The fracture characteristics and dynamic response to hydraulic fracturing in the Gonghe enhanced geothermal system (EGS) field, Qinghai Province, Northwest China

Enhanced geothermal systems (EGS) rely on hydraulic fracturing in strata with abundant natural fractures to create fracture networks for efficient geothermal energy extraction. However, fundamental research on fracturing technologies for high-temperature hot dry rock (HDR) in EGS development remains limited. Taking the case of the Gonghe EGS project in China, this research explores the characteristics of in-situ stress and natural fractures in the reservoir using measured data, while also analyzing the influence of in-situ stress on HDR reservoir development. Additionally, the Coulomb Failure Function (CFF), sliding trend (T s ), and dilation tendency (T d ) were calculated to analyze fracture activity at depths of 3600–3800 m under varying injection pressures. Finally,reservoir fracturing effectiveness was evaluated based on microseismic and time-frequency electromagnetic monitoring data collected during hydraulic stimulation. The results reveal that the granite reservoir (1500–4000 m) exists in a strike-slip and thrust geostress transition zone dominated by horizontal compressive stress. Furthermore, the suitable fracturing pressure for the Gonghe HDR field is 46–54 MPa, and fractures remain open after shear activation (high-dilation tendency). The sliding trend results are supported by the spatial distribution of recorded microseisms. In-situ stress and monitoring results indicate that natural fractures expand both horizontally and vertically during hydraulic fracturing, ultimately forming a horizontal-vertical fracture network. Our findings provide significant insights into fracture activity and opening characteristics during hydraulic fracturing of granite geothermal reservoirs.