Hydrothermal impact fracturing, Fracture complexity, Fracture mechanism, Fractal dimension, Materials of engineering and construction. Mechanics of materials, TA401-492

When extracting coal-bed methane (CBM) from deep ground, conventional hydraulic fracturing struggled to expand fractures due to both inadequate pressure and the water-lock phenomenon, while burgeoning fracturing techniques were unable to provide both high pressure and impact stress. The hydrothermal phase change impact fracturing technology can instantaneously discharge high-pressure thermal fluid and generate impact stress to volumetric fracturing. In order to research the fracturing mechanism of the new fracturing strategy, a separately designed experimental system was utilised for high-pressure thermohydraulic fracturing at different release pressures and different peripheral pressures. The experimental findings: (1) The pressurisation profile in the reactor was divided into five stages: accelerated reaction process, reaction homogeneity process, deceleration process, pressure relief shock stage and residual pressure seam formation process; (2) High-pressure hydrothermal fracture produces both radial and tearing cracks, with radial cracks being the main cracks; (3) The dimension of the fractal can be used as a damage variable to describe both the fracture morphology and the degree of damage.