Viscosity reduction mechanism of surface-functionalized Fe3O4 nanoparticles in different types of heavy oil

Abstract

In-depth investigation of the viscosity reduction mechanism of nanoparticle viscosity reducers in various heavy oil types holds key strategic significance for the rational exploitation of global heavy oil resources. In this work, the dispersion stability mechanism of three surface-functionalized Fe3O4 nanoparticles (NPs) in kerosene was first explored by molecular dynamics (MD) simulation. Then Studies showed that the differences in asphaltene aggregation structures in different types of heavy oils make their initial viscosities significantly different. The addition of NPs could effectively reduce the viscosity of heavy oil and increase the diffusion coefficient of asphaltenes. Importantly, there were differences in the viscosity-reducing ability and viscosity-reducing mode of the NPs in different types of heavy oil. In Oil1, the NPs increased the peak of the radial distribution function curve, the number of hydrogen bonds (2.25–8.63), and the cluster size between asphaltenes (3.72–6.40). However, these property changes of asphaltenes in Oil2 are opposite. The NPs effectively broke the hydrogen bond between asphaltene (number of hydrogen bonds from 22.87–12.50) and reduced its cluster size (8.17–3.25). Among them, Fe3O4-OA and Fe3O4-KH570 showed the most excellent viscosity reduction performance in Oil1 and Oil2, respectively. Finally, by calculating the surface electrostatic potential of each molecule and the weak interaction between molecules, the microcosmic mechanism of the difference in the viscosity-reducing ability and mode of the NPs in different types of heavy oil was revealed. Overall, the NPs effectively depolymerized the high-density aggregation structure of asphaltene, thereby achieving the purpose of reducing the viscosity of heavy oil. However, in Oil1, the viscosity-reducing performance of NPs was mainly related to their ability to adsorb asphaltenes and their dispersion stability. In Oil2, the viscosity-reducing performance of NPs was dominated by their ability to destroy hydrogen bonds between asphaltenes.