Evaluating the CO2 Solubility Trapping Potential and Geochemical Reactions in Saline Aquifers Under Geological Carbon Sequestration Conditions

Abstract CO2 solubility trapping and CO2-brine-mineral interactions are critical in evaluating the reliability of CO2 geological storage. Primarily, a high-temperature and high-pressure reactor was developed to measure the amount of dissolved CO2 in brine and evaluate the CO2-brine-mineral interactions under subsurface temperature, pressure, and salinity conditions. The experimental results were subsequently validated by published data in the literature. However, measuring these properties can be time-consuming and resource-intensive. CO2SolTool, developed by coupling MATLAB with Phreeqc, provides an alternative approach for reliably calculating the CO2 solubility, properties of CO2-saturated brine, and CO2-brine-mineral interactions for carbon geological sequestration. The calculated data for CO2 solubility, CO2-brine-mineral interactions, and properties of CO2-saturated brine are consistent with the experimental findings across a wide range of temperature, pressure, and brine salinity, in the presence or absence of gas impurities. It I found that 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 of CO2-saturated brine. The presence of impurities such as H2S may moderately decrease the pH of the CO2-saturated brine, as it has higher solubility in brine than CO2 under the same conditions. The presence of minerals, e.g., calcite and dolomite, may increase the pH level after CO2-brine-mineral equilibrium. The pH of CO2-saturated brine is not significantly affected by the presence of anhydrite and gypsum. The zeta potential of calcite is largely influenced by the potential-determining ions, HCO3−, CO32-, Ca2+, etc. Predicting CO2 solubility and CO2-brine-mineral interactions allows for better modeling of the fate and transport of CO2 within the subsurface, optimizing storage strategies, and predicting the long-term behavior of CO2 in geological formations.