Coarsening reduction strategies to stabilize CO2-foam formed with a zwitterionic surfactant in porous media

Abstract

Micromodel experiments at high-pressure high-temperature conditions were performed to evaluate the impact of different coarsening reduction strategies on CO2-foams stabilized with a zwitterionic surfactant, using silica nanoparticles in small concentration and mixing CO2 with a less water-soluble gas (nitrogen). The CO2-foam stabilized only by the surfactant showed poor behavior in the porous media, while an improvement in both foam texture (bubble density at the inlet of the micromodel) and gas trapping was qualitatively seen in the experiments using a nanofluid containing silica nanoparticles. The strong adsorption of the nanoparticles at the gas-water interface allowed to reduce the coarsening mechanism, reaching a minimum pressure gradient for strong foam generation throughout the micromodel chip. The use of a small concentration of nanoparticles in combination with the zwitterionic surfactant proved to be effective in reducing gas mobility without significant increase in pressure drop, which could be used as a strategy to control the mobility of injected CO2 in high permeability porous media, with reduced loss of injectivity. Coarsening was also reduced by using a mixture of CO2 and N2 as foaming gas, with an even greater gas mobility reduction, achieving a pressure drop 7.6 times higher compared to the CO2-foam stabilized only by surfactant. Furthermore, larger areas with trapped gas were visualized along the micromodel when co-injecting the mixture of gases and the zwitterionic surfactant solution. The large decrease in gas mobility seen for this strategy suggests that using a gas mixture would be suitable to control gas mobility in high-permeability channels and to block thief zones. The combination of using a gas mixture and a nanofluid to decrease CO2-foam destruction in porous media yielded a slight reduction in gas mobility, similar to that obtained with CO2-foam in the presence of nanoparticles, for they had similar pressure-drop values at same injection flow rate. The results obtained in this work demonstrated the importance of interfacial phenomena for tuning of coarsening and coalescence mechanisms associated with CO2-foam stability to the desired pore-scale application.