Quantifying CO2 solubility and geochemistry reactions in multicomponent electrolyte solutions under CO2 geological sequestration conditions

• An instrument was developed to quantify the CO 2 solubility in brine and CO 2 -brine-mineral interactions. • CO2SolTool can accurately model the CO 2 solubility under wide ranges of aquifer conditions. • The density and pH of CO 2 -saturated brine can also be accurately estimated. • The influences of gas impurities, including H 2 S, CH 4 , and N 2 , were investigated. • The presence of potential determining ions can significantly influence the CO 2 -brine-mineral interactions. CO 2 solubility trapping and CO 2 -brine-mineral interactions are essential for understanding the fate and migration behavior of CO 2 during geological storage. An advanced instrument was developed to accurately quantify the CO 2 solubility in brine and CO 2 -brine-mineral interactions. Nonetheless, the experimental measurements can be time-consuming and resource-intensive. CO 2 SolTool, developed by integrating MATLAB with Phreeqc, provides a reliable approach for determining the quantity of dissolved CO 2 in brine, the properties (e.g., pH and density) of CO 2 -saturated brine, and the interactions between mineral, brine, and CO 2 . The calculated data are consistent with the experimental findings. CO 2 SolTool can accurately simulate the quantity of dissolved CO 2 in brine in the presence of gas impurities throughout a wide range of temperature, pressure, and brine salinity and compositions. The Pitzer model is sufficiently accurate for thermodynamic and geochemical calculations at elevated brine salinity. The solubility of H 2 S is higher than that of CO 2 , while the solubility of N 2 and CH 4 is smaller than that of CO 2 . The electrolytes, especially the HCO 3 − , have a significant effect on the pH value of CO 2 -saturated brine. The presence of impurities such as H 2 S may moderately reduce the pH level of the CO 2 -saturated brine, as it has higher solubility in brine than CO 2 under the same conditions. When minerals, e.g., dolomite or calcite, are present, the pH levels may rise after the CO 2 -brine-mineral is equilibrated. Anhydrite and gypsum have limited impact on the pH value of CO 2 -saturated brine. The potential determining ions, including HCO 3 − , CO 3 2− , Ca 2+ , can largely affect the electrical charge of the surface of calcite.