An experimental study of oil slick contraction by chemical herders and fragmentation by obstacles

Abstract

Chemical herders are a promising technique for treatment of oil spills in icy waters at high latitudes. However, obstacles on the water surface such as floating ice affects or interferes with all spill response countermeasures including chemical herder operations by fracturing the contracting oil slick and trapping small oil patches. Here we experimentally investigate the fluid dynamics of oil slick contraction and the interaction of the contracting oil slick with single obstacles of different shapes and sizes in a laboratory scale basin using Alaska North Slope crude oil and OP-40 herding agent. Oil slick area and thickness, oil-herder interface contraction speed, and the spatial distribution of the slick were optically measured over time, and particle image velocimetry (PIV) was used to measure the flow of the oil slick around the obstacles. For all obstacle sizes and shapes, an oil tail in the obstacle wake was generated as the oil-herder interface passed, which subsequently fractured by a capillary-type instability. Larger and less streamlined obstacles retained greater amounts of oil in these tails. In addition, a widely used theoretical thin film spreading model was successfully used to describe the spreading of the chemical herder against the oil slick at equilibrium. These results provide a foundation for future investigation of synergistic trapping of oil by multiple obstacles as would be seen in the field.