Viscosity reduction mechanism of functionalized silica nanoparticles in heavy oil-water system

The in-depth study of the viscosity reduction mechanism of nanoparticles (NPs) is especially important for the extraction of heavy oil resources. In this work, molecular dynamics (MD) simulation was used to investigate the effect of the difference in hydrophilicity/hydrophobicity of the grafted molecules on the viscosity reduction process of functionalized SiO2 NPs in heavy oil. First, we investigated the distribution of various molecules in the oil-water system, and it was found that the asphaltene and resin components in heavy oil were adsorbed on the surface of the functionalized SiO2 NPs. And with the increase of the surface lipophilicity or grafting density of the surface of the NPs, the more obvious this adsorption phenomenon is. Then, we also found that the ability to adsorb asphaltene and reduce interfacial tension between oil and water was significantly enhanced with the increase of lipophilicity on the surface of the nanoparticle viscosity reducers. And the GLA-K-SiO2 nanoparticle viscosity reducer can reduce the interfacial tension from 51.102 mN/m to 41.956 mN/m, showing the best ability to reduce interfacial tension. In addition, the amphiphilic NPs have both high longitudinal and lateral diffusion coefficients, so they diffuse more easily into the oil phase system and more favorable for adsorption of oil-phase components. Finally, by comparing the adsorption structures of asphaltene on the surface of different functionalized SiO2 NPs, two adsorption configurations were obtained: vertical or large inclined adsorption and parallel or slightly inclined adsorption. Most importantly, it was found that functionalized SiO2 NPs could disassemble the asphaltene large accumulation structure into small asphaltene clusters, which reducing the viscosity of the heavy oil. This work is of great significance to the design and study of grafted nanoparticle viscosity reducers.