The effect of weathering on a crude oil residue exposed at sea

Abstract

Kuwait crude oil residues have been exposed to weathering at sea (Langstone Harbour, Portsmouth) for 2 yr. in the form of a water-in-oil emulsion (“chocolate mousse”) in a floating layer about 1·4 cm thick. One batch of oil was exposed in a tank open to tidal flushing below the water line, and a second batch was exposed in a closed tank. A number of chemical and physical properties of the oil were measured at intervals, as were the concentrations of mineral nutrients and bacterial numbers in the sea water. Asphaltenes, specific gravity and viscosity all increased, as did the “polar” fraction from liquid chromatography. The n-alkanes decreased to about half the original levels in the open tank but were little altered in the closed tank. The constancy of vanadium and nickel concentrations suggest that no net loss of oil occurred, the substantial changes in properties deriving from chemical modification (probably oxidation and polymerization) of oil components, rather than mineralization (conversion to carbon dioxide and water) of some components leaving a residue of altered composition. It was not determined which of several processes predominated in causing these changes, but it is thought likely that in this thick layer of mousse auto-oxidation predominated over biodegradation.