Impact of CO₂-Brine-Shale Interaction on Wettability Change at Reservoir Temperature and Pressure via AFM Characterization

Shale experiences alterations in mineral composition and surface properties after carbon dioxide treatment, significantly influencing the efficacy of the CO₂-enhanced oil recovery and sequestration. This study delves into the impact of CO₂ on shale surface characteristics by treating shale samples with CO₂ in both distilled water and 10 wt % CaCl₂ brine solution. The ion chromatography system was utilized to track ion concentration changes before and after the reaction, pinpointing the specific interactions between CO₂ and shale. Atomic force microscopy further assessed changes in shale’s micromorphology and mineral distribution. This study also reveals how CO₂ affects the shale surface wettability. Our results show that in distilled water, the reaction mainly involves mineral corrosion and calcite dissolution, which increase shale’s porosity and render its surface less hydrophilic. This phenomenon is more significant at lower temperatures and higher pressures. Conversely, in a 10 wt % CaCl₂ brine solution, calcite precipitation changes the shale’s surface composition, making it more hydrophilic, especially under low-temperature and high-pressure conditions. These insights provide a fundamental understanding and valuable guidelines to enhance carbon utilization and sequestration.