Molecular dynamics simulation for oil/water interfacial activity enhancement of surfactant modified SiO₂ nano-particles

After the old oilfield with medium and high permeability enters high water cut developing period, its remaining oil is scatteredly distributed and it is very difficult to enhance oil recovery. Nano-particles have obvious superiority over enhanced oil recovery for old oilfield. The formation of small particles at nanometer scale in water greatly reduces oil-water interfacial tension and makes the oil in the pores easy to be displaced. Meanwhile, nano-particles possess the temporary blocking effect for the small channels and the recovery factor can be improved by spreading sweeping area. Therefore, the dispersity of the solution and interfacial activity with SiO₂ nano-particles grafted with various surfactants were researched on by using molecular dynamics simulation method. First, SiO₂ system modified by carboxylic acid line was obtained through screening and the ability of reducing oil-water interfacial tension (from 50.880 mN/m to 37.956 mN/m) was investigated. Then, SiO₂ nano-particles modified with alkane and carboxylic acid surfactant mixture were designed with the introduction of Janus structure (Gemini structure). The research results indicate that this structure can further reduce oil-water interfacial tension (from 37.956 mN/m to 32.028 mN/m) and show the structure-activity relationship between nano-particles modified with surfactant system at surface and interfacial activity. It also provides certain theoretical basis for the design and experimental synthesis of high-efficiency nanometer oil displacement agents.