Chemical-Mechanical Coupling Effects on the Permeability of Shale Subjected to Supercritical CO 2-Water Exposure

The permeability of shale reservoir rock and caprock is the key parameters influencing the shale gas production and the storage security of CO2. In this study, the ScCO2-water exposure induced chemical-mechanical coupling effects on the permeability of shale was analyzed by a systematic research, including mineralogical analysis, pore structure analysis, uniaxial compression and permeability test at different stress and injection pressure of shale before and after ScCO2-water exposure. After ScCO2-water exposure, the pore volume and average pore size of shale increased, and the initial permeability of shale increased. At the stressed condition, the porosity and permeability of CO2-water treated shale sample is lower than the untreated shale sample. The uniaxial compressive strength and elastic modulus of shale were decreased after ScCO2-water exposure. The shale permeability was increased with the increase of injection pressure, and decreased with the increase of confining stress. The stress sensitivity of permeability in shale is stress-dependent, a higher effective stress corresponding to a lower stress sensitivity of permeability. The damage in the permeability (Δkd) of shale caused by the ScCO2-water exposure is also depending on the confining stress and injection pressure, at a higher effective stress condition, the damage in the permeability of shale is more significant.