ABSTRACT
Small-scale laboratory methods were used to simulate the weathering processes that occur when crude oil is spilled at sea. Changes caused by evaporation and water-in-oil (w/o) emulsification were studied separately. W/o emulsions were assessed for chemical dispersibility using the Institut Français du Petrole (IFP) and Mackay-Nadeau-Steel-man (MNS) methods.
Larger scale experiments were performed in a meso-scale flume. Crude oil was weathered for three days and then sprayed with dispersant. The results show that emulsion breaking is an important part of the mechanism of chemical dispersion. IFP, MNS, and Warren Spring Laboratory (WSL) tests, conducted on w/o emulsions recovered from the flume, produced much lower levels of dispersion than did treatment in the flume. The standard test procedures do not permit emulsion breaking to proceed to the extent observed in the flume.
A sea trial also was conducted. Preliminary evaluation of the results shows that dispersant application partially broke the w/o emulsion that had rapidly formed. Dispersion proceeded at a slow rate but the treated slick was removed from the surface more rapidly than the control slick. The degree of dispersion was difficult to quantify by visual observation due to the weather conditions. A combination of remote sensing, surface sampling, and subsurface fluorometry provided a more reliable estimate.