Hydraulic and Mechanical Responses of Porous Sandstone During Pore Pressure-Induced Reactivation of Fracture Planes: An Experimental Study

Herein, we subjected Kimachi sandstone samples to several experimental tests to identify the hydraulic and mechanical responses associated with fracture plane reactivation induced by elevated pore-fluid pressure. In particular, fracture plane reactivation was achieved through a series of pore pressure increments under stress conditions controlled using a true triaxial test apparatus. A hydraulic line equipped in the direction of the intermediate principal stress allowed direct measurement of each specimen's permeability in the direction nearly parallel to the pre-generated fault plane. Flow pump tests were performed to measure the permeability evolution. Two Kimachi sandstone samples were used to test different confinement conditions, and the measured hydraulic and mechanical responses (stress, displacement, and permeability) exhibited instantaneous changes at elevated pore pressures. Irreversible and anisotropic displacement measurements indicated fracture reactivation. Micro-focused X-ray computed tomography imaging and photomicrography were used to characterize internal fracture configurations and revealed the formation of cataclastic fracture surfaces that contributed to permeability reduction during pore pressure tests.