Abstract
During CO2 geological storage, chemical reactions within reservoir rocks can alter their mechanical properties, posing safety challenges. However, the precise mechanisms by which CO2 injection influences the microstructure and mechanical properties of tight sandstone reservoirs remain unclear. This study investigates the effects of both continuous and intermittent CO2 injection on the rock properties, pore structure, and mechanical parameters of tight sandstone through controlled experiments. The results indicate that CO2 injection dissolves soluble minerals such as feldspar, clay, and calcite, resulting in a substantial increase in pore volume. Consequently, mechanical parameters such as compressive strength and elastic modulus significantly decrease, whereas Poisson's ratio increases. These effects are particularly pronounced under supercritical CO2 (scCO2, defined as CO2 above its critical point of 31.1 °C and 7.38 MPa) conditions but attenuate at higher temperatures. Furthermore, intermittent injection induces more pronounced alterations in mechanical properties compared to continuous injection. Correlation analysis reveals that variations in rock mechanical properties primarily depend on the degree of mineral dissolution and the proliferation of micropores (0.001–0.1 μm). This study provides theoretical insights into ensuring the safety of CO2 storage.
•Both continuous and intermittent CO2 injection significantly increase porosity and permeability in tight sandstone.•Mineral composition shifts, particularly under intermittent injection, exhibit a negative correlation with temperature.•CO2-induced mineral dissolution reduces triaxial compressive strength and elastic modulus while increasing Poisson's ratio.•Mechanical properties are strongly correlated with soluble mineral content and micropore evolution.