A Nano-SiO₂-Based Core-Shell Hybrid as a Dual-Functional Viscosity Reducer and Pour Point Depressant for Heavy Oil

Heavy oil production and transportation are often restricted by high viscosity, poor mobility, and unfavorable low-temperature flow behavior, especially in waxy systems. While conventional polymer-based additives improve flow, they suffer from inadequate thermal stability, poor dispersibility in complex crude oil matrices, and insufficient multifunctionality. To address these issues, a nano-SiO₂-based organic-inorganic hybrid flow improver, denoted as NSDA, was synthesized via in situ free-radical copolymerization of styrene, docosyl methacrylate, acrylic acid, and acrylamide on 3-(trimethoxysilyl)propyl methacrylate (KH-570)-modified silica surfaces. Characterization revealed that this core-shell nanohybrid structure significantly improved thermal stability and oil-phase dispersibility, maintaining nanoscale dispersion in xylene. A remarkable viscosity reduction rate of 90.2% was achieved, accompanied by a substantial pour point depression of 11 °C using only 0.5 wt% of NSDA in Liaohe heavy oil. This dual-functional performance is mainly attributed to the combined effects of the robust nano-SiO₂ core and the multifunctional polymer shell, Specifically, the performance is driven by synergistic wax crystal regulation at low temperatures, alongside weakened intermolecular associations among polar heavy components and nanoparticle-assisted dispersion that govern viscosity reduction.