Enhanced Viscosity Reduction of Heavy Oil by a Synthesized Extended Anionic Surfactant: Mechanistic Exploration and Performance Evaluation

The exploitation and transportation of heavy oil are severely hindered by its high viscosity. In this study, an extended anionic surfactant PE-54 was synthesized via sulfuric acid esterification to improve the flowability of heavy oil. The molecular structure of the surfactant (PE-54) was confirmed by Fourier transform infrared, ¹H nuclear magnetic resonance (NMR) and ¹³C NMR, elemental analysis, and gel permeation chromatography. The critical micelle concentration of PE-54 was determined to be 1.02 mmol/L. The effects of surfactant dosage, oil-water ratio, and salinity on viscosity reduction were systematically investigated. Under optimal conditions (salinity of 10,023 mg/L, temperature of 50 °C, oil/water ratio of 6:4, and dosage of 1500 mg/L, the viscosity reduction rate reached 94%). The viscosity reduction mechanism was further elucidated through particle size analysis, Zeta potential measurements, interfacial tension tests, rheological characterization, and molecular dynamics simulations (MD). PE-54 molecules rapidly adsorbed at the oil-water interface, competitively interacting with asphaltenes and resins. The surfactant formed a stable interfacial configuration, hindering the aggregation of heavy components and enhancing the interfacial stability. These synergistic effects effectively improved emulsion stability and reduced viscosity, providing theoretical and practical guidance for the development of heavy oil viscosity reduction technologies.