Carbon capture and storage (CCS) and CO2-based geothermal energy are promising technologies for reducing CO2 emissions and mitigating climate change. Safe implementation of these technologies requires understanding how CO2 interacts with fluids and rocks at depth, particularly under elevated pressure and temperature. While CO2-bearing aqueous solutions in geological reservoirs have been extensively studied, the chemical behavior of water-bearing supercritical CO2 remains largely overlooked. We address this gap through core-scale experiments using water-saturated CO2 on reservoir and caprock formations, simulating deep reservoir conditions (35 MPa, 150 °C). Our results show that fluid-mineral interactions involving CO2-rich supercritical fluids with water are significantly less severe than those caused by equivalent aqueous CO2 solutions. However, humidity in scCO2 can induce the dissolution of certain minerals like dolomite. The dissolution of dolomite in wet CO2 appears limited, incongruent, and self-sealing, characterized by preferential leaching of calcium ions over magnesium, leading to supersaturation of the scCO2 phase and re-precipitation of secondary carbonates. The presence of Ca2+ and Mg2+ ions transported by wet CO2 challenges prevailing views on this fluid’s chemical reactivity and highlights the need for further study. Understanding the chemical behavior of CO2-rich supercritical fluids is critical for ensuring the feasibility and security of deep geological CO2 storage and CO2-based geothermal energy.