Investigation on the influence of fracture characteristics on thermal recovery in supercritical carbon dioxide enhanced geothermal systems (CO2 -EGS)

Abstract To investigate the thermal extraction performance of supercritical carbon dioxide (ScCO2) in enhanced geothermal systems (EGS) with the influence of hydraulic fractures and natural fractures, the hydraulic fractures in EGS were abstracted, and four geometric models were established and numerically solved. The permeability field, temperature field, and stress field of the model were analyzed to elucidate the interaction mechanism between ScCO2 and hot dry rock reservoirs. The results indicate that an increase in the number of hydraulic fractures can promote heat transfer of ScCO2 within the system, but the relationship is not entirely linearly correlated between them and may lead to early thermal breakthrough in the system. The hydraulic fractures perpendicular to the flow direction of ScCO2 will form non-connected fracture zones that will hinder the convective heat transfer within the system. Differences in hydraulic fracture characteristics can also cause significant variations in flow velocity and pressure within the system. The increase in the number of hydraulic fractures results in more granite blocks being segmented, leading to significant changes in the stress field, thereby ultimately reducing porosity and permeability. The results of this study can provide theoretical guidance for the construction of hydraulic fractures during geothermal development.