Numerical simulation of thermal performance of H2O-EGS and CO2-EGS based on thermal-hydraulic-mechanical coupling method

Abstract

The use of hydrothermal geothermal methods in Enhanced Geothermal Systems (EGS) presents challenges like reduced thermal storage life and high external energy consumption. Due to its stable heat production time and lower external energy demand, CO₂ has the potential to be substituted for H₂O. The research zone for this study was chosen to be located in the HDR reservoir in the Gonghe Basin of Qinghai. A three-dimensional discrete fracture model based on a thermal-hydraulic-mechanical coupling method is established, where numerical simulations are conducted using COMSOL software. The discussion focuses on the comparison of heat production effects between H₂O-EGS and CO₂-EGS in different injection and extraction scenarios are discussed. The results indicate that by lowering the injection temperature and increasing the injection rate, the EGS net heat production rate can be increased, but it also accelerates the heat breakthrough time and shortens the reservoir life. Although CO₂-EGS has a lower heat extraction rate in the early stage of thermal recovery than H₂O-EGS, it has a longer stable heat production time and a more energy-efficient heat production process. Therefore, compared to H₂O-EGS, CO₂-EGS has more economic and social benefits.