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

CO₂ solubility trapping and CO₂-brine-mineral interactions are essential for understanding the fate and migration behavior of CO₂ during geological storage. An advanced instrument was developed to accurately quantify the CO₂ solubility in brine and CO₂-brine-mineral interactions. Nonetheless, the experimental measurements can be time-consuming and resource-intensive. CO₂SolTool, developed by integrating MATLAB with Phreeqc, provides a reliable approach for determining the quantity of dissolved CO₂ in brine, the properties (e.g., pH and density) of CO₂-saturated brine, and the interactions between mineral, brine, and CO₂. The calculated data are consistent with the experimental findings. CO₂SolTool can accurately simulate the quantity of dissolved CO₂ 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 H₂S is higher than that of CO₂, while the solubility of N₂ and CH₄ is smaller than that of CO₂. The electrolytes, especially the HCO₃⁻, have a significant effect on the pH value of CO₂-saturated brine. The presence of impurities such as H₂S may moderately reduce the pH level of the CO₂-saturated brine, as it has higher solubility in brine than CO₂ under the same conditions. When minerals, e.g., dolomite or calcite, are present, the pH levels may rise after the CO₂-brine-mineral is equilibrated. Anhydrite and gypsum have limited impact on the pH value of CO₂-saturated brine. The potential determining ions, including HCO₃⁻, CO₃²⁻, Ca²⁺, can largely affect the electrical charge of the surface of calcite.