Experimental and modeling study of subsea releases of oil and gas. - Oil behavior and effects in a cold or Arctic marine environment as a function of release conditions, oil chemistry and dispersant injection.

Abstract

Abstract

With oil exploration going into deeper waters and more extreme environments, more detailed knowledge is needed about the fate of oil in case of a release. This thesis focuses on initial droplet formation, secondary breakup and fate of oil in a subsurface release and the effect of subsurface injection of dispersants. The objectives were to study initial droplet formation, the effectiveness of different surfactant blends when injected in warm oil, secondary droplet breakup and to model hypothetical oil releases in the Barents Sea. The effectiveness of tested surfactant combinations increased when the temperature of Troll B oil increased. However, a decrease was observed when the commercially available dispersant Corexit 9500A was injected in Kobbe oil at increasing temperatures. This observed change in behavior and effectivity could be related to surfactant and/or oil chemistry. The secondary breakup mechanism tip-streaming, where small droplets shed of the parent droplet due to deformation after surfactant treatment, has been studied and observed to be finished within 10 minutes after the release at different dispersant-to-oil ratios. After one hour in very turbulent conditions, the droplets were stable and spherical in shape. Simulations with the OSCAR model have shown how a reduction in droplet size due to dispersant injection can change the environmental fate of the released oil. Further research could be of interest to see whether the change in dispersant effectiveness is a result of oil or surfactant chemistry and to study tip-streaming at higher oil temperatures.