Pore-scale investigation of dynamic imbibition enhanced by SiO 2 nanoparticle-surfactant systems in ultra-low permeability reservoirs

SiO2 nanoparticle (SNP) surfactants have shown strong potential as chemical agents for enhancing dynamic imbibition in ultra-low permeability and tight oil reservoirs; previous studies have mainly emphasized interfacial tension (IFT) reduction and wettability alteration, particularly regarding their individual contributions to imbibition; however, the role of emulsification, especially its pore-scale synergy with these mechanisms, remains less understood. This study systematically investigated how imbibition fluid, core permeability, and pressure influence the dynamic imbibition behavior of tight cores through comparative experimental analysis. In addition, pore-scale oil recovery characteristics were investigated using nuclear magnetic resonance (NMR) to clarify the differential contributions of various pore systems during the imbibition process. The results show that dynamic imbibition is strongly controlled by imbibition fluid properties, permeability, and pressure. Variations in permeability and pressure significantly affects imbibition efficiency. Furthermore, the type of imbibition fluid plays a critical role: compared with water and the base surfactant system, the SNP surfactant can effectively reduce the oil-water IFT to 10−1∼10−2 mN/m, extend the emulsion water-separation time by more than twofold, and reverse the contact angle by over 10° toward a more water-wet state. With the addition of SNP surfactant, which outperforms water and conventional mixed surfactants, imbibition efficiency is significantly improved, in ultra-low permeability reservoirs due to the synergistic coupling of IFT reduction, emulsification, and wettability alteration. Furthermore, the SNP surfactant lowers the critical pore-size threshold required for oil mobilization and promotes oil recovery from both mesopores and micropores. These findings provide a comprehensive understanding of imbibition and demonstrate the promising potential of SNP surfactants.