Synthesis and Viscosity-Reduction Performance of Zero-Valent Iron-Loaded Amphiphilic SiO2 Nanoparticles for Heavy Oil

High-viscosity oil reservoirs, particularly offshore heavy-oil deposits, exhibit severely impaired mobility, elevated extraction pressures, and constrained transport efficiency due to their extreme viscosity. To prevent issues such as stuck drill pipes and flow blockages during well-bore transportation of heavy oil, this study reports the synthesis, characterization, and application of a novel Fe0/amphiphilic SiO2 composite for viscosity reduction and enhanced flowability. The material comprises silica nanoparticles grafted with hydrophobic organosilane chains and hydrophilic quaternary-ammonium/hydroxyl groups, and is loaded with zero-valent iron (Fe0) to enable in-situ catalytic cracking of high-molecular-weight hydrocarbons. When added at 0.2 wt % in a heavy-oil system at 120 °C, the composite effected significant viscosity reduction: the amphiphilic SiO2 alone delivered reductions starting at approximately 20% and rising steadily to 49.3% as temperature increased, while both Fe0/SiO2 and Fe0/amphiphilic SiO2 achieved reductions exceeding 95% at 160 °C. The average molecular weights of Fe0/SiO2 and Fe0/amphiphilic SiO2 were approximately 928 g/mol and 903 g/mol, respectively—substantially lower than those of other comparative materials—indicating that the introduction of Fe0 markedly lowers molecular weight, likely owing to cracking activity against crude-oil macromolecules. To ensure compatibility with drilling operations, the effect of Fe0/amphiphilic SiO2 on drilling-fluid viscosity and filtrate loss was also evaluated: alteration to drilling-fluid performance was negligible except under extreme high-temperature/high-pressure conditions where filtrate loss increased marginally. Mechanistic investigation revealed a two-stage viscosity-reduction process: firstly, Fe0 catalyzes cleavage of C–C and C–S bonds in asphaltenes and resins, forming smaller hydrocarbon molecules; secondly, the amphiphilic SiO2 particles adsorb at the oil–water interface and mediate emulsification to form a water-in-oil phase, thereby disrupting the viscous network of the oil phase, reducing flow resistance, and improving mobility. This study demonstrates the feasibility of a catalytic–emulsification synergistic approach for offshore heavy-oil production and transport, and offers valuable insights for the design of next-generation multifunctional viscosity-reduction agents.