When spilled at sea, a crude oil is subjected to weathering processes such as evaporation, emulsification, dispersion and photooxidation, which occur under the influence of natural conditions. According to its weathering stage, the oil is continuously changing in terms of chemical composition and physical properties. Understanding and predicting these transformations is a key element in evaluating the potential impacts, optimizing response options and implementing the emergency response plan to spillage.

The objective of this study was to get experimental data on the behavior of crude oils from different oil fields. The various weathering processes were simulated realistically in CEDRE's hydraulic canal, in which different marine water conditions can be recreated: wind, waves, and UV light. All the experiments were carried out with the same agitation level and at two temperatures, 10 and 20°C. Six different oils were tested and the different parameters measured or assessed were: density, viscosity, water content and kinetics of emulsification, chemical composition and kinetics of evaporation, flash point, emulsion stability, oil adhesion, and chemical dispersibility. The evolutions proved to vary considerably according to the nature of the oil, the temperature and the photooxidation process.

The weathering of one crude was also assessed outside in a large pool to provide a calibration of the evaporation and emulsification kinetics in realistic conditions compared to the flume test. The canal speeds up these processes by a factor between 4 and 6.

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