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Oil Weathering Model Updates to Account for Physical Property Changes with Evaporation, Emulsification and Photo-oxidation

SessionOil Spill Science - Modelling

DescriptionWhen oil is spilled into fresh or marine waters it has the potential to form water-in-oil emulsions depending on the spilled oil’s physical and chemical properties, the in-situ conditions, and how the oil weathers upon being released. The formation of emulsions can alter the physical properties of the original oil, sometimes forming a highly viscous mousse. Further, photo-oxidation can greatly influence the physical and chemical properties of oil. Although the factors controlling these processes have been studied for decades, an understanding of the individual importance and inter-relationship of the intrinsic composition of the spilled oil, its degree of evaporative weathering, light intensity, and turbulence remains unclear. Once an oil or emulsion’s viscosity exceeds ~20,000 cP, entrainment is significantly inhibited, whereupon the oil will remain on the surface. To accurately model spilled oil transport and fate in the environment, modelers require consistent quantitative measurements that are representative of field conditions to develop reliable algorithms to predict emulsification and its influence on oil fate and exposure. This paper summarizes the general relationships and recommendations determined from evaluations of laboratory measurements. Herein, we have compared measured results to model-predicted oil densities, identified new relationships (e.g., for oil density, pour point), developed updates to generic weathering coefficients, and discussed the implication of photo-oxidation on oil fate. Findings from this assessment highlight the complexity of measuring oil bulk properties. This underscores the importance of consistent data sets, which are required to improve model fate algorithms. To date, there are large data gaps as it pertains to high viscosity oils and emulsions, which skew the generic relationships used to adjust bulk properties towards those pertinent to low and mid-viscosity oils that have not emulsified.

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