Effects of secondary emulsification of ASP flooding produced fluid during surface processes on its oil/water separation performances

Abstract

Effects of secondary emulsification of field ASP flooding produced fluid by centrifugal pumps and electrostatic field on its oil/water separation performances were evaluated. Secondary emulsification of certain ASP flooding produced fluid with high surfactant content by centrifugal pumps drastically downgraded its oil/water separation performances, increasing the residual water-cuts after 24h static settling at 60 °C respectively by 70% for original o/w emulsion and 1080% for w/o emulsion. Certain w/o emulsion produced by ASP flooding with high surfactant content was susceptible to secondary emulsification in high strength electrostatic field with up to 660% increase of residual water-cut after 24h static settling at 60 °C. Mechanisms governing the effects of secondary emulsification on the oil/water separation performances of ASP flooding produced fluid were discussed. In comparison with produced fluid by water flooding and polymer flooding, the oil/water interfacial tension in ASP flooding produced fluid is much lower, making oil droplets in water and water droplets in oil significantly more sensitive to shear and high strength electrostatic field. Energy dissipation rate, surfactant content and the volume ratio of dispersed phase in the emulsion were identified to be the most important factors affecting the secondary emulsification of ASP flooding produced fluid in turbulent flow. Water in oil emulsion extracted from high water-cut o/w or w/o/w ASP flooding produced fluid was found to have significantly higher water phase surfactant content than the original crude oil emulsion and is much more susceptible to secondary emulsification in turbulent flow than the original reverse emulsion. Surfactant content, content of dual wettability micron and submicron sized particles and the strength of electrostatic field were found to be major factors affecting the secondary emulsification of ASP flooding produced w/o emulsion in AC electrostatic field. As interfacial tension between oil and water in w/o emulsion produced by ASP flooding can be 1 to 2 orders lower than that in the w/o emulsion produced by water flooding and polymer flooding, strength of electrostatic field in electrostatic treaters has to be optimized as per the surfactant content in the ASP flooding produced w/o crude oil emulsion they treat.