Study on the Synergistic Mechanism of Zwitterionic Surfactants and Nano-SiO2 Particles in Oil Displacement

Surfactants and nanoparticles play a crucial role in regulating the properties of the oil–water interface. However, their influence on the initiation and migration patterns of residual oil in pores remains insufficiently characterized. In this study, nanocompounded systems were prepared by dispersing hydrophobic silica nanoparticles (SiO2-N) in solutions of linear and branched alkylbenzenesulfonate betaines (ASB and XSB), respectively. The effects of these compounded systems on the oil/water/solid interface properties were determined through interfacial tension measurements, emulsion observations, and oil-film stripping tests. The results showed that the addition of SiO2-N enabled the ASB- and XSB-compounded systems to exhibit low interfacial tension characteristics and strong oil film stripping capabilities. Meanwhile, the linear ASB-compounded system demonstrated stronger emulsion stability and further reduced the water separation rate of the emulsion. Additionally, in microscopic-scale oil displacement experiments, the oil displacement efficiencies of the ASB- and XSB-compounded systems increased by 14.9% and 6.5%, respectively. The analysis of remaining oil images indicated that the nanocompounded systems better stripped the aggregated columnar remaining oil, increasing the proportion of liquid and droplet remaining oil. That is to say, the ultralow interfacial tension of the nanocompounded system at the oil/water interface prompts the remaining oil in the pores to transform from columnar to film-like and droplet-like; the improvement in emulsion stability enabled the emulsified oil droplets to have better migration capabilities; the enhanced oil film stripping improved the initiation and migration capabilities of remaining oil, thereby increasing the oil displacement efficiency. Therefore, this paper investigates the initiation and migration characteristics of crude oil in porous media by changing the hydrophobic groups of zwitterionic surfactants of both genders and reveals the synergistic oil displacement mechanism of the compounded system of straight-chain and branched zwitterionic surfactants and nano-SiO2 particles.