Comparative study on heat extraction performance of three enhanced geothermal systems

Enhanced geothermal systems(EGSs)in this study are classified as fracturing-EGS(F-EGS),pipe-EGS(P-EGS)and excavation-EGS(E-EGS)according to reservoir stimulation strategies.However,the heat extraction performances of three EGSs employing different stimulation strategies are not fully understood.Here,we define the region where the pore pressure increment calculated by a hydraulic fracturing process is higher than rock tensile strength as the stimulation region for establishing a more accurate F-EGS model,and then compare three geothermal systems to select a appropriate reservoir stimulation strategy.We find that the F-EGS model assuming an entire stimulated region significantly exaggerates the heat extraction results.The optimal conditions for P-EGS are low injection rates and short operation times,which is suiTablefor seasonal heating or multi-energy co-generation projects including a thermal recovery phase.Theoretically,E-EGS has better geothermal extraction performance than F-EGS based on existing model assumptions,but its construction feasibility and economics need further exploration.H2O is more suiTableas a heat exchange fluid in E-EGS than supercritical CO_(2).This study provides a reference for geothermal mining simulation and reservoir stimulation strategy selection.