Prediction of the Formation of Water-in-Oil Emulsions

Abstract

The formation of water-in-oil emulsions, a major complication in oil spills, is described. Research has shown that asphaltenes are the prime stabilizers of water-in-oil emulsions and that resins are necessary to solvate the asphaltenes. It has also been shown that many factors play a role, including the amount of saturates and the oil viscosity. Two schemes are given to describe the formation of emulsions using the characteristics of starting oils including the resin and asphaltene contents and the viscosity. Essentially, water droplets injected into the oil by turbulence or wave action can be stabilized temporarily by the oil viscosity and on a longer-term basis by resins and then asphaltenes. Depending on the starting oil properties, four types of water-in-oil types are created: meso-stable and stable emulsions, entrained water-in-oil and unstable or those-that-do-not-form types. Each type is described and has unique properties. For most oils, loss of lighter components by evaporation is necessary before the oils will form a water-in-oil type. It was noted that variability in emulsion formation is, in part, due to the variation in types of compounds in the asphaltene and resins groups. Certain types of these compounds form more stable emulsions than others within the same asphaltene/resin groupings. A review of numerical modelling schemes for the formation of water-in-oil emulsions is given. A recent model is based on empirical data and the corresponding physical knowledge of emulsion formation. The density, viscosity, asphaltene and resin contents were correlated with a new stability index. A simplified screening approach is also described. Although of lesser accuracy, the approach is simple to implement.