Performance of alkali-free natural petroleum sulfonates: Ultra-low interfacial tension on oil/water interface

Ultra-low interfacial tension (IFT) is one of the most important conditions relating to surfactant flooding for enhanced oil recovery. In this paper, the dynamic interfacial tension (DIT) of an alkali-free petroleum sulfonate surfactant was studied with the spinning drop method aimed at the Daqing oil/water system. The effects of various experimental conditions, such as surfactant concentration, inorganic salt concentration, polar organic compounds, oil-soluble sulfonates, and time stability were investigated. It was shown that the aqueous phase has little effect on DIT. The high molecular weight petroleum sulfonates play an important role in the lowering of oil/water IFT. The non-uniform changes of the oil droplets in DIT measurements were also discussed from the aspects of petroleum sulfonate composition and diffusion rate. The increase of aqueous phase viscosity could only ease the rebound phenomenon, while the increase of heavy components of petroleum sulfonates could both eliminate the non-uniform changes of the oil droplets and reduce the values of the IFT. These results may be helpful in explaining the reasons behind producing ultra-low interfacial tension and the preparation of formulations for practical applications.