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Weathering assessment

In order to simulate the main weathering processes (evaporation and emulsification), the oils to be studied undergo a systematic test procedure.

Crude oils are distilled at 3 different temperatures (vapour temperatures of 150, 200 and 250°C), with the distillation at 250°C repeated to complete the weathering simulation by recreating the equivalent of 4 days of photo-oxidisation in real conditions.

The residues prepared through this process are then emulsified with seawater to different degrees (water contents of approximately 50, 66 and 75%).

In addition to the initial crude, 13 samples representing potential changes at sea are therefore obtained (Daling and Strøm, 1999).

Emulsions are characterised by various physical measurements (viscosity, density, water content) and the dataset for each crude oil can then be fed into forecast models, varying in particular the temperature and wind speed.

The test matrix put forward for this study is concordant with the input data required by the SINTEF Oil Weathering Model.

 

 Table: Characterisation and sample preparation matrix for crude oils

Characterisation

Crude

Distillation residues

(vapour temperature)

 

150°C+

200°C+

250°C+

250°C ph. ox.

Volume evaporated (%)

Residue (% weight)

Density

Pour point (°C)

Flash point (°C)

Viscosity at 25°C (mPa.s)

Viscosity of the emulsion with 50% water

Viscosity of the emulsion with 75% water

Viscosity of the emulsion at max. %

Maximum water content (%)

T1/2 for maximum water (min)

Asphaltenes / Paraffins

-

-

m

m

m

-

-

-

-

-

-

c

m

m

m

m

m

m

m

m

m

m

m

c

m

m

m

m

m

m

m

m

m

m

m

c

m

m

m

m

m

m

m

m

m

m

m

m

-

-

m

m

m

m

m

m

m

m

m

-

Distillation curve up to 250°C

 

 m: measured / - : N/A / c: calculated from measurements taken on the 250°C residue