| In this thesis, the role of asphaltenes in stabilizing water-in-hydrocarbon emulsions was investigated by measuring rheological (elasticity) and mechanical (skin formation) properties of asphaltenic films at the hydrocarbon/water interface. The elasticity measurements were obtained using an IT concept Axisymmetric Drop Shape Analyzer, which involves oscillating a hydrocarbon droplet in an aqueous medium. It was found that the total modulus depends on the frequency of the oscillations, asphaltene concentration, and solvent composition. The modulus was found to increase monotonically with frequency at any given concentration. At very low concentrations, the modulus appeared to be purely elastic. At higher concentrations, a viscous modulus appeared and the elastic modulus decreased as diffusion increasingly affected the measurements. The elastic and viscous moduli both increased as the heptane content increased.; Mechanical film properties, such as crumpling, film lifetime, and film ratio experiments performed on the same apparatus and with the same fluids, measured as a function of the aging time, asphaltene concentration, solvent composition, and temperature. The film lifetime increased with aging time and asphaltene concentration, and there was no trend with heptane content. The film ratio increased with aging time, asphaltene concentration, and heptane content. The results suggest that asphaltenes gradually form a cross-linked network on the interface. Increasing temperature from 23 to 60° C had no observable effect on the film lifetime and film ratio. (Abstract shortened by UMI.)... |
