Potential Assessment of CO2 Geological Storage in Geothermal Reservoirs Associated with Heat Mining: Case Studies from China

Abstract

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 environmental benefits. In this paper, different types of geothermal resources are assessed to screen reservoirs suitable for geological storage and heat mining by CO2 injection, in terms of geological properties, heat characteristics, storage applicability, and development prospects, etc. Deep saline aquifer, geopressured reservoir and hot dry rock are selected as the potential sites, mainly due to their relatively positive geological conditions for CO2 circulation and storage. Reservoir simulations are conducted to analyze the storage efficiency and heat extracting capacity of CO2 in the promising geothermal reservoirs. A simple calculation method is presented to estimate the potentials of CO2 storage and heat mining 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 1.55×1021 J with hot dry rocks as the main contributor. The corresponding CO2 storage capacity is up to 3.53×1014 kg 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.