Flow Dynamics of CO₂/brine at the Interface Between the Storage Formation and Sealing Units in a Multi-layered Model

Pressure distribution and $$\hbox {CO}_{2}$$CO2 plume migration are two major interests in $$\hbox {CO}_{2}$$CO2 geologic storage as they determine the injectivity and storage capacity. In this study, we adopted a three-layer model comprising a storage formation and the over- and underlying seals and determined three distinct flow regions based on the vertical flux exchange of $$\hbox {CO}_{2}$$CO2 and native brine. Regions 1 and 2 showed $$\hbox {CO}_{2}$$CO2 flowing from the storage formation to adjacent seals with counter-flowing brine. The characteristics of these fluxes in Region 1 were governed by permeability change due to salt precipitation whereas buoyancy force controlled the flux pattern in Region 2. Region 3 showed brine flowing from storage formation toward the over- and underlying seals, which enabled the displaced brine to escape from the storage formation and make room for $$\hbox {CO}_{2}$$CO2 to store as well as reduce the pressure build-up. In the multi-layered model, the counter-flowing brine in flow Region 1 resulted in localized salt precipitation at the upper and lower boundary of storage formation. We assessed the bottom-hole pressure and $$\hbox {CO}_{2}$$CO2 mass in caprock with respect to reservoir size. While the formation thickness influenced the bottom-hole pressure in the early stage of injection, the horizontal extension of the reservoir was more influential to pressure build-up during the injection period, and to the stabilized pressure during the post-injection period. The $$\hbox {CO}_{2}$$CO2 mass in caprock gently increased during the injection period as well as during the post-injection period and reached about 4–5 % of injected $$\hbox {CO}_{2}$$CO2. The percentage of escaped brine from the storage formation ranged from 80–100 % of the $$\hbox {CO}_{2}$$CO2 mass stored in the storage formation depending on the reservoir scale.