Comprehensive Review of Property Alterations Induced by CO2–Shale Interaction: Implications for CO2 Sequestration in Shale

CO2–shale interaction performs a crucial role in determining the capacity and leakage risk of CO2 storage in shale reservoirs. In this paper, the alterations of physical and chemical properties of shale triggered by CO2–shale interaction are reviewed, and then the implications for CO2 sequestration in shale formations are discussed. CO2–shale interaction induced the mineral alterations in shale and then further induced the pore structure alterations. The pore structure alterations are mainly controlled by mineral dissolution/precipitation and extraction and CO2 adsorption induced swelling in shale, which is closely related to the reservoir pressures and temperatures. Furthermore, the mineral and pore structure alterations may also influence the wetting behavior of shale. After CO2 exposure, the contact angle of shale increased, indicated the weakening in the hydrophilicity of the shale surface. The microscopic property alterations induced the macroscopic mechanical properties of shale to be weakened after CO2–shale interaction. The permeability variation of shale is significantly influenced by chemical–mechanical coupling effects including mineral dissolution/precipitation, adsorption induced swelling, wettability, and mechanical weakening induced by CO2–shale interaction. The shale property alterations will ultimately affect the CO2 storage capacity and security in shale. Future research needs to focus on the CO2–shale interaction covering multiple spatial and temporal scales at in situ conditions and considering the chemical–mechanical coupling effect on CO2 sequestration in shale.