Experimental investigation of a nano-silica empowered polymer system for emulsification and viscosity reduction of heavy oil

High viscosity and poor mobility severely restrict the efficient development of heavy oil reservoirs, while conventional chemical viscosity reducers often show limited applicability under complex reservoir conditions. In this study, a nano-silica empowered polymer system (NS-NAA) was developed for heavy-oil viscosity reduction and enhanced oil recovery. The hybrid material was designed and synthesized through copolymerizing of KH570-modified nano-silica with N-hydroxymethyl acrylamide (NMA), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), and α-olefin sulfonate (AOS), constructing a multifunctional system integrating dispersion–emulsification viscosity reduction and interfacial regulation capabilities. Using two representative heavy oils as model oils, the experimental results demonstrate that NS-NAA can significantly reduce crude oil viscosity, achieving a maximum viscosity reduction rate exceeding 90%, while decreasing the oil–water interfacial tension from approximately 12–20 mN/m to 0.4–0.8 mN/m. Meanwhile, the system induces a wettability transition of solid surfaces from oil-wet to water-wet, promoting the detachment of adsorbed crude oil. Core flooding experiments indicate that injection of the system after conventional water flooding enhanced oil recovery by 24%–25%, with a drag reduction of 27%–30%. Low-field NMR imaging further confirms the capability of NS-NAA to mobilize residual oil. The results reveal that NS-NAA enhances oil recovery through the coupled effects of viscosity reduction, wettability alteration, and interfacial regulation, providing experimental support for the design and application of efficient chemical viscosity reduction systems for heavy oil reservoirs.