Abstract: In the long-term mining process of the fractured thermal reservoir of the enhanced geothermal system (EGS), due to the constant extraction of heat from the high-temperature dry hot rock mass, the temperature of the high-temperature granite mass drops, which induces the secondary fracture of the rock mass, and even the occurrence of fluid short circuit reduces the mining efficiency of the geothermal system. In order to ensure the stable extraction of EGS heat energy, it is necessary to establish the coupling model of fluid-solid heat transfer, hydrodynamic and fracture deformation in the test site, and analyze the influence of hydrodynamic and thermal effects on the fracture development law of the reservoir. Based on the test data of circulating water injection at the EGS development site in Matouying Bulge area, Hebei Province, this paper established a coupling model of thermo-hydro-mechanical (THM) of microfractures in the site. The accuracy of the THM coupling model was verified by comparing the model simulation results with the field observation results. The increase of permeability of EGS reservoir and the spatial range of stimulation zone reveal that the range of stimulation zone of reservoir fracture is affected by temperature, pressure and injection flow. The results show that increasing the water injection pressure can stimulate the shear fracture of existing fractures and broaden the area of stimulation zone. Reducing the temperature of water injection can improve the permeability of fluid and expand the reservoir stimulation zone. In the initial stage of hydraulic fracturing, the proper use of cold water injection is conducive to improving the reservoir permeability, and increasing the injection flow will expand the range of reservoir stimulation zone.

Key words:  , enhanced geothermal system (EGS), hydraulic fracturing, Matouying uplift area, thermo-hydro-mechanical modeling(THM), TOUGH2Biot