Fragmentation of chemically herded oil slicks by multiple obstacles

Chemical herders contract oil slicks floating on the water surface and will likely be a useful tool at high latitudes for condensing oil spills in ice laden waters for in situ burning. However, floating ice and other obstacles on the sea surface fracture the contracting oil slick and trap patches of oil, thus degrading herder performance and burning efficiency. Using Alaska North Slope crude oil and the herding agent OP-40, we performed laboratory scale experiments to investigate how a contracting oil slick interacts with multiple obstacles arranged at different packing densities and with a bottleneck-type gap between obstacles, with a focus on the fluid mechanics of this interaction. The surface and spatial distribution of the herded oil slick is optically measured over time, and particle image velocimetry is used to measure the oil slick flow around the obstacles. Obstacle groups containing large numbers of tightly packed obstacles acted collectively to trap large amounts of oil while widely spaced obstacles that are fewer in number retained smaller individual tails of oil that then break up via capillary instability. Small bottlenecks delayed the contraction of the herded oil slick and resulted in a jet of herder penetrating downstream of the gap whereas wider bottlenecks allowed faster contraction and thus more fragmentation of the herded slick. These results provided a greater understanding of how a contracting fluid film on the water surface interacts with and is fragmented by different types of obstacles and provide a foundation for future modeling efforts to better understand ice-herder-oil interactions.

Automated summary

Chemical herders can contract oil slicks for in situ burning in ice laden waters, but obstacles on the sea surface can fracture the contracting oil slick and degrade its performance. Laboratory experiments were conducted to study how a contracting oil slick interacts with obstacles and how it is fragmented by them.