal well in the Sabalan geothermal field, Northwestern Iran. According to the literature, previous studies were conducted on the petroleum wells where the temperature is around 120°C and on sedimentary formations. Moreover, this is the first study conducted in the geothermal dry well in a volcanic rock formation with striking differences in the physical properties. Furthermore, the actual geothermal gradient (temperature profile) recorded during drilling and a geological log were used in the simulation model. The main objective of this research is to design a coaxial heat exchanger to reuse an abandoned geothermal well with circulating water in a closed-loop system. Furthermore, a parametric study was conducted to obtain optimum values of parameters such as fluid mass flow rate, heat exchanger length and diameter, and so on. As another novelty of this research, various lengths of the heat exchanger are modeled to obtain the highest temperature with lowest cost. Finally, a binary power plant cycle was modeled using engineering equation solver (EES) software, which utilizes the output hot water from this well to estimate the achievable power production.

2

System description

The technique of the heat extraction from abandoned wells differs from conventional geothermal power plants since there is no natural geofluid and the injected water is not in direct contact with the surrounding hot rocks. A concentric double pipe is placed into the well to produce thermal energy from the well. The fluid circulates in the coaxial double-pipe heat exchanger, and heat transfer occurs without mass transfer. The fluid circulates in the well through a concentric double pipe. Cold water is injected into the well through the outer pipe, and the heat transfers from the hot rock to the fluid during injection heating. The hot fluid rises through the inner pipe and is extracted on the wellhead. To avoid heat transfer between the inner and outer pipes, the inner pipe is insulated using thermal insulation materials.

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3

241

Case study: Abandoned geothermal well (NWS3) in the Sabalan field

The first Iranian geothermal power generation project was started in 1995 in one of the potential regions based on Iran’s geothermal potential map. Fig. 1 shows the geothermal potential map of Iran and its 17 most suitable areas for prospective geothermal power plants. This project is located at the northwest Sabalan geothermal field in northwestern Iran. Between 2002 and 2012, a total of 11 deep exploration wells were drilled to evaluate subsurface geological and reservoir conditions. Unfortunately, one of these wells, named NWS3, did not have any fluid flow during the well testing and discharge flow measurement. According to further surveys and investigations, it was revealed that this well was drilled outside the reservoir area, and there is a sealing fault between this well and the reservoir. Moreover, it is concluded that this well cannot be used even as an injection well due to very low transmissivity. This well was chosen for the investigation of heat extraction using a secondary water loop in this study. The specifications and dimensions of this well are summarized in Table 1. In addition, the geometry of the well is shown in Fig. 2.

Fig. 1 Geothermal map of Iran. The Sabalan geothermal field can be seen in northwest of the country [7].

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Table 1 Specifications of well NWS3. Well name

NWS3

Location Well head elevation (m.a.s.l.) Drilled depth (m) Maximum temperature (°C) Planned orientation

737028 E, 4240784 N 2277 3177 148 Deviated Casing

Name

Size (in.)

Depth (m)

Conductor Surface Anchor Production First liner Second liner

30 20 13–3/8 9–5/8 7 5

24 113 357 1599 2648 3170

Fig. 2 Geometry of the well NWS3.

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The temperature profile of the well is shown in Fig. 3. According to this, the measured temperature, from the top of the well to a depth of 700 m, is suitable for the conduction of heat. In this region, temperature increases up to 145°C indicating a temperature gradient of 1.85°C/m. However, from the depth of 700 to 1900 m, there is no significant temperature increase, based on the well testing data which may be due to the presence of clay minerals and thus, leading to a limited heat transfer in these layers. From 1900 m to the bottom (3197 m) of the well, the conduction condition is identified again.

4

Numerical modeling of a geothermal well

To calculate the output temperature of a coaxial GHE (Ground Heat Exchanger) installed in a geothermal well, a numerical model was developed in FEFLOW software ver.7.1. The model of the well includes inner and outer pipes, casings, grouting cement layers, and the ground layer. The dimension and cross-sectional views of the GHE model are shown in Fig. 4. This model has the shape of a cylinder with a diameter of 12.0 m to consider the heat capacity of the ground and the thickness of each layer in the “z” direction until the bottom of the model is 20.0 m. The meshing around the GHE was refined, to increase the accuracy and obtain precise results. Based on the geological information, this model has seven vertical layers with different thicknesses and rock types of different permeability from the surface to the bottom of the well. The ground thermos-physical properties, the geometry of the well, and the temperature profile of the geothermal well are defined based on the actual well design data provided by Noorollahi et al. [1]. The outer wall of the inner pipe is insulated, and the bottom of the pipes is blocked so that injected fluid can return. The top of the model is subject to atmospheric pressure and open for injecting water as the main fluid at 35°C and 1 atm (different mass flow rate). The thermos-physical properties of the geological layers in the abandoned geothermal well NWS3 obtained from drilling are shown in Table 2. Using these geological data, a 3D model of well and casing with geological conditions is designed (Fig. 5).

4.1 Model validation To validate the model, the measured temperature profile is applied on the lateral surface of the cylindrical model as a condition for the boundary. Afterward, the model was prerun for 10 years to reach a steady-state thermal condition. Fig. 6 shows the calculated temperature around the well after the presimulation run at the set target temperature for the well. According to this figure, the calculated temperature is in agreement with the measured data of the well NWS3.

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Temp (degC) 0

50

100

0

500

Depth (mMD)

1000

1500

2000

2500

3000

Fig. 3 Profile of measured temperature in well NWS3.

150

200

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Fig. 4 3D view and 2D view of the model.

5

Geothermal power plant modeling

A binary power cycle was developed to calculate electricity that can be produced from the extracted heat. Mass flow rate, input velocity, and fluid pressure are also taken into consideration to optimize parameters for obtaining the maximum net power. In the selected power cycle, isobutene was chosen as secondary fluid. Fig. 7 shows the schematic representation of an ORC cycle with an internal heat exchanger. The heat source for the plant is the flow of hot fluid from the coaxial heat exchanger. It enters the plant at a constant temperature and mass flow rate (state 1). This stream heats the working fluid, while simultaneously cooling down due to the heat exchange process. This is followed by reinjection of the exhaust brine through the pipe, which goes back to the heat exchanger inside the well (state 2). In the ORC cycle, working fluid enters the heat exchanger and reaches the saturated condition. Depending on the nature of the working fluid, it turns into superheated steam (state 4). The working fluid then expands through the turbine and condenses by passing through the condenser. Since, in the ORCs despite other cycles, the organic fluid in the turbine outlet and before entering the condenser is still in the vapor phase, installing an internal heat exchanger after the turbine can be effective to utilize more heat from the exhausting stream of the turbine. Additionally, it helps to improve the overall performance of the plant. Therefore, the stream exiting through the outlet of the turbine enters an internal heat exchanger before condensing and thus completing the cycle. In this heat exchanger, the ORC’s working fluid heats up before entering the main heat exchanger unit.

Table 2 Physical properties of the model. Depth (m)

0–80

80–332

332–449

449–888

888–2772

2772–2778

2778–

Geology

Sands and conglomerate 3.10

Andesite and Dacite Breccia 0.69

Crystal tuff

Tuff-Breccia

Andesite

Andesite

0.30

3.70

3.70

Altered Volcanics 3.44

3.70

2.50

3.00

2.21

2.76

2.76

2.82

2.76

Material

Bentonite

Cement coat

Polystyrene

Steel-stainless

Thermal conductivity (W/m/K) Volumetric heat capacity (MJ/m3/K)

2.05

2.9

0.027

13.8

1.703

2.1084

0.06655

3.8664

Thermal conductivity (W/m/K) Volumetric heat capacity (MJ/m3/K)

Thermodynamic modeling of an ORC power plant

247

0.0m Sands & Conglomerate

80m Andesite Dacite Breccia

332m

Crystal tuff

Cementing

449m Tuff-Breccia

888m

Andesite

Casing 2778m Altered Volcanics

2772m

Bentonite Outer pipe Outer flow Insulation Inner pipe Inner flow

Fig. 5 Schematic representation cross-section of the designed heat exchanger. The thick black lines indicate well casing. All casings are stainless steel, and the area between the good casing and outer pipe of the heat exchanger is filled with bentonite clay. Arrows show flow direction in inner and outer heat exchanger pipes.

5.1 Energy analysis According to the first law of thermodynamics, a steady-state energy balance for all component of the cycle was applied as follows [8]: Q_
W_ ¼

X

_ Þout
ðmh

X

_ Þin ðmh

The heat exchange between working fluid of ORC and geofluid in evaporator and also and cooling water in condenser are modeled mathematically based on the concept of pinch point difference. m_ gf ðh1
h12 Þ ¼ m_ wf ðh4
h9 Þ m_ gf ðh12
h2 Þ ¼ m_ wf ðh9
h8 Þ where h9 is the enthalpy of the working fluid at the saturation temperature and h12 is the enthalpy of the brine at the saturation temperature of the working fluid plus pinch point degree. The energy efficiency is defined as ratio of the net power output of the ORC to the input thermal energy from geofluid passing through the heat exchanger [9]. ηenergy ¼

Wnet, orc Wnet,orc ¼ _ _ m Q in gf ðh1
h2 Þ

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Utilization of Thermal Potential of Abandoned Wells

Temp (degC) 0

50

100

150

200

0 Measured temperature profile

500

1000

Depth (mMD)

1500

2000

2500

3000

3500

4000

Fig. 6 Calculated and measured temperature around the well.

Simulated temperature profile (FEFLOW)

250

Thermodynamic modeling of an ORC power plant

249

Fig. 7 Schematic diagram of the binary geothermal cycle.

6

Simulation results

For all the ground layers, the good casing, and the cement, thermal specifications such as thermal conductivity and specific heat capacity are defined based on the well’s design data, material, and geological properties. The outer boundary of the ground layer (lateral area) was set to a fixed temperature based on the temperature profile of the well (Fig. 2). To measure the outlet temperature, calculation started after prestimulation and when all the zones of the model reached a steady state, receiving heat from the outer boundary. The outlet temperature and the bottom-hole temperature of the coaxial GHE for various mass flow rates of injected water were calculated. The relationship between the outlet fluid temperature and the injected mass flow rate is also shown in Fig. 8. As shown in this figure, the bottom-hole temperature decreased with an increase in the mass flow rate due to a higher heat transfer ratio in higher mass flow rates. The higher temperature is observed at a very low flow rate similar to the bottom-hole temperature of the well. However, the peak point of the wellhead temperature was around 133.5°C (which is less than bottom-hole temperature) at a flow rate of around 1.65 L/s. The wellhead temperature is very low at low flow rates due to less amount of water as a heat exchanging medium and lower heat transfer rate. Similarly, at higher mass flow rates the temperature is decreased due to higher mass flow rates and also fewer times to have heat transfer between water and surrounding rocks. Therefore, the trend of the wellhead temperature experiences a peak point as an optimum mass flow rate.

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Utilization of Thermal Potential of Abandoned Wells

Fig. 8 Variation of bottom-hole and output temperature as a function of water flow rate.

Furthermore, wellhead and bottom temperature were analyzed for different lengths of the GHEs which are inserted into the well. These lengths were chosen based on the well’s design and different sections of the casing. The GHE length and also its diameter are selected based on the good geometry. Three different GHE were designed with lengths around 3176, 2654, and 1599 m, to be inserted into the well. The inlet temperature of the GHE is set at 35°C as an estimation of outlet temperature from the condenser. Figs. 9 and 10 show the variation of bottom-hole and outlet temperature as a function of injection rate for various GHE lengths. The maximum outlet temperatures for 2654 m, and 1599 m cases were estimated at around 128.4°C and 129.6°C, respectively, and when the injection rates were 1.0, 3.6, and 1.2 L/s, respectively. The extracted heat from this abandoned well is fed to a binary power plant to generate electricity. The simulation was conducted for predicting extractable power from this well. A binary power cycle was developed in EES software to calculate electricity that can be produced from extracted heat. The initial input parameters for power plant simulation are shown in Table 3. In the selected power cycle, butene was chosen as secondary fluid. Fig. 11 shows the generated power for different mass flow rates and different lengths of the GHE using a binary power plant and butene as working fluids. The maximum net power from the well for various GHE lengths is 270 and 5916 kW for amass flow rate of 3.6 kg/s. Net power naturally decreases with a decreasing flow rate of fluid, due to lower heat exchange rate.

Thermodynamic modeling of an ORC power plant

251

Fig. 9 Variation of bottom-hole and output temperature as a function of water flow rate for GHE length of 2654 m.

Fig. 10 Variation of bottom-hole and output temperature as a function of water flow rate for GHE length of 1599 m.

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Utilization of Thermal Potential of Abandoned Wells

Table 3 Input data in power plant modeling.

Geofluid temperature Geofluid mass flow rate Turbine isentropic efficiency Pump isentropic efficiency Pinch point temperature

3176 m

2654 m

1599 m

133.5°C 1.01 L/s 85% 90% 5°C

128.4°C 3.6 L/s

129.6°C 1.2 L/s

7000

Net power output (kW)

6000 5000 4000 3000 2000 1000 0 3176

2654

4599

Heat exchanger length (m)

Fig. 11 Net power generation as a function of mass flow rate.

7

Remarks

The present study, considered a three-dimensional numerical modeling of an abandoned geothermal well, and the governing equations of heat transfer were applied for simulation. A concentric double pipe heat exchanger was designed to produce an acceptable amount of heat from the NWS3 geothermal well in the NW Sabalan geothermal field. The fluid circulates in the coaxial double-pipe heat exchanger and heat transfer occurs without mass transfer. The maximum fluid temperature at the outlet in the wellhead depends not only on the fluid temperature at the bottom of the well but also on the insulation layer thickness of the inner pipe. The maximum outlet temperature was 133.5°C for a mass flow rate of 1.01 L/s. The extracted thermal energy from the simulation was used as input data to estimate the amount of electricity that can be produced by a geothermal binary power plant. The simulations were conducted to predict extractable power and net power from this well, using butene as a working fluid in the binary cycle. The maximum net powers from the well are 5916 kW for a GHE length of 2654 m.

Thermodynamic modeling of an ORC power plant

253

The main results are as follows: 1-

2-

3-

The secondary mass flow rate has a significant impact on power generation. Although the outlet temperature in GHE was highest at 3176 m, the GHE with 2654 m length results in higher power production. Using shorter GHE showed better results since it was possible to use the pipes with larger diameters. However, for the longer GHE, we had to use smaller pipes due to the smaller diameter of the well in the bottom of the well. Using shorter GHEs can not only produce high power but also can decrease the cost of the project. It can be also considered as an advantage for easier installation of the GHE.

References [1] Y. Noorollahi, S. Mohammadzadeh Bina, H. Yousefi, Simulation of power production from dry geothermal well using down-hole heat exchanger in Sabalan field, northwest Iran, Nat. Resour. Res. 25 (2) (2016) 227–239, https://doi.org/10.1007/s11053-015-9270-3. [2] S. Mohammadzadeh Bina, S. Jalilinasrabady, H. Fujii, Energy, economic and environmental (3E) aspects of internal heat exchanger for ORC geothermal power plants, Energy 140 (2017) 1096–1106, https://doi.org/10.1016/j.energy.2017.09.045. [3] S. Mohammadzadeh Bina, S. Jalilinasrabady, H. Fujii, N.A. Pambudi, Classification of geothermal resources in Indonesia by applying exergy concept, Renew. Sustain. Energy Rev. 93 (2018) 499–506, https://doi.org/10.1016/j.rser.2018.05.018. [4] A. Baba, T. Uzelli, H. Sozbilir, Distribution of geothermal arsenic in relation to geothermal play types: a global review and case study from the Anatolian plate (Turkey), J. Hazard. Mater. 414 (2021) 125510, https://doi.org/10.1016/j.jhazmat.2021.125510. [5] S. Mohammadzadeh Bina, H. Fujii, S. Tsuya, H. Kosukegawa, S. Naganawa, R. Harada, Evaluation of utilizing horizontal directional drilling technology for ground source heat pumps, Geothermics 85 (2020) 101769, https://doi.org/10.1016/j.geothermics.2019. 101769. [6] A. Townsend-Small, T.W. Ferrara, D.R. Lyon, A.E. Fries, B.K. Lamb, Emissions of coalbed and natural gas methane from abandoned oil and gas wells in the United States, Geophys. Res. Lett. 43 (5) (2016) 2283–2290, https://doi.org/10.1002/2015GL067623. [7] H. Yousefi, et al., Developing the geothermal resources map of Iran, Geothermics 39 (2) (2010) 140–151, https://doi.org/10.1016/j.geothermics.2009.11.001. [8] R. DiPippo, Second law assessment of binary plants generating power from lowtemperature geothermal fluids, Geothermics 33 (5) (2004) 565–586, https://doi.org/ 10.1016/j.geothermics.2003.10.003. [9] R. DiPippo, Ideal thermal efficiency for geothermal binary plants, Geothermics 36 (3) (2007) 276–285, https://doi.org/10.1016/j.geothermics.2007.03.002.

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Application of abandoned wells integrated with renewables

13

Yuekuan Zhoua,b, Zhengxuan Liuc,d, and Chaojie Xingc a Sustainable Energy and Environment Thrust, Function Hub, The Hong Kong University of Science and Technology, Guangzhou, China, bDepartment of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China, cCollege of Civil Engineering, National Center for International Research Collaboration in Building Safety and Environment, Hunan University, Changsha, Hunan, China, dFaculty of Architecture and the Built Environment, Delft University of Technology, Delft, Netherlands

Abbreviations AOW BIPVT CCHP CHP COP DPT EMV LCA LCOE LCOH MINLP NPV NSGA-II ORC

1

abandoned oil well building integrated photovoltaic/thermal combined cooling, heat and power combined heat and power coefficient of performance discounted payback time expected monetary value life cycle assessment levelized cost of electricity levelized cost of heating mixed-integer and nonlinear programming net present value nondominated sorting genetic algorithm-II Organic Rankine Cycle

Introduction

Due to the high energy density, thermal performance stability, and large abundance in resources, geothermal energy utilization from abandoned wells is full of promising prospects to promote the carbon-neutrality transition of district energy systems. Depending on the energy forms, the geothermal energy can be used for direct thermal energy supply for district heating [1] or be converted into electricity through the Organic Rankine Cycle (ORC) [2]. Compared to other renewables, such as solar and wind energy, geothermal energy shows advantages such as higher thermal efficiency, higher performance stability, weather-proof and base-load abilities, less land requirement, and less ecological effect [3]. However, barriers limit the widespread application of geothermal energy including high initial investment, long payback time Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00013-0 Copyright © 2022 Elsevier Inc. All rights reserved.

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Utilization of Thermal Potential of Abandoned Wells

and construction time, difficulty in assessing resource, and difficulty in modularization. The combination of abandoned wells with various renewable energy sources can compensate the disadvantages and popularize the widespread applications. On the other hand, due to the intermittence and stochastic nature of solar or wind energy resources, geothermal energy can stabilize the energy supply in terms of fluctuations in renewable energy generation, through the seasonal energy storages. In the academia, typical systems for renewable integrations include solar-geothermal energy systems [4], building integrated photovoltaic/thermal (BIPVT) systems and earth-air heat exchanger systems [5], abandoned wells with waste heat recovery [6], and abandoned wells integrated with renewable systems [1]. Criteria for thermal energy systems include outlet fluid temperature, extracted thermal output, static payback time, and carbon emission. The multicriteria for geothermal-based power systems include electricity generation cost, simple payback time, and levelized cost of electricity. Strategies for performance enhancement of geothermal energy systems mainly include optimal design and smart operation. Approaches for optimal system design include Taguchi Statistical Method [7,8], advanced optimization algorithms such as genetic algorithm, mixed-integer and nonlinear programming (MINLP) optimization [9], mixed-integer linear optimization [10], and a three-stage heuristic approach. Advantages of the Taguchi Statistical Method include dimensionality reduction from redundant experiments, labor cost saving, and time saving. In this chapter, a state-of-the-art review on abandoned wells for thermal and power generations is conducted. In order to overcome the disadvantages of geothermal energy systems, such as high initial investment, high labor cost, long payback time and construction time, and so on, the integrations of abandoned wells with various renewable energy sources with compensatory functions are reviewed, to popularize the widespread applications. Abandoned wells with renewable integrations are reviewed, in terms of different system configurations (such as solar-geothermal energy systems, BIPVT, and earth-air heat exchanger systems) and technologies (such as waste heat recovery). Advanced strategies for multicriteria performance enhancement have been reviewed from perspectives of optimal design and smart operation. Last but not the but not least, real applications and future prospects for geothermal energy from abandoned wells are listed, including techno-economic and environmental performance analysis, geothermal integrated energy systems with synergistic functions, and geothermal energy potential analysis. This chapter can provide preliminary knowledge and cutting-edge technologies on renewable integrations with abandoned wells, so as to demonstrate techno-economic-environmental potentials of abandoned wells and contributions toward the carbon-neutrality transition.

2

Systematic literature review of abandoned wells for thermal and power generations

2.1 Abandoned wells for thermal energy generation Abandoned wells have been applied for thermal energy generation. Moya et al. [11] reviewed the cascade configurations for geothermal energy utilization to improve the thermal efficiency. Over the past several decades, researchers have mainly focused on

Application of abandoned wells integrated with renewables

257

experimental, numerical study, and parametrical analysis. Bu et al. [12] experimentally and numerically studied a geothermal well for space heating. Gharibi et al. [13] developed a three-dimensional numerical model to characterize the thermal performance of a U-tube heat exchanger. Parametrical analysis was conducted on geometrical and operating parameters. The results showed that the optimal outlet temperature at 324.73 K can be achieved, in the case with 288.16 K inlet temperature and 0.03 m/s inlet velocity. The system performance is stable after 5 years. Hu et al. [14] evaluated the geothermal energy potential of abandoned petroleum wells, through a coaxial borehole heat exchanger. Based on the model developed in COMSOL Multiphysics, the temperature and power are stable at  29°C and 0.38 MW. Thermal and energy performances have also been studied. Nian and Cheng [15] applied an abandoned oil well (AOW) for space heating, as shown in Fig. 1. The parametrical analysis indicates that the AOW can maintain the indoor air temperature at 26°C with the water flow rate at 20 m3/h. The annual energy performance indicates that the total geothermal energy was 5.5  1012 J, decreasing the carbon emission by 457 ton each year. Caulk and Tomac [16] applied abandoned oil and gas wells for district heating. The outlet fluid temperatures higher than 40°C can be obtained. Naicker and Rees [17] studied the dynamic performance of a large-scale geothermal system for heating and cooling, with part load ratio, and energy saving. Nian and Cheng [18] studied the geothermal energy performance of abandoned oil and gas wells, in terms of heat transfer models and working fluids. The results showed that the system can keep a 10,000-m2 building at 26°C, with around half the cost of the conventional system.

P Buildings

P

Top view of wellbore

P Heat flux

Injection and extraction pump Working fluid in production pipe Working fluid in injection pipe Insulation layer Shield Surrounding formation

Fig. 1 Geothermal energy for space heating from abandoned oil well. Reprinted from Y.L. Nian, W.L. Cheng, Evaluation of geothermal heating from abandoned oil wells, Energy 142 (2018) 592–607. Copyright with permission from Elsevier.

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Utilization of Thermal Potential of Abandoned Wells

2.2 Abandoned wells for power generation In addition to thermal energy generation, abandoned wells for power generations have also been studied. Geothermal power potentials have been studied in different countries. Pambudi [19] comprehensively reviewed geothermal power generation in Indonesia. Based on the historical power generation data, the geothermal power generation is predicted to be 7000 MW in 2025. Davis and Michaelides [20] studied the geothermal power potential from abandoned oil wells. A total of 2–3 MW of electric power can be generated. Wang et al. [21] reviewed geothermal power generation over the past 60 years in China. The review highlights the necessity for advanced power cycles and multiobjective optimization of geothermal ORC systems. Ahmadi et al. [22] systematically reviewed the applications of geothermal-ORC power systems, in terms of organic fluids’ choice, ORC configurations, operating conditions, and key factors. The economic and environmental performances of the geothermal-ORC power systems validated the feasibility performance of the hybrid system. Parametrical analysis of thermal and energy performance has been carried out. Cheng et al. [23] conducted the parametrical analysis on electricity production from abandoned oil wells, based on a transient formation heat transfer model, Extracted fluid Injected fluid

Injected fluid

Heat flow from the formation

Formation

Insulation

Sealing bottom of the well

Fig. 2 Double-pipe heat exchanger. Reprinted from W.L. Cheng, T.T. Li, Y.L. Nian, C.L. Wang, Studies on geothermal power generation using abandoned oil wells, Energy 59 (2013) 248–254. Copyright with permission from Elsevier.

Industrial production

T p

F T Gas

Liquid

p

HE1

T

i2

g1

T i1

Turbine

4

p F T

p

p

3

p

Generator

Evaporator 5

i3 Pump1

Seperator

T

HE2

p

T p

g2 T

Gathering heat tracing system

p

HE3

i5

T

p Condenser

p T F

p T

Preheat

c2

Pump2

i6

T p

i4 g4

F 1

Oil tank

p

Cooling tower

c1 T p

T p F

g3

T

p

T p

2

Settling tank

6

p

T

F

Cooling water pump

ORC pump

T

Temperature measurement

p

Pressure measurement

F

Flowmeter

i

State point

Oil wells

Pump

Valve

Fig. 3 Schematic diagram of the geothermal ORC system. Reprinted from Y. Yang, Y. Huo, W. Xia, X. Wang, P. Zhao, Y. Dai, Construction and preliminary test of a geothermal ORC system using geothermal resource from abandoned oil wells in the Huabei oilfield of China, Energy 140 (2017) 633–645. Copyright with permission from Elsevier.

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Utilization of Thermal Potential of Abandoned Wells

as shown in Fig. 2. The results showed that an optimal inlet velocity can be obtained to maximize the net power generation, with the trade-off between total obtained heat and the fluid outlet temperature. Kharseh et al. [24] indicated that, maximum electricity generation at 11 kW can be realized. A low-temperature geothermal ORC system, as shown in Fig. 3 [25], consists of oil wells and ORC, with the turbine efficiency at 78.52% and the ORC efficiency at 5.33%. Altun and Kilic [26] studied the thermodynamics of a geothermal ORC power plant. Due to the change of meteorological parameters, the transition from winter to summer will reduce the net power output by 36%.

2.3 System assessment criteria In the academia, criteria for thermal energy systems include outlet fluid temperature, extracted thermal output, static payback time, and carbon emission. Table 1 shows a holistic overview of multicriteria performances of geothermal-based thermal and power systems. Researchers are mainly focused on thermal and power generation of geothermal energy systems. In terms of heating applications, with the abandoned oil well (AOW) for space heating, Nian and Cheng [15] indicate that carbon emission can be reduced by 457 ton each year. Bu et al. [27] concluded that the static payback period was 7.17 and 5.16 years for continuous and intermittent heating, with the extracted thermal output at 448.49 and around 619.12 kW, respectively. With respect to the power generation, Yildirim et al. [28] designed downhole heat exchangers for electricity generation, and concluded that power generation cost was 46 $/MWh and the simple payback time was 2.25 years. Kharseh et al. [29] studied oil wells for power generation. They concluded that the levelized cost of electricity was between 5.6 and 5.2 ¢/kW, and the payback time was between 5.8 and 4.8 years. Systems for thermal energy generation include a U-tube heat exchanger [13] and a coaxial borehole heat exchanger [14]. Variables for parametrical analysis include geometrical and operating variables. With respect to geothermal-based power systems, multicriteria performances include electricity generation cost, simple payback time, and levelized cost of electricity. Systems for thermal energy generation include downhole heat exchangers [28], integrated absorption refrigeration and solar energy [4]. Variables for parametrical analysis include fluid mass flow rate, inner pipe diameter, depth of downhole heat exchanger, and so on.

3

Renewable integrations with abandoned wells for district heating

Barriers limiting the widespread application of geothermal energy include high initial investment, long payback time, and construction time, difficulty in assessing resource and difficulty in modularization. The combination of abandoned wells with various renewable energy sources can compensate the disadvantages and popularize the wide applications. In the academia, typical systems for renewable integrations include

Table 1 A holistic overview on multicriteria performances of geothermal-based thermal and power systems.

Thermal energy generation

Studies

Systems

Variables

Criteria

Results

Nian and Cheng [15]

Abandoned oil well (AOW) for space heating

Water flow rate

The carbon emission can be reduced by 457 ton each year.

Gharibi et al. [13]

A U-tube heat exchanger

Geometrical and operating variables

Indoor air temperature, total geothermal energy and carbon emission Outlet fluid temperature

Caulk and Tomac [16] Hu et al. [14]

Abandoned oil and gas wells for district heating A borehole heat exchanger for geothermal energy utilization Intermittent heating

Depth of wells

Outlet fluid temperature

Working fluid and thermodynamic property

Fluid temperature and generated power

The production temperature and power stabilize at around 29°C and 0.38 MW

Injection temperature and velocity

Extracted thermal output and static payback time

The static payback period is 7.17 and 5.16 years for continuous and intermittent heating, with the extracted thermal output at 448.49 and around 619.12 kW, respectively.

Bu et al. [27]

The inlet velocity and the outlet temperature are 0.03 m/s and 324.73 K, respectively. The outlet fluid temperatures higher than 40°C can be obtained.

Continued

Table 1 Continued

Power generation

Studies

Systems

Variables

Criteria

Results

Yildirim et al. [28]

Downhole heat exchangers for electricity generation

Electricity generation cost and simple payback time

Power generation cost is 46 $/MWh and the simple payback time is 2.25 years.

Kharseh et al. [29]

Oil wells for power generation

Fluid mass flow rate, inner pipe diameter and depth of downhole heat exchanger Optimal working fluid and design

The LCOE is between 5.6 and 5.2 ¢/ kW, and the payback time is between 5.8 and 4.8 years.

Bayer et al. [30]

Geothermal power generation system

Life cycle emissions

Khosravi and Syri [4]

Absorption refrigeration and solar integrated systems

Meteorological and operating parameters

Levelized cost of electricity (LCOE) and payback period Life cycle assessment (LCA) on geothermal electricity production Payback time

Emissions and resource are provided for worldwide geothermal power generation

The payback time is around 8 years.

Application of abandoned wells integrated with renewables

263

solar-geothermal energy systems, BIPVT and earth-air heat exchanger systems, abandoned wells with waste heat recovery, and abandoned wells integrated with renewable systems.

3.1 Solar-geothermal energy system integration Due to the low or moderate temperature (around 150°C) of geothermal systems, Li et al. [31] integrated solar energy to escalate the working temperature and improve geothermal power generation. The state-of-the-art review can promote the synergistic function of solar and geothermal energy for efficiency improvement in power generation. An absorption refrigeration and solar integrated geothermal power system is shown in Fig. 4. The operational principle is that the geothermal fluid absorbs heat from the production well, and the superheated vapor is reheated by a solar collector. Afterwards, the vapor goes to the turbine for power generation, and then moves to the condenser for absorption refrigeration. Due to the intermittence of geothermal energy, the hydrogen system is designed for stable electrical power generation. The technoeconomic performance analysis indicates that the payback time is around 8 years when the interest rate is 3%. In addition, the energy and exergy performances were studied on an integrated BIPVT and earth-air heat exchanger [5], with the annual thermal energy, annual electrical energy, and annual thermal exergy at 3499.59, 5908.19, and 55.59 kWh. Chen et al. [32] studied the combined geothermal and solar systems for district heating, as shown in Fig. 5. The sensitivity analysis results indicate that the annual cost saving ratio can be improved, for a higher solar beam irradiance. Yao et al. [33] studied a combined borehole heat exchanger and solar-assisted PV/T heat pump for space heating of a residential building. The COP of the hybrid system is 7.4, when the solar fraction is 67.5%.

3.2 Abandoned wells with waste heat recovery Waste heat recovery, as an effective strategy for decarbonization, has also been integrated with abandoned wells for thermal and power energy generation. DeLovato et al. [34] comprehensively reviewed advanced heat recovery techniques for energy performance improvement of solar and geothermal power plants. The waste heat recovery can effectively improve the system efficiency. In addition, Loni et al. [6] systematically reviewed the industrial waste heat recovery techniques with ORC. The results showed that the waste heat recovery can increase the system efficiency of up to 70%. Numerical models for heating energy assessment have been studied. Sharma et al. [35] developed an analytical model to study the heat recovery of geothermal energy. The results showed that critical parameters are identified. The heat recovery will improve the power output of the geothermal ORC power plant by 15% [26]. In terms of the application through system integration, Manente et al. [36] studied the hydraulic performance of a district heating system with geothermal and waste energy. Electric power for pumping can be reduced by 30%, and the enhanced

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Utilization of Thermal Potential of Abandoned Wells

Fig. 4 A schematic diagram on an absorption refrigeration and solar-integrated geothermal power system with hydrogen storage. Reprinted from A. Khosravi, S. Syri, Modeling of geothermal power system equipped with absorption refrigeration and solar energy using multilayer perceptron neural network optimized with imperialist competitive algorithm, J. Clean. Prod. 276 (2020) 124216. Copyright with permission from Elsevier.

storage system can save 7000 MWh/year energy, equivalent to 11% to the annual heat demand. Hall et al. [37] studied the heat recovery from underground mines for space heating. The energy source provided by the warm mine water can improve the energy resilience and offset the greenhouse gas emissions. Willems and Nick [38] studied the impact of geothermal heat recovery on demand coverage. The results showed that the heat recovery efficiency can be 30%, and the geothermal heat can cover around 4% of the total demand.

Fig. 5 A district heating system integrated with geothermal and solar resources. Reprinted from Y. Chen, J. Wang, P.D. Lund, Sustainability evaluation and sensitivity analysis of district heating systems coupled to geothermal and solar resources, Energy Convers. Manag. 220 (2020) 113084. Copyright with permission from Elsevier.

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3.3 Abandoned wells and renewable systems for district heating Abandoned wells and renewable systems for district heating have also been studied. Ghasemi et al. [39] analyzed power generation of a solar-geothermal system, to improve the system efficiency. Østergaard and Lund [1] studied the replacement of fossil fuel sources with renewable systems for district heating in Frederikshavn. Østergaard et al. [40] designed a heating system in Aalborg, with geothermal heat, wind power, and biomass. The study indicated that the dependence on neighboring areas is necessary to dynamically balance the energy in the 100% renewable scenario. The system with an absorption heat pump is powerful for carbon reduction, with replacement of natural gas. Hepbasli [41] provided a holistic overview on the performances of geothermal-based heating systems. The review can provide technical guidance on system design and operation. Fabre et al. [42] designed a triple-pipe system to lower the primary return temperature, so as to improve the efficiency of district heating network. The underlying mechanism is the temperature-cascaded district heating, so as to cover heating loads with different temperatures, such as domestic heating and space heating. Ozgener et al. [43] systematically reviewed techniques to improve performance of geothermal heating systems. The results showed that the geothermal heating system in Gonen shows the highest exergy efficiency, whereas the system in Salihli shows the highest energy efficiency. Techno-economic-environmental performances have also been evaluated. Kec¸ebas¸ [44] studied thermo-economic performance of a geothermal heating system in Afyon, Turkey. The results showed that energy and exergy efficiencies are 37.59% and 47.54%, together with energy and exergy loss rate at 5.36 kW/$ and 0.2 kW/$, respectively. Carotenuto et al. [45] studied the energy-economic performance of a novel solar-geothermal system for district heating. The results showed that with the public funding policy, the simple payback time can be reduced from 20.9 to around 10.5 years. Galantino et al. [46] analyzed thermodynamic performance of a geothermal district heating system, from perspectives of levelized cost of heating (LCOH) and carbon abatement. Compared to the conventional system with the LCOH at $15.53/MWhth, the system is more economically competitive with the LCOH at $4.55/MMBTU.

4

Strategies for performance enhancement

Strategies for performance improvement of abandoned wells with renewables can be proposed, from perspectives of optimal design and smart operation. In this section, approaches for optimal system design and smart operation have been reviewed, together with improvement in system performance.

4.1 Optimal system design In the academia, approaches for optimal system design include Taguchi Statistical Method [7,8], advanced optimization algorithms, such as genetic algorithm, mixedinteger and nonlinear programming (MINLP) optimization [9], mixed-integer linear optimization [10], and a three-stage heuristic. The advantages of the Taguchi Statistical

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Method include dimensionality reduction from redundant experiments, the cost saving and time saving. Cheng et al. [7] adopted the Taguchi Statistical Method to improve the geothermal energy extraction. The results showed that the well bottom curvature design can improve the thermal output by 30%. Liu et al. [8] adopted the Taguchi Method for sensitivity analysis of thermophysical and geometrical parameters of PCMs. Furthermore, optimization on geothermal energy with geometrical and operating parameters has been studied. Erdeweghe et al. [47] optimized the temperature and flow rate to maximize the power generation. The results showed that the exergetic efficiency of the hybrid system is higher than that of the pure power plant by 22.8%. Erdeweghe et al. [48] indicated that a geothermal CHP plant shows a net present value (NPV) at 3.46 MEUR. Weinand et al. [10] developed a combinatorial optimization approach to minimize the operating cost. The proposed heuristic approach is more accurate and faster than the traditional optimization approach, with the avoidance on economic performance overestimation. In addition to single objective optimization, multiobjective optimization was conducted to reach the “best of the best” solution along the Pareto front. Gerber and Mar
echal [49] conducted the multiobjective optimization of an enhanced geothermal system. Ren et al. [50] conducted the multiobjective optimization of a combined cooling, heat and power (CCHP) system, using NSGA-II. The results showed that the optimal strategy following electric load strategy is much better than others. Song et al. [51] conducted the multiobjective optimization on a multilateral-well geothermal system for performance improvement, in respect to heat power and flow impedance. With the objective for maximum geothermal production, the optimal parameters are injection flow rate at 62.21 kg/s, injection temperature at 49.98°C, and production pressure at 27.44 MPa.

4.2 Smart system operation In addition to optimal system design, smart operations on geothermal or geothermal integrated systems were investigated. Kharseh et al. [24] studied the optimization on operating parameters, and concluded the maximum electricity generation at 11 kW. Atam et al. [52] developed Hammerstein-Wiener models, and compared it with detailed finiteelement borefield thermal model. The Hammerstein-Wiener models are validated to be effective in advanced model-based control. Bode et al. [53] developed a mode-based control strategy on heat pumps, with integrations of a geothermal field. The results showed that the mode-based control strategy is effective in integrating renewable energies in the built environment. Fallah et al. [54] studied the pressure control of deep closed-loop well systems, and concluded that over 40MW initial thermal power can be generated.

5

Applications, challenges, and future prospects

5.1 Techno-economic and environmental performance analysis Techno-economic feasibility analysis of geothermal systems is critical for the widespread acceptance and social popularity of geothermal energy systems. Guo et al. [55] assessed the sustainability of geothermal resources in an abandoned coal mine.

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Templeton et al. [56] studied the abandoned petroleum wells for geothermal energy supply, with a finite element model. The results showed that the constant power model can extract energy with sustainable manner. Fan et al. [57] studied a regulated geothermal heating system, in terms of annual water consumption and power generation. Compared to an unregulated system, the regulated system can generate 25% more electricity with 50% less water. From the lifetime perspective, lifetime performance analysis is essential, with the consideration on performance degradation, operational stability, and so on. Daniilidis et al. [58] conducted the uncertainty analysis on a deep geothermal heat system, in terms of NPV, LCOH, and expected monetary value (EMV). The results showed that flow rate is the most critical factor for economic performance. Westphal and Weijermars [59] indicated that by extracting geothermal energy from depleted hydrocarbon wells, a NPV of $1.2 billion can be obtained in the United States.

5.2 Geothermal integrated energy systems Although the geothermal energy is characterized with thermal performance stability and large abundance in resources, the disadvantages of geothermal energy need to be noticed, such as initial capital cost and annual thermal imbalance. Future studies can be focused on: (1) geothermal-based hydrogen energy systems for low-carbon energy districts

Ghazvini et al. [60] indicated that the geothermal-assisted hydrogen production cost is much lower than other renewable sources, such as wind, solar PV, grid power, and so on. Fig. 6 shows the roadmap diagram of geothermal-based hydrogen production. The hydrogen can be produced from either thermochemical cycles or electrolyzer, depending on the utilized energy forms from geotherm energy. The geothermalassisted hydrogen production can compensate the high initial capital cost of geothermal systems, so as to popularize its practical application feasibility. (2) synergistic operation of geothermal sources and other renewable system for stable power supply

Due to the spatiotemporally uneven distribution of solar and wind energy sources, the integration of geothermal source can improve the energy supply stability and Fig. 6 Roadmap diagram of geothermal based hydrogen production.

Geothermal Energy Thermal Energy

Electrical Energy

Thermochemical cycles

Electrolyzer

Hydrogen

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reliability. From the long-term perspective, the geothermal storage can act as a seasonal storage, to balance the energy demands and renewable energy generation. Future studies can focus on dynamic and seasonal performance analysis of geothermal integrated hybrid renewable systems.

5.3 Potential assessment of abandoned wells for carbon-neutrality transition Along with the target for the carbon-peak era in 2030, and the carbon-neutrality era in 2060 in China, the roles of abandoned wells in the carbon-neutrality transition need to be studied. Xia and Zhang [61] reviewed the national development of geothermal power systems. They concluded that the development prospects in China under the current condition are not attractive. Tian and You [62] indicated that the transition from natural gas to geothermal energy for electric power supply can decrease the CO2 emission by 24.5%. Phillips [63] studied the trade-off balance between the negative environmental impact and positive socioeconomic impact. Santamarta et al. [64] studied the clean energy transition toward shallow geothermal energy. The case study indicates that the transition toward shallow geothermal energy can lead to 66% energy saving, and emissions savings at 256 tCO2. Tarighaleslami et al. [65] studied sustainable energy transition toward geothermal energy. The comparative analysis indicates that the geothermal-based system shows the lowest carbon emission. Future studies need to focus on (1) potential assessment of geothermal energy provided by abandoned wells with machine learning models; (2) quantifiable roles of abandoned wells in carbon-neutrality transition.

Acknowledgments This research is supported by Hong Kong University of Science and Technology, Delft University of Technology, and Hunan University. The authors also thank the editors for their useful comments and suggestions.

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Ali Sohania, Amir Dehnavib, Farbod Esmaeilionc, Joshua O. Ighalod,e, Abdulmaliq Abdulsalamf, Siamak Hoseinzadehg, Benedetto Nastasi,g and Davide Astiaso Garciag a Lab of Optimization of Thermal Systems’ Installations, Faculty of Mechanical EngineeringEnergy Division, K.N. Toosi University of Technology, Tehran, Iran, bDepartment of Electrical Engineering, Amirkabir University of Technology, Tehran, Iran, cDepartment of Mechanical Engineering, K.N. Toosi University of Technology, Tehran, Iran, dDepartment of Chemical Engineering, Nnamdi Azikiwe University, Awka, Nigeria, eDepartment of Chemical Engineering, University of Ilorin, Ilorin, Nigeria, fDepartment of Chemical and Biomolecular Engineering, University of Houston, Houston, TX, United States, g Department of Planning, Design, and Technology of Architecture, Sapienza University of Rome, Rome, Italy

1

Introduction

There are several wells worldwide which are used for different purposes. They cover a variety of applications, from water supply and agriculture to oil and gas supply for material preparation, energy supply, and processes. Due to the reasons, including decrease in the extraction efficiency, failures, environmental concerns, imposed policies, and so on, the operation of a well might stop, and it might be left. Such well is called abandoned well. Despite not being used anymore, abandoned wells, especially oil and gas ones, have a huge thermal potential. The reason is they are usually deep, and in the deeper part of earth from the ground level, the soil (rock) has a high temperature. Therefore, suitable strategies should be implemented to exploit such a great potential. This not only helps to save energy, but it also has a considerable economic and environmental impact. Countries such as Canada are the leading ones in using the thermal potential of abandoned wells. During the past years, the installed capacity of renewable energy structures has experienced a huge jump, which makes it more available and economically viable worldwide [1]. Therefore, it seems that if the heat extraction from abandoned wells is integrated with renewables, a great condition from all energy-efficiency, economic, and environmental aspects is achieved. Considering this point, different possible ways for integration of heat extraction from abandoned wells with renewables are introduced and discussed in this chapter, while a concise literature review is also done. Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00014-2 Copyright © 2022 Elsevier Inc. All rights reserved.

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After the introduction part, i.e., this section, the chapter continues by introducing and discussing different existing technologies for the integration of heat extraction from abandoned wells with renewables in Section 2. Then, the literature is reviewed in Section 3, while chapter ends by providing conclusions in Section 4.

2

Different ways for integration of heat extraction from abandoned wells with renewables

The international energy industry encounters growing problems in the world where the energy demands extend to raise and energy guidelines progressively follow alternatives for traditional fossil fuel-powered generation [2]. Renewable energy-based systems provide a collection of solutions that are continuously being employed to address these goals [3]. In 2014, the International Energy Agency (IEA) put forward that in 2040, more than half of the overall development in power production must be provided using renewable energy resources [4]. The existing energy market is not inevitably suitable to appropriately hold renewable energy as the contribution of an energy mix besides to fossil fuels while these technologies have technical concerns as the contribution of renewable energy growths [5]. In this case, it is apparent that geothermal systems have the proper potential to deliver continuous base power, while making it a superior option in comparison with obtained outputs by solar PV or wind resources. Hence, in the future, this type of energy system will provide more sustainable power for developed and developing countries [6]. Conventionally, the operation of geothermal systems is based on the hot steam or boiling water exploitation from the earth’s crust. One of the innovative methods for geothermal generation is based on introducing another technique to acquire hot water. In this approach, by combining the geothermal resources (oil or gas wells) to other systems (including renewable energy-based systems), a coproduction by using hot fluids from geothermal resources turns accessible. Although this technique offers progressive potential related to the geothermal generation by coproduced fluids, this method will not be without any problems. Overreliance on the coproduction of hot fluids to power these processes connects all the energy generation units to any (active or abandoned) oil wells. Moreover, by the presence of this direct reliance, while a well shuts down, a coproduction energy unit will be deactivated [7,8].

2.1 Solar and geothermal Among renewable energy resources, PV acts as the most promising supplier to provide electrical power [9,10]. It is projected that at the end of 2025, solar energy will be the main source of renewable energy. However, the announced capacity factor for this type of energy resource is low and the introduction of a novel configuration in which solar energy systems are integrated with geothermal energy cycles would improve the associated capacity factor of these systems. Among all types of renewable energy systems, this kind of hybrid renewable energy system will provide the highest value of the

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capacity factor. Enjoying sufficient solar and geothermal resources with proper infrastructure is important. Obtaining the required heat through the abandoned oil and gas wells which are the lowest (100–150°C) and medium temperatures (150–200°C) has less productivity and provides great charges. Oil and gas bores distribute the required thermal energy, which is employed for the progress in renewable energy resources. In this regard, to meet the security and improvement of energy systems’ efficiency, continuity is a vital subject. In the abandoned oil and gas wells, the required power is used in the injection pumps, which remain the leading challenges of these systems. Therefore, generated electricity power by geothermal abandoned oil and gas wells through combining with solar energy systems is employed to improve the productivity of the entire system and increase the total beneficial features of the economic aspects [11,12]. Geothermal has been introduced as a stable resource of renewable energy aimed at heating or hot water production by a ground source heat pump (GSHP). By using solar energy systems as a supplementary energy resource, fewer operative charges and improved products will be obtainable in comparison with conventional GSHP. A conventional combined solar and geothermal heating system is demonstrated in Fig. 1. This type of integrated system principally contains three subcycles. For avoiding freeze phenomena, saline or water-antifreeze solution is warmed up by solar collectors or ground heat exchangers. The altered operative methods can be planned in accordance with the direct or indirect applications of solar energy [14]. In case that solar energy is not adequate for heating purposes in the preferred temperatures, the working fluid flows through the solar and ground systems, or in another case the solar

Sun VII

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IV VIII

IX

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Valve

50 m

G level dnuor

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I II III IV V VI VII VIII IX X XI I-IV

Compressor Condenser Expansion valve Evaporator Ground heat exchanger Pump II Expansion tank Solar collector Pump I Fan coil Cgreenhouse GSHP

Fig. 1 The integrated system studied in the research work of Ozgener and Hepbasli [13].

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collectors are employed completely in preference to GSHP (when there is enough irradiance). At that moment, an additional loop is conducted for heat transfer through the condenser. Subsequently, the heat transfer fluid, like water, is used to deliver the heat to the sites for hot water and heating applications. Zhou et al. [15] studied a hybrid solar-geothermal system, in which a geothermal ORC was integrated with a solar energy system to produce superheated water (Fig. 2). Here, the geothermal fluid leaves the geothermal heat exchanger and then goes through the solar booster, to enhance the associated heat content with the assistance of solar energy. Here, the hot fluid is employed to drive a turbine for power generation. In some cases, the PTC (parabolic trough collector) is an alternative for solar boosters. Astolfi et al. [16] assessed the thermal capacity of a solar-geothermal system. The working temperature of ORC was between 70°C and 150°C by R134a. The productivity of this system was lower than that of typical fossil fuel power plants, while it represented a suitable outlook of developing low enthalpy geothermal resources with inferior charges of energy production from the sun. Turchi et al. [17] simulated an innovative configuration of the hybrid geothermal-CSP system to deliver feedwater heating to the circuit in the steam power plant. In the proposed cycle (Fig. 3), the obtained energy from the geothermal brine was a replacement for three lowtemperature feedwater heaters. This approach caused the elimination of steam extraction from low-pressure turbines.

Solar Field

Heat exchanger

Evaporator

Production Well Brine Pump

Preheater

ORC Turbine

AC generator

Air Cooled Condenser

Pump

Reinjection Well

Fig. 2 Schematic representation of a hybrid geothermal-solar technology [15].

Reheater 6 Hot Tank

7

Superheater

8

LP Turbine

HP Turbine

HTF2

Generator

Evaporator Solar Field

1 Preheater Steam extraction for feedwater heaters (FWH) HTF1

5

Air Cooled Condenser

Feedwater Pump 4

Cold Tank

FWH-5

3

FWH-4

Hot Brine

Fig. 3 Schematic representation of a hybrid geothermal-CSP technology [17].

FWH-3

b2

FWH-2

FWH-1

Brine / Feedwater Heater

b1

2

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Utilization of Thermal Potential of Abandoned Wells

Fig. 4 Schematic diagram of a geothermal-solar integrated technology to provide heating for a greenhouse [18].

Arabkoohsar et al. [18] used a new solar-geothermal heating system to minimize the heating contribution of diesel air heaters in greenhouses. As indicated in Fig. 4, the system took benefits from three heat exchangers for three different cases, which are the solar and geothermal heat exchangers (SHE and GHE), as well as an auxiliary air heater (AAH). In this regard, various studies have focused on the applications of hybrid solargeothermal systems for using produced thermal energy. Kavian et al. [19] evaluated the PV-GSHP (ground source heat pump), Salpakari and Lund [20] optimized a PV-GSHP to enhance obtained thermal energy from the geothermal well, Chen et al. [21] studied a hybrid PV-GSHP with a solar parabolic concentrated system for heating processes, and Chen et al. [22] analyzed the sustainability of district heating systems integrated with geothermal and solar systems. Along these lines, for heat extraction, the geothermal energy resources can be combined with other renewable energy resources like PV [23], solar thermal [14], PV/T integrated with GSHP system with [24] or without [25] thermal energy storage (TES) systems.

2.2 Biomass and geothermal Owing to the numerous resources that have the abilities to be employed as biomass fuel, the introduction of hybrid systems consisting of biomass resources and other renewable energy sources can be an applicable combination, where proper heat is not flexibly obtainable, especially in various sites where solar or geothermal resources are inadequate. On the other hand, the obtained heat by the geothermal or solar resources is mixed in a superheater throughout the primary steam [26]. As a model of geothermal-biomass hybridization, Fig. 5 is represented to simplify the schematic diagram of a 29 MW power plant [27]. Two-phase geo-fluid is acquired using two wells (RK5 and RK9), which are divided in a separator, and the steam is

Biomass SH added to Rotokawa I 4

CS

4’

ST

3

G

BM-SH 8’

5

E

E T

2

E T

G

6

RK9

G

T

G

9

9

1 PH 2

ACC

PH

7 CP

10

ACC

PH CP

RK5 1 Production wells

RK1

RK11 RK12 Injection wells

Fig. 5 Schematic representation of an integrated biomass-geothermal power generation technology [27].

10

ACC CP

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Utilization of Thermal Potential of Abandoned Wells

conveyed into a turbine from back-pressure steam type and brine is sent to heat exchangers’ binary unit. Thain and DiPippo [28] introduced a geothermal double-flash system that took benefits from a biomass unit. Initially, the high-pressure geo-steam was superheated within the biomass incinerator (Fig. 6). Following that, after power generation in the high-pressure turbine, the associated outlet was gone along with the low-pressure separated steam. In order to preheat the associated air for the combustion process, the hot brine exiting the low-pressure separator was employed. Additionally, the excess hot brine was assisted in the drying process of the biomass at the furnace entrance.

2.3 Wind and geothermal Up to this time, the combinations of wind energy with geothermal energy have not attracted enough attention yet, although, the integration of wind and geothermal systems was introduced in the regions with high potential for both wind and geothermal energies. Jalilinasrabady et al. [29] introduced a hybrid wind-geothermal system while a thermal chimney was used as a driver. The proposed system consisted of a geothermal heat supplier, a wind turbine, and a thermal chimney. The geothermal hot water (at temperatures between 333 and 373 K) entered a pond. A thermal chimney covered the pond. The cold air passed through the chimney while it was heated using geothermal water. Consequently, the warm air was flowed to the higher elevation levels because of passive ventilation. The warm air, then, made wind turbine blades rotate. Østergaard [30] investigated in what manner absorption heat pump and compression heat pump for the production of district heating affect the combination of wind power. A novel configuration of the wind-geothermal technology to supply the heating demands of a greenhouse has been introduced (Fig. 7) [31]. The small-scale wind turbine was powering a geothermal heat pump. The refrigerant, ground coupling circuit, a small-scale wind turbine, and a fan coil circuit were the main subsystems of the considered system. This system was employed to examine different interconnections that outline thermal energy production, geothermal and passive solar heating, and wind energy applications.

2.4 Poly-generation For providing the needed energy for desalination, electricity, heating, and cooling, concurrently, poly-generational systems are proposed [32–34]. The combined heat and power (CHP) cycle is powered via geothermal and solar energy to deliver heating and power demands. Solar radiation is absorbed by solar panels and combined with the turbine exhaust gas recovered heat to drive the refrigeration cycle for the cooling process. The obtained geothermal fluid from the well mixed with the streaming fluid which came from the evaporator of the ORC2 system, and entered the flash separator. Desalination through the technologies like reverse osmosis (RO) could be powered through the produced thermal and electrical energy. The steam, which has high levels of pressure and temperature in turbine 2, produces electricity. Heat transfer from the steam in a heat exchanger took place to meet the space heating demand (Fig. 8).

Reheater/Superheater

10

9

8 11

Scrubber Separator

1

0

1

4 12

FG Recirc

Biomass furnace

Generator Turbine

2

Condenser

3

FG clean-up

13

Separator

R

PW

5

6

7 LP pump

R

Well

Combustion air

Biomass fuel

7 Well

Fig. 6 Schematic representation of a geothermal double-flash system integrated with biomass furnace [28].

SWTS 380V 50Hz AC Wind

380V 50Hz AC

Sun I

XII

VII

GCC

SWC GHP

IV

II

VIII GCC

SWTS

GCC

GCC

VI SWTS 220V 50Hz AC

Water-Cooled Condenser

III IV

Capillary tube Evaporator

V

Ground heat exchanger

VIII

Brine circulating pump

SWTS XIII AC/DC/AC 96/220V 96/380V Underground

V

Solar collector

IX

Water circulating pump

X

Fan coil

XI XII

Greenhouse Wind turbine Electricity production and distribution command center

XIII

XI

Expansion tank GCC

VII

Underground

GCC

VI

Ground level

GCC

II

GCC

Compressor

IX

III

220V 50Hz AC

RC

RC

GCC I

X SWC

90-185 V 32-100 Hz AC SWTS

GCC

SWTS 380V 50Hz AC

RC

RC

Fig. 7 Schematic representation of the integrated wind-geothermal-solar technology [31].

GHP : Geothermal heat pump GCC : Ground coupled circuit (I-VIII) RC : Refrigerant circuit (I-IV) SWTS : Small wind turbine system (XII-XIII) SWC : Secondary water circuit (II, IX-XI)

Turbine 3

18 Solar collectors

City

19 30 condeneser

31

32

Generator

ORC2, ev 27

26

20

17

21 28

25

29

22

8 ORC2,pump

24

9

Turbine 1

GS,ev

3 4

absorber Separator

23

Ind,HX

Evaporator

7 6

Factory GS,pump

2

10

Cold water 11

5

hw,HX

12 ORC1,ev

14

1

Hot water

Reinjection well

Turbine 2

13 Production well

15

ORC1,pump sh,HX 16

Fig. 8 Schematic representation of a solar-geothermal poly-generation technology [35].

City

286

Utilization of Thermal Potential of Abandoned Wells

PTC

5

SCF GF HTF HW for TRG HW for winter thermal recovery Sea water for ACH cooling ChW HW MED system Sea water for MED system Cooling water of ORC

TK1 3

P2 ORC

4

1

P1

6

SecHE 2 19

M1 18

GHE

7

P3

D1

Pgeo

P4 8 20

production well

9

10 12

from user to user 11

from sea ACH RecHE

to sea from user

15

14 TK2

to user 13

16

from sea MED

to user

MedHE P5

20

17

injection well

Fig. 9 Schematic representation of the solar-geothermal poly-generation cycle [36].

Calise et al. [36] studied a multigeneration cycle. In the proposed research, limited residents with the demands for electrical, heating, and cooling, as well as freshwater were sustained using a solar-geothermal poly-generation system (Fig. 9). The medium-temperature geothermal and solar energy were consumed to power the ORC. Low-temperature geothermal energy was employed to deliver space heating at around 360 K, or a cooling power system in hot seasons by an absorption chiller.

Integration of heat extraction from abandoned wells with renewables

287

22 High Pressure Turbine

Bioler Heat Exchanger From Geothermal Reheater 11

QC Condenser

26

QG

Generator 7

27

Heat Exchanger

29

25

30 Drying Chamber

23

Absorption Chiller Cycle Rankine Cycle

32

12 31

28 3

24

4

Reverse Osmosis Cycle Geothermal power cycle

Condenser

8 Heat Exchanger

Expansion Valve 2 9

Pump 1

Evaporator

5 Expansion Valve

19

18

Pump 2

17

Open FWH

16

Pump 1

6 20

21

Throttling Valve

Absorber

13

10 Q

QE

A

Chilled Water to Building

DC/DC

44

From Thermal Oil Heat Exchanger

10,854 kW to RO Plant

51

Inverter

Wind Turbine

Work Input from Wind Turbine

52 To LiBr Absorption Chiller Generator

Steam Turbine

35 37

Static Mixer

39

Filter

40

Pump

12

Throttline Valve

14

50

Closed FWH

45

Brine 6110 ppm 25.2 kg/s 101.325 kPa 15 ⬚C

Throttling Valve

Chilled Water from building

15

43 Mixing Chamber 42 46 RO Module Permeate 20 ppm 75.4 kg/s 101.325 kPa

47

Degassfier 48

49

38

Condenser

Flash Chamber

36

Separator 54

Work Input from Geothermal Turbine 35

8

Pump Saline Water 1550 ppm (parts per milion) or 1.55g/kg 101.325 kPa 15 ⬚C

Throttling Valve

41 Product Water 230 ppm \101.325 kPa 15 ⬚C

48 GeoThermal Production Well

Reinjection Well

Fig. 10 Schematic representation of the integrated energy system investigated by Ghosh and Dincer [37].

A standard integrated energy cycle consisting of geothermal, wind, and solar energy is presented in Fig. 10. The geothermal water cycle included a well, separator, flash chamber, condenser, heat exchanger, and turbine. Geothermal water extracted from the ground continuously flowed to a separator and a flash chamber to eliminate the dissolved gases. High-temperature gas was produced for heating the space. Moreover, the liquid that was warmed up in the heat exchanger (via the heated oil by the solar collector) arrives at low-pressure turbine for electricity production.

3

Literature review

In this section, we conduct a literature review of empirical investigations on the generation of geothermal energy from abandoned oil wells. Such retrofitted oil wells are usually described as geothermal wells [38]. These wells could be utilized as a heat source for various applications such as electricity generation [39], seawater desalination [40,41], underground heat storage [42], integrated cooling systems [43,44], and heating of buildings during the winter [45]. Electricity generation is, however, the most common application. A more detailed summary of the key findings in recent literature regarding energy generation from geothermal wells is presented in Table 1 (it is the dominant application area).

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Utilization of Thermal Potential of Abandoned Wells

Table 1 Summary of recent literature of energy production from abandoned wells. Ref.

Location

Method/approach

Key findings

[46]

Malaysia (Malay, Sarawak, and Sabah basins)

The leveled cost of electricity (LCOE) by the ORC system was reported to be twice that of conventional geothermal technologies

[47]

China (Indus basin)

Computational fluid dynamics (CFD), process simulation and technoeconomic analysis of the use of organic Rankine cycle (ORC), and contrast with the conventional geothermal technologies. Developed a mathematical model of a thermal and hydraulic coupling process and a 3D numerical model

[48]

Canada (Western Canadian Sedimentary Basin)

[49]

Canada (Western Canadian Sedimentary Basin)

[40]

Iran (Ahwaz field, Zagros basin)

[50]

China (unspecified area)

Built a 3D simulation model in COMSOL Multiphysics to investigate geothermal energy extraction from some abandoned petroleum wells using doublet deep borehole heat exchangers (DBHEs). Studied the possibility of using geothermal energy with borehole heat exchangers in abandoned oil wells. Simulated the system with COMSOL and validated their modeling. ANSYS fluent software was used for the oil well simulations, while C++ programming was used for the desalination process equations. The simulation was done by numerical, analytical, and thermal resistance methods.

The exit temperature of the circulating fluid from the sedimentary geothermal system indicated that the abandoned gas wells are appropriate sources of geothermal energy. The doublet DBHEs perform better than singlewell DBHE in energy extraction from abandoned wells.

Production operating temperature and the geothermal well power stabilized at approximately 29°C and 0.38 MW.

Simulation results showed that each abandoned oil well could produce 565 m3 of freshwater from seawater.

The optimum selection criteria of working fluids were presented, and the optimal working fluids with net power were determined.

Integration of heat extraction from abandoned wells with renewables

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Table 1 Continued Ref.

Location

Method/approach

Key findings

[51]

China (unspecified area)

Better economic performance is achieved using low mass injection rates and low injection pressure.

[52]

United States (Permian Basin)

Modeled the mass and heat transfer processes of flowing CO2 in wells from horizontal type. Sensitivities of the injection parameters were assessed by the type curves of CO2 circulating in long tubes and annuli. Developed a predictive tool for estimation of deliverable treated water by heat transfer modeling and water treatment thermodynamics. Used some soon-to-be-shutdown oil and gas wells as sources of geothermal energy.

[45]

China (unspecified area)

[43]

China (unspecified area)

A comprehensive model was built to combine formation heat transfer and wellbore and studying the performance of storage unit of a single depleted oil well (DOW) used for heat storage underground (UTES). The Monte Carlo technique was applied for sensitivity analysis of criteria and efficiency of storing process. Created a model for Lithium bromide/water absorption cooling system integrated with the geothermal system, which provided the possibility of cascade exploitation of energy.

It was reported that a well which has depth of 4000 m and temperature gradient of 0.05°C/m is able to effectively treat water with total dissolved solids of about 170 g L 1 and still deliver approximately 600,000 L of daily fresh water. The geothermal gradient had the most significant effect on the storage efficiency of the system. The DOW system which is around 2000 m deep could store heat almost 4.7  106 MJ.

It was found that the hot water temperature of hot water from would exceed even more than 150°C continuously during a 20year period. It would be able to meet the Libr/H2O refrigeration requirements. At the same time, the provided cooling effect was upper than 9 MkW while the values more than unity for COP was seen. Continued

290

Utilization of Thermal Potential of Abandoned Wells

Table 1 Continued Ref.

Location

Method/approach

Key findings

[53]

China (unspecified area)

High injection pressure places a high amount of equipment requirement. A small injection temperature was also recommended so as a high geothermal energy rate can be achieved.

[39]

Pakistan (Photohar area of Islamabad)

Developed a theoretical model to elucidate the described CO2 heat and mass transfer process in abandoned horizontal wellbores. The model was done computed by a numerical method. The study designed a hybrid plant combining a geothermal unit and a photovoltaic system.

[54]

Iran (Ahwaz oil field)

The study designed a hybrid plant combining a geothermal unit and a photovoltaic system.

[55]

China (Huabei oilfield)

They designed a geothermal organic Rankine cycle (ORC) system for electric power generation using R245fa as working fluid

The system was able to achieve a 35% increase in energy output compared to the photovoltaic system alone The system was able to achieve a 23.5% increase in energy output compared to the photovoltaic system alone They attained a 78.52% turbine efficiency, 5.33% ORC efficiency and an average intermediate cycle efficiency of 77.98%

In recent times, several aspects of electricity generation using geothermal wells as heat sources have been investigated and these include numerical modeling, temperature and pressure profile analysis, economic analysis, etc. Nian and Cheng [50] explained that modeling of geothermal systems can be done analytically and numerically. Analytical models include the cylindrical source model, line source model, finite-source model, and Zeng’s model. However, numerical models are more employed. These models include finite-difference, finite-volume, and finite-element methods hosted on in silico platforms such as ANSYS, COMSOL, and TRNSYS. They are iterative and rigorous in nature and have been shown to be effective for geothermal well modeling. Computational Fluid Dynamics (CFD) can be used to examine the key variables of heat extraction from abandoned oil wells. Based on the CFD modeling studies of Kurnia et al. [46], it was predicted that 0.71 kW of power can be generated at a production cost of 0.062 USD/kWh from the specific oil well with a 73°C water temperature inlet. Numerical modeling has also been employed by Mehmood et al. [47] and Hu et al. [48]. Besides modeling, Yang et al. [55] and Wang et al. [56] have also employed experimental systems (with key findings summarized in Table 1). The analysis of temperature and pressure patterns of the abandoned oil wells is a good indicator of its potential performance as a geothermal well [48]. Geothermal

Integration of heat extraction from abandoned wells with renewables

291

energy can be harnessed when the well is considered a thermal reservoir [57]. The high temperatures can be used for the conversion of water to steam for driving turbines and producing electricity. Hu et al. [49] examined several aspects of the temperature of geothermal wells in Hinton, Alberta. These include geothermal gradient, surface temperature, variation of the temperature field, wellbore temperature distribution, and so on. Based on the observations of Hu et al. [48], it is of advantage when the static inlet pressure is greater than the static outlet pressure; in such cases, no pumping power is needed for water circulation. Also, the injection pressure into the geothermal well affects production cost as this is recommended to be kept as low as possible to reduce cost [51]. Pressure considerations are generally important because besides steam, CO2 can also be used as the working fluid and the intricacies of both systems are different due to their different properties [53]. Economic analysis is an important aspect of renewable energy technologies as it helps determine its viability in the long and short term and its attractiveness to potential investors [58]. Novel processes that are expensive would not be able to compete favorably with other more conventional technologies even if they possess other environmental advantages. Many research works have evaluated the economic aspects of geothermal energy generation from oil wells. Kurnia et al. [46] observed that conventional geothermal technologies can be twice as expensive when compared with the generation from abandoned oil wells. In order to further reduce cost, Noorollahi et al. [54] developed a hybrid geothermal power generation system assisted by a photo-voltaic (solar) system to yield a 23% increase in power generation. Economic analysis is also important because the thermal energy output gradually declines with time, hence a reduction in performance over time [59]. Besides the conventional application energy generation, geothermal wells can be used to generate energy for seawater desalination [40]. Basically, this involves harnessing the thermal energy in the well to serve as an evaporator for seawater, which is then condensed to produce clean water (as the salt is not volatile) [60]. Based on the investigation of Kiaghadi et al. [52], it was observed that a geothermal well of 0.05°C/m thermal gradient (up to 4000m deep) can desalinate water at 600,000 L per day. Research has also shown that a single geothermal well can be used for a combined power and desalination unit [44]. Besides desalination for domestic use, the system can be used for the treatment of wastewater [61] and water purification for agriculture [62]. He and Bu [45] has also shown that geothermal energy can also be harnessed to heat buildings during the winter.

4

Conclusions

This chapter gave information about different technologies for the integration of heat extraction from abandoned wells with renewables, while it also provided a concise review of the recent studies. It was found that, in general, the integration ways could be divided into four items. Three of them were combining with solar, wind, and biomass energy, while another was a poly generation strategy. Moreover, it was observed that heat exchangers and organic Rankine cycle technologies have been very popular for integration purposes.

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Acknowledgment The first (corresponding) author of this book chapter sincerely thanks Dr. Muhammad Nihal Naseer, the editor of the book, for all his kind help and support during the preparation of the chapter and wishes him the best.

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A Kalina cycle for low and medium enthalpy abandoned oil and gas reservoirs incorporated with solar technology for power production

15

Jainam Panchal and Manan Shah Department of Chemical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar, India

1

Introduction

Energy is a fundamental factor of the macroeconomic growth, prosperity, and economic development of a nation [1]. The major share of energy is contributed by fossil fuel-driven plants in power generation compared to traditional energy resources [2]. Using renewable and sustainable energy sources and which provides the major advantage of the prevention of greenhouse gas emissions. As the environment is concerned and moving toward sustainable development it is found to be a more appropriate arrogate solution to it. In order to fulfill global energy needs, geothermal energy is proven to be a promising, environmentally friendly source of energy. The unexploited potential, consistency, availability, and wide area of application such as in various chemical processes plant and similar areas where the geo heat can be utilized influencing the feasibility of its potential [3]. It has titled the continuous as the heat is trapped inside the surface of the earth is not exhausted. In the near future, it is believed that geothermal energy will play a major role in the global pursuit of identifying alternative resources. Since renewable energy is cost-efficient and on the other way conventional, especially coal or black energy is being costlier compare to it. This gives researchers motivation to carry out more experiments and research to obliged the world [4]. Many technologies, cycles, and power plant models have been studied and scrutinized regarding the availability of exploration of the geothermal source. After calculations of exergies and energies, a plant or model has been set up or developed by scientists and researchers [5]. According to Valdimarsson [6], configuration or models have been suggested by the literature i.e., dry steam [6], single flash steam [7], double flash steam [7], binary [6], and advanced conversion method of geothermal energy [6]. In a dry steam plant, very high enthalpy steams from the reservoir is directly led to the turbine with minor operations in it [8]. The economical alternative in terms of availability of the sources and the temperature-wise adaptable, i.e., 190°C, is single flash power plants. The steam is Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00015-4 Copyright © 2022 Elsevier Inc. All rights reserved.

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treated in the separator and dry steam is allowed to pass through the turbine. The capacity range of the dual flash steam is around 4.5–105 MW, which is expected to be 14%–22% more than the single flash [7]. The advantage of the dual flash is that the saturated liquid from the separator of the first stage is passed to the second stage by lowering the pressure, resulting in greater amounts of steam to rotate the turbine and hence capacity is enhanced. Binary cycle power plants are commonly designed and set up models or technology for power production with the low and medium stream of geothermal sources [9]. Binary cycle power plants can be further categorized into two types: organic Rankine cycle (ORC) and Kalina cycle. In ORC, the working fluid is generally steam or any hydrocarbon. In the Kalina cycle, a mixture of water and ammonia with proper mass fractions are used as working fluid. In ORC and Kalina power plants powered by low and medium enthalpy steams, generally the geo heat is transferred to the working fluid to increase the temperature and serves to convert the saturated liquid to vapor as the boiling point of the working fluid used is lower and has higher vapor pressure [10]. Exergy destruction and the overall efficiency and the effectiveness of the model/cycle are increased as the boiling point is variable concerning the composition. The Kalina cycle has the benefit here that as we are having the variable boiling point over a particular range of a working fluid (water-ammonia mixture) [11]. Some of the stainless steel types and many of the alloys are inert with the corrosion with the ammoniawater mixture and the fluid is also environmentally friendly and safe. As ammonia has a distinctive odor, if there is leakage of something else it can be easily known and this also makes the owners of look in an efficient way for the safety of the plant and locality [12]. A further advantage of ammonia is that the storage and transportation costs are often reduced. It costs around 0.02$/kg ammonia or 1.09$/GJ having the density 682 kg/cubic meter. It can be easily transported to a large-scale production site and is easily viewable at economic point of view. This gives the extra benefits to it. In this chapter, the authors are discussing the Kalina cycle power plant in the geothermal sources’ region with their working principle, advantages, and future scopes. In addition, getting coal-free energy using low and medium enthalpy streams of geothermal energy will lead the plant toward obtaining renewable and environmentally friendly energy. The Kalina cycle is not only a better alternative to the organic Rankine cycle but also energy efficient. The authors’ motive in writing this chapter is to underline the unexploited geothermal energy in India and contribute to better utilization of natural resources with the emerging technologies. It is said that nature returns to us everything in varied forms and keeps nothing with it. Over here we can see that firstly we are obliged with the crude oil which is sometimes known as “black gold.” Once the crude has been taken out and the capacity is filled, these wells are shut off as the main profit makers have been taken out. But there are several resources available in the basins of the crust. Mainly we talk about the geothermal reservoirs that are accessible in the prevailing oil and gas oilfields. Any nation’s economy is estimated and the leading component is the crude. As the efforts have been supplied for making them well so it should be utilized with the resources. It has been observed that geothermal energy is a comparatively cheaper and consistently renewable energy source. After the crude has been taken out, we can use the geothermal energy available in the crust of the Earth with advanced technology to serve mankind with the gift of nature.

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In the innermost region of the abundant wells of oil and gas there exists crude oil, which is the form of hydrocarbon and geothermal energy in the form of low and medium streams. They both coexist in the sedimentary region or basins in the geothermal resource in the wells [13]. The oilfields of the wells of petroleum and natural gas are produced under specific temperatures and pressure. The parameters’ conditions were nearly alike to those of the streams of the geothermal streams of the reservoirs and the wells (abandoned). The groundwater which is found in the depth of the well and they are affected in a direct or subsidiary with the primary temperance of the oil and the source rock and the secondary moderation of the reservoirs of oil and gas which were available and some of the content [14]. In a similar situation, it is found that the geothermal reservoir’s capacity and strength are much higher than those of the olefins capacity, which indirectly indicates that the geothermal energy content is higher [15] and the utilization will be profitable if both are used wisely. However, the energy density of the geothermal resource is much lower than the oil and natural gas resource [16]. In addition, in the alternate situation where the capacity of the oil and natural gas is higher than the geothermal one, we can use it for the extraction of olefins, and then one can go for the geothermal one. Furthermore, some wells are described as “abundant reservoirs” where the producers have extracted the oil and natural gas, but the geothermal strings are there with a good capacity that can be utilized for generating the electricity via employing the binary cycles and the ORC. For exploiting and utilizing the hidden potential of geothermal energy, oil and natural gas utilities and companies have applied efforts for the exertions and utilize with the amalgamation of the current new technologies in recent times [17]. Researchers have discussed and presented many possibilities of the application of geothermal energy being the treasure of the Earth in many direct and indirect applications. The low and medium enthalpy streams are found in general cases and they are utilized more precisely. The economical and sustainable development of any nation depends on how the end resource or product is prepared and utilized until it reaches the end customer it is striking and believed by the experts and researchers. Utilizing geothermal energy efficiently and effectively in the abundant oil fields with existing and efficient technology and infrastructure can create wealth and value from the unused source. In India, there are many wells of oil and natural gas that are soon to off or will be shut up in the near future which can have good potential for geothermal sources and the abandoned oil and gas fields where the oil and gas have been taken off and the well has no further utilization have the high amount of heat content and the flow rate of the hot water springs [18]. These water springs can be further utilized for many applications like electricity generation, cooling and heating of the space or vacuum for operations, water inundating, and various direct applications. Water cut in various fields and locations of the oil and gas fields are considered and treated as the annoyance to oil and gas utilities and exploring companies as the water needs to be disposed of or reinjected as the cycle needs to be completed and get the constant crude or gas without the water content so through another injection wells to reservoirs they are injected. This additional management and the organization lead the utilities to the extra cost of the operation comparatively other well-combined services.

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There is a high water cut in the oilfields or the wells of the oil and natural gas; for the coal fields it is around 97%–98% and the water which is there or produced is generally taken into consideration. This causes an issue for both oil and gas utilities and coal miners, as they needed to be reinjected again as discussed is found to be high around which consequences the overall net profit [19]. Binary power cycle technologies are playing and will continue to play a vital role in the modern geothermal-based market of power generation. If we consider the independent unit of the geothermal-based power plant, the capital expenditure is divided into about 30% for reservoir development and around 70% in the plant operation. However, we can save here the section of approximately 30% of the reservoir as we have abundant wells of oil and gas. The electricity productivity per well is a function or they are affected by the property of the fluid and the reservoir one but more we are concerned with the temperature and the phase of the streams. The higher the temperature of the streams, the higher the ultimate output of the electricity will be [20]. The beauty of the binary system is the reinjection system; although it affects the additional pumping costs to the plant, the equilibrium can be maintained and the cycle will occur in a regular fashion. Even the water which is injected can be utilized for direct use after the primary and secondary treatments are required. Here is the point of our interest: if this situation or the place is there, over here if we have the abandoned field of oil and gas and enough hot water is available, we can bring the power generation cycles for generating the power and utilizing the in-use or ready and prepared wells for it. The organic Rankine cycle is the conventional method for this. But with the updated technology and considering the cost and performance efficiency, we have the Kalina cycle over here for the power production.

2

Related works

Bu, Ma, and Li [21] presented a feasible model for portraying the mechanism of transfer of heat from the rocks to the streams of the fluid present with numerical methods. They further analyzed and calculated the geothermal energy from the mathematical model. That energy exploited for streams of the geothermal struck the computational and intended results from the model designed for the wells which are abandoned or oilfields subjected mainly to the rate of the flow of fluid and the gradient of the geothermal energy. The results showed that a solitary well gave the net power output of around 53 kW for the gradient of the geothermal around 44–45°C/km and the outlet temperature of the produced water was in the range of 128–130°C was steady and which leads a fact setup using geothermal streams of the abandoned well with the process will work progressively in the long run. It was observed that the optimum flow rate was around 0.028–0.031 m/s and the highest level was around 0.048–0.05 m/s. It was suggested that the inter wells should be in the distance of 40 m to avoid disturbances in the interoperations. The economic return was found to be around 36,000 US$/year for a retrofitted well with the steam temperature of around 45°C and it can be increased if the steam is >45°C. The wastewater found was around 56°C with a flow rate of around 5 t/hour, which can be utilized for other applications like direct

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heating and cooling. Along with the theoretical calculations provided the researchers also focused on the practical considerations, mainly regarding the double pipe used and its physical properties, and the material made with the insulation material used for the isolation of the heat. In a nutshell, it was found that converting abundant oilfields or the wells of oil and natural gas to the source of the geothermal low-medium enthalpy geothermal stream wells for power production was fruitful. Yang et al. [22] displayed the creation, design, and simulated geothermal-based power production system based on the organic Rankine cycle applied and utilizing the geothermal streams from the abundant oil wells as a source of heat from the Huabei oilfield situated in China which was abandoned for a long time but had major geothermal potential. Six major portions were studied with consideration of six sections with genuine engineering problems. For the prevention of the possible blockage of the keynote apparatus, an intermediate cycle was proposed. An axial turbine with the fourstage was expressly designed, engineered, and manufactured, and the efficiency of the turbine, efficiency of the intermediate cycle, and efficiency of the ORC were evaluated and analyzed as assessment criteria ion of the system. Ultimately the water cycle in the intermediate mode was found to be a feasible approach to avoid pipe blockage and flow and the cleaning tech equipment with real-time monitoring will accomplish and that will decrease the cost. The intermediate temperature of the heat absorption of the organic cycle setup reduced, which further decreased the ORC efficiency. The average efficiency of the axial turbine was obtained at around 78%. The average efficiency of the organic Rankine cycle was evaluated to be in the range of 4.35%–4.41% and at the most it was 5.29%–5.55%. The causes for the lower efficiency were lower flow rate, off of preheating, lower inlet and outlet pressure of the turbine. Harris, Lightstone, and Reitsma [23] studied geometry with a numerical model to evaluate, and calculated the temperature of the outlet streams and the heat extraction rate of the system for predicting and analyzing the geothermal extraction of the geothermal energy and the power generation. Their results showed that at a depth of around 3900–4000 m and at a horizontal distance of 4700–4800 m, 2 MW of thermal energy was found in the form of a geothermal stream which was capable of producing 200 kW using the organic Rankine cycle. They proposed a methodology for utilizing the geothermal low-medium enthalpy stream from the wells of oil and gas which were not in use where two adjoining drilled directionally were connected to set up a continuous loop. The geothermal energy exploitation expansion path, being cost- and energy-effective, was stipulated for the expansion of geothermal energy. The flow conditions were analyzed at the rate of fluid flow of 8.9–9 kg/s for the location at the base. The researchers noticed that minimizing the temperature at the inlet was favorable. In addition, when the gradient of geothermal streams increases by 9–9.29°C/km, it showed around power generated elevates at the values of around 27%–28% at the 10% power cycle efficiency. After conducting some simulations, it was found that the insulation thickness provided of 3 cm trivial improvements at the results of enhanced efficiency around 4% increase in power production. The authors concluded that more applied research should be conducted to assess the economic aspects and ensure more exploration with the in-situ testing.

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Caulk and Tomac [24] described the temperature profile of the abundant wells in the countries - Santa Clara, Monterey, and Santa Barbara, and the gradient was found to be up to 2.2°C/100 m. They suggested the deep coaxial BHE method was costflexible and low-risk, and thus a good alternative to the EGS method. The results of the study concluded that the temperature at the outlet, if it is greater than 40°C, is straightforwardly attainable for the countries having a temperature gradient of 7°C/100 m. In addition, they state the values of flow rates with the 180 mm dia coaxial BHE for temperatures higher than 40°C and good depths for >1250 m were around 1–4.3 L/s. The flow rate adversely affects the COP; for moderate flow rates and good depth, the COP is enriched. While the accumulation of a heat pump reduces efficiency and effectiveness, solar couples or solar cells can counterpoise the economic aspects of the energy and other requirements which can also collaborate with exclusive direct application of the geothermal streams and other ways too. Water desalination with greenhouse gases or thermal desalination can also be employed. The reverse osmosis methodology can also be adopted as the criterion and the overall situation configurations or combined profile. The lesser geothermal conditions can compensate for the generation of the heat when the loading of thermal is cyclical rather than steady. The abandoned oil/gas wells whitethorn provide the preliminary point for well deepening, but in other scenarios, the wells might merely demand unplugging and the recasing operation for insulation to refrain the formation of the sandstone of interest to EGS to elevate the casing contact with the surroundings (i.e., deep coaxial BHE). Wight and Bennett [25] proposed and evaluated a scheme utilizing water from the wellbore and the amalgamation of the water available of low and medium enthalpy streams of the geothermal potential from the wells of oil and natural gas which aren’t in use, and a wellbore which is shut which played a role as a heat exchanger. The objective is to generate power with a medium-scale power system based on the binary cycle. They utilized the log data for the wells situated in Texas of around 2000–2500 to analyze the energy gradient of the geothermal energy and the temperature of the surface. The parameters were found to be around 0.0311°C/m for the geothermal gradient, 130°C stream temperature with the wellbore of a depth of 4200 m, and a rate of flow of the geothermal stream of 2.5 kg/s. The net power produced was 108 km– 628 kW via a medium-scale power plant based on a binary cycle with a multistage heat exchanger. The authors believed that to approach with the other than the conventional one to go with the geothermal gradient available in the abundant wells of oil and gas. An innovative approach utilized an unused well of oil and natural gas with the equipment heat exchanger developing and an essential section power plant based on the binary cycle. The authors firmly believed that abandoned wells of oil and natural gas have a potential source of energy of geothermal which is utilized for impartial electricity generation and that can accomplish deprived of several dependence on the stream of geothermal empowering a coordination or process design and engineered using wellbore resource and maximize the electricity production. Davis and Michaelides [26] performed simulation for determining parameters for the power generation empowered by streams of the geothermal energy from the wells on oil and natural gas which are abandoned by inserting repossessing a secondary fluid. They selected isobutane under the section of secondary fluid which is used

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to insert and is allowed to increase the temperature or heat the vapor generated and at optimum pressure. A computational model has been developed including energy and mass calculations and conservation equations. The power production depends upon the lowest temperature of the geothermal streams and the pressure of the secondary fluid injected. In the south Texas region, it was found around 2.1–3.2 MW of electricity was generated for this well. These values of the electricity generated aren’t the recurrent like with other sources of energy in the renewable form which are accessible at the peak and basic demand of the situation. The produced power is dependent and varies with factors like stream temperature, the pressure of the inserted secondary fluid, and the fluid velocity with it is inserted of the secondary fluid. For a certain point at a depth of 3000 m, the streams were at 450 K were found and examined in the south Texas wells of oil and the 30-bar pressure was optimal and ideal for system operation in this condition. Around 2.50–2.55 cm insulation material was able to maintain the steady fluid temperature with the time. With the optimal or ideal velocity of the injection of the secondary fluid diameter of the inner pipe, the system is capable of generating around 3.3–3.5 MW power. Kharseh, Al-khawaja, and Hassani [27] examined the geothermal stream and surrounding properties like geothermal gradient, stream flow rate, dimensions, and the physical characteristics of the real-time conditions of the oilfields in Qatar and the neighboring countries having similar characteristics. The objective of their work was to stipulate the optimal and peak WPs, which comprise the heat transfer rate, the flow rate of geofluid, and temperature difference between well outlet and inlet to maximize the exploration of geothermal energy and simulate the model for generating power. In the working and on-field conditions of Qatar, it was confirmed during the time slam of around 25 years that the maximum power generation would be around 11 kW. To calculate the WPs, the flow rate is around 3.66–4.65 kg/second of geothermal fluids, the heat transfer rate is 275 kW, and there is a 15–17°C temperature difference. A suitable assortment of working parameters can notably enhance the power production of the plant. With time, the temperature outlet of the geothermal stream reduced naturally; subsequently, the power production will decrease if the resources of geothermal energy are used incorrectly. Though the optimum group to working parameters enlarges electricity production also assure the sustainable consumption of the geothermal streams stored in the abandoned wells of the oil and gas. In addition, the rate of optimal extraction is found to be time-independent. Kiaghadi, Sobel, and Rifai [28] studied and investigated the geothermal sources to convert salt water to freshwater using a desalination system. To overcome the drilling costs and other practical problems, the unused and soon-to-close wells of oil and natural gas are used as a resource of the geothermal energy. Water-treated thermodynamics and heat transfer modeling were combined to develop and demonstrate the estimation of the daily deliverable treated water as a predictive and calculative tool. The model was found to be more considerate with the parameters like the gradient of geothermal energy and TDS in the water obtained. It was found that at a depth of 4000 m, a geothermal gradient was around 0.05°C/m and TDS as 170,000 mg/L approximately, and was still able to give 600,000 L of pure water. Energy requirements were found to be feasible the reinjection of water produced was sounded better

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in the work. The authors added that the freshwater generated denotes a continuous and consistent supplier of freshwater that will be consumed for agriculture, ongoing oilfields operations, and local usage. The developed model was used to increase the cumulative water delivery over time to industrial areas and locations of need, and to investigate the interactions and the operations between the surrounding wells. The areas of Eagle Ford Shale in Texas have a high quality of heat resources and they are capable of coproducing electricity with the water. Noorollahi, Taghipoor, and Sajadi [29] stated that the abandoned wells of oil and gas are not used in general but we can use them like the heat source empowered by low and medium enthalpy streams of geothermal and adopt them for the desalination of the water. These abandoned wells are capable of providing value to geothermal energy without investing in drilling exploration. The authors discussed the analysis of the simulations numerically for the unemployed and unexploited wells of Ahwaz oilfields of south Iran of oil and gas. The objective was to set up a multieffect desalination process and the heat source was taken from the low and medium enthalpy streams of the geothermal source from the abandoned wells of oil and gas and generated the freshwater about 550 m3/day. The desalination process helps to solve the water problem and the crisis faced by the state. The major problem seems using the geothermal resources but abandoned wells solve this problem which the expensive one and the advantage is that. They showed in their work that, in the lifespan of the desalination plant, they’re a difference in the emissions of greenhouse gases. And using it. It reduces greenhouse gas emissions and leads to sustainable development, and helps in solving the water crisis problem of Iran and creates wealth from the unused resources with the technology.

3

Theory and working principle

In the 1980s, Dr. Alexander Kalina proposed a novel thermodynamic power cycle called the Kalina cycle, recognized as using the binary mixture as its working fluid [30]. The foremost modification we can observe from the Rankine cycle is that the condensation and evaporation takes place at variable temperature. There is a range of temperatures for a particular pressure and composition. As the temperature of the boiling point is viable, the fluid can take the heat of the geo source and transfer it to working fluid to turn the phase from saturated liquid to vapor [31]. The ammonia and water mixture is heated with the geothermal stream in the heat exchanger and the phase transferred from the saturated liquid to vapors; these vapors are then expanded to the turbine, and a turbine is rotated. The heat exchanger used in this process is designed so that the vapors are created in such a way that only geothermal steams are employed rather than any other external source. As the boiling temperature is low is to be done. Then the working fluid will leave the turbine having a composition of ammonia up to 70% (by wt.) to the condenser. However, according to the T-S curve, as the composition of ammonia is high the condensation temperature should be very low. For condensing such a high composition of the fluid,

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we need to supply the low-temperature coolant, which is not practical. For this, the equipment separator is employed before allowing the fluid to enter the condenser [32]. The separator separates the mixture into a rich mixture and a lean mixture. The lean mixture has a composition of ammonia up to 30% and it mixes with the fluid coming from the turbine and produces a mixture of around 40% ammonia (by weight). Such a mixture has a higher condensing temperature and can be condensated by regular cooling water. Fig. 1 represents the schematic of the binary cycle power plant. To regain the original composition of ammonia in the other part of the cycle, the rich mixture separated by the separator mixes with the coming stream to make the original composition 70%. To increase the efficiency of the power plant and to

Geothermal Binary Cycle Power Plant CONDENSER TURBINE Level I TURBINE Level II

SEPARATOR GENERATOR VAPORIZER

NON CONDENSABLE GASES (NCG) COMPRESSOR

BRINE

MOTIVE FLUID PUMP

MOTIVE FLUID

PREHEATER

INJECTION PUMP

PRODUCTION

WELL

HOT GEOTHERMAL FLUID

INJECTION

WELL

COOLED GEOTHERMAL FLUID

Fig. 1 Schematic flow diagram of a binary cycle power plant. Adapted from Das, Ritwik, Ritesh Kant Gupta, Tapapriya Gupta, and Chiranjit Maji. 2016. Study on geothermal power generation techniques related to Bakreswar-Tantloi geothermal area. International Conference on Renewable Energy- Extension & Outreach, no. March.

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Generator

G

Separator

Turbine Recuperator

Heat exchanger

Evaporator

Condenser

Pump

Cooling tower

Pump

Thermal plant

District heating

Production well Pump Reinjection well

Fig. 2 Kalina cycle used in a 2 MW geothermal power plant in Husavik, Iceland. Adapted from Ahmad, Tubagus, and Fauzi Soelaiman. 2016. Geothermal Energy. Electric Renewable Energy Systems. Elsevier Inc https://doi.org/10.1016/B978-0-12-804448-3/00007-4.

lessen the load of the geothermal stream for heating, the heat exchanger, called a recuperator, is provided to transfer the heat from the vapors coming out of the turbine to the initial composition mixture. As we are going to condense the vapors, the heat of the vapor is going to be elaborated to the environment so that heat is also utilized over here. The simple Kalina cycle has been modified according to the application and usage. The Kalina cycle model is also utilized in waste heat recovery where heat is expounded without taking the energy from it. Several numbers have been assigned to the particular cycles: for example, KCS 2 is used for low-temperature geothermal applications, whereas KCS 5 is used for direct fuel-fired plants. Several parameters and pieces of equipment are fixed; only the capacity and design factors vary with the situation [33]. The Kalina cycle power plant schematic at the Husavik in Iceland is shown in Fig. 1. The plant produces both thermal and electric power. Electric power is up to 1.5–1.8 MW and 15–18 MW of thermal power [34]. Fig. 2 shows a Kalina cycle system schematic of a 2 MW geothermal power plant.

A Kalina cycle for low and medium enthalpy abandoned oil

4

307

Comparison of Kalina cycle with other cycles

The thermal efficiency of the cycle was found to be elevated around 9%–19% compared to the steam organic Rankine cycle (ORC) when analyzed with the same external factors and boundary conditions [35]. Here we need to pressurize the mixture of working fluid via a pump for the separation of the vapors into the rich mixture and lean mixture. Therefore, the pressure requirement is higher in the Kalina model than the Rankine one. However, it varies with the model and the application it is used for. Like KCS 11 configuration has a good performance at moderate pressures for the lowtemperature geothermal heat source [36]. The working fluid composition should be in the optimum condition for the operation to be around 60%–70% [35]. By changing the independent parameters like pressure and temperature, we can see the change in the efficiency of the power plant. By increasing the inlet pressure of the mixture at the inlet point of the turbine and increasing the temperature of the absorber, the efficiency can be increased. The phase diagram shows the thermodynamic feasibility of the cycle; by comparing the T-h and T-s diagram and their slopes, we can identify the heat gain and heat loss of the cycle. The heat gains or losses by the system and work are represented as the length of the x-axis in the temperature- enthalpy (T-h) curve, while the area under the curve has the same parameters in the temperature-entropy (T-s) curve. The saturated liquid and saturated vapor state of the pure component of the working fluid at the equilibrium conditions and the pressure levels are shown in Figs. 2 and 3, respectively, and are adapted from Rogdakis and Lolos [37]. It was concluded from the curves that as the inlet temperature of the source (i.e., the inlet working fluid) is increased, thermal efficiency showed a similar fashion to it. To maintain the thermal efficiency of the system/cycle, the mass fraction of ammonia in the working fluid should be maintained and should be ironic to avoid losses. For the operation to be stable, the mass fraction of ammonia should be in the range of 0.54–0.89. It varies with the atmospheric and local climatic conditions [38]. It should be mentioned that for having the fixed pressure of the evaporator, we can have maximum thermal efficiency by increasing the temperature if the concentration is low. Fig. 3 represents the T-h curve for the low-temperature Kalina cycle and Fig. 4 represents the T-S curve for the low-temperature Kalina cycle. For designing the plant, the variables are pressure, temperature, and concentration of ammonia in the working fluid. Making design flexible and optimum requires suitable strategy and planning. The economic factor plays a critical role in the design, as the design should be compatible with the economic factor. The cost per kilowatt should cover the installation, as well as the operating cost within a certain span of the year, and should also match with the current trend of the cost per kilowatt of other resources [39]. The maximum power output reached is around 28 KW at the temperature range of 135–140°C of the geothermal brine and with the working fluid having a mass fraction of 84% [40].

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Utilization of Thermal Potential of Abandoned Wells

Fig. 3 T-h curve for the low-temperature Kalina cycle.

Fig. 4 T-s curve for the low-temperature Kalina cycle. Adapted from Rogdakis, Emmanouil, and Periklis Lolos. 2015. Kalina cycles for power generation. Handbook of Clean Energy Systems, no. point 7: 1–25. https://doi.org/10.1002/ 9781118991978.hces014.

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5

309

Proposed idea

As the world is moving toward sustainable development, and the utilization of renewable energy plays a very prominent role in this. The major share relates to thermal power plants using coal for power production, which leads to an increase in carbon footprint and an increase in the concentration of greenhouse gases. Over here we included the Kalina cycle over the organic Rankine cycle for achieving better efficiency, as we also incorporated the geothermal low and medium enthalpy streams for the heat transfer so that we can utilize a minimum form of nonrenewable energy resources. However, we develop and design the processes or cycle there will be some more additions for making it more effective and efficient. Similarly, we can amalgamate solar system for heating water, and this hot water or perhaps the working fluid can increase the temperature or the working fluid of the Kalina cycle, i.e., an aqueous mixture of ammonia. Including solar heating, we can increase the capacity of the plant and this will be observed in the overall enhanced efficiency of the plant. Using renewable forms of energy, i.e., geothermal and solar, and providing similar outcomes of the thermal power plant can give society clean and green energy without greenhouse gas emissions. There are other ways to assemble the solar thermal collector in the cycle. We can assemble at the preliminary hearing of the vapors or liquid. Depending upon the design and situation of the assists and equipment suitable for it. The same vary with the quality and quantity of the geothermal streams. For our arrangement, we can use the solar collector or the solar heater for heating the saturated liquid mixture to convert it into saturated vapor before expanding it to the turbine. Along with the geothermal brine, our solar system will help increase the temperature and according to the thermodynamic calculations, the inlet temperature should be higher for getting maximum work. The arrangement and the assembly of the system would be the same as discussed in the working principle. Vapors converted from the saturated liquid are expanded to the turbine and then after they are passed through the separator and the composition is varied, the vapors are condensed with normal cooling water. Then the rich mixture separated from the separator is mixed with the separator and the condensed liquid is mixed and passed through the recuperator (heat exchanger); the heat is transferred from the exit vapors of the turbine and this mixture of the inlet. If we are using a solar water heater, we can easily heat the mixture primarily up to a certain level after the heat exchanger transfers the heat. Solar collection and direct heating can be also be done if permeable with the design. By incorporating the solar with the geothermal system, we can increase the capacity of the plant and the plant will be truly based on renewable energy. This combination can be very beneficial to the system and with proper design, engineering, and vision for making the world free from the dependency of black energy. Fig. 5 shows the schematic diagram of the solar-driven Kalina cycle system. If we increase the capacity of the plant, we can heat the liquid in parallel or in a series; with this the load is not only on the one source. If seasonal wise if we look out the things if sunlight is not sufficient then geothermal can compensate for the loss

310

Utilization of Thermal Potential of Abandoned Wells Turbine

Separator

Heat source

solar Collector heater

Recovery heat exchanger

Recovery economizer Geothermal Heat transfer

High pressure Condenser pump

Cooling water Low pressure pump

Fig. 5 Solar-driven Kalina cycle integrated with geothermal.

of that thing. The main constraint is getting the geothermal well with a constant discharge over a certain range. If solar is concluded then if somewhere the only lowtemperature streams are available with low temperature we can take into account as we can counterbalance the heat and heat transfer with the solar collector.

6

Challenges and future scope

We are dealing with the ammonia-water mixture in the cycle so its chemical stability plays an important role. Corrosion problems are potentially caused by it. Experimentally, results indicate that ammonia above 400°C is not advisable for the design constraint because it causes corrosion. Above the specified temperature, ammonia becomes unstable and leads to nitride corrosion, which further can harm the overall effectiveness of the plant. The major challenges are that of properly optimized and applicable design of the plant and other equipment utilized in the plant and of managing the economic side too. As the Kalina cycle for waste heat recovery is the developed version than for power production so that for calculation of various parameters we need to design and assemble the setup prudently. The Kalina cycle without geothermal or with geothermal steam can be operated replacing the organic Rankine cycle for establishing such new concepts and technology. The Kalina cycle can also be implemented alone with the solar concept. Another major challenge would be finding the appropriate geographical location and getting the desired discharge of the steams from the geothermal well. To overcome the problem of corrosion, mild steel and aluminum with their alloys can work with the system as they will remain inert compared

A Kalina cycle for low and medium enthalpy abandoned oil

311

to other ones. SS-304, SS-316, nitronic 60 and its duplex, and 6Al-4 V titanium were found to be optimum for such system and conditions. Thus, the corrosion problem can be resolved using specified metals up to a certain level. The additional cost barrier in the proposed idea will be of the solar collector or the solar heater utilized of the proper specifications. We need to balance the cost and quality systematically so that it will not affect the efficiency of the plant, as well quality issues should be taken care of as they relate to the safety issues of the locality. As ammonia has a distinctive odor, it has the advantage that if there is a leak it can easily be detected. Safety comes first before any economic benefit. As we are moving toward carbon-free energy having a sustainable development, steadily energy is transforming from coal to renewable energy, i.e., wind, solar, geothermal. Massive research and development are going in every nation via government, industry, and universities for generating alternatives in the form of ideas, startups, and models for energy with renewable sources. The Kalina cycle is itself efficient technology and is more suitable with the geothermal low and medium streams, as the temperature gradient is satisfied. If we found a suitable geographical location with the desired streams, then this plant model could be set up on a pilot basis with the solar collector or heater system. If a pilot plant was successfully worked, an actual capacity plant could give promising results. Design and thermal calculations are major tasks but they can also be solved as today many universities are producing technically sound engineers and researchers to achieve this heavy task. Using the latest software, a 3D overview can be generated for the proposed idea, and similar calculations can be carried out effectively. Furthermore, using data science, we can calculate reversely and can establish in how much time the plant can be made free from the capital invested and operational cost, termed as CAPEX and OPEX, respectively. The proposed idea can compensate the installation cost within 2–3 years with the earnings made by the plant. Maintenance and the commission of the plant are required if they are installed within a specific period. Thus, by amalgamating and employing geothermal and solar energy systematically with accurate engineering, we can get the desired output. Power requirement for any nation is not going to decrease, so that creating standby alternatives leads a nation toward the goal of sustainability.

7

Conclusion

To summarize, we have identified some parameters for which the proposed idea/concept and the Kalina cycle power plant using low and medium enthalpy steam is that a composition of mass fraction 84% ammonia and 16% water is considered optimum for operation in the working fluid. Furthermore, technology is providing around 15%–18% more net power than ORC and also requires 35%–37% less mass flow rate of the working fluid utilized, if any. In addition, the cost of electricity was around 16%–18% lower for the Kalina cycle concerning ORC for an EGC having parameters of around 95–100°C and mass flow rate of 190–200 kg/s. It was feasible to adopt the Kalina cycle power plant for the geothermal-based system as the temperature and

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other important aspects provided better results in the performance. If ORC is employed for the geothermal-based system, then it is better to choose the Kalina cycle system over it. The main aspects ifs to commercialize the plant and make it viable for power production or we can also include the Kalina cycle technology with the existing power plants. In addition, solar can be included with an existing or new setup. Focusing on the main goal of sustainable development and creating alternatives powered by renewable energy can lead to clean and green energy. Thus, this chapter will be useful for readers and can act as a guide for the incorporation of various other technologies and parameters to enhance efficiency and effectiveness.

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Abandoned oil and gas wells for geothermal energy: Prospects for Pakistan

16

Muhammad Jawad Munawara, Xianbiao Bub, Saif Ur Rehmana, Naveed Ahsana, Hafiz Ahmed Raza Hassana,c, and Muhammad Talhaa,c a Institute of Geology, University of the Punjab, Lahore, Pakistan, bInstitute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, China, cSchool of Geosciences, China University of Petroleum, Qingdao, China

Abbreviations AOGW BHT CD CPEC CV D DBHE EDBHE EGS HDR MBT MMT RO TAI

1

abandoned oil and gas well borehole temperature conduction-dominated China-Pakistan economic corridor convection-dominated Darcy (unit of permeability) deep borehole heat exchanger enhanced deep borehole heat exchanger enhanced geothermal system hot dry rock main boundary thrust main mantle thrust vitrinite reflectance thermal alteration index

Introduction

Fossil fuels are not eternal, and their consumption embraces adverse impacts on the environment. So, it is the need of the hour to shift toward renewable energy resources. Today, Pakistan generates 64% of its total electric power from fossil fuels [1], as a consequence releases 180 Mt of CO2 into the atmosphere [2]. Geothermal energy contributes a major share to the global environmentally sustainable energy output. Owing to its numerous advantages such as low environmental effects, sustainable power supply, low greenhouse gas emissions, and worldwide availability, geothermal energy has gained massive attention and has become a possible contender to conventional energy resources recently. Geothermal electricity production has increased significantly over the past few decades. The installed generating capacity in the world was 1300 MW in

Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00016-6 Copyright © 2022 Elsevier Inc. All rights reserved.

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1975 [3]; it had been raised to 15,406 MW by the end of 2019 [4]. More than 30 million oil and gas wells are indicated as abandoned throughout the world, and they cause serious pollution problems including contamination hazards, exposure pathway routes, and biological receptors. The reuse of AOGWs for harnessing geothermal energy can not only eliminate prospecting risks and drilling liabilities, but also overcome the pollution. First and foremost interest for geothermal energy development has conventionally focused on the generation of electricity and potential exploitation of hot water in deep sedimentary basins with higher temperatures [5]. Electricity generation is now feasible with moderate to low temperature (80–150°C) or even lower (20% and permeability >1 darcy (D) is considered as an excellent reservoir [39]. In the Indus Basin, porosities of sandstones range from 5% to 30%, with an average porosity of 12%–16%. Permeability ranges from less than 1 mD to more than 2 D, with an average range of 5–300 mD [40] making these reservoirs proficient for fluid transfer. The porosity and permeability values of some potential reservoirs of Pakistan are reviewed in this work. Effective porosity is inversely proportional to the depth and geothermal gradient. As stratum temperature increase with depth, it increases the rate of chemical reaction (dissolution/precipitation) causing authigenic mineralization and ultimately porosity loss in the reservoir.

3.2 Thermal gradient The geothermal gradient refers to the rate of temperature transition with depth, as a consequence of the outward flow of heat from the hot interior of the earth. It is a decisive parameter for the evaluation of reservoir as thermal gradient bestow clue to possible outlet temperature. The geothermal gradient can be calculated using borehole temperatures at certain depths. Khan and Raza [40] used bottom-hole temperatures (BHT) recorded in different wells (not corrected for true formation temperatures) to study the geothermal gradient of the Indus Basin using the following equation. G¼

T2  T1 D2  D1

(1)

where G is the geothermal gradient in °C/100 m and T2 and T1 are temperatures in °C at depths D2 and D1, respectively. The unit of depth is meter. A well with a geothermal gradient of 3°C/100 m and a total depth of 4 km is presumed to proffer outlet temperature greater than 130°C, which is enough for a binary power plant. Wells with outlet temperature >150°C are ideal for large-scale electricity generation using dry steam or flash steam power plants. However, wells with outlet temperatures between 90°C and 150°C are satisfactory for closed loop—binary cycle power plants. Outlet temperature and thermal gradient of prominent AOGWs of the country are appraised in this study for their feasibility in energy production. Results have shown that AOGWs have geothermal gradient ranging from 1°C/100 m to more than 4°C/ 100 m and outlet temperature from 40°C to more than 170°C.

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Table 1 Geothermal applications with respect to thermal maturation of reservoir. Hydrocarbon resource in reservoir

Temperature range (°C)

Geothermal play type

Geothermal application

Biogenic gas only

65–82

Hydrothermal— water saturated

0.5–0.9

Oil and gas (the oil window)

82–132

Hydrothermal— steam and oil saturated

2.5–3

0.9–1.7

Gas condensate

132–163

Petrothermal— steam moisture

3–4

1.7–2.4

Dry gas

163–260

Petrothermal— dry

4+

2.4+

Barren

More than 260

Petrothermal— dry

Building heating, heat pumps Drying, deicing, and binary fluid electric generation Conventional electric generation Electricity production (dry steam) None (rare within AOGWs)

TAI (1–5)

% RO

1–2

0.1–0.5

2–2.5

Reservoir quality (porosity and permeability) can also be guessed by studying geothermal gradient, as a degree of compaction is directly proportional to temperature [41]. An increase in temperature and burial depth reduces reservoir quality. Porous and permeable rocks, deep within the crust, are either saturated with fluid (water, oil, etc.) or unsaturated (gas/air). It is a general consensus in the petroleum discipline that certain temperature windows generate a certain type of hydrocarbons from source rocks (Table 1). The main differences in hydrocarbon generation through different wells are due to differences in thermal gradients [42]. Thermal maturation can also be estimated by vitrinite reflectance (% RO) [43] and Thermal Alteration Index (TAI) [44] given in Table 1. Geothermal play type and applications [8] are correlated with RO and TAI of the reservoir in Table 1; which shows that stratum temperature at a certain depth actually determines the saturation of reservoir rocks. Reservoir having formation temperature greater than 130°C is characteristically dry (HDR) and best suited for electricity generation using closed-loop DBHE technique. Geothermometers, vitrinite reflectance (Vr or RO), thermal alteration index (TAI), and other geochemical instruments (isotopic ratios, mercury, and CO2 concentrations) can be used in subsurface temperature estimation. The aeromagnetic survey is helpful in the identification of curie depth (depth at which rock of specific area encounter curie temperature). Magnetotellurics (MT) or resistivity anomalies indicate a zone of low resistance caused by geothermal waters and high temperatures. This zone of low resistance is suspected to indicate a geothermal reservoir that can be mapped using this technique.

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3.3 Lithofacies According to various permeability models, effective porosity is the function of lithofacies, diagenesis, grain size, pore geometry, cementation factor, grain packing, and sorting [9]. Permeability anisotropy is extremely controlled by lithofacies and geological structures. Generally, intergranular spaces serve as the primary porosity in clastic lithologies. While, unstable minerals (e.g., feldspar) dissolve to create secondary porosity in which later, the authigenic quartz or clay minerals crystallize with respect to geothermal gradient [45]. In an open-loop system, injection of cold water causes dissolution/precipitation and thermo-geomechanical deformation of the reservoir [46]. Authigenic mineralization and clay minerals transformation is a function of increasing stratum temperature [47]. As stratum temperature increase downward, kaolinite and smectite transform into illite; which blocks throats and fine pores, resulting in loss of permeability [48]. The formation of fibrous illite can be modeled to predict reservoir quality [9]. The geothermal gradient also affects other diagenetic processes and the compressive strength of reservoirs. High temperature reduces rock rupture strength. Thermal conductivity [49], P-wave velocity [50,51], thermal diffusivity [52], specific heat capacity [53], and Young’s modulus [54,55] decrease with increasing porosity in dry rocks. But, P-wave velocity [50,51] and thermal conductivity [49] increase with increasing clay content. Temporal factor also controls reservoir quality. It is defined as the heating time interval a stratum experienced. Reservoirs that experienced long-term high temperatures are more likely to reach a higher reaction degree and poor reservoir quality [56]. Generally, hydrothermal systems have sufficient permeability, hot wet rocks (HWR) have poor to moderate permeability, and hot dry rock (HDR)—petrothermal plays have very poor permeability. Thus, HDR systems require stimulation of reservoir by EGS technology [8] or fetching more durable option, i.e., EDBHE [57].

3.4 Fault/fractures Active faults are suspected to produce frictional heat that increases the geothermal gradient along the fault zone. On the contrary, fractures are crucial in heat and fluid flow in low permeability—HDR reservoirs. In geologically complex conditions, fractures can significantly influence on heat exchange rate. In the Indus Basin, about 60% of the identified reservoirs are carbonated in which fractures along with karstified zones facilitate fluid flow. Therefore, proper estimation of fracture orientation, intensity, distribution, and extension can enhance the understanding of the reservoir [58,59]. Fracture corridor can be detected by the use of lithologic core data [60], sonic log [61], rock physics, and seismic data [62]. Gravity method aids in the characterization of subsurface fault/fractures as well as detection of depth and lateral trend of dense anomalous bodies such as petrothermal basement. Generally, convective geothermal systems are associated with active fault/fractures. Seismic studies assist in the diagnosis of fault/fractures or other tectonic activity by natural or induced seismicity. The alignment of the fractures induces anisotropy that can affect the velocity and amplitude of seismic waves. Commonly desecrate fracture network models are used

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to describe the geometrical properties and anisotropic effect of each fracture set separately [63]. Anisotropic variations can be analyzed through prestack data [64] whereas fracture intensity, orientation and extent can be analyzed with the help of geometrical poststack attributes [58,65]. Geometric attributes such as dip azimuth [66], coherency [67], and curvature [68] can be used to predict the fractures and subtle fault displacement whereas ant-track attribute can improve the fracture visualization [69]. Hence the combination of geometric and ant-track attributes can be successfully applied to accurately predict the fractures and subtle fault displacements [65,70]. The obtained results can be correlated with the cores and logs to check the authenticity of the work.

4

Geothermal energy extraction through AOGW

The process of geothermal energy extraction from AOGWs involves retrofitting into heat exchangers. There are two solutions to retrofit AOGW into the geothermal well, i.e., open loop and closed loop. Most of the cased studies explored open-loop structures to harvest energy from abandoned petroleum wells. Open-loop systems comprise of minimum one injection and one extraction well. Fluid is injected into a reservoir through an injection well, where it absorbs heat from nearby rocks until it circulates well through an extraction. The open-loop configuration can use the technology of an enhanced geothermal system (EGS), which can be implemented through hydraulic fracturing or acid fracturing to create artificial permeability. EGS with a water injection rate of 50 kg/s and producing boiling water, will generate 3.5 MW electricity and 25 MW heat energy [71]. But unfortunately, hydraulic fracturing technology has a huge capital investment and the risk of induced seismicity at the present stage. Moreover, the open-loop system often faces some problems like corrosion and scaling, fluid loss, and pore clogging in the reservoir. Fluid flow through open-loop reservoirs causes pore clogging, permeability loss, and eventually stemming the flow, by dissolution and redeposition of minerals. This can limit the productive lifetime of the geothermal reservoir in spite of the fact that heat may still be available at depth. On the contrary, in the closed-loop system, fluid does not touch directly with rocks, and thus the aforementioned problems can be avoided. As a typical closed-loop system, a deep borehole heat exchanger (DBHE) is one of the alternative technologies to utilize AOGW for acquiring geothermal energy, as shown schematically in Fig. 2A. Many experimental and simulation researches have been carried out on DBHE, and revealed that poor thermal conductivity of rocks is a key obstacle to its performance improvement. Therefore, it is necessary to find a special way of improving the thermal conductivity of rocks in order to make use of AOGW full and efficient. There are rich fracture pathways and storage space for depleted oil and gas reservoirs, which should be utilized adequately to boost the thermal conductivity of rocks. Inspired by this, a novel enhanced deep borehole heat exchanger (EDBHE) is proposed [57], which is implemented by actively filling composite materials with higher thermal conductively into depleted oil and gas reservoirs (leakage formation), as shown in Fig. 2B–D. Composite material is prepared by mixing graphene or carbon

Fig. 2 Schematics. (A) DBHE, (B) SWEDBHE (single-well EDBHE), (C) left view of DWEDBHE (double-well EDBHE), and (D) front view of DWEDBHE.

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fiber with mud or cement or other materials at a low price. The filling process is easy to implement by adjusting the backpressure, viscosity, and density of composite materials [57]. Filling technology may refer to the technologies of loss of drilling fluid and leakage-blocking, which is common in oil and gas as well as a geothermal industry during drilling. Advantages of EDBHE technology:

▪ No dependence on hot water reservoir makes it practicable in various HDR— petrothermal plays.

▪ Enhanced thermal conductivity of closed-loop channel, as well as surrounding rocks, are due to the filling of composite material (graphene mud and cement) into leakage formation.

▪ No direct contact of circulating water with the surrounding rocks assures clean energy as fluid chemistry remain unaltered.

▪ The energy input is 2.36 times more as compared to ordinary DBHE [57].

5

Geothermal energy potential of Pakistan

Although geothermal energy is present everywhere on the globe, it is present at different depths beneath different locations. On one hand, geothermal energy reaches the surface (e.g., volcanism, geysers, hot springs, fumaroles, etc.) at some locations. On the other hand, deep drilling into thousands of meters is required to hit geothermal reservoirs of suitable temperature. In the past, extensive drilling has been carried out in Pakistan. As of June 2020, 1123 exploratory wells were drilled out of which, 411 resulted in hydrocarbon discovery [72]. The rest are abandoned. Pakistan is located in a tectonically active region at the convergence of three tectonic plates; Eurasian, Indian and Arabian plate [73]. A variety of geothermal plays exist; ranging from convection-dominated geothermal plays (e.g., Chagai magmatic arc, seismotectonic zones along Indus suture, and some locations of Gilgit) to conduction-dominated geothermal plays (e.g., Himalayan foreland, intracratonic Indus). Active faults are suspected to produce frictional heat that increases the geothermal gradient along the fault zone. As Pakistan lies in active tectonic realm, hundreds of minor and major normal faults, reverse/thrust faults as well as transform faults are present in NW Himalayas, Karakoram Block, Kohistan Magmatic Arc, Sulaiman Belt, Kirthar fold and thrust belt, Makran Accretionary Zone, and Kharan Basin [74]. The spatial distribution of geothermal gradient indicates definite geothermal patterns. Past researchers [40,73,75,76] divided Pakistan geothermally into three zones, viz., (1) northern geothermal system or Himalayan collisional zone, (2) Balochistan Basin or Chagai Magmatic Complex, and (3) Indus Basin zone. The latter is of prime importance for geothermal energy extraction as 95% of the petroleum wells in Pakistan are drilled within the Indus Basin. i. Northern Geothermal Zone

The Northern Geothermal Zone of Pakistan is bounded by Main Boundary Thrust (MBT) in the south and geographic border with China in the north. This zone consists of the mightiest mountain ranges of the world, i.e., Himalayas, Karakoram, and

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Hindukush. Heat energy in this zone is delivered by seismotectonic—suture related geothermal systems. There are numerous surface manifestations in the form of hot springs, geysers, and fumaroles of hydrothermal orogenic type (CD2)—geothermal plays. These plays flow year-round and provide temperatures up to 140°C in northern Himalayan valleys. Hot springs of Sassi, Mushkin, and Tatta Pani are associated with Main Mantle Thrust (MMT) [75]. In Gilgit-Hunza, hot springs of Murtazabad, Budalas, and Dasu are associated with MKT [77]. Other hydrothermal—orogenictype plays (CD2) include Garm Chashma Valley in Chitral [78], Pechus glacier near Mastuj [79], and Rawat village in Yasin district. There is a significant hydrogeothermal system along the faulted margins of Nanga Parbat Haramosh Massif [75]. Nanga Parbat Haramosh Massif (NPHM) also host Pleistocene magmatism making a convection-dominated (CV2) plutonic geothermal play [74]. To deal with AOGW-based geothermal potential of the Northern Geothermal Zone, less than 10 wells are being drilled in this area; all of which are in the developmental stage and their data is not accessible. ii. Balochistan Basin Zone

This basin covers the Tethyan zone in the west of the Indus Basin. Chagai magmatic arc is formed by subduction of Arabian plate beneath the Eurasian plate. This arc serves as convection-dominated (CV1 and CV2) magmatic geothermal play which hosted quaternary volcanism. Although Chagai Volcanic Arc is deemed dormant, hydrothermal activity implies the presence of a magma chamber beneath Sinjrani volcanics. Sulfur mineralization and emanations of H2S from acidic hot springs and fumaroles around Koh-i-Sultan are ongoing, suggesting some convective/magmatic source of geothermal energy beneath the Chagai complex [77]. Temperatures of springs on the surface are equal to or less than ambient temperature [80]. However, Shuja et al., in 1984 used a silica geothermometer to estimate the geothermal reservoir temperature of the Koh-i-Sultan hydrothermal system, i.e., approximately 160°C. Heat and fluid discharge from mud volcanoes, hot springs, geysers/fumaroles can be utilized in power generation. More than 80 mud volcanoes are discovered so far, a maximum number of that are in Lasbela, Makran coastal belt, and Gawadar peninsula. These mud volcanoes hold and often eject hot geothermal fluids enriched in economically important elements such as lithium, base metals, alkali metals, colloidal silica and REEs, which can be recovered using either electrochemical techniques or simple separating methods. To deal with the prospecting of geothermal energy on the basis of abandoned petroleum wells, there are less than 60 wells drilled in the Balochistan Basin, most of which are abandoned due to no indication of hydrocarbon. However, there are surface manifestations in the form of mud volcanoes and gas seepages in the coastal area. Also, gas was encountered in a coastal well in Dhak. The highest geothermal gradient encountered in the Balochistan Basin is 2.55°C/100 m in Garr Koh well [81,82] which is located in CPEC anchored Gwadar district. China-Pakistan Economic Corridor (CPEC) is a socioeconomic development program that stretches throughout Pakistan but is enrooted in Gwadar port city. Power generation with development in science and technology is one of the key agendas of CPEC. Gwadar district host a geothermal

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gradient of up to 3°C/100 m (Fig. 4). Thus, AOGWs in this area are of prime importance for carbon-free power generation under the CPEC platform. Parkini Formation is a calcareous mudstone of Miocene from 2175 to 4200 m [40,81] in which Garr Koh well is drilled along with structural complexities. It is estimated that a maximum stratum temperature of about 135°C can be achieved through this well, which is sufficient for electricity production. Kech Band well is 3349 m deep and display a temperature gradient of 1.5°C/100 m [40,82]. Dhak-1 (2562 m deep) and Dhak-2 (4455 m deep) show the geothermal gradient of 1.95°C/100 m and 1.70°C/100 m respectively. Most of the wells drilled in this basin are up to 4000 or 5000 m deep and met with repeated sequences due to structural complexities. Whereas, total drilled depth of Jal Pari 1-A (an offshore well) is 2008 m with the geothermal gradient of 1.48°C/100 m [40,82]. All wells in the Balochistan Basin are abandoned and can be utilized for heat extraction after a detailed study of geological parameters (lithofacies, petrophysical properties, rock-fluid interaction, and thermal diffusivity) of the reservoir rock. iii. Indus Basin Zone

In Pakistan, the Indus Basin covers more than 5 lac km2 area in the NW portion of the Indian Plate. It hosts up to 15-km thick sedimentation from Precambrian to recent (Fig. 3). This basin forms conduction-dominated hydro-geothermal plays (CD1 and CD2) as well as petrothermal plays (CD3) where hot dry rocks (HDR) of the basement and of thick piles of siliciclastic and carbonate sediments are highly dependent on permeability and anisotropy of the rock. In the past, extensive drilling in Indus Basin has been carried out with more than 1000 exploratory petroleum wells, out of which, approximately 600 wells are abandoned. Geothermal energy prospects of Upper, Central, and Lower Indus Basins are discussed below using thermal and reservoir evaluation of AOGWs.

5.1 Upper Indus Basin This basin, also called Kohat-Potwar Province, is bounded by MBT in the north and Sargodha High in the south. It includes Potwar Plateau, Bannu Basin, Cis and TransIndus Salt Range, and northern Punjab Platform. It is the major oil-producing area of the country and contains complex structural and stratigraphic sequences from Precambrian to recent (Fig. 3). More than 20 oilfields or petroleum systems are discovered so far in this area [42]. A series of faulted and unfaulted anticlines developed on multiple detachment surfaces. These detachment surfaces are deep as Cambrian and trend parallel to the plate-collision boundary in the southwest to northeast directions. This region has an average thermal gradient of 2°C/100 m. Though, oil window exists at depths of 2750–5200 m; oil-producing horizons start from depths of 3000 m and below. Reservoir rocks in this area are alluvial sandstones from Miocene, carbonates from the Paleogene shelf, continental sandstones from Jurassic and Permian, and Cambrian alluvial and shoreface sandstones [83,84]. Kherwa sandstone, Kussak, and Jutana from Cambrian; Permian Tobra, Amb, and Wargal; Datta from Jurassic; Cretaceous Lumshiwal; Lockhart, Patala, and Nammal from Paleocene; Eocene Bhadrar, Chorgali, and Margala Hill Limestone; and Miocene Murree are produced

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Fig. 3 Geothermal gradient at generalized stratigraphic levels of Indus Basin. Modified from C.J. Wandrey, B.E. Law, H.A. Shah, Sembar Goru/Ghazij Composite Total Petroleum System, Indus and Sulaiman-Kirthar Geologic Provinces, Pakistan and India. USGS Bulletin, 29, 2004; M.A., Khan, H.A. Raza, The role of geothermal gradients in hydrocarbon exploration in Pakistan, J. Pet. Geol. 9(3) (1986) 245–258.

in the Potwar Plateau [40]. Porosities of sandstones range from 5% to 30%, with an average porosity of 12%–16%. Permeability ranges from less than 1 millidarcy (mD) to more than 300 mD, with an average range of 4–17 mD [40]. Average porosities of Jurassic to Paleocene succession encountered in Injra and Nuryal wells in Western Potwar subbasin were calculated by Khalid et al. [85]. The total drilled depth of these

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wells is 4625 m and 4760 m, respectively, hitting a quality reservoir; Early Jurassic Datta Sandstone with average porosity of 19%–23%. Data Sandstone in Kala Chitta Range has average permeability of 2.1–6.1 mD. The porosity of Late Miocene Chinji Formation is 15%–17%, Middle Miocene Kamlial formation is 12%–15%, Early Miocene Murree Formation is 11%–14%, Early Eocene Sakesar Limestone and Chorgali Formation is 6%–10% and 12%–15%, respectively, in western Potwar subbasin [85]. About 60% of the identified reservoirs in the Upper Indus are carbonates. Hydrocarbons in carbonate reservoirs are mainly from tectonically induced fracture porosity on strike with structural trends at the Dhurnal field and probably elsewhere in the basin [86]. Eocene carbonates, i.e., Sakesar and Chorgali are encountered as fractured reservoirs in Dhilian, Meyal, Dhurnal, Balkassar, Dakhni, and Adhi oilfield. The average porosity and permeability of Sakesar Limestone encountered in Balkassar wells (7, 8, and OXY-01) is 12% and 51.14 mD, respectively. However, Chorgali Formation possesses better reservoir quality in this area with average porosity of 18% and permeability 116 mD [87]. Late Permian Wargal Limestone also acts as fractured reservoir in Dhurnal field. Infra-Cambrian oil shale of Salt Range Formation is present at the bottom of Mahesian and Qazian Well with a depth of 5150 m and 4700 m respectively. The average geothermal gradient of Mahesian and Qazian well is 2.05°C/100 m and 2.3°C/100 m, respectively [40]. Khewra Sandstone and Kussak Formation exhibit good reservoir quality and form a geothermal play of temperature from 90°C to 120°C at a depth between 3 and 4 km. Wells in Adhi, Missa, Kiswal, and Rajian oilfield are drilled into Khewra Sandstone; a quality reservoir of the Upper Indus Basin. Khewra Sandstone has log derived average porosity of 14%–22% and permeability between 20 and 58 mD [88]. Adhi oilfield has Paleozoic to Eocene succession from 2400 to 5100 m depth with an average geothermal gradient of 2.05°C/100 m–2.3°C/100 m [40]. About 82-m thick Warchha sandstone is present at a depth of 2500 m that exhibits excellent reservoir properties with effective porosity ranging from 27% to 35% [89]. Abandoned wells in the Adhi oilfield are anticipated to provide a temperature of about 135°C in Khewra Sandstone at depth of 5 km. In the south-west of the Adhi oilfield, two other oilfields named; Balkassar and Karsal are present with an average geothermal gradient of 2.05°C/100 m in well depth up to 5200 m [40]. Wells in the Kallar Kahar region are drilled up to 3200 m hitting Salt Range Formation. The geothermal gradient in the Kallar Kahar area is also relatively low, i.e., 1.7°C/100 m [40], which is insufficient to produce steam for electricity production. However, Dhulian oilfield indicates a geothermal gradient of 2°C/100 m–2.3°C/100 m [40]. Four wells (Dhulian 2, 3, 42, and 43) have been drilled in this oilfield. A sedimentary succession of Tertiary to Precambrian (missing Upper Jurassic and Cretaceous) is present between depths of 2400 m and 5300 m in these wells. Thus, Dhulian geothermal play is expected to provide a temperature of more than 135°C at depth of 5200 m, making this field appropriate for clean energy production. In the east of Dhulian, there are three wells in Meyal oilfield (Meyal 4, 5, and 6) with a geothermal gradient ranging from 2.15°C/100 m to 2.3°C/100 m [40]. The maximum depth achieved in these wells is 4900 m imparting sufficient temperature for electricity generation. Toot oilfield lies in the western part of Potwar Basin with similar succession in which; wells are drilled up to 4850 m depth. Oil well Toot-5 and Toot-9 have a geothermal gradient of

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2.18°C/100 m and 2.4°C/100 m respectively. Like Adhi and Dhulian oilfield, wells of the Toot oilfield are also presumed to offer a temperature of about 135°C at depth of 4800 m. To sum up, all oilfields except the Kallar Kahar region (owing to its low geothermal gradient) can be utilized for electricity generation by water circulation through abandoned wells.

5.2 Central Indus Basin Central Indus Basin, also called Sulaiman Province, is bounded by Sargodha High (Pezu uplift) in the north, and Sukkar Rift and Mari-Jacobabad Highs in the south. These highs (Sargodha and Jacobabad) along with regional arches and wrench faults were generated as a result of oblique convergence of Indian and microplates; comprising the southern edge of the Eurasian Plate [90]. Central Indus Basin comprises [91] Sulaiman Fold Belt, Sulaiman Foredeep, and Punjab Platform with rocks from Precambrian to recent. Lumshiwal Formation [42] Sui Main Limestone (SML), Habib Rahi Limestone (HRL), Lower Goru and Chiltan Formation are principal reservoirs in this basin. Lumshiwal formation has porosities between 12% and 32% in various areas of this basin [92]. The porosity of SML varies from 6.7% to 28.4% and permeability varies from 0.1 to 12.9 mD [93]. It means that SML can be utilized for water circulation after the surety of desired thermal output. SML act as a reservoir in Sui, Kandhkot, Loti, Kandra, Qadirpur, and Bhadra fields. Khan and Khan [94] reported effective porosity of Lower Goru between 12% and 23% and permeability range from 0.7 to 5 D in Kadanwari gasfield. Very low geothermal gradient (1.12–1.71°C/100 m) is calculated in the southern plain margin of Sargodha High, by drilling five wells viz. Karampur, Tola, Sarai Sidhu, Budhuana, and Kamaib [40]. On the other hand, Dhodak, Domanda, and Sakhi Sarwar wells were drilled in Sulaiman Foredeep. Dhodak well showed a remarkable geothermal gradient of 3.2°C/100 m which declines to 2.1°C/100 m in Domanda and Sakhi Sarwar wells. The maximum depth achieved by these wells is 5 km. This region can supply extraordinary outlet temperatures of 180°C (in Dhodak) to 130°C (in Domanda and Sakhi Sarwar). However, a maximum geothermal gradient, i.e., 4.1°C/100 m is found at Giandari well, which is located in the center of Sulaiman Basin. This gradient is encountered in Parh Formation above fractured Chiltan Formation up to which; Giandari well is drilled [95]. The average geothermal gradients of well-known Sui and Mari gasfield are 3°C/100 m and 3.2°C/100 m respectively. These gasfields form a crescent shape to the west of the Giandari well. Habib Rahi Limestone is a gas reservoir in Mari gasfield that has a very low petrophysical quality to meet geothermal requirements. Whereas, Qadirpur gasfield has a gradient between 2.5°C and 3°C/100 m with a maximum well depth of 4703 m [96] drilled into Sui Main Limestone that has an average porosity of 23% [97]. The geothermal gradient of 2.4°C/100 m is available in Jandran Well and Tadri Well which are drilled to 4400 m and 4000 m depth, respectively [40]. Hence, abandoned wells in Sulaiman Foredeep, the central region of Sulaiman Basin, and the area of Sui and Mari are preferable for the extraction of geothermal energy.

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5.3 Lower Indus Basin Lower Indus Basin, also called Kirthar Province, is bounded by Sukkar Rift in the north and Murray Ridge in the marginal zone of the Arabian Sea in the south. It includes Thar Platform, Kirthar foredeep, Kirthar fold Belt, Karachi Trough and offshore Indus [95]. The geothermal gradient of 2.5°C/100 m is available in Khairpur and Jacobabad wells. But these wells are drilled to just 2100 m making them implausible for power production. This geothermal gradient drops further to 1.7°C/100 m in the Jhatpat well which is situated near Jacobabad Well. However, the Lakhra field is worthy for geothermal energy extraction. More than five wells are drilled in this area. Lakhra-1 is drilled up to 3200 m. It proffers a geothermal gradient of 3.3°C/100 m [40]. A formation temperature of nearly 130°C is estimated at endpoint of this well. In the south-west of Lakhra field, Sunbak and Sari Singh wells are present hosting a geothermal gradient of 2.7°C/100 m and 3°C/100 m, respectively. Khan and Raza [40] identified two geothermal regimes in Badin Block, viz., eastern regime and western regime. The western regime showed a higher geothermal gradient as compared to the eastern regime. Nabisar, Digh, Badin, and Patar wells are drilled in the eastern regime with geothermal gradients between 2.1°C/100 m and 2.3°C/100 m. Except for Patar well, all other wells in the eastern regime are abandoned. While western regime manifested a geothermal gradient of 2.65°C/100 m–3.1°C/100 m in Talhar, Tarai, and Khaskeli well, 4°C/100 m in Damiri well, and 2.9°C/100 m in Mirpur-Batoro well [40]. Cretaceous-Paleocene basaltic lava-flows are considered a source of higher geothermal temperatures in the western geothermal regime of Badin Block, where the hottest spot is at the Damiri well. About 14 wells have been drilled so far in the offshore Lower Indus Basin with a maximum drilling depth of 5 km. Marine A1, B1, and C1 have geothermal gradients of 2.43°C/100 m, 2.6°C/100 m and 2.27°C/100 m, respectively. Five wells: Karachi-1 and 2, Korangi Creek, Dabbo Creek, and Paitiani Creek, are drilled in coastal areas of Kirthar Basin. Karachi 1 and 2 showed a geothermal gradient of 2.3°C/100 m and 3°C/100 m, respectively. Dabbo well indicated an extraordinary geothermal gradient of 3.7°C/100 m providing a stratum temperature of 163°C at the bottom of the well. Paitani and Korangi Creek also showed similar geothermal gradients, making them favorable for geothermal energy extraction. In Kirthar Basin, Early Paleocene Ranikot Group, Late Cretaceous Pab Sandstone, and Early to Middle Cretaceous Lower Goru formation are major reservoirs. Wells in Kirthar Basin encounter Pab Sandstone at an average depth of 2254 m, Goru at 2359 m, Sembar at 3542 m, and Chiltan Formation at averagely 3578 m depth [98]. All are very good reservoirs that fulfill petrophysical requirements for efficient water flow. Pab Sandstone bears porosity of 20% and permeability up to 3 D [99] and functions as a reservoir in Mazarani, Mehar, Zamzama, Bhit, and Bhadra gasfield. Lower Goru is of prime importance as it is deeper among other formations with favorable reservoir properties in Lower Indus. About 65% of the AOGWs have a drilling endpoint in Lower Goru that bears average effective porosity of 16%–30% and permeability from 1 to 2000 mD [42]. Lower Goru functions as a quality reservoir in more than 50 AOGWs (including Khaskeli, Matli, Tando Adam, Turk, Duphri, Lashari, Kato, and Bhatti) drilled in Badin area, Hyderabad district, Mirpurkhas,

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and Sanghar. Upper Goru acts as seal/cap rock while Lower Goru is an excellent reservoir [100]. This property of Goru formation is promising for CO2 sequestration that not only enhances heat storage capacity of the reservoir, but also reduces CO2 concentration in the atmosphere. Potential geothermal zones of Pakistan are illustrated in Fig. 4 which incorporate all types of geothermal plays. Chagai Complex forms convection dominated— magmatic geothermal system (CV1 and CV2) which offer remarkable geothermal

Fig. 4 Isogeothermal map showing potential geothermal zones of Pakistan. Modified from M.A. Khan, H.A. Raza, The role of geothermal gradients in hydrocarbon exploration in Pakistan, J. Pet. Geol. 9(3) (1986) 245–258; M.A. Bakr, Thermal Springs of Pakistan, 1965; M.N. Mughal, Geothermal Resources of Pakistan and Methods for Early Stage Exploration. United Nations University. Geothermal Training Program, Iceland. Report; 1998: 9, 1998, pp. 239–254.

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manifestation but there is no drilled well available to alleviate the cost of a geothermal project. However, shallow drilling into hot spring aquifers present around Koh-isultan may bestow obligatory thermal values for energy production. Similarly, frequent hot springs, geysers and fumaroles are present especially in deformed areas throughout Pakistan which validate the hydro-geothermal (CD1 and CD2) resource potential of Pakistan. On the other hand, more than 700 petroleum wells in Pakistan are abandoned; a large number of which show favorable thermal gradients for electricity generation. The geothermal resource potential of Central and Lower Indus Basin is noteworthy as compared to Upper Indus (Kohat-Potwar) and Balochistan Basin due to higher geothermal gradients as well as a large number of available AOGWs (Fig. 4). The area between Karachi, Badin, east Sibi and west Bahawalpur contains an average geothermal gradient of 4°C/100 m. As Pakistan lies in active tectonic realm, a lot of structural complexities (fault/fractures) are present to facilitate water circulation through the geothermal reservoir. In case of no structural features; such as in intracratonic basin (CD1) and petrothermal hot dry basement (CD3-HDR), hydraulic fracking will be required to enhance reservoir properties. Geothermal energy production through most of the AOGWs present in Himalayan foredeep, Sulaiman Foredeep, and Kirthar Basin are anticipated to supply appreciable, sustainable, clean, and carbon-free power to the country. Fig. 5 graphically represents the electric production feasibility of some AOGWs in Indus Basin with respect to their thermal potential.

6

Conclusions

There is a prolific potential of geothermal energy trapped in various abandoned petroleum fields of Pakistan. AOGWs have geothermal gradient ranging from 1°C/100 m to more than 4°C/100 m and outlet temperature from 40°C to more than 170°C. Ø In the Upper Indus Basin, preferable geothermal plays for electricity generation include Adhi oilfield, Dhulian and Meyal oilfield, Toot oilfield, Balkassar, Karsal, Qazian, and Mahesian. However, wells in Kallar Kahar exhibit characteristically lower geothermal gradient which is appropriate for building/space heating, deicing, and drying purposes. Ø In the Central Indus Basin, AOGWs in Sulaiman Foredeep (particularly Domanda, Dhodak, Sakhi, and Giandari) are anticipated to provide the highest outlet temperatures. Sui and Mari gasfield, and Jandran well are also appropriate for electric power generation in this area. The rest of the wells in the Sulaiman Basin (Karampur, Kamaib, Tola, Sarai Sidhu, and Budhuana) are very unlikely to produce electricity. Ø In Lower Indus Basin, Lakhra field, Sari Singh, and wells in the western geothermal regime of Badin Block (Talhar, Khaskeli, Damiri, and Mirpur-Batoro) manifest high geothermal potential and suitable reservoir properties. Also, Coastal (Paitani, Korangi, and Dabbo creek), as well as offshore wells, are suitable for generating electricity. While Khairpur and Jacobabad wells are recommended for space heating owing to their low thermal output. Ø In Balochistan Basin, wells in or near CPEC held Gwadar port district are promising for heat extraction due to the considerable thermal gradient in the subsurface and the possibility of equipment availability under CPEC manifesto.

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Fig. 5 Graphical representation of electric production feasibility of some AOGWs with respect to their thermal potential. Wells with outlet temperature below the red line (gray in print version) (90°C) are not appropriate for power generation.

In the Indus Basin, porosities of sandstones range from 5% to 30%, with an average porosity of 12%–16%. Permeability ranges from less than 1 mD to more than 2 D, with an average range of 5–300 mD; making these reservoirs proficient for fluid transfer. Most of the carbonate reservoirs are naturally fractured. Very little treatment/ stimulation is required to transform them into the geothermal heat exchanger. On account of huge capital investment and risk of induced seismicity by hydraulic fracking for EGS development, two closed-loop models (SWEDBHE and DWEDBHE) of Enhanced deep borehole heat exchanger (EDBHE) are recommended

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for heat extraction through HDR geothermal plays, which involve active filling of composite material (with higher thermal conductivity) into leakage formation (depleted oil and gas reservoir) in order to improve heat transfer. However, a detailed case study of geothermal reservoir characterization of potential geothermal plays is required to present an efficient working model of EGS or EDBHE for implementation in HDR geothermal plays of Pakistan.

References [1] NEPRA, State of industry report 2020, Regulation 53 (9) (2020) 1689–1699. [2] N. Abas, A. Kalair, N. Khan, A.R. Kalair, Review of GHG emissions in Pakistan compared to SAARC countries, Renew. Sustain. Energy Rev. 80 (March) (2017) 990–1016. [3] R. Bertani, Geothermal power generation in the world 2005-2010 update report, Geothermics (2012). [4] A. Richter, Top 10 Geothermal Countries—Based on Installed Power Generation Capacity in MWe, ThinkGeoEnergy Research, 2020. [5] J. Majorowicz, S.E. Grasby, High potential regions for enhanced geothermal systems in Canada, Nat. Resour. Res. (2010). [6] J. Raymond, R. Therrien, Low-temperature geothermal potential of the flooded Gasp
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[56] C. Lei, J. Luo, X. Pang, C. Li, J. Pang, Y. Ma, Impact of temperature and geothermal gradient on sandstone reservoir quality: the Baiyun Sag in the Pearl River Mouth Basin study case (northern South China Sea), Fortschr. Mineral. 8 (10) (2018). [57] Y. He, X. Bu, A novel enhanced deep borehole heat exchanger for building heating, Appl. Therm. Eng. 178 (April) (2020) 115643. [58] H.M. Basir, A. Javaherian, M.T. Yaraki, Multi-attribute ant-tracking and neural network for fault detection: a case study of an Iranian oilfield, J. Geophys. Eng. (2013). [59] P.O. Roehl, P.W. Choquette, Carbonate Petroleum Reservoirs, Springer, New York, 1986. [60] X. Song, Y. Zhu, Q. Liu, J. Chen, D. Ren, Y. Li, B. Wang, M. Liao, Identification and distribution of natural fractures, in: SPE International Oil and Gas Conference and Exhibition in China, Society of Petroleum Engineers, 1998, p. 7. [61] K. Hsu, A. Brie, R.A. Plumb, A new method for fracture identification using array sonic tools, J. Pet. Technol. 39 (06) (1987) 677–683. [62] D.E. Lumley, R.A. Behrens, Practical issues of 4D seismic reservoir monitoring: what an engineer needs to know, SPE Res. Eval. Eng. 1 (06) (1998) 528–538, https://doi.org/ 10.2118/53004-PA. [63] M. Cacas, J.-M. Daniel, J. Letouzey, Nested geological modelling of naturally fractured reservoirs, Pet. Geosci. 7 (2001). [64] H. Ikawa, G. Mercado, A case study of seismic anisotropy analysis on multi-azimuth OBC seismic data in an offshore carbonate oil field, U. A. E, in: Society of Petroleum Engineers—14th Abu Dhabi International Petroleum Exhibition and Conference 2010, ADIPEC 2010, 2, 2010. [65] X. Zhang, T. Li, Y. Shi, Y. Zhao, The application of fracture interpretation technology based on ant tracking in Sudeerte Oilfield, Acta Geol. Sin. Engl. Ed. 89 (2015) 437–438. [66] E.J.H. Rijks, J.C.E.M. Jauffred, Attribute extraction: an important application in any detailed 3-D interpretation study, Lead. Edge 10 (9) (1991) 11–19, https://doi.org/ 10.1190/1.1436837. [67] K.J. Marfurt, R.L. Kirlin, S.L. Farmer, M.S. Bahorich, 3-D seismic attributes using a semblance-based coherency algorithm, Geophysics 63 (4) (1998) 1150–1165. [68] B.S. Hart, R. Pearson, G.C. Rawling, 3-D Seismic Horizon-Based Approaches to Fracture-Swarm Sweet Spot Definition in Tight-Gas Reservoirs, Leading Edge, Tulsa, OK, 2002. [69] A. Ngeri, A. Amakiri, Ant-tracker attributes: an effective approach to enhancing fault identification and interpretation, IOSR J. VLSI Signal Process. 5 (2015) 2319–4200. [70] C. Silva, C. Marcolino, F. Lima, Automatic fault extraction using ant tracking algorithm in the Marlim South Field, Campos Basin, SEG Tech. Program Expand. Abstr. 24 (2005), https://doi.org/10.1190/1.2148294. [71] K. Evans, N. Deichmann, C. Heinrich, Deep geothermal energy, in: Abstract Volume 9th Swiss Geoscience Meeting – 20 (November 2011). [72] MNPR, Investment Opportunities in Pakistan Upstream Petroleum Sector, Ministry of Energy (Petroleum Division), 2020. [73] M.N. Mughal, Geothermal Resources of Pakistan and Methods for Early Stage Exploration, United Nations University. Geothermal Training Program, Iceland. Report; 1998: 9, 1998, pp. 239–254. [74] A.H. Kazmi, M. Jan, Geology and Tectonics of Pakistan, 1997. [75] N.A. Zaigham, Geothermal Energy Resources of Pakistan, April, 2005, pp. 24–29.

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Mandaree, North Dakota: A case study on oil and gas well conversion to geothermal district heating systems for rural communities

17

Jessica Eagle-Bluestonea, Moones Alamootia, Shane Namiea, Jerjes Porllesa, Nnaemeka Ngobidia, Nicholas Fryb, Matthew Villanteb, Chioma Onwumelua, Ogonna Obinwaa,c, and Will Gosnold, Jr.a a University of North Dakota, Grand Forks, ND, United States, bIceland School of Energy, Reykjavik, Iceland, cCalifornia Geologic Energy Management Division (CalGEM), Sacramento, CA, United States

1

Geothermal district heating for the oil patch

The initial motivation for this work is the Geothermal Collegiate Design Competition of 2021, held by the National Renewable Energy Laboratory (NREL) on behalf of the US Department of Energy (DOE). The theme of the competition is to characterize the whole system potential of geothermal direct use for a community of choice. While it is clear that high heat density urban areas could benefit from geothermal direct uses, the team felt an emphasis should be on proving the technologic potential in more difficult rural areas. The University of North Dakota is a primary public research institution of a very rural, oil-producing state with a research goal to address economic and societal grand challenges [1]. The result of this work, therefore, is meant to highlight the increasing feasibility of geothermal district heating (GDH)—primarily as an energy transition technology for the state’s experienced oil and gas workforce—to benefit even the most disadvantaged communities across the region. North Dakota is looking to make a green recovery from the coronavirus pandemic with investments in renewable greenhouses using Coronavirus Aid, Relief, and Economic Security (CARES) Act funds, passed by the US Congress, aimed at putting gas pipeline laborers back to work.a Our research could provide the groundwork for accelerating North Dakota’s renewable transition and provide support to the people of Mandaree. This work can also serve as a springboard for further study of geothermal heat uses from late-stage oil and gas wells, including combined heat and power (CHP). a

State agencies are eager to reignite economic activity as evidenced by the following websites: https://www. jamestownsun.com/news/government-and-politics/6901002-Greenhouse-project-receives-renewableenergy-grant; https://www.dmr.nd.gov/oilgas/2628_001.pdf.

Utilization of Thermal Potential of Abandoned Wells. https://doi.org/10.1016/B978-0-323-90616-6.00017-8 Copyright © 2022 Elsevier Inc. All rights reserved.

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Most importantly, the project can serve as an educational tool—exploring not only the technically possible, but economically feasible. The DOE’s GeoVision for the United States envisions an exponential increase in the utilization of low-enthalpy geothermal resources for DH and direct use [2]. To make this possible we must find innovative ways to utilize the resources we have available to us. Repurposing oil and gas wells, in a state with over 13,000 drilled wells [3], will reduce cost barriers to the deployment of GDH schemes similar to our study. As a result of such developments, the business-as-usual potential (Fig. 1) could prove to be much greater for GDH in North Dakota. Using Mandaree, North Dakota as a demonstration site for our exploratory research, we seek to answer the following: 1. What key benefits could GDH bring to a rural town like Mandaree?

Fig. 1 GeoVision relative favorability for geothermal district heating by county in 2050 under a business-as-usual scenario. Mandaree is shown with a red star (dark gray in print version). Conversion of abandoned oil and gas wells could increase the immediate GDH potential across the State of North Dakota. Modified from K. McCabe, K.J. Beckers, K.R. Young, N.J. Blair, GeoVision analysis supporting task force report: Thermal applications. Quantifying technical, economic, and market potential of geothermal district heating systems in the United States (No. NREL/TP6A20-71715), National Renewable Energy Lab. (NREL), Golden, CO, 2019. https://doi.org/10. 2172/1524767.

Mandaree, North Dakota: A case study on oil and gas well

343

2. Which geothermal resources do existing oil and gas wells intersect on the way to their target formations? 3. Are these geothermal resources technically feasible options for exploitation? 4. How should we match the resource to the demands of the community? 5. Does the plan deliver geothermal energy in a way that meets the needs of the community?

2

Innovations in district heating

Direct use of geothermal resources is the use of produced hot fluids to heat buildings, raise plants in greenhouses, farm fish, dry grains, melt snow, provide balneological services, and complete industrial processes. One way to accommodate all these uses is through a heat network or district heating (DH) system [4,5]. Where energy demand is adequate, or the price of the incumbent fuel is high, then geothermal fluids can provide low marginal heat generation costs (MHGC)—the cost of producing one additional unit of heat—for space heating (SH) and domestic hot water (DHW). The MHGC is closely linked to the profitability of DH [6]. Factors that determine the overall power production recoverability for a GDH are reservoir size (thickness), porosity, permeability, recovery rate, sustainable rate of pumping, accessibility, fluid temperature, the efficiency of heat exchange, heat losses in the distribution pipe, and the overall change in temperature from the production fluid to end use (△ T) [4,7]. Fortunately, the trend in modern DH is enabling all these direct use applications for GDH. These include lower temperatures ( 1. Case 1B. Electric power costs for lifting the water at a stable mine water level can be optimized based on the thermal energy demand in the area of the geothermal system location. Taking into consideration the circulation system peculiarities, Eq. (1) is modified as ξE ¼

Php,th Δtop
Utr
ω Pmw,el + Php,el + Ptr,el + Pr,el Δtop

(4)

where Pmw, el is the power required to pump mine water and Pr, el is the power to discharge the thermally used water back to the mine. The cost criteria (Eq. 3) change accordingly: ξC ¼

Chp,th
Ctr,th Cmw, el + Chp, el + Ctr,el + Cr,el + Cman

(5)

where Cmw, el and Cr, el are, respectively, the electric power costs for pumping out mine water and its discharge after thermal use. Cases 2A and 2B. Electric power is not required for pumping; however, it is consumed by pumps providing circulation of the heat-transfer fluid in the geothermal probe and by operating heat pumps. The energy balance, determined as the difference between the recovered thermal energy and the thermal equivalent of electric power used for geothermal system operation, is the main criterion for the feasibility of heat recovery. The energy criterion for cases 2A and 2B when replacing the electric power for pumping mine water Pmw, el by the electric power for circulating the fluid in the probe Pp, el is changed accordingly: ξE ¼

Php,th Δtop
Utr
ω Pp,el + Php,el + Ptr,el Δtop

(6)

Given the costs of electric power for circulating the fluid in the probe Cp, el, Eq. (3) can be changed as follows: ξC ¼

Chp,th Cp,el + Chp,el + Cr,el + Ctr

(7)

434

Utilization of Thermal Potential of Abandoned Wells

Eqs. (1)–(7) may include additional terms for quantifying power consumption and operating costs of internal pumps, fancoils, circulation in heated buildings, etc. The energy balance depends on the ambient temperature and should be adjusted for different seasons, given the option of cooling spaces in the summer. The thermal energy of mine water generated on the ground can either fully cover the local heat load or reduce the overall thermal energy deficit near the site of installation; parameters of Eqs. (1)–(7) should be appropriately optimized, keeping in mind that the electric power for pumping the mine water and heat output depends on the depth of pumping and the water level in the shaft or in the well. The deeper the pump is installed, the warmer the mine water, and its energy potential is higher; however, pumping will consume more electric power. In this case, the water is more likely to have higher mineralization, which can complicate heat exchange and increase capital and operating costs. The critical parameter for assessing the overall efficiency of the geothermal system is the distance to the nearest consumer. Similarly to LANUV [13], it makes sense to introduce a so-called zone of influence, determined by the maximum distance to thermal energy consumers, within which the heat losses along the routes of supply remain acceptable. The radius of this zone around six centralized water-lifting stations in Germany is estimated from 500 to 5000 m, depending on the heat output and consumer needs. The contribution of the geothermal system to the local heat supply can be assessed as follows. The maximum achievable thermal capacity generated by mine water-based heat pumps is calculated by the formula Php,th ¼ QCf ρf ðTmw,in
T0 Þ

(8)

where Q, Cf, and ρf are the pumping rate, specific heat capacity, and density of water, respectively, Tmw, in is the temperature of mine water entering into the heat exchanger, and T0 is the temperature of water cooled in heat pumps. The temperature Tmw, in decreases to the initial mine water temperature Tmw, out when moving upward into the shaft or well to the heat exchanger; thus Tmw,in ¼ Tmw,out
ΔTc

(9)

where Δ Tc is the difference of mine water temperatures due to cooling in the shaft. Since the time of water movement upward is relatively short, it can be assumed approximately that Δ Tc ¼ 1–2°C and clarified in further feasibility studies based on thermodynamic and hydrodynamic ratios. In the absence of measurements, mine water temperature TNat at the depth of z can be calculated by a geothermal gradient TNat ðzÞ ¼ Tnl + Гðz
Hnl Þ, Г ¼ q=λr,av

(10)

where Tnl and Hnl are the temperature and depth, respectively, of the neutral layer defined as the depth below which the annual temperature fluctuations of the soil

Comparative analysis and evaluation of the geothermal system

435

can be neglected, z is the depth, Г is the geothermal gradient, q is the deep geothermal flux, and λr, av is the average thermal conductivity of the rock. The theoretically achievable heat pump COP is determined as COP ¼ ηhp

Ths Ths
Tmin

(11)

where ηhp s the heat pump efficiency, Ths is the temperature of the heat-transfer fluid delivered to the heating system, and Tmin is the minimum temperature of the cooled fluid. The electric power consumed by heat pumps is calculated as follows: Php,el ¼

Php,th COP

(12)

The electric power required to pump out mine water is calculated by the formula [15] Php,el ¼ κs

g  Q  H  ρf ηp  ηht

(13)

where κs is the safety factor depending on the pump engine type, g is the gravitational acceleration, Q is the pumping rate, H is the pressure head, and ηp and ηht are the efficiency of the pump and heat-transfer fluid, respectively. The pump capacity required to maintain the return flow of cooled water on the ground from the heat exchanger back to the underground mine workings is calculated by Eq. (13). In this case, the pressure head H, being replaced with the pump pressure head Hp, is calculated as follows: Hp ¼ Hg + Hf Hf ¼

(14)

αf L ν2 Q πd2  , ν¼ , S¼ S d 2g 4

where Hg is the difference in the absolute heights of the heat exchanger and the pump in the flooded shaft, Hf is the pressure loss due to friction resistance, αf is the friction coefficient, L is the path length of cooled water transportation, d, S are the diameter and internal cross-sectional area of the tube of passing the heat-transfer fluid, and ν is the fluid velocity in the tube. The total electric power consumed by an open circulation system is calculated as follows: Psum,el ¼ Pmw,el + Php,el + Pr,el

(15)

Assuming that electric power is generated by coal-fired or gas-fired power plants, we determine the thermal equivalent of the total electric power for geothermal energy production as follows:

436

Utilization of Thermal Potential of Abandoned Wells

Php,th ¼ ωPsum, el

(16)

with ω calculated by Eq. (2). In case 1A, Php, th ¼ Php, el. Without taking into account the heat transportation cost, the criterion of thermal efficiency of an open circulation system is determined as the ratio ξE ¼

Php,th Pth,eq

(17)

where Pth, eq ¼ Pth, g for gas or Pth, eq ¼ Pth, c for coal, depending on the fuel used to generate electric power. Eq. (17) shows how much additional thermal energy can be produced by an open geothermal system using coal or gas. The higher the ξE value, the more the thermal energy that can be additionally recovered from the mine water. Geothermal system operation makes sense in terms of energy production if ξE > 1, and the additional heat output is determined as ΔPth ¼ ðξE
1ÞPth,eq

(18)

If the mine water after thermal use on the ground does not return to the mine, the energy consumption for discharge can be neglected. The costs of thermal energy Сth produced by the system and the consumed electric power Cel are calculated as follows: Cth ¼ ath Php,th , Cel ¼ ael Psum,el

(19)

where ath is the heating tariff and ael is the electricity tariff. Regarding the costs for management and maintenance Cman, the additional cost Cadd obtained at the expense of the geothermal system can be calculated as follows: Cadd ¼ Cth
Cel
Cman

4

(20)

Geological and geothermal conditions of the Donetsk coal-mining area

The efficiency and environmental safety of geothermal systems for heat recovery from mine water and rock depend strongly on careful accounting of geological, hydrogeological, and geotechnical conditions. Next, we analyze the factors that should be considered in the design and operation of geothermal systems in the conditions of the Donetsk coal-mining area (Donbas), where most of the closed Ukrainian mines are located, and it is expected that their thermal potential will be much higher than in other areas of the coal-mining sector of the country [19].

Comparative analysis and evaluation of the geothermal system

437

The rocks of coal deposits in Donbas include sandstones, siltstones, and argillites with alteration of coal seams and limestone layers of shallow thickness [25]. The total thickness of coal-bearing deposits increases from 700 m in the west of Donbas to 18 km in the east near the border with Russia. Coal-bearing rocks are quite anisotropic; fracture occurrence and rock porosity decrease with an increase in the depth under growing geostatic pressure, which is confirmed during mining operations. Depending on the aquifer type and water saturation, carboniferous sedimentary rocks are divided into two different strata; the lower one in limestone rocks contains a large, fractured karst aquifer, and the upper one contains numerous aquifers in sandstone and limestone rocks [22]. The general direction of the groundwater flow to river valleys in natural conditions is changed due to mine drainage and local withdrawal for water supply. The conductivity of intact and disturbed coal-bearing rocks can significantly differ at the same depth due to high heterogeneity; it ranges from 6.9  10
9 m s
1 to 2.7  10
5 m s
1. Among the water-saturated rocks of the Visean stage, sandstones are the most widespread in the zone of coal seams; their conductivity decreases from the surface to deeper layers from 2.2  10
6 m s
1 to 3.5  10
8 m s
1, whereas the transmissivity is from 1.5  10
4 m2 s
1 to 6.6  10
7 m2 s
1. The carboniferous rock heterogeneity leads to a variety of water migration paths of mine water and groundwater, with a predominant flow in underground mine workings and through large fractures. In the case of installing a circulation geothermal system, mixing of cooled discharged water with warm water in deeper mine workings will be intensified, thereby influencing the heat output. The available data on the flooding of closed mines at coal deposits of Ukraine is quite fragmentary. Since a significant number of the country’s coal mines are located outside the area controlled by the state, the data on the majority of them either refer to 2014 or are incomplete. This information is partially available in studies by Shcherbak and Arseniuk [27] and Ulytskyi et al. [29], while the data on mine drainage are presented in a study by Fomin [5] Fig. 1. The geothermal system efficiency also depends on the volume of available underground space partially or completely flooded in the studied region. According to the report of the Artemivsk Geological Department [18], this parameter reaches 7.876 million m3 in the D.S. Korotchenko Mine, 11.76 million m3 in the Novogrodivska Mine, 20.882 million m3 in the Selidivska mine; all these sites of the Selidovo mine group are located in the controlled area. The Donbas region of Ukraine is the one most studied for geothermal energy with about 6000 deep heat flux measurements in individual wells, grouped at about 2700 points within an area bounded by faults, the border with Russia and a conventional line separating the western part of Donbas from the neighboring Dnipro-Donetsk basin [8]. Well depths rarely exceed 1 km, so the calculated flux values refer to a depth of 0.5– 1 km, which is feasible for possible geothermal plants in closed mines. A background value of deep geothermal flux, slightly below 50 mW m
2, is widespread in about two-thirds of the Donbas area (Fig. 2). At the northern and southern edge faults, points of high heat flux values (60–70 mW m
2) occur; the maximum values of 70–80 mW m
2 are measured within the main anticline and in the

438

Utilization of Thermal Potential of Abandoned Wells

Fig. 1 Mine water level in the mines of the Donetsk coal-mining area [18,27,29].

Fig. 2 Deep geothermal flux in the area of Eastern Ukraine [8] and the location of the mines: (1) Selidivska, (2) Novogrodivska 2, (3) D.S. Korotchenko, (4) Izotov, (5) Oleksandr Zakhid, (6) Kondratyevka, (7) Vuglegirska, (8) Bulavinska, (9) Olkhovatska, (10) Rumyantseva, (11) Artyom, (12) Gagarin, (13) Komsomolets Donbasu, (14) Lenin, (15) Kochegarka, (16) Karl Marx, (17) Chervonyi Profintern, (18) Poltavska, (19) Yenakievska, (20) Rodina, (21) Pervomaiska, (22) Kirov, (23) Sokologorovka. (24) Golubovska, (25) Bezhanivska, (26) Gaievoy, and (27) 60 years of Soviet Ukraine.

440

Utilization of Thermal Potential of Abandoned Wells

Southwestern Donbas. The mines of the Selidovo group (Table 4) are located in the areas with a heat flux of 50–55 mW m–2, the Central Donbas mines have maximum heat flux values of 65–70 mW m
2, whereas the mines in the northeast of the region have lower values of 45–50 mW m
2. The thermal conductivity λ of rocks in the Central Donbas is estimated to be within the range of 1.7–1.85 W m
1 K
1, as in the west of the Dnieper-Donets depression. In general, the values of λ do not exceed 2 W m
1 K
1; in relatively loose sediments, λ decreases to 1.7 W m
1 K
1. The highest thermal conductivity up to 2.6 W m
1 K
1 occurs mainly at the depth of the lithified rocks of Lower Carboniferous sedimentation, mainly in the central part of the main anticline, especially in conditions of sandstone predominance. The ranges of thermal conductivity λ, thermal diffusivity a, and heat capacity C for carboniferous and sedimentary rocks were analyzed by Sadovenko et al. [25], based on previous geological studies in Donbas.

5

Results and discussion

The expected performance indicators of geothermal systems in the mining conditions of Donbas are calculated by Eqs. (1)–(14) for drained mines with reliable data on mine drainage (Table 4). The following parameters are used in calculations: the minimum temperature in the heat pump Tmin ¼ 6°С, the maximum temperature in the heating system Th ¼ 55°С, heating season duration Δ top ¼ 3000 h, and heating system efficiency ηhs ¼ 0.9. The theoretically achievable thermal capacity of noncirculation systems in the studied area reaches several MW at COP ¼ 4.1–6.8 (Table 3), which is consistent with the available data on the heat output of the geothermal plants studied above. The use of gas instead of coal to generate electric power increases the expected efficiency of the system in proportion to the efficiency of power facilities; however, this scenario now Table 3 Estimated efficiency indicators of open geothermal systems (case 1A in Table 1) in the conditions of Donbas mines. Mine Novogrodivska 1–3 Artyom Golubovska Kirov Lenin Vuglegirska Poltavska Chervonyi Profintern

Php, th (MW)

COP

ΔPth, c (MW)

ξE,c

ΔPth, g (MW)

ξE, g

Rank ξE

ΔCO2, kt

12.93

6.82

8.66

3.03

9.92

4.31

1

8.17

6.16 5.53 1.74 3.63 13.93 1.15 18.74

4.21 4.58 4.50 4.90 4.89 4.16 6.48

2.87 2.81 0.87 1.96 7.52 0.53 12.23

1.87 2.03 2.00 2.18 2.17 1.85 2.88

3.84 3.62 1.13 2.46 9.42 0.71 14.16

2.66 2.89 2.84 3.09 3.09 2.62 4.09

7 5 6 3 4 8 2

2.71 2.65 0.82 1.85 7.09 0.5 11.54

Comparative analysis and evaluation of the geothermal system

441

Table 4 Estimated efficiency indicators of a circulation geothermal system (case 1B in Table 1) for the mines of Selidovo group in Donbas.

Mine Selidivska Novogrodivska 2 D.S. Korotchenko

Mine water depth below the ground (m)

Estimated temperature of mine water at its level (°С)

Php, th (kW)

COP

Δ Pth, c (kW)

ξE, c

ΔCO2 (t)

41.5 83.6

10.9 12.2

120.2 150.9

3.64 3.74

35.2 39.1

1.41 1.35

33.2 36.9

30

10.6

111.8

3.61

34.3

1.44

32.4

looks rather hypothetical from the point of view of the dominance of coal-fired capacities in the Ukrainian electric power sector. The value of the energy criterion ξE depends on the water temperature and pumping depth, as well as on other parameters in Eqs. (8)–(14). The estimates of ξE  2 are obtained for coal as a fuel; higher values of this criterion for the Novogrodivska Mine 1–3 and Chervonyi Profintern Mine are associated with a deeper pumping position and an expected higher water temperature, which is typical for a lower drainage level. A value ξE ¼ 2 means that a geothermal system consuming electric power generated from 1 kWh of thermal energy from fossil fuel allows the recovery of 2 kWh of heat from mine water. This ratio changes if the electric power consumed by the heat pumps is partially covered by renewable energy sources such as solar or wind power facilities. The mine rank by the criterion ξE can be interpreted in terms of the expected heat recovery efficiency or the priority of geothermal system installation. Besides, the heat demand of local consumers should also be included in the feasibility study, with a preliminary estimate of cost criteria (Eqs. 3, 5, 7). The expected reduction in CO2 emissions △CO2 due to the recovery of additional thermal energy after the heating season, calculated according to [2]) with average characteristics of local coal quality, can reach several thousand tons per heating season. The performance indicators of open circulation geothermal systems can be calculated using Eqs. (8)–(14), similar to systems that discharge water into streams and ponds after using the heat. The estimates given in Table 4 refer to the already flooded mines of the Selidovo group, where it is technically feasible to install geothermal systems and there are potential consumers of thermal energy nearby. We assume that pumping is maintained slightly below the mine water level and the temperature is calculated by Eq. (10). Calculations show that deepening the pump can significantly increase the system efficiency. For example, pumping out of warmer water in the shaft of the Novogrodivska Mine 2 at a depth of 260 m below the mine water level allows to increase COP from 3.74 to 4.56, the maximum heat output Php, th

442

Utilization of Thermal Potential of Abandoned Wells

by 50%, and the additional heat output △ Pth, c by 123% in comparison to pumping out from the water level in the shaft. Then we assess the potential of the geothermal systems presented in Table 4 in terms of covering the heat load of residential buildings located near one of the Selidovo group mines in local climatic conditions. The overall system efficiency depends on a rational balance between the available capacity and the heat demand throughout the year. Therefore, the heat output should be adjusted taking into account seasonal fluctuations of thermal energy consumption. Following the methodology for assessing the heat load [28], we consider heating of residential buildings with a total heating area of 16,200 m2 and a space of 40,500 m3, which can accommodate up to 900 people. Since residential buildings are usually located at a certain distance from the shaft or drainage, we assume that a higher output water temperature Ths ¼ 60°C should be reached in heat pumps to compensate for heat losses during transportation, so that the temperature of the water entering the heated buildings must exceed 55°C. The estimated heat demand includes heating and hot water supply; the option of centralized cooling in summer is not considered. The total heat load varies from 275 kW in summer, which is calculated for hot water supply only, and increases to almost 800 kW in winter with the addition of heating. It is expected that the shares of heating and hot water supply during the year will amount to 35% and 65%, respectively, of the total annual thermal energy consumption. These indicators look quite achievable given the experience of operating the geothermal systems under similar conditions [6,16]. Thus, the calculated heat load can be fully covered by thermal power facilities with a heat capacity of up to 1 MW under the conditions of the mines listed in Table 3 (Fig. 3).

Fig. 3 Estimated annual heat load of residential buildings housing up to 900 people in the climatic conditions of Donbas.

Comparative analysis and evaluation of the geothermal system

6

443

Conclusions

The experience of the geothermal system operation in closed coal mines around the world demonstrates the feasibility of mine water heat recovery even at relatively low mine water temperatures (12–14°С). Most thermal power facilities have a relatively low heat output of up to 1 MW, which, however, is sufficient for heating one or more buildings located nearby. An increase in the heat output and COP of heat pumps is possible due to the pumping out of mine water with a temperature above 20°C. By comparing the recovered thermal energy with the required energy consumption, we have developed energy and cost criteria for evaluating the efficiency of geothermal systems; these criteria make it possible to assess the efficiency of operating geothermal systems and to prioritize their installation at several potential sites. The hydrogeological and geothermal conditions of the mines in the Donetsk coal-mining region, where most of the closed mines in Ukraine are located, have been analyzed. The depth of underground mine workings available for the installation of geothermal systems in the 27 closed mines studied ranges from 320 to 1200 m with a depth of up to the mine water level of 50–1000 m. The deep geothermal flux within the areas where the mines are located ranges from 45 to 80 mW m
2. According to the performed calculations, the expected heat output of open noncirculation geothermal systems in closed mines of Donbas can reach several MW with COP ¼ 4.1–6.8, which is comparable to systems of this type currently operating in the world. The expected heat output of open circulation systems at the flooded Selidovo group mines in the presence of potential consumers of thermal energy ranges from 111 to 150 kW with COP ¼ 3.5–4.5, assuming pumping out from the mine water level; the heat output can be significantly increased by deepening the pumps below the water level in shafts. In addition, the feasibility of covering the heat load of residential buildings up to 900 people with the capacity of an open geothermal system at one of the mines under local climatic conditions, taking into account seasonal fluctuations in heat load, has been substantiated. The developed approach may be of interest to stakeholders in the mining and energy sectors interested in the sustainable use of renewable energy sources from abandoned wells and shafts in closed coal mines.

Acknowledgment This study was supported by the National Research Foundation of Ukraine (Project No. 2020.01/0528) within the “Science for the Safety of Human and Society” program.

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[22] I.A. Sadovenko, A.V. Inkin, Z.N. Yakubovskaya, N.A. Maksimova-Gulyayeva, Evaluation of gas losses during storage in aquifers of the western Donets basin, Naukovyi Visnyk Natsionalnoho Hirnychoho Universytetu 6 (2012) 18–24 (in Russian). [23] I. Sadovenko, O. Inkin, N. Dereviahina, Y. Khryplyvets, Actualization of prospects of thermal usage of groundwater of mines during liquidation, E3S Web Conf. 123 (2019), https://doi.org/10.1051/e3sconf/201912301046, 01046. [24] I. Sadovenko, D. Rudakov, O. Inkin, Geotechnical schemes to the multi-purpose use of geothermal energy and resources of abandoned mines, in: Progressive Technologies of Coal, Coalbed Methane, and Ores Mining, 2014, pp. 443–450, https://doi.org/10.1201/ b17547. [25] I.A. Sadovenko, D.V. Rudakov, A.V. Inkin, Geotechnology for the development of capacitive and gas-hydrothermal resources of Donbas, DVNZ “NGU”, Dnepropetrovsk, 2016 (in Russian). [26] L.A. Serbinova, Ecological and economic substantiation of the use of mine waters as secondary resources, Visnyk KrNU of Mykhaila Ostrohradskoho 4 (2017) 82–87 (in Ukrainian). [27] V.V. Shcherbak, S.I. Arseniuk, Analysis of threats and environmental risks arising from the damage of mining companies in the area of local military conflict in eastern Ukraine, Zbirnyk naukovykh prats DonDTU 47 (1) (2018) 40–46. [28] A.K. Tikhomirov, Heat Supply of the City District, Pacific State University Publishing House, Khabarovsk, 2006 (in Russian). [29] O.A. Ulytskyi, V.M. Yermakov, O.V. Lunova, K.I. Boiko, On the issue of predictive estimation of changes in hydrogeological conditions within the techno-ecosystem of the Selidovo group of mines, Environ. Safety Nat. Res. 32 (4) (2019) 32–42 (in Ukrainian). [30] Viessman, Planungshandbuch. W€armepumpen, Viessman GmbH, 2011. Available at: https:// www.viessmann.de/content/dam/vi-brands/DE/PDF/Planungshandbuch/ph-waermepumpen. pdf/_jcr_content/renditions/original.media_file.download_attachment.file/ph-waermepumpen. pdf. (Accessed 4 January 2021). [31] M.H. Yu, I. Jefferson, M. Culshaw, Geohazards caused by rising groundwater in the Durham Coalfield, IAEG 2006, paper nr. 367, 2006, pp. 1–12.

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Index Note: Page numbers followed by f indicate figures and t indicate tables. A Abandoned geothermal wells environmental impacts, 109–110 permeability, 99–100 petroleum wells reclamation, 108–109 stimulation, 110–112, 111–112t (see also Enhanced geothermal system (EGS)) Abandoned oil wells in Alberta, 76, 76t to borehole heat exchanger (BHEX) binary geothermal power plant, 83, 84f coaxial BHEX, 82–83, 83f fluid temperature, 83–84, 84f U-tube heat exchanger, 84, 85f conventional fossil reservoirs, 76 energy from coproduced water, 77 direct steam cycle, 86–87, 86f organic Rankine cycle (ORC), 86–87, 86f thermal efficiency, 88 variables, 87, 87t wellhead temperature and temperature profile, 87 further studies concentrated solar power (CSP), 88 enhanced oil recovery (EOR) method, 88 horizontal well to BHEX, 89, 89f multieffect distillation (MED) system, 88–89 thermoelectric devices, 89, 90f water desalination, 88–89 geothermal resources, 75 geothermal utilization, 75–76 heat production performance (see Productivity evaluation of abandoned wells) hydrocarbon production, 76 literature review conversion to heat exchangers, 151

hydrodynamic and heat transfer modeling, 152 levelized cost of electricity (LCOE), 153 numerical model, 152 open-loop system, 149 power generation potentials, 152–153 methane emission, 76–77 opportunities and challenges, 89–91 simulation and thermodynamic modeling (see Heat extraction model for abandoned wells) stored geothermal energy chemical contaminants, 79 direct utilization, 80f, 81, 82t features, 77–79, 78t, 78f indirect utilization, 81–82, 82t temperature variation, 77–78, 78t, 78f utilization, 79–82, 80f, 82t water-to-oil (WOR) and water-to-gas (WGR) ratio, 79 Abandoned wells energy (AWE) system desalinating produced water system, 182, 183f geothermal heat pump system feasibility, 180–181 heat transfer fluid, 180, 180f schematic diagram, 179–180, 179f geothermal power generation system, 181–182, 181f, 182t geothermal utilization efficiency, 183–184, 183f schematic diagram, 164–165, 166f Abandonment, 108–109, 137 Achievements of 20th century, 8t Acid fracturing, 105 Acidizing acid fracturing/fracture acidizing, 105 matrix acidizing, 103–104 techniques, 103 Acoustic stimulation, 107

448

Active cavitation, 107 Adriano boiler, 6 Advantages of geothermal energy, 11–12, 217–219, 218f Applications of geothermal energy, 35–36 direct geothermal heating aquacultural heating, 31 crop drying, 30 examples, 26–27 greenhouse heating, 28 ground source heating and cooling, 29–30 industrial process heat, 31 other uses, 31 snow melting, 30–31 space and district heating, 28, 28–29f worldwide utilization, 27, 27f downhole flow loop, 62–63 illustration, 24, 25f power generation, 26, 27f Aquacultural heating, 31 Artesian bar, 7 Assam-Arakan basin, 377–379, 378t B Binary cycle power plant, 397 conventional utilization methods, 75 design, 83, 84f Freon R12, 235 Kalina cycle, 234–235, 234f, 298, 300 Kamchatka power plant, 235 layout diagram, 233, 233f organic Rankine cycle (ORC), 245, 249f power from reservoirs, 62 Rankine cycle, 233–234 working fluid, 233 Biomass-geothermal power generation technology, 280, 281f Borehole heat exchanger (BHEX) coaxial BHEX binary geothermal power plant, 83, 84f configuration, 82–83, 83f fluid temperature, 83–84, 84f U-tube heat exchanger, 84, 85f Bouguer correction, 421 Bouguer gravity, 418 Building cooling/heating abandoned wells energy (AWE) system

Index

desalinating produced water system, 182, 183f geothermal heat pump system, 179–181, 179–180f geothermal power generation system, 181–182, 181f, 182t geothermal utilization efficiency, 183–184, 183f schematic diagram, 164–165, 166f geothermal utilization advantages, 159–160 categories, 163–165, 164–166f literature review, 161, 162t, 163f practical application, 184–185 ground source heat pump (GSHP) system common underground buried tubes, 165–166, 167f ground-coupled heat pump (GCHP) system, 166–168, 168f groundwater heat pump (GWHP) system, 168–170, 169–170f schematic design, 163, 164f renewable energy (RE) technology, 159 underground duct system (UDS) horizontal UDS system, 171–173, 171–173f operation principle, 163–164, 165f UDS-advanced energy-saving technology system, 177–178, 177f UDS-phase change material (PCM) system, 175–177, 176f vertical UDS system, 173–175, 174f Building integrated photovoltaic/thermal (BIPVT) system, 263, 265f C Cambay basin, 374, 376t, 376f Carbon dioxide (CO2) as working fluid, 107–108 Carbon-neutrality transition, 269 Casing perforation, 106 Cation-anion balance (CBE), 411–412 Cauvery basin, 377 Closed-loop geothermal system, 35 Coaxial borehole heat exchanger (BHEX), 379–380 binary geothermal power plant, 83, 84f configuration, 82–83, 83f fluid temperature, 83–84, 84f

Index

Combined cycle, 235–237, 236f Commercial Building Energy Consumption Survey (CBECS) gas consumption values, 344, 345t Comparative analysis and evaluation of mines annual heat load of residential buildings, 442, 442f closed and flooded mines, 427 Donetsk coal-mining area carboniferous sedimentary rocks, 437 coal deposits, 437 deep heat flux, 437–440, 439f mine drainage data, 437, 438f thermal conductivity, 440 efficiency indicators circulation geothermal system, 441t open geothermal systems, 440t electricity costs for drainage, 432–433 electric power costs for water lifting, 433 energy criterion, 441 geothermal system closed system, 428, 431–432 cost analysis, 429–431 discharge of mine water, 431 existing geothermal systems, 428–429 mine water/rock heat recovery, 429t open system, 428 recorded geothermal plants, 430t mine water, 427–428 performance indicators, 441–442 pumping cost COP, 435 costs for management and maintenance, 436 costs of thermal energy, 436 electric power for fluid circulation, 433–434 electric power to pump out mine water, 435 energy criterion, 433 geothermal energy production, 435–436 maximum achievable thermal capacity, 434 mine water temperature, 434–435 open circulation system, 435 overall efficiency, 434 power consumption and operating costs, 434

449

pump pressure head, 435 thermal efficiency, 436 Concentrated solar power (CSP), 88 Conduction-dominated (CD) geothermal plays, 318–319 Continuity equations, 144, 145f Convection-dominated geothermal plays (CV), 318 Conversion technology binary geothermal power cycle, 397 dry steam technology, 397 flash steam technology, 397 Rankine cycle, 397, 398f Coproduced water, 76–77 direct steam cycle, 86–87, 86f organic Rankine cycle (ORC), 86–87, 86f thermal efficiency, 88 variables, 87, 87t wellhead temperature and temperature profile, 87 Crop drying, 30 D Darajat power station, 228, 229f Decarbonization, 263, 352–354 Definition of geothermal energy, 11–12 Desalination, 182, 183f and abandoned wells, 195–196 economic analysis, 207–208, 208–209f freshwater production conventional multistep desalination process, 200, 204t, 204f multistage desalination simulation with secondary preheating, 200, 204, 205f, 205t multistage desalination simulation with secondary preheating, external and internal flash box, 207, 207t, 208f multistage desalination simulation with secondary preheating and external flash box, 205–206, 206t, 206f freshwater scarcity, 191 geothermal energy and, 193, 195 inflation rates vs. net present value, 209f vs. return on investment (ROI), 208f Kalina cycle, 303–304 membrane distillation technology, 192

450

Desalination (Continued) methods, 191–192 multistage desalination method conventional multistage geothermal desalination, 198, 199f design parameters, 196–198, 198t schematics, 196, 197f with secondary preheating, 198–200, 201f with secondary preheating, external and internal flash box, 200, 203f with secondary preheating and external flash box, 200, 202f water reclassifiers, 196 reception structure, 192 using renewable energy, 192–193, 194f District heating, 28, 28–29f aquifer access through existing wells Darcy flow rates, 352 doublet configuration, 352, 354f resource parameters, 352, 354t surface separation between wells, 352, 353f aquifer temperature Bakken shale, 346–348, 351f formation temperature, 346–348, 351f hot sedimentary aquifers, 348 Inyan Kara formation, 348, 351f completed design, 364, 365f contingency planning, 361 decarbonization, 352–354 downhole pump flow rates, 355 economic feasibility, 360–361 energy use patterns, 360 energy utilization factor, 359–360, 360t fluid chemistry and maintenance considerations, 363 funds, 361–362, 362t future work, 364, 366 GEOPHIRES, 356, 356t, 357f geothermal resources classification, 345–346, 348t GeoVision economic potential, 342, 342f heat network service area, 354–355, 355f industrial heat loads, 356–357, 357f, 358t innovations, 343 limitations, 364, 366 linear heat density (LHD), 354–355 Mandaree energy demand

Index

building-level heat demand map, 345, 347f Commercial Building Energy Consumption Survey (CBECS) gas consumption values, 344, 345t map reference system, 344, 344f preliminary annual energy consumption, 345, 346f Residential Energy Consumption Survey (RECS) gas consumption values, 344, 345t for oil patch, 341–343, 342f payback period, 364, 365f peak heating source (PHS) sizing and load allocations, 358–359, 359f production costs, 364 production temperature decline curve, 356, 357f production test, 356, 356t, 357f recompletion and heat network costs, 362–363, 363t regulatory conditions, 364 resource availability, 352–354 study site, 343–344 tariffs, 364 Williston Basin geological setting, 346, 349–350f Double flash steam plant, 231–232, 232f, 283f Double-pipe heat exchanger, 258–260, 258f Doublet well system, 379 Downhole geothermal power generation concept, 66 horizontal well feature, 68–69 TEG installation, 69–70, 70f temperature distribution, 70, 71f unconventional wells, 68–69 mechanism, 62–63 vertical well constraint, 68–69 downhole power generation design, 66, 67f mathematical model, 68, 68f TEG installation, 66, 66f temperature distribution, 68, 69f tubing wall temperature, 66–67, 67f Dry steam power plant, 228, 229f, 297–298, 397

Index

E Earth asthenosphere, 15 classes of global geothermal regions hyperthermal, 18 normal, 17 semithermal, 17 composition and structure, 12–13, 13f core, 13 crust, 14 exosphere, 16 internal energy, 17, 18f ionosphere, 17 lithosphere, 15 mantle, 14 mesosphere, 15–16 stratosphere, 16 thermosphere, 16 total flow of heat, 35 troposphere, 15 Earth-air heat exchanger, 263, 265f Earth energy designer model (EED), 381 Electricity generation advantages of geothermal energy comparatively ecologically clean, 226 costly installation, 227 ecological problem, 227 geographical limits, 227 large capacity, 226 little noise work, 226–227 permanent power supply, 226 possible exhaustion, 227 security of energy, 227 seismic instability, 227 small operating costs, 226 stable price, 226 sustainable and renewable, 226 binary cycle power plant Freon R12, 235 Kalina cycle, 234–235, 234f Kamchatka power plant, 235 layout diagram, 233, 233f Rankine cycle, 233–234 working fluid, 233 combined cycle/hybrid plants, 235–237, 236f dry steam power plant, 228, 229f flash steam power plant concept, 230

451

double flash steam plant, 231–232, 232f single flash steam plant, 230–231, 230–231f geothermal energy resources geo-pressurized resources, 222 hot dry rock resources, 222–223, 223f liquid/hot water resources, 221–222, 221f magma resources/molten rock, 224, 225f radiogenic resources, 225, 225f vapor-dominated resources, 220, 220f harvesting geothermal energy, 227, 228f steam and water, 217–218 Electric stimulation, 107 End-on spread, 414 Energy equations, 147–149 Enhanced deep borehole heat exchanger (EDBHE), 323–325 Enhanced geothermal system (EGS) acidizing acid fracturing/fracture acidizing, 105 matrix acidizing, 103–104 techniques, 103 acoustic stimulation, 107 carbon dioxide (CO2) as working fluid, 107–108 casing perforation, 106 electric stimulation, 107 high-energy gas fracturing (HEGF)/ explosive stimulation, 106 hydraulic fracturing contact circle radius, 102 effective stress, 102 elastic deformation, 102 fracture aperture, 102–103 fracture conductivity, 103 fracture element, 101–102 fracture porosity and permeability, 103 pad stage, 100–101 process, 100 proppant distribution density, 101 proppant embedment, 101, 101f slurry stage, 100–101 permeability, 99–100 thermal fracturing, 105–106 Exploration techniques data collection and evaluation, 405–406 direct exploration, 407 factors, 406

452

Exploration techniques (Continued) features, 407, 407–408t geochemical study cation-anion balance (CBE), 411–412 cost, 412–413 description, 410–411, 412f geothermal water characteristics, 410–411 source and subsurface geological parameters, 413 subsurface fluid patterns, 412 geophysical studies, 405 geophysical techniques categories, 413 gravity method (see Gravity method) magnetics, 424 method, 413 micrometer survey method (MSM), 413 resistivity and magnetotellurics, 423–424 seismic method (see Seismic method) indirect exploration, 407 reconnaissance study, 405–406 remote sensing techniques active and passive remote sensing, 409 infrared and thermal infrared imagery instruments, 410 Landsat/TM (ETM+), 410, 410t NOAA/AVHRR, 410, 411t satellite remote sensing, 409 TERRA/ASTER, 410, 411t types, 409 workflow, 409, 409f stages, 405, 406f Explosive stimulation, 106 Extraction techniques abandoned geothermal wells (see Enhanced geothermal system (EGS)) closed-loop circuit extraction technique, 21, 23f coaxial wellbore heat exchanger (WHE), 379–380 conductive fractures horizontal wellbore, 21–24, 24f vertical wellbore, 21–24, 23f deep borehole heat exchanger (DBHE), 323, 324f doublet well system, 379 Earth energy designer model (EED), 381

Index

enhanced deep borehole heat exchanger (EDBHE), 323–325 heat exchange from single well, 379, 380f injection and production heat technique, 21, 22f in situ combustion, 382–383 thermal impact graph, 381, 381–382f F Fault/fractures, 322–323 Feasibility studies economic feasibility investment cost (INV), 394 profitability, 394 purchasing cost, 394 environmental feasibility (see life cycle assessment (LCA)) life cycle assessment (LCA) examples, 395f functional unit (FU) and study boundaries, 395 impact results, 396 life cycle impact assessment, 396 Life Cycle Inventory (LCI), 396 thermodynamic feasibility closed-loop heat exchange, 392–393 numerical model, 392 tri-diagonal matrix algorithms (TDMA), 393 tube-in-tube heat exchange process, 392, 393f FEFLOW software ver.7.1, 243 Flash steam power plant, 397 concept, 230 double flash steam plant, 231–232, 232f single flash steam plant, 230–231, 230–231f Fracture acidizing. See Acid fracturing Fracture parameters fracture aperture, 129, 130f fracture permeability, 127, 128–129f fracture thermal conductivity, 129, 131f G GEOPHIRES, 356, 356t, 357f Geophones, 413 Geo-pressurized resources, 222

Index

Geothermal cyclic system (GCS). See 3D mathematical model Geothermal energy extraction, 323–325, 324f Geothermal heat pump system feasibility, 180–181 heat transfer fluid, 180, 180f schematic diagram, 179–180, 179f Geothermal patterns of Pakistan Balochistan Basin Zone of Pakistan, 326–327 electric production feasibility, 332–333, 334f extensive drilling, 325 Indus Basin Zone of Pakistan central Indus basin/Sulaiman province, 330 geothermal gradient, 327, 328f lower Indus basin/Kirthar province, 331–332 upper Indus basin/Kohat-Potwar province, 327–330 Northern Geothermal Zone of Pakistan, 325–326 potential geothermal zones, 332–333, 332f Geothermal plays classification, 317, 317f conduction-dominated (CD) geothermal plays, 318–319 convection-dominated geothermal plays (CV), 318 definition, 317 heat transfer regime, 317–318 Geothermal power generation system, 181–182, 181f, 182t Geothermal reservoir (GR), 35–36 fault/fractures, 322–323 lithofacies, 322 porosity and permeability, 319–320 thermal gradient, 320–321, 321t Geothermal resources, 75 GeoVision economic potential, 342, 342f Gravity method Bouguer gravity, 418 Bouguer gravity anomalies Bouguer correction, 421 latitude correction, 420 terrain correction, 420 concept, 418 derivatives of gravity field, 421–423

453

gravimeters, 420 principle, 420 regional and residual gravity fields, 421, 422f upward and downward continuation, 423 Green energy, 3 Greenhouse heating, 28 Ground source heat pump (GSHP) system, 29–30, 277–278 common underground buried tubes, 165–166, 167f ground-coupled heat pump (GCHP) system heat exchange efficiency, 168 heat source/sink, 166–167 horizontal buried tube system, 166–167, 168f vertical buried tube system, 166–167, 168f groundwater heat pump (GWHP) system intake and return water modes, 169, 170f operation principle, 168–169, 169f prerequisite, 170 types, 169 schematic design, 163, 164f H Harvest technique. See also Oil field geothermal power generation dry rock fracturing concept, 18 rock region temperature, 18–19, 19f temperature distribution, 18–19 thermal energy inside Earth, 19–20 time to extract, 20 hot igneous systems, 18 natural hydrothermal circulation/hot aquifer concept, 18 hot water inside aquifer, 20, 20f thermal properties, 20 time to extract, 21 Heat capacity, 142–143 Heat conductivity, 143 Heat energy, 17, 18f Heat extraction model for abandoned wells continuity/mass conversion equations, 144, 145f energy equations, 147–149

454

Heat extraction model for abandoned wells (Continued) material property design, 140, 142f heat capacity, 142–143 heat conductivity, 143 heat recovery system operation, 140, 141f specification, 142, 142t temperature dependency, 142–143 mesh in numerical simulation cylindrical mesh, 149, 151f quadrilateral mesh, 149, 150f model definition, 138 momentum equation, 144, 146 temperature distribution in wellbore, 143–144 turbulence intensity, 149 well temperature and depth, 138–140, 139f thermal storage system classification, 140, 141f Heat recovery system, 140, 141f High-energy gas fracturing (HEGF), 106 Historical overview ancient Mediterranean civilizations, 4 balneological uses, 5 boric acid, 6–7 chemical productions, 6 Etruscans, 4 first usage, 3 Lumaie, 5–6 middle ages, 5–6 modernization period, 7, 8t 19th century, 6–7 Roman Empire, 4–5 upto 1000 CE, 5 Hot dry rock resources, 222–223, 223f Hot water springs, 299 Hybrid power plants, 235–237, 236f Hydraulic fracturing contact circle radius, 102 effective stress, 102 elastic deformation, 102 fracture aperture, 102–103 fracture conductivity, 103 fracture element, 101–102 fracture porosity and permeability, 103 pad stage, 100–101

Index

process, 100 proppant distribution density, 101 proppant embedment, 101, 101f slurry stage, 100–101 Hydrocarbon reservoir, 61 Hydrogen energy system, 268, 268f Hydrothermal-intracratonic-type (CD1) geothermal play, 318–319 Hydrothermal-orogenic-type (CD2) geothermal plays, 318–319 I Indian petroliferous basins Assam-Arakan basin, 377–379, 378t Cambay basin, 374, 376t, 376f Cauvery basin, 377 downhole temperature, 374 heat recovery methodology bottom-hole heat exchanger assembly, 383, 384f reservoir simulators, 383 in situ combustion, 383 T-I-GER (Thermal Impact Graph) system, 383 Krishna Godavari (KG) basin, 375–377 major basins, 374, 375f organic Rankine cycle (ORC), 374 Industrial heat loads, 356–357, 357f, 358t Industrial process heat, 31 Injection temperature, 131, 132f In situ combustion, 382–383 Integrated system abandoned wells double-pipe heat exchanger, 258–260, 258f geothermal ORC power plant, 258–260, 259f power generation, 258–260, 258f thermal energy generation, 256–257, 257f advantages, 255–256 carbon-neutrality transition, 269 decarbonization, 263 for district heating absorption refrigeration, 263, 264f building integrated photovoltaic/thermal (BIPVT) system, 263, 265f earth-air heat exchanger, 263, 265f

Index

ORC power plant, 263 performance, 266 solar-geothermal energy system, 263, 264–265f waste heat recovery, 263–264 future studies, 269 heat extraction biomass and geothermal, 280, 281f, 282, 283f combined power and desalination unit, 291 coproduction system, 276 economic analysis, 291 International Energy Agency (IEA), 276 literature review, 287, 288–290t numerical models, 290 poly-generational system, 282, 285–287f, 286–287 single geothermal well, 291 solar and geothermal (see Solar and geothermal system) temperature and pressure profile analysis, 290–291 wind and geothermal, 282, 284f hydrogen energy system, 268, 268f performance enhancement optimal system design, 266–267 smart system operation, 267 stable power supply, 268–269 system assessment criteria, 256, 260, 261–262t techno-economic-environmental performance analysis, 267–268

455

T-h diagram, 307, 308f T-s diagram, 307, 308f power plant model, 297–298 related works desalination system, 303–304 geometry with numerical model, 301 geothermal stream and its properties, 303 heat transfer model, 300–301 organic Rankine cycle power plant, 301 power generation parameters, 302–303 temperature profile of abundant wells, 302 wellbore as heat exchanger, 302 single and double flash power plant, 297–298 solar-driven Kalina cycle benefits and constraint, 309–310 schematic diagram, 309, 310f solar heating, 309 solar thermal collector, 309 stream temperature vs. output, 300 theory, 304 thermal efficiency, 307 2MW geothermal power plant, 306, 306f vs. steam organic Rankine cycle (ORC), 307 water cut, 299–300 working fluid, 298 working principle, 304–306, 305f Kamchatka power plant, 235 Krafla power plant, 231–232, 232f Krishna Godavari (KG) basin, 375–377 L

K Kalina cycle, 234–235, 234f benefits, 298 binary cycle power plant, 298, 300 challenges, 310–311 chemical stability, 310–311 dry steam plant, 297–298 economic factor, 307 future scope, 311 geothermal reservoir capacity and strength, 299 global energy needs, 297 hot water springs, 299 phase diagram

Latitude correction, 420 Levelized cost of electricity (LCOE), 153 Limitations of geothermal energy, 12 Linear heat density (LHD), 354–355 Liquid/hot water resources, 221–222, 221f Lithofacies, 322 Low and medium enthalpy streams. See Kalina cycle M Magma resources/molten rock, 224, 225f Magnetics, 424 Mass conversion equations. See Continuity equations

456

Index

Mathematical model. See 3D mathematical model Matrix acidizing, 103–104 Membrane distillation technology, 192 Methane emission, 76–77, 137 Micrometer survey method (MSM), 413 Momentum equation, 144, 146 Multigeneration cycle, 286, 286f Multiple productive well system, 47, 47–48f

energy analysis, 247–249 heat source, 245 schematic representation, 245, 249f working fluid, 245 Indian petroliferous basins, 374 Kalina cycle, 298, 301, 307 numerical model of geothermal well 3D view and 2D view, 243, 245f FEFLOW software ver.7.1, 243 heat exchanger, 243, 247f model validation, 243, 248f thermos-physical properties, 243, 246t Sabalan geothermal field study geometry of well, 241, 242f geothermal map of Iran, 241, 241f specification of NWS3 well, 241, 242t temperature profile of NWS3 well, 243, 244f simulation results bottom-hole temperature vs. water flow rate, 249–250, 250–251f input parameters, 250, 252t net power generation vs. mass flow rate, 250, 252f system description, 240 waste heat recovery, 263

N Nonmagmatic geothermal plays (CV3), 318 O Oil field geothermal power generation geothermal energy binary cycle power plant, 62 vs. classical geothermal fields, 62 downhole flow loop, 62–63 drilling problems, 61–62 heat exchange, 62 horizontal well feature, 68–69 TEG installation, 69–70, 70f temperature distribution, 70, 71f unconventional wells, 68–69 thermal energy, 61 thermoelectric technology dimensionless figure of merit, 63–64 efficiency, 63–65, 65f schematic representation, 63, 64f Seebeck effect, 63 thermoelectric materials, 65, 65f vertical well constraint, 68–69 downhole power generation design, 66, 67f mathematical model, 68, 68f TEG installation, 66, 66f temperature distribution, 68, 69f tubing wall temperature, 66–67, 67f One-injection and one-production model, 118, 119f Open-circuit geothermal system, 35–36 Organic Rankine cycle (ORC) power plant, 75, 79–81, 86–87, 86f geothermal power plant model binary power cycle, 245, 249f

P Payback period, 364, 365f Peak heating source (PHS), 358–359, 359f Petrothermal-hot dry basement-type (CD3) plays, 319 Plutonic type-magmatic geothermal play (CV1), 318 Poly-generational system, 282, 285–287f, 286–287 Porosity and permeability, 319–320 Power generation, 26, 27f Prefeasibility features depth of well, 390 direction of drill, 390 flow characteristics, 391 geothermal gradient, 390 level of water-cut, 390–391 thermal properties, 391 thermo-economic and environmental studies, 391 Production costs, 364

Index

Productivity evaluation of abandoned wells fracture parameters fracture aperture, 129, 130f fracture permeability, 127, 128–129f fracture thermal conductivity, 129, 131f injection and production analysis pressure contour distribution, 121, 122–123f production temperature and heat extraction rate, 121, 124f temperature distribution, 120–121, 120f injection temperature, 131, 132f mathematical model assumption, 116 computational models, 118, 119f coupling process, 118 governing equations, 116–117 model parameters, 118, 119t one-injection and one-production model, 118, 119f two-injection and one-production model, 118, 119f rock mass parameters rock mass permeability, 125, 126f rock mass porosity, 127, 127–128f specific heat capacity, 121–125, 125f thermal conductivity, 121–125, 124f R Radiogenic resources, 225, 225f Rankine cycle, 397, 398f. See also Organic Rankine cycle (ORC) power plant Reclamation, 108–109 Recompletion and heat network costs, 362–363, 363t Regional and residual gravity fields, 421, 422f Regulatory issues, 364 Remediation, 108–109 Remote sensing techniques active and passive remote sensing, 409 infrared and thermal infrared imagery instruments, 410 Landsat/TM (ETM+), 410, 410t NOAA/AVHRR, 410, 411t satellite remote sensing, 409 TERRA/ASTER, 410, 411t types, 409 workflow, 409, 409f

457

Renewable resources, 3 Residential Energy Consumption Survey (RECS) gas consumption values, 344, 345t Resistivity and magnetotellurics, 423–424 Resources of geothermal energy geo-pressurized resources, 222 hot dry rock resources, 222–223, 223f liquid/hot water resources, 221–222, 221f magma resources/molten rock, 224, 225f radiogenic resources, 225, 225f vapor-dominated resources, 220, 220f Revitalization conversion technologies binary geothermal power cycle, 397 dry steam technology, 397 flash steam technology, 397 Rankine cycle, 397, 398f feasibility studies economic feasibility, 394 environmental feasibility, 395–396, 395f thermodynamic feasibility, 392–393, 393f leakages and emissions, 389 practical case studies, 397–398, 399–400t prefeasibility features depth of well, 390 direction of drill, 390 flow characteristics, 391 geothermal gradient, 390 level of water-cut, 390–391 thermal properties, 391 thermo-economic and environmental studies, 391 Rock mass permeability heat extraction ratio curves, 125, 126f production temperature curves, 125, 126f porosity, 127, 127–128f specific heat capacity, 121–125, 125f thermal conductivity, 121–125, 124f Rock types, 14 S Seebeck effect, 63 Seismic method acquisition configurations, 414, 415f

458

Seismic method (Continued) critical occurrence, 415 end-on spread, 414 procedure, 415–416, 418–419f processing flowchart, 415, 416f refracted and direct seismic wave, 415, 417f Snell’s Law, 415 split spread survey, 414 travel time curves, 415, 417f geophones, 413 interpretation, 416–417, 419f seismic refraction vs. reflection method, 413, 414t source generation, 413 Single flash steam plant, 230–231, 230–231f Single well system, 379, 380f Snell’s Law, 415 Snow melting, 30–31 Solar-geothermal energy system, 263, 264–265f demonstration, 277–278, 277f ground source heat pump (GSHP), 277–278, 280 hybrid geothermal-CSP system, 278, 279f hybrid solar-geothermal system, 278, 278f photovoltaics (PV), 276–277, 280 solar-geothermal heating system for greenhouse, 280, 280f studies, 280 temperatures vs. productivity, 277 Space heating, 28, 28–29f, 282, 285–286f, 286 Specification, 142, 142t Split spread survey, 414 Stable power supply, 268–269 Steam power plants, 75 T Terrain correction, 420 Thermal Alteration Index (TAI), 321 Thermal characteristic curve, 381, 381f Thermal fracturing, 105–106 Thermal gradient, 320–321, 321t Thermal impact graph, 381, 381–382f, 383 Thermal plume graph, 381, 382f Thermoelectric devices, 89, 90f Thermoelectric generator (TEG), 61 dimensionless figure of merit, 63–64

Index

efficiency, 63–65, 65f schematic representation, 63, 64f Seebeck effect, 63 thermoelectric materials, 65, 65f 3D mathematical model closed-loop geothermal system, 35 future research, 49 geothermal cyclic system (GCS), 36–37 geothermal reservoir (GR), 35–36 multiple injection well system pressure distribution, 48, 50–51f thermal fields, 48, 52–53f water temperature in producing wells, 48–49, 53f well location, 47–48, 50f multiple productive well systems, 47, 47–48f and numerical algorithm aquifer with injection and producing wells, 37, 38f boundary conditions, 39, 39f finite difference method, 41 fluid filtration velocity, 40 GCS operation, 41, 42f hydrostatic pressure, 39 lateral boundary condition, 40 optimization parameters, 40–41 piezoconductivity equation, 39–40 reservoir pressure field, 41, 41f temperature equation, 40 velocity field, 41, 42f water filtration, 41, 42f water flow in productive layer, 38 numerical simulation average temperature in production well, 44, 44f pressure in wells, 44t splitting method by spatial variables, 43 temperature field, 43–44, 43f, 45f open-circuit geothermal system, 35–36 seasonal regimes, 45–46, 46f two injection well system, 47, 49f Tincal, 6 Tube-in-tube heat exchange process, 392, 393f Turbulence intensity, 149 Two-injection and one-production model, 118, 119f Two injection well system, 47, 49f

Index

U Unconventional wells, 68–69 Underground duct system (UDS) horizontal UDS system common SGV system, 171–172, 171f with double-layer buried tubes, 172, 173f with parallel PVC pipes, 171–172, 172f transient model, 172–173 operation principle, 163–164, 165f soil temperature, 170 theoretical and practical research, 170–171 UDS-advanced energy-saving technology system, 177–178, 177f UDS-phase change material (PCM) system annular PCM component, 175 PCM around buried tubes, 175–177, 176f schematic diagram, 175, 176f site construction, 175, 176f types, 175 vertical UDS system, 173–175, 174f

459

Upward and downward continuation, 423 U-tube heat exchanger, 84, 85f V Vapor-dominated resources, 220, 220f Volcanic type-magmatic geothermal play (CV1), 318 W Waste heat recovery, 263–264 Water desalination, 88–89. See also Desalination Water reclassifiers, 196 Water-to-oil (WOR) and water-to-gas (WGR) ratio, 79 Wellbore heat exchanger (WHE), coaxial, 379–380 Wind-geothermal technology, 282, 284f

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