Dispersant Testing Under Realistic Conditions

The objective of this research program was to assess the efficiency of mineral fine to disperse crude oil under arctic conditions.

In a first stage, a total of 150 laboratory tests were performed to select the most efficient clay (kaolinite, barite, calcite or bentonite) and to define the MOR (Mineral Oil Ratio) and mixing condition which enable OMA (Oil Mineral Aggregates) formation. The dispersion rates of four oils (Grane, Alaska North Slope, Troll and Oseberg) were assessed at two salinities (5 and 35 ppt). Dispersion was characterized in term of oil concentration in the water column and median OMA size (d0,5) after one hour of resting time. The results obtained during the first stage highlighted that calcite can be considered as the best candidate at MOR 2/5. High mixing energy is required for OMA formation in the water column and then, after test completion, a very low energy is sufficient to avoid the OMA to resurface. Additional tests were performed to assess the combination of mineral fine with dispersant at 2 Dispersant to Oil Ratios (DOR). These tests confirmed that calcite can be considered as the best candidate for OMA formation. Moreover, it was clear that using dispersant for low viscous oils (<23 mPa.S @ 5°C) did not enhance significantly the dispersion compared with results obtained while a mineral was used alone (except for Troll crude oil @ MOR 1/10).

In a second stage, two tests were performed in Cedre’s flume tank. The oil dispersion using Corexit 9500 have been compared with oil dispersion using bentonite at MOR 1/10. The oil was weathered in the flume for 18 hours before dispersant or mineral application. The dispersion efficiency was very low for both conditions and reached 21% and 2% respectively for dispersion and mineral treatment. Without agitation, OMA were observed at the water surface and needed slight agitation to resuspend in the water column.