Intrusion dynamics of small oil droplets from a deep ocean blowout

Abstract

This paper presents an experimental study of the behavior of oil plumes in ambient stratification and a mild current, in which the flow is classified as stratification-dominated. Experiments are conducted in an inverted framework by releasing a continuous stream of dense glass beads from a carriage towed in a salt-stratified tank. Non-dimensional particle slip velocity UN ranged from 0.1 to 1.9. While particles of all sizes were affected by the stratification, only those with UN less or equal to 0.5 were observed to enter the intrusion layer. The spatial distributions of beads, collected on a bottom sled towed with the source, present a Gaussian distribution in the transverse direction and a skewed distribution in the along-current direction. Dimensions of the distributions increase with decreasing UN. The spreading relations can be used as input to far-field models describing subsequent transport. The average particle settling velocity, Uave, was found to exceed the individual particle slip velocity, Us, which is attributed to the initial plume velocity near the point of release. Additionally, smaller particles exhibit a "secondary plume effect" as they exit the intrusion as a swarm. The secondary effect becomes more prominent as UN decreases. These findings might explain the observations from the 2000 Deep Spill field experiment where oil was found to surface more rapidly than predicted based on Us. An analytical model predicting the particle deposition patterns, was developed based on findings above and validated against experimental measurements. The model estimates near-field oil transport under the Deepwater Horizon spill conditions, with and without chemical dispersants.