Impact of Reservoir Permeability on the Choice of Subsurface Geothermal Heat Exchange Fluid: CO2 Versus Water and Native Brine

Abstract

Geothermal systems utilizing carbon dioxide (CO2) as the subsurface heat exchange fluid in naturally porous, permeable geologic formations have been shown to provide improved geothermal heat energy extraction, even at low resource temperatures. Such systems, termed CO2 Plume Geothermal (CPG) systems, have the potential to permit expansion of geothermal energy utilization while supporting rapid implementation through the use of existing technologies. Here, we explore CPG heat extraction as a function of reservoir permeability and in comparison to water and brine geothermal heat extraction. We show that for reservoir permeabilities below 2x10-14 to 2x10-13 m2, depending on formation temperature and pressure, CPG provides better electric power production efficiency than both water- and brine-based systems.