The oil industry is now developing small conventional reservoirs as well as heavy oil and oil sand reservoirs. Production problems such as the precipitation of asphaltenes and the formation of water-in-oil emulsions can be significant for such resources. Since asphaltenes are commonly identified as an emulsion stabilizer, their phase behavior and the means by which they stabilize emulsions are of great interest. To date, only partial success has been achieved in predicting asphaltene solubility. Furthermore, asphaltene stabilized emulsions are so little investigated that even the phase(s) of the asphaltenes that stabilizes water-in-oil emulsions is unknown.

In this thesis, asphaltene phase behavior and asphaltene stabilized emulsions are studied at low asphaltene concentrations. The concentrations are chosen so that the asphaltenes do not form micelles or colloids but exist as free molecules or precipitated solid particles. Asphaltene phase behavior is examined in toluene and hexane solvent mixtures. A thermodynamic model is developed to predict asphaltene solubility at low concentrations. Correlations are developed for the asphaltene molar volumes and solubility parameters required to employ the model. The thermodynamic model successfully fits the experimental data for the toluene/hexane solvent system and predicts asphaltene solubility in a variety of organic solvents. The thermodynamic model is a useful starting point for the development of a model to predict asphaltene solubility in crude oils at production conditions.

The asphaltene phase responsible for stabilizing water-in-toluene/hexane emulsions is determined by comparing the surface areas stabilized by different asphaltene subfractions. The asphaltene subfractions each have a different molar mass and form a different two phase mixture in a given toluene to hexane ratio. The comparisons indicate that asphaltenes stabilize emulsions as a molecular surfactant. The asphaltene stabilized emulsions are resistant to coalescence but do destabilize through a modified form of Ostwald ripening. The accelerating shrinkage of emulsion droplets that occurs with typical ripening is retarded perhaps because the asphaltenes adsorbed on the interface form a membrane. The membrane may become impermeable when the droplets shrink. Further investigation of the asphaltene membrane is recommended because it may affect the outcome of many emulsion treatments.