Abstract:The fracture network formed by hydraulic fracturing of deep hot-dry rocks is the fluid flow and heat exchange channel of the underground “cold injection, thermal production” circulation system. The essence of “difficult injection and low output” in circulating system is the conductivity fracture network system has not yet established between injection and production wells. The thermal (T) -hydraulic (H) -mechanical (M) -chemical (C) coupling determines the conductivity of the fracture network system. Laboratory tests and THMC coupling numerical simulation studies have proved that the deformation of natural fractures is the premise and mechanism of shearing stimulation. When the horizontal slip reaches 5mm, the effect of roughness on the crack opening will disappear, and the total opening of the fracture is almost all effective conductivity aperture. Low-rate and low-temperature injection cannot quickly consume the thermal energy of the matrix, and the thermally induced openings of natural fractures affect range is only 5m. Increasing the injection rate is a necessary method to further expand the range of natural fracture conductivity. The thermal induced opening formed by heat exchange (TH) in the near-well zone contribute up to 92% of the total conductivity aperture, ranging from 9.4 m. The conductivity of the area far from the well is mainly determined by the fracture dilation (M), and its contribution has gradually increased from 50% to 99%. When the temperature of the injected cold fluid keeps increasing, which exacerbates the dissolution capacity of the siliceous minerals. The maximum chemical dissolution induced aperture (C) is 0.48mm, and the largest contribution to the total conductivity aperture is 16.3%.
