Skimmers operating in waves often recover a large amount of water, both in the form of water-in-oil emulsions and free water. Recovered water dramatically reduces the temporary storage capacity available for oily fluids offshore. The addition of chemical emulsion breakers to the recovery system has been shown to increase the amount of water that can be quickly decanted when recovering emulsions. A significant potential impediment to the application of emulsion breakers to extend temporary storage capacity is the ultimate fate of the emulsion breaking chemical(s). If they end up in the separated water, they will be discharged into the marine environment when the water is decanted.

The objective of this study was to research the partitioning of emulsion breakers injected into an oil spill recovery system at both lab-scale and mid-scale, at Ohmsett. The experiments were designed to simulate the conditions in an offshore oil spill recovery operation. The ability of emulsion breaker addition to reduce water contents of the recovered fluid and the effects of demulsifier addition of the oil content of decanted water were also assessed.

The formation of micelles by the surfactants in the water at high concentrations and the resulting limitations of the analytical technique used to measure high concentrations of the demulsifiers in the decanted water make definitive, quantitative conclusions about the partitioning of the demulsifier between oily and water phases impossible. The following general conclusions could be made:

  • A large fraction of the demulsifier injected into the recovered fluid stream appears to end up in the decanted water.

  • The concentrations of demulsifier in the decanted water are well in excess of 100 ppm and could be as high as 1000's of ppm.

The use of a demulsifier injected into a recovery system, combined with decanting, substantially reduced the volume of water in temporary storage tanks and the water content of emulsions for disposal/recycling. The efficacy of the demulsifier was a strong function of free water content: if the free water content exceeded approximately 55%, the effect of the surfactant was substantially reduced. The degree of emulsion breaking increased with increasing mixing energy applied to the fluid. Increasing the flow rate (and hence turbulence level) and increasing the length of the flow path both resulted in increased emulsion breaking. Primary break occurred in only a few minutes: the application of demulsifier did not appear to affect the time required compared to previous tests without demulsifiers. The results indicated that the use of a demulsifier increased oil droplet concentrations in the decanted water by approximately a factor of two compared to similar tests without demulsifier.

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Author notes

1 The opinions, conclusions, and recommendations contained in this report are those of the authors and do not necessarily reflect the views and policies of the U.S. Minerals Management Service. The mention of a trade name or any commercial product in this report does not constitute an endorsement or recommendation for use by the U.S. Minerals Management Service.