EXPERIMENTS ON NATURAL AND CHEMICAL DISPERSION OF OIL IN LABORATORY AND FIELD CIRCUMSTANCES

Abstract

ABSTRACT At the Delft Hydraulics Laboratory a laboratory flume has been constructed to aid research into natural and chemically induced dispersion processes as well as to test the effectiveness of dispersant in specific conditions. The flume allows the selection of variables and conditions, for instance, the generation of nonbreaking and breaking waves and currents, the variation of temperature, salinity, oil layer thickness, dispersant spray droplet size, and the droplet impact on the slick surface. The flume has been verified with empirical data gathered from an extensive sea survey on the natural and chemical dispersion of a number of oil slicks. The field experiments on natural dispersion can be modeled satisfactorily in the flume with respect to the formation of oil droplets from the oil slick and the initial intrusion in the water column. The further mixing of oil droplets in the water mass are to be calculated from diffusion theories and other transport processes. Field experiments on the natural and chemical dispersion of 10 artificial oil spills in the North Sea led to the remarkable conclusion that spraying an oil slick with chemical dispersant did not enhance the (natural) dispersion process, while a premixed dispersant in oil was very effective. The ineffectiveness of sprayed dispersant could not be explained from a limited series of experiments performed in the laboratory flume on the effects of evaporation, photo-oxidation, emulsification, and layer thickness on natural and chemical dispersion.