Abstract:

To simulate hydraulic fracturing and heat injection and extraction effect in hot dry rock reservoir, we established a  thermo-hydro-mechanical  coupling hydraulic fracture propagation and heat transfer model for simulating the complex fracturing fracture morphology of dry hot rock and conducting injection-production thermal analysis. Taking the hot dry rock（HDR） in Qinghai Gonghe basin as a reference, we constructed two case considered the geo-mechanical parameter characteristics and simulated the multi-well fracturing and heat recovery process, the numerical results of fracturing and heat injection and recovery show that: In HDR, the fracture initiation is influenced by the non-uniform stress field, exhibiting volumetric fracture characteristics. Fractures created through multi-well fracturing connect via natural fractures, providing over 95% of the heat exchange flow channels for heat injection and production. During heat injection and production, fluid mainly flows along the connected fractures, forming dominant heat exchange channels. This leads to a significant decrease in outlet temperature during the initial stage of heat injection and production, with the outlet water temperature dropping by 30-50 ℃ within the first three years, followed by a gradual slowdown in the later stages. Enhanced fracture complexity can increase effective heat transfer area, while optimized well placement and injection-production parameters improve thermal efficiency, enabling sustainable geothermal energy exploitation.

Key words: hot dry rock, hydraulic fracture propagation, natural fracture, heat recovery, thermo-hydro-mechanical coupling, discontinuous discrete fracture model, heat transfer, Qinghai Gonghe basin