This paper provides an overview of conventional geothermal systems and unconventional geothermal developments as a common reference is needed for discussions between energy professionals. Conventional geothermal systems have the heat, permeability and fluid, requiring only drilling down to < 3.5 Km. Low-temperature (LT) systems can be everywhere, have <100 ° C, normal heat flow or decaying radiogenic granite as heat sources, and used in district heating. Medium-temperature (MT) 100 ° C - 190 ° C, and high-temperature (HT) 190 ° C - 374 ° C resources are mostly at plate boundaries, with volcanic intrusive heat source, used mostly for electricity generation. Single well capacities are <2 MWe and <5 MW (LT), <7 MWe and <15 MW (MT), <25 MWe and <125 MW (HT). Unconventional geothermal alternatives have heat (8 ° C - 500 ° C) and a range of depths (1 m to 20 Km), but lack permeability or fluid, thus requiring stimulations for heat extraction by conduction. HVAC is 1 - 2 m deep and shallow geothermal down to 500 m in wells, both capturing < 25 ° C, with <10 kW and <5 MW unit-capacities. Technologies targeting ≤ 500 ° C are either advanced by geothermal developers at <7 Km depth (Enhanced Geothermal Systems (EGS), drilling below brittle-ductile transition zones and under geothermal fields), or by the Oil & Gas industry (Advanced Geothermal Systems, heat recovery from hydrocarbon wells or reservoirs, Superhot Rock Geothermal, and millimeter-wave drilling down to 20 Km). Their primary aim is electricity generation, relying on closed-loops, but EGS uses fractures for heat exchange with earthquake risks during fracking. Unconventional approaches could be everywhere, with shallow geothermal already functional. The deeper and hotter unconventional alternatives are still experimental, overcoming costs and technological challenges to become fully commercial. Meanwhile, the conventional geothermal resources remain the most proven opportunities for investments and development.
KeywordsConventional Geothermal SystemsUnconventional Geothermal DevelopmentsShallow and Deep Closed-LoopsEnhanced Geothermal SystemsSupercritical and Millimeter-Wave Drilling
United States Geological Survey. https://www.usgs.gov/centers/gmeg/science/geothermal-resource-investigations-project
Muffler, L.P.J. and Cataldi, R. (1978) Methods for Regional Assessment of Geothermal Resources. Geothermics, 7, 53-89. https://doi.org/10.1016/0375-6505(78)90002-0
Williams, C.F., Reed, M.J. and Anderson, A.F. (2011) Updating the Classification of Geothermal Resources. Proceedings of the 36th Workshop on Geothermal Reservoir Engineering, Stanford University, 31 January-2 February, 2011, SGP-TR-191.
White, D.E. and Williams, D.L. (1975) Assessment of Geothermal Resources of the United States, 1975, U.S. Geological Survey Circular 727, U.S. Government Printing Office, 155 p. https://doi.org/10.3133/cir726
Sanyal, S.K. (2005) Classification of Geothermal Systems—A Possible Scheme. Proceedings of the 30th Workshop on Geothermal Reservoir Engineering, Stanford University, SGP-TR-176.
Moeck, I. (2014) Catalogue of Geothermal Play Types Based on Geologic Controls. Renewable and Sustainable Energy Reviews, 37, 867-882. https://doi.org/10.1016/j.rser.2014.05.032
Moeck, I., Bendall, B., Minnig, Ch., Manzella, A. and Yasukawa, K. (2020) Geothermal Play Typing—Current Development and Future Trends of a Modern Concept for Geothermal Resources Assessment. Proceedings of the World Geothermal Congress, Reykjavik, 26 April-2 May 2021, 1-6.
Axelsson, G. (2008) Production Capacity of Geothermal Systems. The Workshop for Decision Makers on Direct Heating Use of Geothermal Resources in Asia, Tianjin, China, 11-18 May 2008, 15 p.
Department of Energy, USA. https://www.energy.gov/eere/geothermal/electricity-generation
Boden, D.R. (2016) Geologic and Tectonic Settings of Select Geothermal System. In: Ghassemi, A., Ed., Geologic Fundamentals of Geothermal Energy, 1st Edition, Taylor & Francis, CRC Press, Boca Raton, 159-205. https://doi.org/10.1201/9781315371436-8
Technical University of Zurich, ETZ, Switzerland. http://www.seismo.ethz.ch/en/knowledge/things-to-know/geothermal-energy-earthquakes/forms-of-geothermal-energy/
International Renewable Energy Agency and International Geothermal Association (2021) United Nations Framework Classification for Geothermal Energy: Pilot Applications in the Caribbean, Ethiopia and Indonesia. International Renewable Energy Agency, Abu Dhabi, International Geothermal Association, Bonn, 40 p.
Williams, D.L. and von Herzen, R.P. (1974) Heat Loss from the Earth; New Estimate. Geology, 2, 327-328. https://doi.org/10.1130/0091-7613(1974)2 2.0.CO;2
Chapman, D.S. and Rybach, L. (1985) Heat Flow Anomalies and Their Interpretation. Journal of Geodynamics, 4, 3-37. https://doi.org/10.1016/0264-3707(85)90049-3
Kovacs, I. (2005) Origin of the South Australian Heat Flow Anomaly. Journal of the Virtual Explorer, 20, Paper 14. http://virtualexplorer.com.au/ https://doi.org/10.3809/jvirtex.2005.00137
Giggenbach, W.F. (1988) Geothermal Solute Equilibria. Derivation of Na-K-Mg-Ca Geoindicators. Geochimica et Cosmochimica Acta, 52, 2749-2765. https://doi.org/10.1016/0016-7037(88)90143-3
Mueller, S., Melnik, O., Spieler, O., Scheu, B. and Dingwell, D.B. (2005) Permeability and Degassing of Dome Lavas Undergoing Rapid Decompression: An Experimental Determination. Bulletin of Volcanology, 67, 526-538. https://doi.org/10.1007/s00445-004-0392-4
Koudina, N., Garcia, R.G., Thovert, J.F. and Adler, P.M. (1998) Permeability of Three-Dimensional Fracture Networks. Physical Review E, 57, 4466-4479. https://doi.org/10.1103/PhysRevE.57.4466
Heap, M.J. and Kennedy, B.M. (2016) Exploring the Scale-Dependent Permeability of Fractured Andesite. Earth Planetary Science Letters, 447, 139-150. https://doi.org/10.1016/j.epsl.2016.05.004
Darcy, H. (1856) Les fontaines publiques de la ville de Dijon. Dalmont, Paris.
Magoon, L.B. (2004) Petroleum System: Nature’s Distribution System for Oil and Gas. In: Encyclopedia of Energy, Elsevier Science, Amsterdam, 823-836. https://doi.org/10.1016/B0-12-176480-X/00251-5
Norton, D. and Knight, J. (1977) Transport Phenomena in Hydrothermal Systems: Cooling Plutons. American Journal of Sciences, 277, 937-981. https://doi.org/10.2475/ajs.277.8.937
Björnsson, G. and Bödvarsson, G. (1990) A Survey of Geothermal Reservoir Properties. Geothermics, 19, 17-27. https://doi.org/10.1016/0375-6505(90)90063-H
Bodvarsson, G. (1964) Physical Characteristics of Natural Heat Sources in Iceland. Proceeding of UN Conference on New Sources of Energy, 2, 82-89.
Axelsson, G. and Gunnlaugsson, E. (2000) Geothermal Utilization, Management and Monitoring, in Long-Term Monitoring of High- and Low-Enthalpy Fields under Exploitation. World Geothermal Congress: Short Course, Mori Oka, 3-10.
Hochstein, M.P. (1988) Assessment and Modeling of Geothermal Reservoirs (Small Utilization Schemes). Geothermics, 17, 15-49. https://doi.org/10.1016/0375-6505(88)90004-1
Nicholson, K. (1993) Geothermal Fluids. Springer Verlag, Berlin, 264 p. https://doi.org/10.1007/978-3-642-77844-5
Arnórsson, S. (1995) Geothermal Systems in Iceland: Structures and Conceptual Models—II. Low-Temperature Areas. Geothermics, 24, 603-629. https://doi.org/10.1016/0375-6505(95)00026-7
Sanliyuksel, D. and Baba, A. (2011) Hydrogeochemical and Isotopic Composition of a Low-Temperature Geothermal Source in Northwest Turkey: Case Study of Kirkgecit Geothermal Area. Environmental Earth Sciences, 62, 529-540. https://doi.org/10.1007/s12665-010-0545-z
Xu, P., Li, M., Qian, H., Zhang, Q., Liu, F. and Hou, K. (2019) Hydrochemistry and Geothermometry of Geothermal Water in the Central Guanzhong Basin, China: A Case Study in Xi’an. Environmental Earth Sciences, 78, Article No. 87. https://doi.org/10.1007/s12665-019-8099-1
Torfason, H. (2003) Geothermal Map of Iceland and Geothermal Database. Report National Energy Authority of Iceland OS-2003/062 and Museum of Natural History Ní-03016, 167 p. (In Icelandic)
Khodayar, M. and Björnsson, S. (2021) Fracture Permeability: Outcrop Analogues from Active Plate Boundaries and Intraplate Contexts of Iceland. Open Journal of Geology, 11, 621-657. https://doi.org/10.4236/ojg.2021.1112031
Reed, M.J., Ed/ (1983) Assessment of Low Temperature Geothermal Resources of the United States-1982. U.S. Geological Survey Circular, No. 892, 73 p. https://doi.org/10.3133/cir892
Wilmarth, M. and Stimac, J. (2015) Power Density in Geothermal Fields. Proceedings of the World Geothermal Congress 2015, Melbourne, 19-25 April 2015, 1-7.
Franco, A. and Villani, M. (2009) Optimal Design of Binary Cycle Power Plants for Water-Dominated, Medium-Temperature Geothermal Fields. Geothermics, 38, 379-391. https://doi.org/10.1016/j.geothermics.2009.08.001
Guzovic, Z., Majcen, B. and Cvetkovic, S. (2012) Possibilities of Electricity Generation in the Republic of Croatia from Medium-Temperature Geothermal Sources. Applied Energy, 98, 404-414. https://doi.org/10.1016/j.apenergy.2012.03.064
Zhang, L., Chen, S. and Zhang, C. (2019) Geothermal Power Generation in China: Status and Prospects. Energy Science & Engineering, 7, 1428-1450. https://doi.org/10.1002/ese3.365
Arnórsson, S. (1995) Geothermal Systems in Iceland: Structures and Conceptual Models—I. High-Temperature Areas. Geothermics, 24, 561-602. https://doi.org/10.1016/0375-6505(95)00025-9
White, D., Muffler, L. and Truesdell, A. (1971) Vapor-Dominated Hydrothermal Systems Compared with Hot-Water Systems. Economic Geology, 66, 75-97. https://doi.org/10.2113/gsecongeo.66.1.75
Allis, R. (2000) Insights on the Formation of Vapor-Dominated Geothermal Systems. Proceedings of the World Geothermal Congress 2000, Kyushu-Tohoku, 28 May-10 June 2000, 2489-2496.
Raharjo, I.B., Allis, R.G. and Chapman, D.S. (2016) Volcano-Hosted Vapor-Dominated Geothermal Systems in Permeability Space. Geothermics, 62, 22-32. https://doi.org/10.1016/j.geothermics.2016.02.005
Grant, M.A., Donaldson, I.G. and Bixley, P.F. (1982) Geothermal Reservoir Engineering. Academic Press, New York, 369 p.
Petrica, V.C. (2016) Common Geothermal Well Design and a Case Study of the Low-Temperature Geothermal Reservoir in Otopeni, Romania. United Nations University Geothermal Training Programme (UNU-GTP) Report No. 32, 24 p.
Sveinbjörnsson, B.M. (2016) Medium Enthalpy Geothermal Systems in Iceland: Thermal and Electric Potential. Report íSOR-2016/008, 123 p.
Sveinbjörnsson, B.M. and Thorhallsson, S. (2014) Drilling Performance, Injectivity and Productivity of Geothermal Wells. Geothermics, 50, 76-84. https://doi.org/10.1016/j.geothermics.2013.08.011
Largest Geothermal Power Plants in the World. https://www.worldatlas.com/articles/largest-geothermal-power-plants-in-the-world.html
Huddlestone-Holmes, C., Hadley, T., Cousins, A. Hayward, J. and Li, C. (2015) Geothermal Heat Use in Gas Processing Facilities, a Feasibility Study. Technical Report, Energy flagship, CSIRO, 185 p.
Georgsson, L.S., Jóhannesson, H. and Bjarnason, P. (2010) Geothermal Activity in Borgarfjörður, W-Iceland, and the Exploration, Development and Utilization of the Varmaland/Laugaland Geothermal Field. Proceedings of the World Geothermal Congress 2010, Bali, 25-29 April 2010, 10 p.
Yearsley, E. (2023) Geothermal Pumped Well. GeoExpro, 20, 58-60. https://geoexpro.com/pumped-geothermal-power-projects-a-global-overview/
Lindal, B. (1973) Industrial and Other Applications of Geothermal Energy (Except Power Production and District Heating). In: Armstead, H.C.H., Ed., Geothermal Energy: Review of Research and Development, UNESCO, Paris, 135-148.
Bolton, R.S. (1998) Notes on the Early History of Wairakei. Proceedings of the 20th New Zealand Geothermal Workshop, Auckland, 1998, 13-20.
Ragnarsson, A., Steingrímsson, B. and Thorhallsson, S. (2021) Geothermal Development in Iceland 2015-2019. Proceedings of the World Geothermal Congress 2020 + 1, Reykjavik, April-October 2021, 1-15.
Andresh, M., Johst, C.B. and Parada Perez, R.E. (2023) A Geothermal Approach to Power-to-X in El Salvador, Chile, and Kenya. Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH, 46 p.
Balta, M.T., Dincer, I. and Hepbasli, A. (2009) Thermodynamic Assessment of Geothermal Energy Use in Hydrogen Production. International Journal of Hydrogen Energy, 34, 2925-2939. https://doi.org/10.1016/j.ijhydene.2009.01.087
Active Sustainability. https://www.activesustainability.com/sustainable-development/what-is-green-hydrogen-used-for/?_adin=02021864894
Yilmaz, C., Kanoglu, M., Bolatturk, A. and Gadalla, M. (2012) Economics of Hydrogen Production and Liquefaction by Geothermal Energy. International Journal of Hydrogen Energy, 37, 2058-2069. https://doi.org/10.1016/j.ijhydene.2011.06.037
News Release (June 30, 2022) Toshiba to Survey on Hydrogen Production Using Unused Geothermal Energy. https://www.global.toshiba/ww/news/energy/2022/06/news-20220630-01.html
News Release (November 11, 2022) Pertamina NRE, Keppel Infrastructure, and Chevron Sign Agreement to Explore Green Hydrogen and Green Ammonia Development Projects in Indonesia. https://www.pertamina.com/en/news-room/news-release/pertamina-nre-keppel-infrastructure-and-chevron-sign-agreement-to-explore-green-hydrogen-and-green-ammonia-development-projects-in-indonesia
News Release (September 13, 2023) Reliable and Always On: Unlocking the Next Generation of Geothermal Energy. https://www.chevron.com/newsroom/2023/q3/reliable-and-always-on-unlocking-the-next-generation-of-geothermal-energy
News Release (January 18, 2022) CeraPhi Energy and Climate Change Ventures Collaborate for Baseload Green Hydrogen. https://ceraphi.com/ceraphi-energy-and-climate-change-ventures-collaborate-for-baseload-green-hydrogen
The Royal Society (February 19, 2020) Ammonia Key to Reducing Shipping’s carbon Emissions. https://royalsociety.org/news/2020/02/green-ammonia-report/
Cleantech (November 25, 2019) Green Ammonia—Potential as an Energy Carrier and Beyond. https://www.cleantech.com/green-ammonia-potential-as-an-energy-carrier-and-beyond/
Siemens Energy (2023) “Green” Ammonia Is the Key to Meeting the Twin Challenges of the 21st Century. https://www.siemens-energy.com/uk/en/offerings-uk/green-ammonia.html
Fant, S. (2022) The World Is Craving Lithium, and Geothermal Could Relieve It. But at What Impact? https://www.renewablematter.eu/articles/article/the-world-is-craving-lithium-and-geothermal-could-relieve-it-but-at-what-impact
Stringfellow, W.T. and Dobson, P.F. (2020) Retrospective on Recent DOE-Funded Studies Concerning the Extraction of Rare Earth Elements & Lithium from Geothermal Brines (Final Report). Technical Report of Lawrence Berkeley National Laboratory, 100 p. https://doi.org/10.2172/1667374
Vulcan Energy (2023). https://v-er.eu/zero-carbon-lithium-optimisation-plant-opening/
Galiègue, X. and Laude, A. (2017) Combining Geothermal Energy and CCS: From the Transformation to the Reconfiguration of a Socio-Technical Regime? Energy Procedia, 114, 7528-7539. https://doi.org/10.1016/j.egypro.2017.03.1904
Pruess, K. (2006) Enhanced Geothermal Systems (EGS) Using CO2 as Working Fluid—A Novel Approach for Generating Renewable Energy with Simultaneous Sequestration of Carbon. Geothermics, 35, 351-367. https://doi.org/10.1016/j.geothermics.2006.08.002
Miranda-Barbosa, M., Sigfússon, B., Carlsson, J. and Tzimas, E. (2017) Advantages from Combining CCS with Geothermal Energy. Energy Procedia, 114, 6666-6676. https://doi.org/10.1016/j.egypro.2017.03.1794
Climeon (2023). https://climeon.com/
Abesser, C. and Walker, A. (2022) Geothermal Energy. Postbrief 46, UK Parliament POST (Parliamentary Office of Science and Technology), 71 p.
Greenfire Energy (2023). https://www.greenfireenergy.com/greenloop-technology/
Eavor (2023). https://www.eavor.com/technology/
Toews, M. and Holmes, M. (2021) Eavor-Lite Performance Update and Extrapolation to Commercial Projects. GRC Transactions, 45, 86-109.
News Release (June 22, 2023) MOECO and Chevron to Explore Advanced Closed Loop Geothermal Pilot in Hokkaido Japan. https://www.chevron.com/newsroom/2023/q2/commencement-of-pilot-tests-of-new-geothermal-technology-with-chevron-in-japan
Dash, Z.V., Murphy, H.D. and Cremer, G.M. (1981) Hot Dry Rock Geothermal Reservoir Testing: 1978-1980. Los Alamos National Laboratory, Report LA-9080-SR, 62 p. https://doi.org/10.2172/5347800
Brown, D.W., Duchane, D., Heiken, G. and Hriscu, V.T. (2012) Mining the Earth’s Heat: Hot Dry Rock Geothermal Energy. Springer-Verlag, Berlin and Heidelberg, 655 p. https://doi.org/10.1007/978-3-540-68910-2
Mertoglu, O., Simsek, S., Basarir, N. and Paksoy, H. (2019) Geothermal Energy Use, Country Update for Turkey. European Geothermal Congress 2019, Den Haag, 11-14 June 2019, 1-10.
Downing, R.A. and Gray, D.A. (1986) Geothermal Energy—The Potential in the United Kingdom. British Geological Survey, HMSO, London, 170 p.
Fervo Energy (2023). https://fervoenergy.com/technology/
Norbeck, J., Latimer, T., Gradl, Ch., Agarwal, S., Dadi, S., Eddy, E., Fercho, S., Lang, C., McConville, E., Titov, A., Voller, K. and Woitt, M. (2023) A Review of Drilling, Completion, and Stimulation of a Horizontal Geothermal Well System in North-Central Nevada. Proceedings of the 48th Workshop on Geothermal Reservoir Engineering, Stanford University, 6-8 February 2023, SGP-TR-224.
Patel, S. (2023) EGS, AGS, and Supercritical Geothermal Systems: What’s the Difference? Power Magazine. https://www.powermag.com/egs-ags-and-supercritical-geothermal-systems-whats-the-difference/
Hill, B.L. (2022) Superhot Rock Energy: A Vision for Firm, Global Zero-Carbon Energy. Clean Air Task Force Report, USA, 27 p.
Watson, S.M., Falcone, G. and Westway, R. (2020) Repurposing Hydrocarbon Wells for Geothermal Use in the UK: A Preliminary Resource Assessment. Proceedings of the World Geothermal Congress 2020 + 1, Reykjavik, April-OCtober 2021, 1-13.
Auld, A., Hogg, S., Berson, A. and Gluyas, J. (2014) Power Production via North Sea Hot Brines. Energy, 78, 674-684. https://doi.org/10.1016/j.energy.2014.10.056
Gluyas, J., Mathias, S. and Goudarzi, S. (2018) North Sea—Next Life: Extending the Commercial Life of Producing North Sea Fields, Petroleum Geology of NW Europe: 50 Years of Learning. Proceedings of the 8th Petroleum Geology Conference Series, 8, 561-570. https://doi.org/10.1144/PGC8.30
MEET Project: Multidisciplinary and Multi-Context Demonstration of Enhanced Geothermal Systems Exploration and Exploitation Techniques and Potentials. European Horizon 2020. Project Results. https://www.meet-h2020.com/project-results/deliverables/
Santos, L., Dahi Taleghani, A. and Elsworth, D. (2022) Repurposing Abandoned Wells for Geothermal Energy: Current Status and Future Prospects. Renewable Energy, 194, 1288-1302. https://doi.org/10.1016/j.renene.2022.05.138
Xin, S., Liang, H., Hu, B. and Li, K. (2012) Electrical Power Generation from Low Temperature Co-Produced Geothermal Resources at Huabei Oilfield. Proceedings of the 37th Workshop on Geothermal Reservoir Engineering, Stanford University, 30 January-1 February 2012, SGP-TR-194.
Gosnold, W. (2015) Electric Power Generation from Low to Intermediate Temperature Resources. Final Report DOE EE00271-1. https://doi.org/10.2172/1186077
Rybach, L. (2003) Geothermal Energy: Sustainability. Geothermics, 32, 463-470. https://doi.org/10.1016/S0375-6505(03)00057-9
Kong, Y., Pang, Z., Shao, H., Hu, S. and Kolditz, O. (2014) Recent Studies on Hydrothermal Systems in China: A Review. Geothermal Energy, 2, Article No. 19. https://doi.org/10.1186/s40517-014-0019-8
Alimonti, C., Soldo, E., Bocchetti, D. and Berardi, D. (2018) The Wellbore Heat Exchangers: A Technical Review. Renewable Energy, 123, 353-381. https://doi.org/10.1016/j.renene.2018.02.055
Collins, M. and Law, R. (2017) The Development and Deployment of Deep Geothermal Single Well (DGSW) Technology in the United Kingdom. European Geologist Journal, 43. https://eurogeologists.eu/european-geologist-journal-43-collins-the-development-and-deployment-of-deep-geothermal-single-well-dgsw-technology-in-the-united-kingdom/
Scherer, J., Golla, G., Chandrasekar, H., Amaya, A., Chin, H., Brown, S., Sonnenthal, E., Rutqvist, J. and Oldenburg, C. (2023) The GreenLoop Closed-Loop Geothermal (CLG) System: Optimizing Power Generation and Evaluating Its Impact on the Reservoir. Proceedings of the 9th Indonesia International Geothermal Convention & Exhibition 2023, Jakarta, 1-8.
CeraPhi (2023). https://ceraphi.com/case-studies/
Dong, X., Liu, H., Chen, Zh, Wu, K., Lu, N. and Zhang, Q. (2019) Enhanced Oil Recovery Techniques for Heavy Oil and Oilsands Reservoirs after Steam Injection. Applied Energy, 239, 1190-1211. https://doi.org/10.1016/j.apenergy.2019.01.244
Hascakir, B., Babadagli, T. and Akin, S. (2008) Experimental and Numerical Modeling of Heavy-Oil Recovery from Oil Shales by Electrical Heating. Energy Fuels, 22, 3976-3985. https://doi.org/10.1021/ef800389v
Hasibuan, M.Y., Regina, S., Wahyu, R., Situmorang, D., Azmi, F., Syahputra, R., Batubara, L.P.Y., Prabowo, F., Setiawan, A., Afin, M.F., Afdhol, M.K. and Erfando, T. (2020) Electrical Heating for Heavy Oil: Past, Current, and Future Prospect. Preprints, 2020010115. https://doi.org/10.20944/preprints202001.0115.v1
Butler, R. (1991) Thermal Recovery of Oil and Bitumen. Prentice-Hall, Englewood Cliffs, 104 p.
Jacobs, T. (2017) Heavy-Oil Technology May Be a Perfect Fit for Geothermal Power. Journal of Petroleum Technology. https://jpt.spe.org/renewable-opportunities-heavy-oil-technology-may-be-perfect-fit-geothermal-power
ABClean Energy (2023). https://www.abcleanenergy.com/
Dobson, P., Asanuma, H., Huenges, E., Poletto, F., Reinsch, T. and Sanjuan, B. (2017) Supercritical Geothermal Systems—A Review of Past Studies and Ongoing Research Activities. Proceedings of the 41st Workshop on Geothermal Reservoir Engineering, Stanford University, 13-15 February 2017, SGP-TR-212.
Baccarin, F., Büsing, F., Buske, S., Dini, A., Manzella, A., Rabbel, W. and The DESCRAMBLE Science and Technology Team (2019) Understanding Supercritical Resources in Continental Crust. European Geothermal Congress, Den Haag, 11-14 June 2019, 1-10.
Sigurðsson, O. (2020) Stimulation of the RN-15/IDDP-2 Well at Reykjanes Attempting to Create an EGS System. Proceedings of the World Geothermal Congress 2020 + 1, Reykjavik, April-October 2021, 1-12.
Jolie, E., Liotta, D., Garduno-Monroy, V.H., Gutiérrez-Negrín, L.C., Arango Galván, C., Hersir, G.P., van Wees, J.D., Aragón Aguilar, A., López Hernández, A., Bruhn, D., Kieling, K. and The GEMex Team (2020) The GEMex Project: Developing Los Humeros (Mexico) as a Superhot Geothermal Site. Proceedings of the World Geothermal Congress 2020 + 1, Reykjavik, April-October 2021, 1-10.
Naganawa, Sh., Tsuchiya, N., Okabe, T., Kajiwara, T., Shimada, K. and Yanagisawa, N. (2017) Innovative Drilling Technology for Supercritical Geothermal Resources Development. Proceedings of the 42nd Workshop on Geothermal Reservoir Engineering, Stanford University, 13-15 February 2017, SGP-TR-212.
Bignall, G. and Carey, B. (2011) A Deep (5 km?) Geothermal Science Drilling Project for the Taupo Volcanic Zone—Who Wants In? Proceedings of the New Zealand Geothermal Workshop, Auckland, 21-23 November 2011, 1-5.
AltaRock Energy (2023). https://altarockenergy.com/
Cladouhos, T.T., Petty, S., Bonneville, A., Schultz, A. and Sorlie, C.F. (2018) Super Hot EGS and the Newberry Deep Drilling Project. Proceedings of the 43rd Workshop on Geothermal Reservoir Engineering, Stanford University, 12-14 February 2018, SGP-TR-213.
Energy Startups (2023). https://www.energystartups.org/startup/altarockenergy/
Quaise Energy (2023). https://www.quaise.energy/
Blain, L. (2022) Fusion Tech Is Set to Unlock Near-Limitless Ultra-Deep Geothermal Energy. New Atlas. https://newatlas.com/energy/quaise-deep-geothermal-millimeter-wave-drill/?itm_source=newatlas&itm_medium=article-body
Oglesby, K., Woskov, P., Einstein, H. and Livesay, B. (2014) Deep Geothermal Drilling Using Millimeter Wave Technology (Final Technical Research Report). U.S. Department of Energy Office of Scientific and Technical Information, 206 p. https://doi.org/10.2172/1169951
Rassenfoss, S. (2023) Microwave Drilling Sounds Like Science Fiction, but So Does Drilling Down to the Hottest Rock. Journal of Petroleum Technology, 75, 18-23. https://jpt.spe.org/microwave-drilling-sounds-like-science-fiction-but-so-does-drilling-down-to-the-hottest-rock https://doi.org/10.2118/0123-0018-JPT
BAFA, Federal Office for Economic Affairs and Export Control in Germany (Bundesamt für Wirtschaft un Ausfuhrkontrolle) (2022) Warmepumpen mit Prüf-/Effizienznachweis, heizen mit Erneuerbaren Energien (Heat Pumps with Efficiency Validation). Report, 131 p. http://www.bafa.de/
McClure, M. (2021) Why Deep Closed-Loop Geothermal Is Guaranteed to Fail? ResFrac Blog Post. https://www.resfrac.com/blog/why-deep-closed-loop-geothermal-guaranteed-fail
Sanyal, S.K., Morrow, J.W., Jayawardena, M.S., Berrah, N., Li, S.F. and Suryadarma (2011) Geothermal Resource Risk in Indonesia—A Statistical Inquiry. Proceedings of the 36th Workshop on Geothermal Reservoir Engineering, Stanford University, 31 January-2 February 2011, SGP-TR-191.
Lukawski, M.Z., Silverman, R.L. and Tester, J.W. (2016) Uncertainty Analysis of Geothermal Well Drilling and Completion Costs. Geothermics, 64, 382-391. https://doi.org/10.1016/j.geothermics.2016.06.017
Beckers, K.F. and Johnston, H.E. (2022) Techno-Economic Performance of Eavor-Loop 2.0. Proceedings of the 47th Workshop on Geothermal Reservoir Engineering, Stanford University, 7-9 February 2022, SGP-TR-223.
Wang, J. and Gates, I.D. (2023) On Geothermal Energy Recovery from Post-SAGD Reservoirs. Geothermics, 112, Article 102732. https://doi.org/10.1016/j.geothermics.2023.102732
Banks, G. and Ball, P. (2023) Superhot Rock Energy Glossary. Clean Air Task Force Project (Living Glossary). https://www.catf.us/superhot-rock/glossary/
Soon Min, H., Wagh, S., Kadier, A., Gondal, I.A., Bin Abdul Azim, N.A.P. and Kumar Mishra, M.K. (2018) Renewable Energy Technologies. In: Soon Min, H., Ed., Renewable Energy & Wastewater Treatment, Ideal International E-Publication Pvt. Ltd., Indore, 1-32.
Moeck, I., Uhlig, S., Loske, B., Jentsch, A., Ferreiro Mahlmann, R. and Hild, S. (2015) Multiphase Normal Faults—Prime Targets for Geothermal Drilling in the Bavarian Molasse Basin? Proceedings of the World Geothermal Congress 2015, Melbourne, 19-25 April 2015, 1-7.
Chelle-Michou, C., Do Couto, D., Moscariello, A., Renard, Ph. and Rusillon, E. (2017) Geothermal State of the Deep Western Alpine Molasse Basin, France-Switzerland. Geothermics, 67, 48-65. https://doi.org/10.1016/j.geothermics.2017.01.004
Laplaige, Ph., Lemale, J., Decottegnie, S., Desplan, A., Goyeneche, O. and Delobelle, G. (2005) Geothermal Resources in France—Current Situation and Prospects. Proceedings of the World Geothermal Congress 2005, Antalya, 24-29 April 2005, 1-13.
Jaudin, F., Le Brun, M., Bouchot, V. and Dezaye, C. (2009) French Geothermal Resources Survey, BRGM Contribution to the Market Study in the LOW-BIN Project (TREN/05/FP6EN/S07.53962/518277). Report BRGM/RP-57583-FR, 39 p.
Dentzera, J., Lopezc, S., Violettea, S. and Bruelda, D. (2016) Quantification of the Impact of Paleoclimates on the Deep Heat Flux of the Paris Basin. Geothermics, 61, 35-45. https://doi.org/10.1016/j.geothermics.2016.01.006
Aichholzer, C., Duringer, Ph., Orciani, S. and Genter, A. (2016) New Stratigraphic Interpretation of the Soultz-sous-Forêts 30-Year-Old Geothermal Wells Calibrated on the Recent One from Rittershoffen (Upper Rhine Graben, France). Geothermal Energy, 4, Article No. 13. https://doi.org/10.1186/s40517-016-0055-7
Sanjuan, B., Négrel, G., Le Lous, M., Poulmarch, E., Gal, F. and Damy, P.C. (2021) Main Geochemical Characteristics of the Deep Geothermal Brine at Vendenheim (Alsace, France) with Constraints on Temperature and Fluid Circulation. Proceedings of the World Geothermal Congress 2020 + 1, Reykjavik, April-October 2021, 1-12.
Baujard, C., Rolin, P., Dalmais, E., Hehn, R. and Genter, A. (2021) Soultz-sous-Forêts Geothermal Reservoir: Structural Model Update and Thermo-Hydraulic Numerical Simulations Based on Three Years of Operation Data. Geosciences, 11, Article 502. https://doi.org/10.3390/geosciences11120502
Liotta, D., Brogi, A., Ruggieri, G. and Zucchi, M. (2021) Fossil vs. Active Geothermal Systems: A Field and Laboratory Method to Disclose the Relationships between Geothermal Fluid Flow and Geological Structures at Depth. Energies, 14, Article 933. https://doi.org/10.3390/en14040933
Gola, G., Bertini, G., Bonini, M., Botteghi, S., Brogi, A., De Franco, R., Dini, A., Donato, A., Gianelli, G., Liotta, D., Manzella, A., Montanari, D., Montegrossi, G., Petracchini, L., Ruggieri, G., Santilano, A., Scrocca, G. and Trumpy, E. (2017) Data Integration and Conceptual Modelling of the Larderello Geothermal Area, Italy. Energy Procedia, 15, 300-309. https://doi.org/10.1016/j.egypro.2017.08.201
Bargiacchi, E., Conti, C., Manzella, A., Vaccaro, M., Cerutti, P. and Cesari, G. (2021) Thermal Uses of Geothermal Energy, Country Update for Italy. Proceedings of the World Geothermal Congress 2020 + 1, Reykjavik, April-October 2021, 1-15.
Baba, A. and Sözbilir, H. (2012) Source of Arsenic Based on Geological and Hydrogeochemical Properties of Geothermal Systems in Western Turkey. Chemical Geology, 334, 364-377. https://doi.org/10.1016/j.chemgeo.2012.06.006
Carlos Nunes, J., Coelho, L., Carvalho, J.M., do Rosário Carvalho, M. and Garcia, J. (2021) Portugal Country Update 2020. Proceedings of the World Geothermal Congress 2020 + 1, Reykjavik, April-October 2021, 1-12.
Vogt, P.R. and Jung, W.Y. (2004) The Terceira Rift as Hyper-Slow, Hotspot-Dominated Oblique Spreading Axis: A Comparison with Other Slow-Spreading Plate. Earth and Planetary Science Letters, 218, 77-90. https://doi.org/10.1016/S0012-821X(03)00627-7
Franco, A., Guimarães, T. and Henneberger, R. (2018) Geothermal Geology of the Outflow Zone of the Ribeira Grande Geothermal System, São Miguel Island, Azores. GRC Transactions, 42, 1316-1326.
Khodayar, M., Björnsson, S., Kristinsson, S.G., Karlsdóttir, R., ólafsson, M. and Víkingsson, S. (2018) Tectonic Control of the Theistareykir Geothermal Field by Rift and Transform Zones in North Iceland: A Multidisciplinary Approach. Open Journal of Geology, 8, 543-584. https://doi.org/10.4236/ojg.2018.86033
Khodayar, M., Björnsson, S., Guðnason, E.á., Níelsson, S., Axelsson, G. and Hickson, C. (2018) Tectonic Control of the Reykjanes Geothermal Field in the Oblique Rift of SW Iceland: From Regional to Reservoir Scales. Open Journal of Geology, 8, 333-382. https://doi.org/10.4236/ojg.2018.83021