Study on Hydraulic Fracture Propagation in Rock with a Coupled Hydro-Mechanical Phase-Field Model

Hydraulic fracture propagation directly affects stimulation efficiency in low-permeability unconventional reservoirs and is influenced by in situ stress, fluid injection, and bedding structure. In this study, a coupled hydro-mechanical phase-field model was developed by combining solid mechanics, porous media flow, and phase-field fracture theory. Bedding planes were represented as lower-dimensional interfaces. The model was used to investigate the fracture initiation and propagation under different stress ratios, fluid injection rates, and bedding angles. The results show that under anisotropic stress conditions, fractures propagate mainly in the direction of the maximum principal stress. Under equal stress conditions, no consistent preferred direction is observed during the fracture initiation or subsequent propagation. Increasing the fluid injection rate results in a higher initiation pressure and an earlier initiation time while producing little change in the final fracture geometry. For bedded rock, three typical fracture propagation patterns are identified: bedding-dominated, stress-dominated, and mixed-control propagation. Under equal biaxial stress conditions, bedding-dominated propagation occurs regardless of bedding angle. These results indicate that the final fracture morphology is governed mainly by the relative influence of the stress field and bedding interfaces, whereas the fluid injection rate primarily affects the fracture initiation pressure and initiation time.