Caprock integrity susceptibility to permeable fracture creation

Abstract

Caprock leakage is of crucial concern for environmentally and economically sustainable development of carbon dioxide sequestration and utilization operations. One potential leakage pathway is through fractures or faults that penetrate the caprock. In this study, we investigate the permeability induced by fracturing initially intact Marcellus shale outcrop specimens at stressed conditions using a triaxial direct-shear method. Measurements of induced permeability, fracture geometry, displacement, and applied stresses were all obtained at stressed conditions to investigate the coupled processes of fracturing and fluid flow as may occur in the subsurface. Fracture geometry was directly observed at stressed conditions using X-ray radiography video. Numerical simulation was performed to evaluate the stress distribution developed in the experiments. Our experiments show that permeability induced by fracturing is strongly dependent on the stresses at which the fractures are created, the magnitude of shearing displacement, and the duration of flow. The strongest permeability contrast was observed when comparing specimens fractured at low stress to others fractured at higher stress. Measureable fracture permeability decreased by up to 7 orders of magnitude over a corresponding triaxial confining stress range of 3.5MPa–30MPa. These results show that increasing stress, depth, and time are all significant permeability inhibitors that may limit potential leakage through fractured caprock.