A concise chemical kinetics algorithm for carbonated brine injection in carbonate reservoirs

A single-cell segregated solver for calculating the behavior of carbonated brine injection in carbonate rocks aiming at carbon geological storage is presented. The approach is designed to represent an element in computational fluid dynamics simulations and enhance customization to include dissolution chemistry by integrating a CO2 solubility model, speciation calculations, mineral dissolution reactions and the consequent change in reservoir properties over time. The equilibrium and dissolution reactions are calculated sequentially, where an adaptive control of the time step ensures that the dissolution rate is computed from the correct equilibrium condition. A pseudo-homogeneous medium represents the reservoir, where alterations in rock structure are computed via a formulation based on Kozeny-Carman. Finally, a stabilization algorithm based on the Bjerrum plot of H2CO3 provides numerical robustness for the speciation calculations. The results can estimate the time frame for the system to reach equilibrium and the corresponding changes in rock structure. The solubility model was validated against experimental data, while the speciation model was compared to more rigorous thermodynamics models such as electrolyte-NRTL and Pitzer, showing minor differences. The algorithm as a whole provides similar results for the pH when compared to a state-of-the-art single-cell model with an extensive chemical system for a real reservoir, proving it can be a viable option for numerical simulations.