Swelling of shale in supercritical carbon dioxide

Abstract

Shale gas is an unconventional but promising natural resource. One means of producing this gas is by injecting CO2 into shale formations, and this technique has received widespread attention of late. This method not only allows the possibility of storing CO2 in shale formations but also enhances the gas recovery process. The swelling of the shale matrix caused by CO2 adsorption has important consequence with regard to the production of shale gas and the sequestration of CO2 in shale formations. In this study, an apparatus was designed and used to measure CO2-induced swelling in shale samples at temperatures between 308 and 348 K and pressures up to 15 MPa. The results show that CO2-induced swelling occurs in shale samples. With increasing CO2 pressure, the swelling of shale samples initially increases and then lessens. With increasing CO2 temperature, the maximum swelling of the shale gradually decreases. The strain induced in the shale during this process in response to a constant CO2 pressure can be divided into three regions: transient shrinkage, slow swelling and stable strain. The results of calculations employing a simplified local-density model were in agreement with the experimental data obtained from CO2-induced swelling in shale. All experimental samples exhibited anisotropic strains in response to CO2 injection, with the strains always being less in the direction parallel to the bedding plane.