Dynamic Dilational Properties of Oil/Water Interfacial Films Versus Emulsion Stability: Influence of pH, Asphaltenes and Other Surface Active Fractions from Heavy Crude Oils

S. Poteau*, J-F. Argillier*, D. Langevin**

*Institut Français du Pétrole, Rueil Malmaison, France

** Laboratoire de Physique des Solides, Université Paris-Sud, Orsay, France

The transportation of heavy crude oils as oil in water emulsions can be proposed as an alternative to blending the crude oil with a diluent or heating the pipelines. This method is very efficient for enhancing the flow properties of heavy viscous crude oils, and can be achieved either by adding a hydrophilic surfactant or by modifying the pH of the aqueous phase. The complexity of petroleum emulsions comes from the oil composition in terms of surface active molecules contained in the crude, such as naphthenic acids and asphaltenes. These molecules can reorganize and interact at oil/water interfaces. The knowledge of surface tension alone is not sufficient to understand emulsion properties, and surface rheology plays an important role in a variety of dynamic processes. The dilational viscoelasticity behaviors of oil-water interfaces containing different surface active fractions from crude oil diluted in toluene, such as asphaltenes and lower molecular weight fatty acids, were investigated alone and for mixed systems. Results obtained at different pH enables to get a better understanding of the role played by high molecular weight asphaltenes and low molecular fatty acids on film properties and emulsion stability. Relationship between the microscopic properties of the interface and the macroscopic behavior of the emulsions will be discussed.