The Variation Law of Mineral Composition and Pore Structure in the Shale Oil of Mabei Fengcheng Formation Under the Action of CO2

This study investigates the effects of CO2–water–rock interactions on shale oil reservoirs, specifically focusing on the mineral dissolution and pore structure alterations in shale samples from the second section of the Permian Fengcheng Formation in the Mahu Depression, Junggar Basin. Core soaking experiments were conducted under high-temperature and high-pressure conditions to simulate reservoir environments. Mineral evolution, ion migration, and microstructural changes were qualitatively and quantitatively analyzed using X-ray Diffraction (XRD), Inductively Coupled Plasma (ICP) spectroscopy, and Scanning Electron Microscopy (SEM). The findings indicate that CO2-induced mineral dissolution follows a distinct sequence: calcite > dolomite > potassium feldspar > sodium feldspar, which is directly reflected in the concentration of ions (Ca2+ > Mg2+ > K+ > Na+) in the solution. The dissolution rate and pore structure enhancement are significantly influenced by lamina density, with dolomitic rocks with high lamina density showing greater dissolution and porosity increase, and the lamina area greater than the matrix area. This study demonstrates that the dynamic changes of rock minerals are the core mechanism for controlling the pore structure of reservoirs, showing how CO2–water–rock reaction enhances the porosity and connectivity of shale reservoirs, thereby improving oil recovery potential.