Synergistic enhancement of heavy oil recovery using modified nano-silica reinforced surfactant flooding: Emulsification and pore-scale mechanisms

This study presents an enhanced oil recovery system based on dodecyltrimethylammonium bromide-modified nano-silica synergized with nonylphenol polyoxyethylene ether carboxylate surfactant for heavy oil recovery. The modified nano-silica significantly improves emulsification capability, reducing emulsification speed by 50%–70% while maintaining long-term stability (<5% water separation after 30 days). Rheological tests reveal increased bulk viscosity and storage modulus (G′) in both surfactant solutions and emulsions, suggesting the formation of elastic interfacial films. Confocal microscopy and interfacial tension analysis further confirm rigid interfacial films resulting from nano-silica adsorption at oil–water interfaces. Sandpack flooding experiments demonstrate an incremental heavy oil recovery of 18.6% of the original oil in place, representing a 10.85% improvement over conventional surfactant flooding. Micromodel studies elucidate the recovery mechanisms: enhanced displacement efficiency via rapid in situ oil emulsification and improved sweep efficiency through selective pore-throat blocking. These findings establish modified nano-silica as an effective additive for optimizing surfactant flooding in heavy oil reservoirs.