Mesoscale evaluation of oil submerging and floating processes during marine oil spill response: Effects of dispersant on submerging stability and the associated mechanism

The migration of oil spills in marine environment is still not clear, especially the key processes of submerging and floating, which is an important concern for effective disposal of oil spills. In mesoscale wave tank (32 m x 0.8 m x 2 m), this study has evaluated the characteristics of oil submergence based on oil concentration and oil droplet size. The concept of effective submergence is put forward for the first time, utilized to analyze the effects of dispersant on submerging stability and associated mechanisms. The results indicate dispersants increase submerged oil concentration and promote homogeneous distribution and vertical penetration. Of concern is that dispersants increase the proportion of small oil droplets (2.5-70 mu m), prolonging the residence time of oil droplets in water by delaying the floating process. Dispersants sharply reduce oil droplets size (VMD < 44 mu m) thus decreasing the coalescence probability. These contribute to better submerging stability. By contrast, the submerged oil, formed as oil patches, oil streamers, and large oil droplets (VMD > 170 mu m) when without dispersant, will float and reattach to oil slicks more quickly due to their large volume. These findings help to clarify spilled oil behaviors and provide a new idea for the research on oil submergence.