Comparison of Production Characteristics of A Horizontal-Well Multi-Fracture Enhanced Geothermal System With Co2 and Water

The horizontal-well multiple-fracture enhanced geothermal system (EGS) is expected to be a significant approach to effectively developing the hot dry rock (HDR). The reasonable selection of the working fluid plays a significant role in the EGS performance. Nevertheless, the application studies of the working fluid, particularly the CO2 and water, in the horizontal-well multiple-fracture EGS are rarely implemented. Therefore, a flow and heat transfer model is established for the horizontal-well multiple-fracture EGS. Subsequently, the difference in flow and temperature fields between CO2 and water EGSs are comprehensively investigated. The influences of CO2 and water on the production characteristics of the horizontal-well multiple-fracture EGS are compared. The results show that the geothermal reservoir with water circulating has a serious thermal breakthrough and the injection pressure is remarkably higher than that with CO2 circulating. The water is beneficial to enhance heat extraction, while the energy efficiency is lower than that of CO2 EGS. The efficiency of the fluid production of the CO2 EGS is noticeably higher although the difference in the fluid production between CO2 and water EGSs is minor. Further EGS economic analysis indicates that fluid selection is closely related to the injection rate. The CO2 is preferred when the injection rate is relatively high, while the water is favorable if a low injection rate is applied. The findings offer a valuable reference for the scientific study of the EGS working fluid, particularly the horizontal-well multi-fracture EGS.