Effect of Oil Composition on Chemical Dispersion of Crude Oil

Abstract

Effects of oil composition on dispersion effectiveness (defined as the mass fraction of oil entrained as droplets in the water column) and droplet-size distribution were investigated using baffled-flask mixing systems. The composition of oil samples used in dispersion experiments was systematically manipulated by varying the relative concentrations of the saturates, aromatics, resins, and asphaltenes (SARA) fractions. Forward stepwise linear regression was used with a generalized linear model that included main effects and two-factor interactions to evaluate the effects of oil composition on chemical dispersion. Limited sensitivity analysis was used to determine whether the significant effects were strongly dependent on the specific combination of responses observed in these experiments or insensitive to small changes within the range of variation that was observed. The concentration of the aromatics fraction and the saturates–resins interaction exerted statistically significant, positive effects on dispersion effectiveness (p<0.05). Regardless of composition, the droplet-size distributions observed in these experiments were multimodal consisting of small- (<7 μm), medium- (7–20 μm), and large-sized (>20 μm) droplets. Higher concentrations of the saturates fraction favored the entrainment of floating oil as small and medium-sized droplets, whereas the aromatics–asphaltenes interaction reduced the amount of oil present as small droplets. Aromatics–asphaltenes interaction increased the overall diameter of mean volume (DMV) of the dispersed oil droplets, and the saturates–asphaltenes interaction reduced it.