Modeling Mineral Reaction at Close to Equilibrium Condition During CO2 Injection for Storage in Carbonate Reservoir

CO₂ injection for Carbon Capture and Storage (CCS), particularly in carbonate formations, will disturb the chemical equilibrium between the rock and formation fluids, causing reactions to occur. The use of a reliable geochemical model of the system will help to understand the overall geochemical interactions and the risk and opportunities that these interactions will introduce for safe and secure storage. In this work, reactive transport modeling was conducted to investigate the dissolution rates of carbonate minerals upon injection of bicarbonate (HCO₃) saturated brine at temperatures between 21°C and 90°C. The injection of the HCO₃ saturated brine is performed to mimic the condition of the reservoir in the long-term where the system is re-equilibrating after the injection of CO₂. The reaction rate calculation was performed by adopting two different reaction rate models (1) Transition-State-Theory (TST) and (2) Arrhenius rate models. The predictions were calibrated with measured dissolution rates obtained from a set of core flood experiments conducted on outcrop and field samples. This work suggests that the TST model cannot accurately predict the reaction rate, particularly in the saturation regime close to equilibrium. The Arrhenius rate model was found to be better in predicting the dissolution rate under those conditions.