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 °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.