Potential of CO2 based geothermal energy extraction from hot sedimentary and dry rock reservoirs, and enabling carbon geo-sequestration

Carbon capture and sequestration (CCS) is necessary to mitigate global warming caused by anthropogenic CO2 emissions in the atmosphere. However, due to very high storage cost, it is difficult to sustain the CCS industry. The hot sedimentary and dry rock reservoirs with very high temperature can support both geothermal energy production, and carbon geosequestration economically, provided the CO2 is used as a heat-carrying fluid with proper optimization of injection parameters according to reservoir conditions. In this paper we have reviewed past studies discussing the working mechanisms, pressure management strategies and various advantages of energy extraction from hydrothermal reservoirs by CO2 plume geothermal technology and hot dry rock-enhanced geothermal system (EGS) technology. Past studies highlighted that due to very high thermal expansivity and mobility, supercritical CO2 can produce more heat than water-EGS. For low enthalpy (around 50 degrees C) and shallow (0.5-1.5 km) reservoirs, CO2 can fetch more heat than water because of higher heat capacity. Other advantages of CCS and EGS are (i) the production of brine or CO2 assisting to manage the reservoir pressure and restrict the fluid interference with neighboring reservoirs, (ii) the fluid loss, which is a significant concern in a water-EGS but for CO2-EGS it is environmentally friendly, and (iii) higher pressure and cold fluid injection induced geological deformation and microseismicity are relatively less for CO2-EGS than water-EGS. In this paper, we have also discussed various challenges of CO2-EGS to enable CCS in hydrothermal reservoir and hot dry rock system.