The impact of supercritical CO2 exposure time on the effective stress law for permeability in shale

Abstract

Carbon dioxide (CO2) sequestration in shale formations is regarded as an effective approach for reducing CO2 emissions. Permeability is critical for CO2 geological sequestration as it impacts migration of CO2 in shale formations. The effective stress coefficient for permeability (χ) scales the relative influence of pore pressure on permeability compared to confining pressure. This study examined the changes in χ of dry and wet shale samples with different times of supercritical CO2 (ScCO2) exposure. The results suggest that, as ScCO2 exposure time increases from 0 to 40 days, the χ of dry shale increases from 0.8304 to 0.9563, and that of wet shale increases from 0.8379 to 1.0134. Wet shale exhibits a greater increase in χ than dry shale for the same exposure time. These changes in χ may result from CO2-shale interaction that converts smaller-sized pores in shale into larger-sized pores, based on nuclear magnetic resonance (NMR) measurements. Furthermore, the presence of water intensifies the response of shale to ScCO2, thereby enhancing this transformation. Our findings provide insights into the accurate prediction of shale permeability evolution during CO2 storage, and can assist in optimizing CO2 injection strategies as well as evaluating the potential for CO2 sequestration.