Emulsifying stability and viscosity reduction for heavy crude oil in surfactant-polymer composite system

Heavy crude oil is one of the most precious and complex molecular mixtures available, with considerable economic relevance. Nevertheless, its high viscosity and complicated chemical compositions pose an exceptional challenge for viscosity reduction with a compound emulsification system in heavy oil exploitation. Here, two types of polymers were synthesized and compounded with surfactant SDS to reduce the heavy crude oil viscosity. Their emulsifying properties in demineralized water and mineralized water were measured to evaluate their differences from macroscopic views. Furthermore, the corresponding emulsion system (involving resins, asphaltenes, surfactants, polymers, etc.) was also simulated and computed using molecular dynamics simulation to investigate the relationships of various compositions on emulsifying properties at the molecular scale. The results showed that the surfactant-polymer composite system formed by the amphiphilic polymer had an obvious advantage in emulsifying stability with the water segregation rate of 60.6% after 48 h in the simulated salinity and the viscosity reduction rate reached more than 92.1% after optimization. Besides, the electrostatic interaction is the major part of the potential energy in emulsion systems at a ratio of 87.8%. The divalent cations (Ca2+ and Mg2+) resulted in the shrinkage or collapse of molecular conformation of the water-soluble polymer by 19%. The variation of interaction energy in salt solutions for different emulsifying systems caused a series of experimental and simulated distinctions, such as solution viscosity, interface behaviors, the number of hydrogen bonds, and the spatial distribution function, which ultimately determined the emulsifying properties of heavy crude oil. Notably, this work offers insight into the interactions and influences of complex mixtures in oil–water systems. It also facilitates to design and apply the innovative functional chemical additives in heavy crude oil extraction and transportation.