Experimental and Numerical Investigation of Injection-Induced Shear Slip in Granite Fractures

Interface properties and loading conditions influence fracture reactivation during fluid injection, but their roles must be interpreted in relation to interface preparation and loading history. This study examines injection-induced shear slip using laboratory tests on granite specimens with partially bonded interfaces and a separate numerical model of a frictional interface. The experiments compare responses for different surface roughnesses, confining pressures, and differential stresses. The simulations evaluate prescribed pressure histories, rock–water temperature differences, and applied stresses. Experimental displacement evolved through an abrupt increment, slower accumulation, and renewed sliding. Rougher interfaces and higher confining pressures were associated with higher apparent friction coefficients, whereas the coefficients were similar in the two differential-stress cases. In the simulations, a temperature difference of 45 °C produced greater slip and higher peak velocity than the 0 °C case. Higher maximum pressure increased slip, while lower pressurization rates and longer holding periods produced greater accumulated displacement at 300 s. Displacement at this time increased with shear stress and decreased nonlinearly with normal stress. The results characterize interface-dependent experimental responses and loading-dependent numerical trends, with the latter representing transient displacement where sliding continued at 300 s.