A useful application of foam for fast-tracking residual gas saturation process and reducing leakage risk during CO2 injection

Carbon dioxide (CO₂) storage in subsurface formations is recognized as the most effective method of permanently sequestering greenhouse gases. However, the possibility of leakage of mobile gases from the storage reservoir is a cause of environmental concern. This study aims to address this concern. A method is presented that can fast-track capillary trapping of gas during gas injection into subsurface geological formations such that a limited amount of free gas is available in case a leakage occur. The method can reduce the time scale of capillary (residual) trapping from decades to weeks. A laboratory experiment indicated that this can be achieved with foam-assisted water alternating gas (FAWAG) injection. In the laboratory setup, capillary trapping of gas was monitored in real time for every successive FAWAG cycle. The trapped gas were stable and remained trapped even after a prolonged water injection. The foaming agents added to the injected water facilitated the increased trapped gas saturation. However, high temperature and salinity significantly reduced the effectiveness of the foam. The type or composition of the injected gas also affect the effectiveness of the foam. The foam is most effective in N₂ or N₂-rich gas compared to CO₂ gas. This was due to the low interfacial tension between the CO₂ and the foaming solution. Improvement in foam effectiveness in high temperature high salinity and low IFT environment is much possible as ongoing research works indicate.