SORHEIM K.R., SINGSAAS I., DALING PS. SINTEF Materials and Chemistry, Norway

The behavior of spilled crude oils and refined oil products depends on the prevailing conditions (e.g. temperature, sea-state, currents) and on the chemical composition of the oil.

Large variations in crude oil properties cause them to behave differently when spilled at sea. The Gullfaks crude spilled at the "Braer" incident in the Shetlands had a low content of waxes and asphaltenes, which are important compounds for stabilizing water-in-oil (w/o) emulsions formed on the sea surface. This, combined with violent weather conditions, resulted in consequences that were much less severe than might have been expected. Almost all of the 84,000 tons of the spilled Gullfaks crude oil was naturally dispersed. During the "Sea Empress" spill, a significant amount of the surface oil was converted into w/o emulsions.

Prior knowledge of the likely behaviour and weathering of a spilled crude oil and pre-spill analyses of the feasibility and effectiveness of different response strategies for the actual oil under various environmental conditions should therefore be an essential part of any oil spill contingency planning to optimize the overall "Net Environmental Benefit" of a combat operation. SINTEF has developed a methodology for studying the weathering behavior of oils in the small scale laboratory, combined with meso scale studies and verification through experimental field trials and data from real oil spill incidents.

This empirical approach has been used in the development of the SINTEF Oil Weathering Model (OWM). Weathering data from field trials with experimental oil spills during the past 15 years have been a fundament for the evolution of the algorithms used in the model. This, combined with a standardized laboratory study of each specific oil, including a bench-scale ("step-wise") weathering investigation, a chemical dispersibility investigation and a meso-scale flume basin weathering investigation, form the basic input to the model.

This paper presents the methodology as it has been developed and is being used in Norway, for producing experimental data used as input to the SINTEF-OWM. Furthermore, the correlations obtained between oil weathering values predicted by the model and ground-truth data obtained from field trials (NOFO 1994 and 1995 trials) are presented. It also describes an approach on how this methodology can be used to establish weathering data on Russian crude oils and oil products as a valuable knowledge for Russian as well as Norwegian authorities for preparing oil spill contingency plans and in a potential real spill situation.

OIL AND GAS OF ARCTIC SHELF 2006 (PROCEEDINGS OF INTERNATIONAL CONFERENCE)