Verification study of weathering properties of Draugen crude oil - re-check of oil properties related to oil spill response
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SINTEF has conducted a verification study (re-check) of Draugen crude oil collected in 2018 to determine if weathering data collected from Draugen crude oil collected in 2008 is still valid. Weathering properties of Draugen 2018 were obtained in the laboratory following standard methods and compared to the laboratory data of Draugen 2008. The only significant difference between Draugen 2018 and Draugen 2008 were the viscosities of evaporated 250°C+ residue, which decreased from 7190 and 1490 mPa.s in 2008 to 1658 and 645 mPa.s in 2018, for water-free and emulsified residues, respectively. The decrease in the water-free viscosity for Draugen 2018 could be explained by the variation of the topped 250°(+ residue between the oil samples from 2018 and 2008). All other Draugen 2018 analytical data were not significantly different from Draugen 2008. The weathering data from this 2018 verification study was combined with the existing weathering data of Draugen 2008 as input to SINTEF's Oil Weathering Model (OWM) to run predictions. The time window for dispersant use increased with Draugen 2018 compared to Draugen 2008 based on the lower emulsion viscosities of Draugen 2018. Although not analytical significant, the slightly higher pour point in Draugen 2018 may cause the oil to solidify faster on the sea surface compared to Draugen 2008, which may also reduce the effectiveness of dispersant use. Solidification (high pour point) is therefore likely to be the limiting factor for use of dispersant in an oil spill operation, particularly at winter conditions. Moreover, the use of weir skimmers should be efficient on the Draugen 2018 emulsions after several days of weathering for viscosities < 15-20 000 mPa.s.