Simulation study on hydrothermal phase transition double-hole fracturing and gas extraction

As coal mining depths increased, ground stresses intensified and coal seam permeability decreased, making it necessary to employ fracturing measures to enhance permeability improvement within the coal seam. Hydrothermal phase transition technology combines the advantages of high-temperature, high-pressure water wedging and dynamic impact, presenting promising prospects for application in enhancing permeability within deep coal seams. The study established dual-borehole hydrothermal phase-change fracturing and gas extraction models. By controlling variations in borehole spacing and in situ stress parameters, distinct fluid temperature–pressure variation curves and fracturing outcomes were obtained. The damage fracture extraction method was employed to establish a coalbed methane extraction model, validating the extraction efficacy under varying borehole spacings and in situ stress conditions. The principal conclusions were: (1) the damage fractal dimension of dual-hole fracturing first increased and then decreased as the hole spacing decreased, achieving optimal fracturing results at a spacing of 1200 mm under specific experimental conditions. (2) When stress in the x- or y-direction increased, the angle between the corresponding damage propagation direction and the principal stress direction decreased. (3) At inter-hole spacings of 800 and 1000 mm, the fluid pressure within the fractures between holes showed no significant reduction. (4) In dual-hole fracturing gas extraction, a hole spacing of 1200 mm was the fastest to reduce gas pressure, indicating that the area of damage fractures generated by hydrothermal phase-change fracturing is the primary factor influencing gas extraction.