Influence of CO 2 migration from geological storage on the chemical composition of groundwater and monitoring indicators

In the process of CO 2 geological sequestration, there is a risk that CO 2 will leak into groundwater, resulting in a series of physical and chemical reactions, with influence on chemical compositions of groundwater. In this work, numerical simulation is conducted to study the influence of CO 2 migration on the chemical composition of groundwater. The modeling results indicated that when CO 2 leaks into groundwater, gaseous CO 2 will migrate upward and diffuse laterally under the effect of buoyancy. The acidity of groundwater is enhanced and the pH is significantly reduced, leading to dissolution of calcite, illite, oligoclase, K-feldspar, chlorite and hematite, and precipitation of quartz, kaolinite, smectite-Na, siderite and smectite-Ca. The porosity of the formation increases. The concentrations of K + and Fe 2+ in groundwater gradually increase, the concentrations of Ca 2+ and HCO 3 − basically remain unchanged after increasing to a certain value, the concentrations of Mg 2+ and AlO 2 − first increase and then decrease, and the concentrations of Na + , Cl − and SO 4 2− first decrease slightly and then gradually increase, but the change in concentration is small. Therefore, Fe 2+ , Mg 2+ , Ca 2+ and pH can be used as important monitoring indicators of whether CO 2 leakage into groundwater during geological storage.