Studies on the Physical and Chemical Behavior of Oil and Dispersant Mixtures

ABSTRACT 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.