Abstract
It is of great significance for the sustainable development of global energy to develop hot dry rock (HDR) geothermal resources by using enhanced geothermal system (EGS) technology. Different working fluids in EGS have different heat recovery efficiencies. Therefore, this paper takes water and CO2 as the heat-carrying media and establishes a thermal hydraulic mechanical coupling model to simulate the heat recovery process in high-temperature rock mass. By considering the different confining pressures, rock temperature, and injection pressure, the advantages of H2O-EGS and CO2-EGS are obtained. The results show that with the increase of confining pressure, the heat recovery efficiency of water is significantly higher than that of CO2, but at higher reservoir temperature, CO2 has more advantages as a heat-carrying medium. The net heat extraction rate will increase with the increase of injection pressure, which indicates that the mass flow rate plays a leading role in the heat recovery process and increases the injection pressure of fluid which is more conducive to the thermal recovery of EGS. This study will provide a technical guidance for thermal energy exploitation of hot dry rock under different geological conditions.
Highlights
The huge consumption of coal, oil, and other fossil fuels leads to energy crisis and causes significant environmental and climate problems [1, 2]
This study focuses on the influence of the change of reservoir seepage field, reservoir temperature field, and reservoir stress field on the seepage and heat transfer of a heatcarrying medium, establishes a thermal-fluid-solid coupling model, and, respectively, analyzes the influence of injection pressure, sample temperature, and the change of confining pressure on the heat recovery efficiency when H2O and CO2 are used as working fluids
CO2 injection, it is found that the net heat extracted after water injection is slightly higher than that of CO2 injection mm Temperature (K) mm mm (a) 26 MPa confining
Summary
The huge consumption of coal, oil, and other fossil fuels leads to energy crisis and causes significant environmental and climate problems [1, 2]. Some scholars pointed out that the use of H2O-EGS will cause a lot of water resource loss [13] and cause a series of problems that are not conducive to the operation and maintenance of geothermal system [14,15,16,17]. To solve these problems, in 2000, Brown first proposed that it can use supercritical CO2 (SCCO2) instead of water as a heat-carrying medium [18]. This study will provide technical guidance for improving hot dry rock productivity under different geological conditions
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