Floating Crude Oils Slicks are Thickened by Chemical Herder and Fragmented by Obstacles Protruding through the Water Surface

Chemical herding agents may be applied around marine oil spills to contract and thicken the oil slick in preparation for in situ burning and will likely prove useful in ice-infested waters in the Arctic or Antarctic. However, the presence of obstacles (e.g. ice or rocks) reduces the effectiveness of chemical herders and subsequent burning by fragmenting the contracting oil slick. The fluid mechanics of oil slick contraction via chemical herders and oil slick fragmentation by obstacles is not well understood. Here we present controlled laboratory experiments investigating Alaska North Slope crude oil slick contraction by the chemical herder OP-40 in an oil spill basin (92×42×20 cm) within a fume hood. A high-speed camera is used to visualize the oil slick contraction after the application of herder. Using 3D-printed obstacles, the effect of obstacle size and shape on oil slick area, contraction speed, and spatial distribution is determined at multiple time points. The effect of obstacle density is determined by testing multiple obstacles in various arrangements. Particle image velocimetry also is used to measure spatial variations in the slick contraction speed. Obstacle size and shape did not affect slick contraction speed or final slick area but did affect the spatial distribution of the oil slick as quantified by the central normalized moment.