Study on an Extended Surfactant Heavy Oil Viscosity Reduction Emulsification System

Fatty alcohol polyoxypropylene polyoxyethylene ether sulfate (C₁₂₁₄P₈E₂S, C₁₀P₈E₂S, C₁₀P₅E₂S, and C₁₀P₃E₂S) extended surfactants were used as the research subjects. These surfactants exhibited exceptional emulsification and viscosity-reducing properties for heavy oil, achieving viscosity reduction efficiencies in excess of 97%. Further investigations revealed that as the number of PO groups in the surfactant molecules increased, the viscosity-reducing efficacy was further enhanced, with a corresponding decrease in the droplet size of the resultant emulsion. The PO groups have a significant effect on the self-emulsification behavior of heavy oil and the oil-water interfacial tension. Their introduction enhances the interfacial interactions between the surfactant and heavy oil components, leading to ultralow interfacial tension and self-emulsification of the system at relatively low sodium chloride concentrations. Molecular dynamics simulations elucidated the viscosity reduction mechanism at the molecular level via detailed calculations and analyses of interfacial film thickness, radial distribution functions, potentials of mean force, energy barriers, and intermolecular interaction forces. The PO groups are primarily distributed in the oil phase and adopt a helical conformation that envelops the hydrophilic oxygen atoms. This allows the methyl groups on the PO chains to interact closely with heavy oil components, thereby promoting the dissolution, dispersion, and restructuring of heavy oil aggregates. In summary, extended surfactants exhibit great application potential in heavy oil recovery. The findings of this study offer valuable theoretical guidance and practical references for the development of novel and highly efficient heavy oil viscosity reducers.