Physical Processes in the Spread of Oil on a Water Surface

Abstract

Formulae are recommended for calculating the extent of the spread of oil slicks on water as a function of time. They are based on empirical measurements of spreading rates and analytical and theoretical studies of the physical processes which accelerate or retard the spread of a film. Both one-dimensional and two-dimensional (axisymmetric) slicks are treated. Comparisons of the recommended formulae are made with the limited number of field observations, both for the rate of spread and the maximum slick size.

The oil spill model OILTRANS and its application to the Celtic Sea

“…The spreading of the oil on calm waters is due to the force of gravity and the interfacial tension between oil and water, with the oil viscosity and inertia retarding the spreading forces (Fay, 1969). The most widely used formulations for determining the rate of spread of oil on the water"s surface are the equations proposed by Fay (1971), or versions thereof. Fay divided spreading into three phases.…”

“…The area (m 3 ) over which the oil slick has spread at the end of this first spreading phase was determined by Fay (1971) to be:…”

“…The general spreading formulae proposed by Fay (1971) only deal with an idealised spreading of a slick in a radial manner on calm seas. They take no account of wind conditions, which play an important role in determining the shape and area of actual spills.…”

“…The classical Fay (1971) formulation for mechanical spreading, in the absence of wind effects, is also encoded in the OILTRANS system for sensitivity analyses and to give end users the options to choose an alternative algorithm for local implementations.The calculation of the elliptical spreading of the oil slick is undertaken during the gravity-viscous phase of the spreading of the oil slick and only until the terminal oil slick thickness is reached. Once the terminal oil slick thickness is reached the spreading assumption is removed and the slick is allowed to spread under the influence of horizontal diffusion, surface winds and water current shears, as detailed below, to represent complex, realistic surface slicks.…”

Investigation of self-help oil-spill response techniques and equipment

“…Sea surface and air temperature affect oil evaporation, viscosity, and gravitational spreading (Fay 1971). The Intracoastal Waterway connects centers of maritime commerce from New York to Brownsville, Texas, with a system of protected channels more than 2,700 nm long.…”