Injection-induced slip of splitting granite fracture

Massive fracturing fluid injection in reservoir stimulation can alter the fluid pressure field, potentially inducing the faults to slip in an aseismic or seismic phenomenon. In this work, laboratory friction experiments were performed on split-cutting granite fracture to investigate the effect of fluid pressure on injection-induced slip behavior. The injection experiments spanned a fluid pressure range of 1-20 MPa, which was up to half of the confining pressure. The laboratory results demonstrated that an increase in confining pressure led to a marginal reduction in the friction coefficient, decreasing from a range of 0.70-0.80 at 10 MPa to 0.71-0.75 at 40 MPa. Friction constitutive parameters in experiments with fluid pressure above 10 MPa exhibited a transition from velocity-strengthening to velocity-weakening behavior, while remaining consistently velocity-strengthening below this threshold. Similarly, measurements of dilatancy and critical slip distance exhibited a similar evolution, first increasing and then becoming approximately constant, independent of fluid pressure. The observed microstructural evolution of the split-cutting fractures during slip testing supported these mechanical responses. Post-shear slip, a decrease in the fracture roughness and asperity distribution of the split-cutting fracture was noted, with the decrease in amplitude being more pronounced at high confining pressure. Research may provide a prospect on slip-on faults with fluid pressure.