Potential assessment of CO2 injection for heat mining and geological storage in geothermal reservoirs of China

Supercritical CO2 has good mobility and certain heat capacity, which can be used as an alternative of water for heat recovery from geothermal reservoirs, meanwhile trapping most of injected CO2 underground to achieve the environmental benefits. In this paper, different types of geothermal resources are assessed to screen reservoirs suitable for heat mining and geological storage by CO2 injection, in terms of geological properties, heat characteristics, storage applicability, and development prospects, etc. Hot dry rock, deep saline aquifer, and geopressured reservoir are selected as the potential sites for this study, mainly due to their relatively positive geological conditions for CO2 circulation and storage. Reservoir simulations are conducted to analyze the heat extracting capacity and storage efficiency of CO2 in the promising geothermal reservoirs. A simple calculation method is presented to estimate the potentials of heat mining and CO2 storage in the major prospective geothermal regions of China. The preliminary assessment results show that the recoverable geothermal potential by CO2 injection in China is around 1.55×1021J with hot dry rocks as the main contributor. The corresponding CO2 storage capacity is up to 3.53×1014kg with the deep saline aquifers accounting for more than 50%. CO2 injection for geothermal production is a more attractive option than pure CO2 storage due to its higher economic benefits in spite of that many technological and economic issues still need to be solved in the future.