Comparative study on heat extraction performance of three enhanced geothermal systems

Abstract

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 CO2. This study provides a reference for geothermal mining simulation and reservoir stimulation strategy selection.