Investigations on the Influencing Mechanisms of SiO2 Nanoparticles on Foam Stability

Foam stability is significantly important for enhancing oil recovery and sequestration of carbon dioxide underground. Nanoparticles have been widely used to improve foam stability, but traditional experiments cannot well reveal the mechanisms of nanoparticles on stabilizing foams and the interactions among nanoparticles, surfactants, and liquid films. In order to clarify the mechanisms of enhancing foam stability by nanoparticles, the adsorption behaviors of nanoparticles with different modification degrees on the liquid film and the effects of different compounded systems of nanoparticles and surfactants on the foam stability were studied by molecular simulation. Moreover, the foam stability of the compounded systems was evaluated by experiments. The results show that the foam stability of single nanoparticles increases first and then decreases with the increase of hydrophobic properties. The electrically charged properties of nanoparticles can significantly affect the foam stability of the compound system with nanoparticles and surfactants. The electrostatic repulsion between hydrophilic nanoparticles and anionic surfactants results in irregular arrangement of surfactants in the liquid film, which reduces foam stability. On the contrary, the electrostatic attraction between cationic surfactants and hydrophilic nanoparticles can promote the orderly arrangement of cationic surfactants and thus enhance the foam stability. Amphiphilic nanoparticles can interact with anionic or cationic surfactants, which not only strengthens the regular arrangement of surfactants on the interface but also fills the interface cavity and improves the foam stability. In addition, the experimental results show that there is an optimal ratio between nanoparticles and surfactants. Nanoparticles can reduce the foaming volume to a certain extent, but appropriate nanoparticles can effectively prolong the foam half-life. This study elucidates the mechanism of the nanoparticles/surfactant system in enhancing foam stability and provides an important theoretical basis and guidance for nanoparticle modification and optimization of foam flooding.