Swelling of Shales by Supercritical Carbon Dioxide and Its Relationship to Sorption

Shale gas is a promising energy source offering additional energy security over concerns of fossil fuel depletion. Injecting CO2 into depleted shale gas reservoirs might provide a feasible solution for CO2 storage and enhanced gas recovery. However, shale strain caused by the CO2 injection as well as CO2 sequestration in the reservoir needs to be considered during shale gas production. For this purpose, this paper examines the adsorption capacities, CO2-induced swelling, and He-induced strain of shales at 0-16 MPa and 35-75 degrees C. The maximum excess adsorption at different temperatures correlated with the bulk phase density: as the CO2 temperature increased, the maximum excess adsorption density decreased. The density of the adsorbed phase, obtained using the Dubinin-Radushkevich model, was used to fit the excess adsorption data. At low pressure, the CO2-induced strain on shale was caused by the gas adsorption, whereas at high pressure, it was caused by gas pressure. The absolute adsorption linearly correlated with the adsorption-induced strain.