Stability Mechanism of Nitrogen Foam in Porous Media with Silica Nanoparticles Modified by Cationic Surfactants.

This work aims at studying the effect of electrostatic interactions between cationic surfactants and silica nanoparticles (NPs) on foam stability in porous media. The physio-chemical property of NPs, the gas-liquid interface properties, the foam flow characteristics, together with the stability under different concentrations of surfactant and NPs were investigated and compared. It was found that the affinity of silica NPs to the surface is tunable by variation of surfactant concentrations. NPs and surfactants as a whole assembling at the surface substantially improve the foam stability in static and dynamic tests. These surfactant-modified NPs accumulate at the bubble surface and remain stable under dilution of brine, providing a barrier effectively preventing coalescence. In addition, foam stability is enhanced since the layer of NPs significantly reduces the mass transfer rate, consequently mitigating the Ostwald ripening.