Nanoparticles (NPs) have shown great potential in stabilizing foam for enhanced oil recovery (EOR). However, conventional NPs are difficult to recover and may contaminate produced oil, increasing operational costs. In contrast, superparamagnetic Fe₃O₄ NPs can be efficiently recovered using external magnetic fields, offering a sustainable solution for foam stabilization. In this study, Fe₃O₄ NPs were coated with SiO₂ using tetraethyl orthosilicate (TEOS) and further modified with dodecyltrimethoxysilane to enhance their hydrophobicity. The modification effects were characterized, and the optimal foam-stabilizing Fe₃O₄@SiO₂ NPs were found to have a contact angle of 77.01°. The foam system formed with α-olefin sulfonate (0.2 wt%) as the foaming agent and the optimal modified NPs exhibited a drainage half-life of 452 s. After foam-stabilization experiments, the NPs were recovered and reused, with the results indicating that three recovery cycles were optimal. Finally, visual microscopic displacement experiments demonstrated that the foam stabilized by modified NPs effectively mobilized clustered, membranous, and dead-end residual oil, increasing the recovery rate by 17.01% compared with unmodified NPs. This study identifies key areas for future investigation into the application of magnetic nanoparticles for enhanced oil recovery.

The reservoir could be divided into three zones: steam zone with saturated steam temperature, condensate zone and reservoir temperature zone. Experiments were conducted to investigate influence of mass fraction of foaming agent and temperature on interfacial tension at reservoir pressure and temperature, by means of high temperature and high pressure interfacial tension instrument. The results showed that increasing mass fraction of foaming agent and temperature would result in decreasing minimum dynamic interfacial tension and steady interfacial tension. As temperature increased, it would take less time for the system to reach minimum dynamic interfacial tension. In steam zone and condensate zone, the interfacial tensions between water and heavy oil all keep magnitude of 10-2mN/m, but it keeps magnitude of 10-1mN/m in reservoir temperature zone. So the foaming agent has better displacement efficiency for heavy oil in steam zone and condensate zone.