The Properties of Sable Island Crude Oil In Relation to Its Behavior in the Event of a Spill at Sea
Authors: McLean A.Y. , Odedra D.A. 
Published: October 2008

INTRODUCTION

When any hydrocarbon product enters the marine environment, it proceeds to interact with it under the influence of a variety of processes, the most important of which are evaporation, emulsification, dispersion, solution and oxidation. These processes bring about changes in the physical properties of the hydrocarbon product and these changed physical properties govern further interactions The relative importance of the various processes depends very much on the properties of the original product. Evaporation, obviously, will playa far greater role in the instant of a jet fuel spill than in a spill of an in volatile, residual fuel oil spill, whereas emulsification (i.e. the formation of stable water-in-oi1 emulsions) is a phenomenon associated with spills of crude oil and residual fuel oils and does not occur, to any great extent, with distillate fuel oils. These various processes can result in a major modification of the chemical composition and properties of the original oil. For example the viscosity of emulsified (i.e. water-in oil) bunker fuel oil can be 10 times that of the original oil. The "new" values of physical properties often determine the effectiveness of clean-up techniques and for a rational selection of clean-up techniques appropriate to a given spill, knowledge of the properties of an oil after it has been subjected to the various weathering processes is extremely desirable. Obviously it is very desirable to have the basic knowledge as to how a specific oil might behave subsequent to a spill, before the spill takes place, in order to anticipate the consequences.

This approach was the basis of a project, funded by Mobil Oil Canada Ltd., to examine the characteristics of crude oil, found on Sable Island, Nova Scotia, with a view to establishing the possible behavior of this oil if it were spilled at sea. The effect was studied of various weathering processes on pollution relevant physical properties such as specific gravity, viscosity and surface tension and on the chemical composition of the oil.

The weathering processes studied were evaporation, biodegradation, solution and emulsification. The effectiveness of some typical cleanup techniques was examined for oil after various degrees of weathering.

EVAPORATION

1. The Process of Evaporation

The most immediate process of environmental interaction after the spill of a hydrocarbon product is evaporation, the extent of which is related to the vapour pressure of the hydrocarbon product and the ambient temperature. In the case of an oil spill at sea, wind speed is also relevant. Refined hydrocarbon products, such as gasoline with high vapour pressures, evaporate almost completely whereas low vapour pressure products, such as residual fuel oils, experience quite minor losses due to evaporation More complex mixtures such as crude oil will evaporate, losing light ends and progressively less volatile material until a relatively inert residue is left. Berridge, Dean, Fallows and Fish (1) demonstrated the variations in the effect of evaporation for different crudes by comparing the residue boiling above 700°F.