Sustainable geo-energy technologies, including geothermal energy, hydrogen/carbon dioxide capture, utilization, and storage, and aquifer thermal energy storage, have received significant attention from the global scientific community and industry due to their pivotal roles in achieving international decarbonization targets. While numerous stand-alone simulation tools to assess the feasibility of these geo-energy systems have been developed, existing tools often focus on simulating individual components, such as subsurface, wellbore, surface, and economic. Relying solely on such tools tends to overlook the comprehensive techno-economic evaluation of these integrated geo-energy systems. Although some simulation tools with integrated modeling capabilities exist, their flexibility and extendibility to various geo-energy systems remain limited. We present TANGO, an acronym for Techno-economic ANalysis of Geo-energy Operations, which is a newly developed integrated techno-economic simulation tool designed to offer flexibility, allowing for a comprehensive evaluation of various geo-energy operations across different fidelity levels. The applications of TANGO to a series of numerical examples of geothermal systems utilizing carbon dioxide (e.g. CO₂ Plume Geothermal – CPG), ranging from rapid site screening with the low fidelity modeling capability to detailed simulation studies using the high-fidelity modeling capability, will be presented to demonstrate TANGO’s distinctive features and capabilities.

How to cite: Onishi, T., Esmaeilpour, M., Leal, A., Huang, P., and Saar, M.: Techno-economic Analysis of Geothermal Operations Utilizing Carbon Dioxide, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21517, https://doi.org/10.5194/egusphere-egu24-21517, 2024.

Geothermal energy production and CCS (Carbon Capture and Storage) represent promising technological solutions to help mitigate climate change and aid the current global energy crisis. In recent years, the number of concepts that propose to combine and mutualize these technologies has risen dramatically. While a number of concepts (notably CPG and CO₂-EGS) use supercritical CO₂ as the heat vector, another promising route for hybridization is to inject dissolved CO₂ in the geothermal brine. This is the focus of our current work. An extensive literature review was carried out of the concepts, complemented by interviews of some of the developers.

A few concepts are still theoretical (only described in the literature), but most technological ones are on the way to pilot/demonstration projects at progressively increasing scale. The main projects and their associated sites are:

• CO₂-DISSOLVED technology, with potential sites identified in the Paris basin (France);
• AAT-G / Cleag technology, with a site in Croatia;
• Related projects CarbFix, GECO and SUCCEED, with sites in Hellisheidi (Iceland), Nesjavellir (Iceland), Bochum (Germany), Kızıldere (Turkey), Castelnuovo in Italy (as case study due to permitting issues);
• Reinjection of CO₂ from geothermal brines at Ngatamariki and Te Huka sites in New Zealand.

Despite similarities, these solutions are differentiated by their purpose:

• either to store CO₂ from an external industrial emitter (notably for the CO₂-Dissolved concept), thus bringing a contribution to CCS,
• or to reinject CO₂ emitted by CO₂-rich brine during geothermal exploitation, thus bringing geothermal to near-zero emissions.

Because of the CO₂ solubility limit in brine, the performance of heat extraction is generally higher than that of CO₂ storage. For instance the CO₂-DISSOLVED technology is particularly well-suited to small CO₂ industrial emitters (ca. <150,000 t CO₂/year). Unlike concepts using supercritical CO₂, those using dissolved CO₂ can be deployed at much lower depths (no need to exceed the supercritical point). The concepts still need a tight caprock, but the high solubility trapping represents a lower risk of leakage. The geothermal system behaves mainly as a water-driven system, but the adjunction of dissolved CO₂ can in some cases increase thermo-hydrological performance (pH decrease might avoid clogging and/or open porosity in carbonate reservoirs).

A number of challenges still need to be addressed, including complexity of regulations and validation of some technical aspects. Besides, considering the variety of underground configurations, there is no turnkey solution, which might hamper the economics of such small-scale projects.

Acknowledgements: This work is in part taken from a study published in the report ‘IEAGHG, “Prospective integration of Geothermal Energy with Carbon Capture and Storage (CCS)”, 2023-02, August 2023’. We are grateful to IEAGHG, especially to Nicola Clarke, for proposing and funding this topic and for interesting scientific discussions and debates as part of this work.

How to cite: Loschetter, A., Kervévan, C., Stead, R., and Le Guénan, T.: Water-driven geothermal heat extraction with simultaneous CO2 injection: overview of concepts, benefits and challenges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10031, https://doi.org/10.5194/egusphere-egu24-10031, 2024.

The properties of carbon dioxide (CO2) under deep geologic conditions make it an excellent subsurface working fluid in geothermal systems, including CO2-Plume Geothermal (CPG) systems, Enhanced Geothermal Systems (EGS), and deep closed-loop Advanced Geothermal Systems (AGS). Supercritical CO2’s low viscosity, high density, and high thermal expansion coefficient render CO2 a highly efficient energy transfer, extraction, and storage fluid. These properties typically overcompensate the lower specific heat capacity of CO2, compared to brine, which is the conventional working fluid underground. Furthermore, CO2 can also reduce fluid-mineral reactions, such as mineral precipitation, which often clog reservoirs, wells, and equipment. Applying geothermal energy extraction to CO2 Capture and Sequestration (CCS) in deeper reservoirs results in true CO2 Capture Utilization and Sequestration (CCUS), enabling these projects to ultimately sequester all initially injected CO2 underground at reduced cost. In this presentation, I give an overview of how CO2 can be used to efficiently produce geothermal energy, store surface-generated energy underground, and/or support CCS operations to promote energy security while combating climate change.

How to cite: Saar, M. O.: Overview of how subsurface carbon dioxide promotes geothermal energy extraction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10470, https://doi.org/10.5194/egusphere-egu24-10470, 2024.

Subsurface reservoirs play an important role in decarbonizing the energy sector, be it through geothermal energy production or carbon capture and storage (CCS). In recent years, there has been an increasing interest in CO₂-Plume Geothermal (CPG), which combines CCS with geothermal, using CO₂ instead of water as a subsurface heat and pressure energy carrier. CO₂ as a subsurface working fluid is more efficient as it has a higher mobility (inverse kinematic viscosity) and its large thermal expansion coefficient results in a thermosiphon effect that reduces the pumping power required. CO₂ can also be directly utilized in a turbine for power generation. Furthermore, since CPG systems are added to full-scale CO₂ Capture and Sequestration operations, all of the initially injected CO₂ is ultimately stored. CPG therefore constitutes both CO₂ Capture Utilization as well as Storage (i.e. CCUS).

In recent years, CPG has experienced increasing interest from academia and industry. Several in-depth studies have assessed the impact of various parameters such as the geothermal gradient, wellbore diameter or reservoir permeability on the CPG performance. However, these studies have not evaluated the potentially significant impact of the varying ambient conditions on the CPG performance profile. The potential effect of the air temperature on the CPG performance has only been discussed in a paper by Adams and Kuehn (2012) and in a more recent work by van Brummen et al. (2022), but without considering the the off-design behaviour of the main components, such as the turbine or compressor. This contribution assesses and discusses how the CPG performance profile might vary across several geographical settings and how the design point of the CPG components affect their achievable net power outpt. Therefore, valuable insights regarding the most attractive settings for future CPG systems can be drawn.

How to cite: Schifflechner, C. and Spliethoff, H.: The impact of the ambient conditions and component’s part-load behaviour on the actual annual power output of CO2-Plume Geothermal (CPG) systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12517, https://doi.org/10.5194/egusphere-egu24-12517, 2024.

The urgent need to combat climate change underscores the importance of reducing anthropogenic CO2 levels in the atmosphere through geological sequestration. While Carbon Capture and Storage(CCS) has been applied in various settings and has demonstrated its potential over the recent decades, economic challenges associated with CCS continue to be a significant barrier to its extensive large-scale implementation. This abstract discusses a promising solution: using CO2 as a geothermal working fluid to extract heat from deep, naturally porous, and permeable geologic formations, a concept known as CO2 Plume Geothermal (CPG). Oil fields in particular are attractive candidates for the deployment of CPG due to the presence of existing well infrastructure, extensive reservoir and production data, and an effective caprock. This innovative approach not only enables enhanced oil recovery through CO2-EOR, at an initial stage, and sustainable power generation but also ensures permanent carbon sequestration. Consequently, CPG in oil fields can serve as a catalyzer to deploying large-scale CCS projects, leveraging multiple co-benefits such as energy offset, decarbonization, carbon market development, and extended operational field life.

Through a combination of advanced non-isothermal and compositional numerical reservoir models, we comprehensively examine the geotechnical feasibility of deploying CPG at oil fields. The primary objectives of this study include evaluating the geothermal energy extraction efficiency, assessing the economic and environmental co-benefits, and addressing associated performance uncertainties. Building on crucial insights from existing CO2-EOR studies, we consider factors such as the mobility differences between injected and displaced fluids, interactions between CO2, oil, reservoir brine, and rock, and flow channeling through high-permeability pathways created by the heterogeneous nature of geological reservoirs. Furthermore, we delve into the thermal and compositional variations within the reservoir induced by water flooding operations during the secondary oil recovery stage, analyzing their effects on CPG performance in comparison to unperturbed saline aquifers. Integrating geothermal energy production, enhanced oil recovery, and permanent carbon sequestration, CPG in oil reservoirs can advance the integration of renewable energy and greenhouse gas management in the global effort to combat climate change.

How to cite: Kucuk, S., Brehme, M., Farajzadeh, R., Rossen, W., and Saar, M. O.: Simulation of CO2 Injection in Mature Oil Fields: Implications for Geothermal Energy Generation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12872, https://doi.org/10.5194/egusphere-egu24-12872, 2024.

CO2-Plume Geothermal (CPG) is a technology that employs the benefit of CO2 as a geothermal working fluid to turn CCS into CCUS (Carbon Capture, Utilization and Storage), both by producing more power compared to conventional geothermal systems (Randolph and Saar, 2011), as well as improving the performance of the base CO2 storage project. Following a decade of research, a CPG consortium has started in March 2023 to pave the way for de-risking this emerging technology to a Technology Readiness Level (TRL) of 7. This industry-academic initiative unlocks a larger joint portfolio of opportunities, financing options and domain knowledge, thereby enabling a systematic and standardized approach to evaluating candidate CPG field demonstration sites and concepts. A workflow is presented to define several potential field demonstration concepts, leveraging site-specific risk registers, opportunity framing sessions, competitive scoping and multi-scenario modelling. Using a trade-off table, the highest value field demonstration project can be selected for execution in the subsequent phase of the CPG consortium.

How to cite: de Reus, A. J., Onishi, T., Brehme, M., Games, F., Hau, K. P., Hefny, M., Kucuk, S., Kong, X.-Z., Pokras, D., Rangel Jurado, N., and Saar, M. O.: De-risking CO2-Plume Geothermal (CPG) for commercial field deployment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16553, https://doi.org/10.5194/egusphere-egu24-16553, 2024.

Advanced Geothermal Systems (AGS) are power systems that harness energy by circulating a working fluid through a closed-loop circuit, extracting thermal energy from deep geologic reservoirs via conductive heat transfer across an impermeable wellbore wall. AGS benefit from using carbon dioxide (CO2) as the working fluid within the wellbores, at least for electricity generation and possibly also for direct heat usage. Here, we investigate a range of configurations for combined electricity and heat production. These designs aim to enhance flexibility and efficiency in AGS while reducing system costs. Central to this research is formulating an optimal AGS pilot plant design, complemented by a comprehensive techno-economic feasibility study. Compared to the design benchmarks of previous work on AGS for electricity generation only, this optimization yields an improvement in the Specific Capital Cost (SpCC) by approximately 215%. Furthermore, by incorporating heat co-generation with electricity, the SpCC is considerably further reduced. 

How to cite: Pokras, D., Hefny, M., Huang, P., and Saar, M. O.: Techno-Economic Optimization of a CO2-based Advanced Geothermal System (AGS), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19014, https://doi.org/10.5194/egusphere-egu24-19014, 2024.

Mitigating the global climate crisis is the greatest challenge facing humanity this
century. The transition of current energy systems towards carbon-neutral energy
is inevitable. Renewable energy sources, particularly those that are both baseload-
and dispatch-capable, such as geothermal energy, are essential to replace current
energy systems that emit large amounts of CO₂. In addition, permanent isolation
of CO₂ from the atmosphere, using carbon capture and sequestration (CCS), is
indispensable to limit global warming to 1.5°C.
To enable the full potential of geothermal energy extraction and of CCS, their
efficiencies need to be improved. One possibility is to integrate both technologies.
Using CO₂ as the geothermal energy extraction fluid approximately doubles energy
generation rates, compared to conventional, brine-based geothermal systems under
our base-case conditions. Such CO₂ Plume Geothermal (CPG) systems reinject
the produced CO2, eventually sequestering all CO₂ underground. Extracting the
geothermal energy from the CCS reservoir results in additional CO₂ storage poten-
tial, as, for example, the CO₂ density increases and the overall reservoir pressure
decreases. The CPG-generated heat, electricity, and/or revenue could “subsidise”
CCS operations. Consequently, CPG could increase both the geothermal energy
and the CCS capacities.
Our CPG feasibility study combines an integrated production system modeling
approach with a history-matched reservoir model of an active CCS site (Aquistore,
Canada). The integrated modeling approach is used to account for all relevant
processes, from well-bore pressure and temperature drops to multi-phase, multi-
component fluid flow in the reservoir to fluid separation, power generation, and
continuous with reinjection of CO₂ at the land surface, in a fully implicit matter.
Our results suggest that stable CO₂ circulation, extracting geothermal energy
between the underground CO₂ plume in the saline reservoir and the land surface,
is possible. Furthermore, we see additional CO₂ storage potential, caused by the
circulation of CO₂. Our simulations indicate that Aquistore may provide a unique
opportunity for pioneering a CPG field test.

How to cite: Hau, K. P., Brehme, M., Rangriz-Shokri, A., Malakooti, R., Nickel, E., Chalaturnyk, R. J., and Saar, M. O.: Integrated reservoir and production system modeling of geothermal energy extraction at the Aquistore CCS site in Canada, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19289, https://doi.org/10.5194/egusphere-egu24-19289, 2024.

Geothermal energy is poised to play a pivotal role in the renewable energy transition by providing baseload, dispatchable, and carbon-free heat and power. Nonetheless, in contrast to its renewable energy alternatives, such as solar or wind, geothermal energy is harnessed beneath the Earth’s surface, inherently increasing the challenges, risks, uncertainties, and opportunities related to its exploration and utilization. As a result, numerous concepts and field development strategies for exploiting geothermal energy have been proposed over the last century. The seemingly overwhelming abundance of choices has prompted widespread confusion regarding the optimum approach to developing geothermal energy across multiple sectors. In this study, we attempt to answer this question by conducting a scenario analysis consisting of three geological reservoirs developed through various geothermal technologies to generate heat and electricity. Stochastic analyses for each of the geological reservoirs considered is also performed in a second set of simulations to account for subsurface uncertainties. Using a combination of advanced numerical simulators, we evaluate and compare the techno-economic performance of water-based geothermal systems (i.e., Conventional Hydrothermal Systems, Enhanced Geothermal Systems (EGS) and Advanced Geothermal Systems (AGS)) against their conceptual counterparts that use CO₂ as the subsurface working fluid (i.e., CO₂ Plume Geothermal (CPG), CO₂-EGS, and CO₂-AGS). Our results show that water-based energy extraction and open-loop configurations distinctly favor higher production temperatures owing to the superior thermodynamic properties of water and the ability to accommodate larger reservoir volumes, respectively. However, these operating conditions also exhibit lower heat-to-electricity conversion efficiencies, thereby significantly impacting economic returns when electricity generation is intended. In contrast, the value of CO₂-based energy extraction and closed-loop configurations, to some extent overlooked in direct-heat-use applications, is considerably highlighted when targeting electricity production. Our work underscores the critical interplay between a geothermal reservoir's thermal and hydraulic performances across various system types. A comprehensive analysis of the relationships exposed in this study can assist geothermal operators in selecting appropriate end-user applications, predicting long-term reservoir performance, and ultimately enhancing the economic success of geothermal projects.

How to cite: Rangel Jurado, N., Kucuk, S., Pokras, D., Degen, D., Games, F., Brehme, M., and Saar, M.: The Geothermal Paradox of Choice: A Comparative Techno-Economic Assessment of Geothermal Energy Production for Heat and Power Applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21446, https://doi.org/10.5194/egusphere-egu24-21446, 2024.