Characterization of pore structure evolution in brine layer cores after supercritical CO₂ action

Geological storage of CO2 in saline formations has gradually become an important technology for mitigating the rise of greenhouse gas concentrations in the atmosphere due to its multiple advantages, such as wide distribution area and large storage potential, and has attracted much attention in recent years. The injection process of CO2 triggers complex physicochemical reactions in the reservoir rocks and leads to a significant evolution of the pore structure of the rocks, which in turn affects the long-term stability of the reservoirs and the efficiency of storage. In this study, based on experimental techniques such as X-CT, low-field nuclear magnetic resonance spectroscopy, and electron scanning microscopy, we systematically investigated the evolution of microstructures induced by CO2-brine-rock interactions in brine formation cores under different CO2 soaking times, pressures, and mineralization levels. After being soaked in CO2, the porosity and pore diameter of the core increase. The growth rates of porosity vary under different soaking times, pressures and salinities. The T2 spectrum peak shifts to the right, and micro-cracks and the like increase. As the soaking time lengthens, the debris spreads more widely. The increase in the concentration of the mineralized solution leads to the dissolution of feldspar and the precipitation of minerals, while the indentation depth of quartz changes little. Increased concentration of mineralizing solution leads to dissolution of feldspar and formation of siliceous minerals that precipitate in cracks and residual rock debris.