Effect and Analysis of Mixed Non-Ionic Surfactants on Viscosity Reduction in Heavy Oil

This study investigates improving the flowability of heavy crude oil using non-ionic surfactants that modify interfacial properties, thereby enhancing emulsification and dispersion. A mixture of Span 85 (HLB = 1.8) and Tween 20 (HLB = 16.7) was selected to meet the affinity requirements of both oil and water phases. Experiments were conducted on five different densities of heavy crude oil, evaluating viscosity reduction, emulsion droplet size distribution, and interfacial tension. Notably, this work presents the first systematic examination of interactions between various heavy crude oil densities and mixed emulsifiers. Results show that aligning the HLB value of the mixed emulsifier with that of the heavy crude oil enhances electrostatic repulsion between droplets, reducing droplet size and optimizing surfactant arrangement at the interface. The optimal HLB value for viscosity reduction was determined to be 8.0, at which a viscosity reduction rate of over 89% was achieved for high-density heavy crude oil. A quantitative relationship between emulsion droplet size and viscosity reduction rate was also established, leading to improved emulsion stability and significant viscosity reduction. These findings provide a theoretical framework for applying non-ionic mixed surfactants to enhance heavy crude oil flowability, and deliver experimental data to support field applications in petroleum engineering.