CO₂ Leakage Behaviors in Typical Caprock-Aquifer System during Geological Storage Process

In this study, a 3D reactive flow simulation model is built to simulate the leakage processes though assumed leakage channels. The geochemical reactions are coupled with fluid flow simulation in this model with consideration of reservoir minerals calcite, kaolinite, and anorthite. As an essential trigger for geochemical reactions, changes in pH value are investigated during and after the CO₂ injection process. By comparing CO₂ migration with/without geochemical reactions, the influence of geochemical processes on CO₂ leakage is illustrated. The leakage behaviors through leakage channels with different permeabilities are evaluated. Influence of reservoir temperature on CO₂ leakage is also exhibited. Furthermore, the effects of the distance between the injection well and leakage zone on the leakage potential are studied. The results indicate that the geochemical reactions have impact on the leakage processes, which can decrease the leakage level with the presence of geochemical reactions. The region of low pH enlarges with continuous injection of CO₂. Hence, monitoring changes in pH can reflect the migration of CO₂, which can provide an alert for CO₂ leakage. The occurrence of the leakage phenomenon is postponed with increasing the distance between the CO₂ injection well and the leakage channel. However, the leakage level tends to be consistent with injecting more CO₂. The CO₂ leakage risk can be reduced through the leakage channels with lower permeability. With the presence of higher reservoir temperatures, the leakage risk can be improved. These results can provide references for the application of monitoring methods and prediction of CO₂ front associated with geochemical processes.