Geochemical effects of carbonated water on reservoir and caprock minerals for carbon capture and storage

CO2 can be safely stored in geological formations, such as deep saline aquifers and depleted oil or gas reservoirs. However, knowledge about caprock and storing bed integrity is essential for safe storage in sedimentary porous rocks. In this study typical carbonate and sandstone minerals present in the reservoir and caprocks have been exposed to carbonated water above supercritical conditions of CO2 for short time periods (7 days) to investigate the CO2-brine-rock interactions and their effects on mineral stability. After exposure, the equilibrated brine composition was determined and any changes to the mineral samples were examined by SEM, EDX and XRD analyses. The solubility of CO2 in brines was low, increasing with pressure and decreasing with salinity, and no significant increase in CO2 solubility was observed above critical pressure and temperature for CO2. Quartz and clay minerals were the least reactive sandstone minerals, while ion exchange reactions were observed for the feldspar minerals. For calcite minerals, calcium ion liberation was observed accompanied by a pH increase, which is linked to mineral dissolution. SEM, EDX and XRD analyses did not detect any changes on the surfaces of silicate and carbonate minerals exposed to the carbonated water. The overall results confirm minimal effects on silicate and carbonate minerals after short-term exposure to carbonated water above supercritical conditions of CO2.