CARBON-DIOXIDE PLUME GEOTHERMAL (CPG) SYSTEMS, AN ALTERNATIVE ENGINEERED GEOTHERMAL SYSTEM (EGS): NET ENERGY PRODUCTION POTENTIAL COMPARED TO TRADITIONAL WATER-BASED GEOTHERMAL SYSTEMS

In a carbon dioxide plume geothermal (CPG) system, carbon dioxide (CO₂) is pumped into existing geologic formations with sufficiently high permeability and porosity that reservoir-scale artificial stimulation is not required, and which are overlain by a low-permeability caprock. The resulting CO₂ plume largely displaces native formation fluid and is heated by the natural in-situ heat and background geothermal heat flux. A portion of the heated CO₂ is piped to the surface to produce power and/or to provide heat for direct use before being returned to the subsurface. Non-recoverable CO₂ in the subsurface is geologically sequestered, serving as a CO₂ sink. Besides improving electricity production efficiencies compared to water, all else being equal, this approach results in a geothermal power plant with a negative carbon footprint.

Here, we compare the geothermal heat energy extraction and power production potentials of CPG and traditional water-based geothermal approaches. Included in this analysis are the consequences of a CO₂ thermosyphon, which reduces CO₂ pumping requirements, and choice of power system configuration. While additional research is required, numerical simulation results at present suggest CPG systems would be viable geothermal energy sources for electric power production, even in regions with low geothermal temperatures, low heat flow rates, and/or relatively low permeability geologic formations.