Synergy between Nanoparticles and Surfactants in Stabilizing Foams for Oil Recovery

Surfactant-stabilized foams have been used in the past for vertical conformance and mobility control in gas-enhanced oil recovery processes. Lack of stability of these foams often limits their application. The goal of this study is to investigate the synergistic effects of using a blend of silica nanoparticles (NPs) and anionic surfactants on foam stability in both bulk and porous media. First, the stability of static foams was studied using surfactants and surfactant-NP mixtures with and without the presence of a crude oil. Second, the foam drainage behavior and thickness of the foam lamella were studied by fluorescence microscopy. Third, the mobility of foams was measured by coinjecting the surfactant or surfactant-NP solution with nitrogen gas through a Berea sandstone core at a fixed foam quality (gas volume fraction). Finally, oil displacement experiments were conducted in Berea cores using these foams. Static foam tests indicated a stabilization effect of nanoparticles on surfactant-NP-stabilized foams in the absence of crude oil. Adding nanoparticles at low concentrations (0.3 wt %) improves the foam stability and increases the mobility reduction factor by a factor of 2 in the absence of oil. Fluorescence and confocal laser scanning microscopy elucidated the trapping of nanoparticles in Plateau borders as well as lamellas, which retards liquid drainage and bubble coalescence. Core floods with a reservoir crude oil showed about 10% incremental oil recovery by an immiscible foam (with the surfactant-NP blend) over a water flood. This study shows that nanoparticles have the potential to increase the stability of surfactant-stabilized foams in subsurface applications.