Entrainment of Oil from Oil Spills into the Water Column: A New Theory

Abstract

ABSTRACT Dispersion of oil into the water column is one of the oil spill response options. Under certain circumstances natural dispersion may be efficient enough. In other situations dispersant may be added to improve the dispersion efficiency. An empirical model for natural dispersion, based on laboratory results of Delvigne and Sweeney (1988), has been used for many years now, to estimate the entrainment of oil in the water column. That model, however, does not include surface rheological properties and, hence, is not sufficient to describe both natural and chemical dispersion. In the present paper we propose a new approach based on theory on emulsification processes as occurring in homogenizers. This approach includes all relevant physical characteristics of water and oil and their interface and of the turbulence of breaking waves. The deformation of oil droplets in the turbulent flow, the adsorption of surface active material to the surface of oil droplets, the encounter between oil droplets and the eddies of the turbulent flow were each described in a characteristic time. This characteristic time gives an indication of the time needed for the process to proceed. The ratios between the characteristic times of the different processes determine to what extent droplets can be broken-up. Maximum and minimum droplet sizes were estimated, from which a droplet size distribution was calculated. From the size distribution the percentage of the oil that would be present in droplets smaller than 100 μm, was estimated. The results show similarities with observations from practice. A large influence of the wave height, interfacial tension and oil viscosity was noticed. Therefore, this new approach may form the basis for a new oil spill dispersion model.