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This paper summarizes the results of a study that examined the basic mechanism by which asphaltenes, resins, and waxes stabilize water-in-oil emulsions. Experiments were conducted on the emulsification behavior of model oils that contained alkane and aromatic components and emulsifying agents. Results clearly demonstrate the importance that the physical state of an emulsifying agent has upon its ability to stabilize emulsions. It was found that, to be effective, emulsifiers, asphaltenes, resins, and waxes must be in the form of finely divided, submicron particles. In addition, it was shown that the solvency strength of an oil, which is determined by its alkane and aromatic components, controls the solubility/precipitation behavior of these emulsifiers. The chemical composition of the oil determines not only the amount and size of precipitated particles, but also the composition and wetting properties of the particles. All these factors were shown to influence emulsification. The use of a solubility model, using the Hildebrand-Scatchard equation, to predict the physicochemical conditions that favor water-in-oil emulsification, is discussed.

Laboratory studies on dispersant effectiveness were conducted to assess the effects of several variables and to determine the action mechanisms of dispersants. The variables examined were temperature, salinity, and dispersant quantity. Dispersant effectiveness was measured as a function of the five oil bulk components: asphaltenes, aromatics, polar compounds, saturate compounds, and waxes. The effect of water temperature variation is logarithmically correlated with dispersant effectiveness. With regard to salinity, effectiveness is at a peak when salinity is about 40%c (parts per thousand) of typical commercial dispersant formulations and falls to nearly 0 as salinity decreases to 0. Effectiveness also falls to 0 as salinity rises from 40 to 80%o. This behavior is explained by the necessity for a certain level of ionic strength to stabilize the surfactant between the oil droplet and the water. Dispersant quantity was also found to be an important factor. Dispersant-to-oil ratios greater than about 1:40 or 1:60 result in very low dispersant effectiveness. Effectiveness is logarithmic with respect to dispersant-to-oil ratio. Dispersion experiments wee conducted to investigate the effects of oil composition. Dispersant effectiveness is positively and strongly correlated with the saturate concentration in the oil and is negatively correlated with aromatic, asphaltene, and polar compound contents of the oil. Dispersant effectiveness is only weakly correlated with oil viscosity. Dispersant effectiveness is primarily limited by oil composition.

We have reviewed the laboratory testing of the chemical and natural dispersion of oil, noting the weaknesses of the Mackay test and comparing it to other methods. Results of both chemical and natural dispersion tests show that anomalous test results are produced in the Mackay apparatus at 0° C. This is attributed to preferential viscous shearing when the oil viscosity is 30 to 200 centistokes (cs). A new test uses a small swirling flask. Dispersant effectiveness results for ten oils from the Mackay, Labofina, and swirling flask tests were compared and the correlation found to be low. Results from the new swirling flask test correlate well with physical property data, especially viscosity. Each laboratory test produces somewhat unique results, and no way has yet been found to determine which test most accurately represents reality.