Professor Saar, chair of the Geothermal Energy and Geofluids (GEG.ethz.ch) group at ETH Zurich, and other researchers are exploring how this approach could transform CO2, currently considered a waste product, into a valuable resource for generating electricity. Indeed, CPG uses CO2 as a working fluid in geothermal power plants instead of geothermal brine.
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The implementation of CPG systems relies on a carefully designed process that maximises both energy production and carbon sequestration benefits. CPG works by first injecting CO2 into naturally permeable reservoirs, as is conventionally done in CO2 Capture and Sequestration (CCS) projects. However, CPG extends this process by extracting the geothermally heated CO2 in offset wells, turning CCS into CO2 Capture, Utilisation and Sequestration (CCUS). The produced CO2 powers turbines to generate electricity before being cooled, condensed and re-injected in the reservoir, ensuring the permanent sequestration of all of the captured CO2. In the process, CPG has the potential to generate over two times the power of conventional water-based geothermal systems due to its unique thermodynamic properties.
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CPG offers several benefits compared to regular geothermal systems. It helps CCUS projects work better and more economically by cooling the underground CO2, making it denser so more can be stored in the same space. Additionally, the CO2 itself becomes easier to control and monitor through production wells, making the system more efficient than in typical CCUS projects. Furthermore, the CPG-produced heat and/or electricity can be used for the CCS operations.
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While this technology shows great promise, several technical challenges need to be solved before it can be widely used. We can build on existing CO2-Enhanced Oil recovery and carbon capture projects, but we still need improvements in these key areas:
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• Creating systems that can handle the mix of CO2 and other underground fluids that come up during operation
• Designing special turbines that can efficiently convert CO2’s heat energy into electricity
• Improving cooling systems to effectively condense the CO2 after it generates power so it can be pumped back underground
• Developing comprehensive monitoring methods to ensure both the heat extraction and carbon storage parts work properly

These challenges necessitate extensive research and field testing before CPG can move from concept to commercial reality.
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The CPG Consortium (GEG.CPG.ethz.ch) was formed specifically to address these important questions, bringing together researchers and industry partners who are working to deploy this technology as part of the energy transition. Ad Terra is an active participant in this consortium, which is hosted by Prof. Saar’s Geothermal Energy and Geofluids group.
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The advancement of CPG technology represents a significant opportunity in our collective effort to develop integrated solutions for climate challenges. By reimagining CO2 as a working fluid rather than merely a waste product, CPG offers a pathway to transform carbon management by creating economic incentives that align with environmental objectives.
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Ad Terra participates in the CPG Consortium
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A CPG Consortium was formed in March 2023 to mature this technology. Leveraging the synergies of an end-to-end integrated academic and industry consortium, CPG systems can be investigated efficiently. The objective is to demonstrate the potential and technical feasibility of commercial-scale CPG to enable Final Investment Decisions (FIDs) on subsequent commercial-scale projects.
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A second phase of the consortium will focus on CPG field development optimisation and de-risking. Well location optimisation and the monetisation of additional CO2 storage space in the reservoir will be central to this effort. This will be achieved using the techno-economic simulator developed by the GEG group at ETH Zurich, TANGO, which is coupled to novel flow diagnostic models. The latter enables reservoir simulations to be conducted on the order of seconds instead of hours, a key enabler for the robust optimisation of CPG.
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Ad Terra, led by Federico Games, has played a pivotal role in helping the CPG Consortium achieve these objectives. It actively contributed to the development of CPG workflows, risk registers, and the exploration of synergies between geothermal energy and CCS.
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Don’t hesitate to visit the consortium website to stay updated.
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Note:

[1] Randolph, J.B., and M.O. Saar, Combining geothermal energy capture with geologic carbon dioxide sequestration, Geophysical Research Letters, 38, L10401, 2011. https://doi.org/10.1029/2011GL047265

[2] Randolph, J.B., and M.O. Saar, Combining geothermal energy capture with geologic carbon dioxide sequestration, Geophysical Research Letters, 38, L10401, 2011. https://doi.org/10.1029/2011GL047265