Research on Enhanced Oil Recovery Potential in High Water Cut Reservoirs Using Amphiphilic SiO ₂ Nanofluids

This study addresses the challenge of low oil recovery in Y Reservoir, by water flooding with high-water-cut stage (80.1%) and low natural emulsification capability. An interfacial component compensation-synergistic enhancement strategy was proposed to design a benzoic acid-modified nano-SiO 2 emulsifier (BHSD). The BHSD was compounded with Tween 20 to form an emulsification system, named TBHSD. The system’s dispersion stability, emulsification performance, interfacial properties, and wettability alteration capabilities were systematically evaluated. Pore-scale displacement experiments revealed that the TBHSD system effectively forms high-internal-phase (up to 75–85%) water-in-oil emulsions, significantly reduces interfacial tension (to as low as 0.69 mN/m), enhances interfacial film strength (integrated modulus up to 20.63 mN/m), and alters rock wettability. The core flooding experiments demonstrated that the TBHSD system, followed by subsequent water flooding, achieved an additional oil recovery of 27.8%, primarily by mobilizing crude oil from small pores. The mechanism involves synergistic viscosity enhancement, adaptive mobility control, and improved microscopic displacement efficiency.