Determination of the limiting oil viscosity for chemical dispersion at sea: Final Report

Abstract:

<p>The ability to disperse spilled oils at sea depends on several factors, including oil properties, prevailing sea-state and the treatment rate of oil spill dispersant applied to the oil.</p> <p>Oil spill dispersants function by allowing a high proportion of the spilled oil volume to be converted by cresting wave action into very small oil droplets that are permanently dispersed. Oil spill dispersants do this because the surfactants that they contain are capable of causing a very large decrease in the oil / water interfacial tension (IFT). IFT (or surface free energy) is caused by the dissimilarity between the polar nature of the molecules of water and the non-polar nature of the hydrocarbon molecules of oil.</p> <p>The work described in this report was a 'return to the basics' of using dispersants; an attempt to use a matrix of oil viscosity, dispersant brand, dispersant treatment rate and prevailing sea conditions to provide information on the limiting oil viscosity of dispersion by using a very simple method of visual observation to determine whether dispersion was or was not occurring.</p> <p>The report concludes that some oil spill dispersants will be an effective response to oils with viscosity of 2,000 cP, but will not be effective on oils with a viscosity of 7,000 cP or more, in waves associated with wind speeds of 7 to 14 knots. The precise limiting viscosity between 2,000 and 7,000 cP is not known. The limiting viscosity will increase with wind speed; it is possible that oil with a viscosity of 7,000 cP will disperse at 20 or more knots wind speed. However, it was not possible to test this at sea.</p> This report is divided into the following sections: <ol> <li>Reasons for the Work</li> <li>Dispersion of Spilled Oil at Sea</li> <li>The 2003 UK Sea-Trials</li> <li>Comparison of the Sea Trial Results with Results from Laboratory Tests</li> <li>Conclusions</li></ol><ul> <li>Appendix 1 - Results obtained in Sea Trials</li> </ul>

Author(s):

Lewis, A.