Unveiling the Effects of CO₂ Injection on Reservoir Aquifer Properties

This work aimed for implementing PHREEQC for assessing the interactions between CO2, brine, and the aquifer minerals, with more focus on implementing equilibrium and kinetic batch modeling for understanding the properties changes up to the stable equilibrium state induced by injecting a fixed partial pressure CO2 into a carbonate aquifer. Equilibrium modeling suggested a slight reduction in porosity up to equilibrium driven mainly by chalcedony precipitation, where mineral trapping was mainly from dawsonite precipitation in addition to a small amount from dolomite precipitation. Running a kinetic model for 10,000 years showed that the later precipitation of secondary minerals made the porosity decrease to a value of 11.77%. Mineralogy has a profound effect. Carbonate mineral dissolution provides more bicarbonate ions to the solution to reach a higher equilibrium pH. Calcite, though it affected mineral trapping slightly, allowed quick mineralization with its quick dissolution in addition to inducing less effect on other minerals reaction rates when its volume fraction increased. This resulted in less porosity reduction in the long term. Conversely, albite affected mineral trapping significantly due to its direct effect on dawsonite precipitation. However, more effect would be induced on system storage in the long term as more chalcedony would form with a higher albite fraction.