Colloidal interactions in water-in-diluted-bitumen emulsions

The large scale development of heavy oil and oil sand reserves poses several technical challenges including the elimination of undesirable water-in-oil emulsions. In the oil sands industry, water-in-bitumen emulsions are formed during the water extraction process used to separate bitumen from oil sands. Asphaltenes are commonly identified as the bitumen fraction responsible for emulsion stability. However, very little is known about how the asphaltenes stabilize the emulsions. There is a need for quantitative information about the structure of the bitumen/water interface and the surface forces that exist between emulsified water droplets.; The stability of water-in-bitumen emulsions depends, among other things, on the thin film of oil formed between two approaching water droplets. In this study, the Thin Liquid Film-Pressure Balance Technique is used to create microscopic water/solvent diluted-bitumen/water films. The films provide a physical model to study the interaction between two water droplets immersed in a continuous phase of diluted bitumen. Several properties of the film were measured as a function of solvent:bitumen ratio, including film thickness, drainage rate, and film lifetimes. Information about the surface forces and film structure was also obtained from measured disjoining pressure-thickness isotherms. Results indicate that the film was probably stabilized by steric repulsion generated by surface active material from the asphaltene fraction of bitumen. It was estimated that the surfactant material had a length of about 4 nm. There was also evidence that a change in the solvent:bitumen ratio may have caused a change in the surfactant structure within the film. Hence, a relationship probably exists between the surfactant structure within a film and the bulk phase behaviour.; To study this relation, comparisons were made between the bulk phase behaviour and thin foam film behaviour of a model sodium naphthenates-water system. There appeared to be a clear link between the formation of bulk lamellar liquid crystal and the formation of a liquid crystal-like layered structure within the film. A lamellar structure was also observed in the films drawn from an isotropic solution, although it was not clear if the structuring was due to layers of spherical micelles or liquid crystal-like layers of sodium naphthenates.