Impact of Surfactant-Induced IFT Reduction and Wettability Alteration on CO₂ Foam Injectivity in Saline Aquifer Storage

Foam-assisted CO2 injection enhances CO2 storage in saline aquifers. However, most previous studies focused only on the benefits afforded by foam injection; they did not address the associated downsides, such as the high injection pressure that impedes CO2 injectivity. This study investigated the effects of foam-based CO2 storage on CO2 injectivity using three scenarios: a base case (supercritical CO2 injection without foam); conventional foam injection (CFI), where only the reduction in CO2 mobility is considered; and foam injection into a reservoir preflooded with surfactant (Surf-FI). In the last scenario, the effect of surfactant on interfacial tension (IFT) reduction and changes in wettability were considered, as was the reduction in CO2 mobility induced by the foam. In addition, the study evaluated the impact of injection well orientation on CO2 injectivity by considering both horizontal and vertical wells. We used the MATLAB Reservoir Simulation Toolbox (MRST–CO2 Lab) to forecast the long-term behavior of injected CO2 with and without foam. The results show that foam injection reduced the travel distance of the CO2 plume and increased the vertical extent thereof (the CO2 plume depth). However, foam injection impeded CO2 injectivity, reducing the anticipated injection rates. Surfactant reduced the IFT and also affected wettability during foam injection; this reduced the pressure buildup and increased the CO2 injection rate. A horizontal well exhibited better injectivity than a vertical well. We offer the following insights based on the simulation results. First, foam injection into reservoirs experiencing high CO2 injectivity levels may be inappropriate. Conversely, for reservoirs into which smaller amounts of CO2 are injected, and for which CO2 storage optimization is paramount, foam injection may be helpful. Second, horizontal wells are best suited to foam-based CO2 storage, especially in reservoirs requiring high-volume CO2 injection. Third, the economic aspects of foam injection into saline aquifers require further study.