A numerical study of the effect of brine displaced from CO2 storage in a saline formation on groundwater

This paper presents a numerical simulation study that examines the CO2 injection-induced salinity changes in groundwater formations. We use a simplified numerical model to simulate the migration of formation water caused by pressure build-up during CO2 injection. A stacked reservoir consisting of a storage formation overlain by a geological seal and groundwater aquifer is modeled. We use a commercial reservoir simulator to run various realizations with different seal permeabilities, injection rates, lateral boundary conditions, and groundwater production rates. We then track salinity changes calculated by the simulations. We find that lateral boundary conditions and seal permeabilities are the most critical parameters that govern lateral and vertical displacement of formation water. If the seal permeability is high enough or the lateral boundary is closed, the vertical fluid displacement dominates the lateral displacement. Depending on seal thickness, injection rate and reservoir salinity, this has the potential to cause significant salinity change in the overlying groundwater aquifer. If the seal permeability is low or the lateral boundary is open, then the lateral displacement becomes dominant. If the storage formation extends to an up-dip shallow groundwater formation, the higher the lateral fluid displacement the higher the increase in salinity of the groundwater. Moreover, salinity changes occur in the deeper part of the groundwater formation because displaced water is heavier than groundwater. This study shows that tracking salinity changes in numerical simulations may provide a quantitative measure of the change in groundwater quality. (c) 2015 Society of Chemical Industry and John Wiley & Sons, Ltd