Total Heat Energy Output from, Thermal Energy Contributions to, and Reservoir Development of Conventional, Hydrofractured, and CO2 Plume Geothermal (CPG) Systems

Abstract

CO2-Plume Geothermal (CPG) energy capture involves injecting CO2 into naturally-permeable sedimentary basins to serve as the working fluid for geothermal energy extraction. The injected CO2 forms a large subsurface CO2 plume that extracts heat energy from the reservoir, whereafter the CO2 is produced to the surface to drive a power system, is cooled and reinjected into the subsurface. While the heat density of sedimentary basins is typically relatively low, the large volume of such natural reservoirs accessible using CO2, compared to conventional and hydrofractured reservoirs, may counteract this limitation and in some cases surpass the total heat energy output possible from the latter. Here, we analyze the volume of CO2 that is required to form a CPG system as a function of the desired longevity of geothermal heat extraction, the reservoir temperature and depth, and the desired power production rate. In addition, we analyze the contribution of the reservoir rock/sediments, the native reservoir fluids, the over- and underlying low-permeability capping units, and the geothermal heat flux to the total extracted geothermal heat energy. To conclude, we show that, depending on system configuration and operation, a CPG system can operate for several decades with little decrease in produced fluid temperature.