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

Abstract

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.