Impacts of fracture network geometries on numerical simulation and performance prediction of enhanced geothermal systems

The effects of fracture distribution on the heat extraction performance of enhanced geothermal system (EGS) are very significant. Referring to lots of EGS fracturing projects, the fractures around wellbore are denser than other regions in fracture reservoir. Therefore, it is essential to understand the link between the thermal exploitation of EGS and fracture distributions around injection wells. We built a three-dimensional thermal-hydrologic (TH) coupling model to simulate thermal energy transfer and pressure distribution in reservoir. Taking Qiabuqia geothermal field as a case study, the impacts of fracture morphology (like length, quantity, position and complexity) on heat extraction are compared. The contributions of fracture networks’ aperture and permeability are also investigated. Results indicate that denser fracture network significantly improves heat extraction performance and extends system lifetime. Longer primary fracture length around injection wells decreases mass flow rate of working fluid and elevates fluid temperature at the exhausts of production wells. The non-uniform distribution of the primary fracture has negative effects on EGS performance. More complex and connected fractures lead to fluid loss, and larger fracture aperture and permeability decrease mass flow rate at the outlet of production wells. •Various complex fracture geometries around injection wells were simulated.•Denser fracture network around injection wells prolongs fracture reservoir lifetime.•Fracture length has opposite effects on production temperature and mass rate.•More interlacing fractures around injection wells lead to lower production mass rate.•Small fracture aperture and permeability increase heat extraction.