Validating Dispersant Effectiveness

The use of chemical dispersants is an important oil spill response countermeasure.  In the past seven years 15 major dispersant research projects funded by the Bureau of Ocean Energy Management, Regulation, and Enforcement (BOEM) were conducted at Ohmsett.

The most recent research project conducted during the week of November 1, 2010, was a BOEM funded series of dispersant experiments at the Ohmsett Facility to address several different operational issues from ongoing research projects.  Scientists from SL Ross Environmental Research Ltd assisted the Ohmsett staff in conducting these experiments. 

In the first set of the experiments, dispersant effectiveness (DE) testing was conducted on two heavy crude oils obtained from platforms located offshore California.  These two crude oils were not available during the April, 2010 DE testing program Dispersant Effectiveness Testing on Heavy California Oils at Ohmsett.  The established Ohmsett DE test protocol and Corexit 9500 dispersant were used in these experiments.  DCOR, LLC provided the crude oils to BOEM for testing.  Results from these experiments will be used to determine the limiting viscosity for the effectiveness of chemical dispersants applied to viscous U.S. Outer Continental Shelf (OCS) crude oils from the Gulf of Mexico and Pacific. 

The next set of tests conducted later that week, addressed questions that had arisen during earlier test programs.
In past studies, laboratory-scale experiments were conducted at the SL Ross Environmental Research lab using the same dispersant and oil combinations that were tested at Ohmsett. These experiments were designed to determine if small-scale test results can be used to provide reasonable estimates of field performance. Results from the November, 2010 Ohmsett experiments will be used in an ongoing project to correlate the results of bench scale tests to one another. The mixed results suggest that few, if any, of the tests are representative of real-world situations. 

In April, 2010 Heavy Oil Dispersion experiments were conducted using two dispersion application processes to examine the viscosity mechanisms that limit the effectiveness of dispersants. One process was to test the ability of applied dispersant to penetrate into the viscous oil in sufficient quantity to be effective before it is washed away in the dominant water phase. The other process was to test the internal visco-elasticity of the oil that may prevent the oil from being broken into small droplets. Results from these experiments confirmed that dispersant effectiveness is controlled by oil viscosity preventing the penetration of dispersant into the oil where it could work.  A second set of experiments conducted in November, 2010 was to confirm the methodology and results from the April, 2010 experiments.  "We wanted to investigate two levels of the process; how to get the dispersant through the oil and how the internal elasticity of the oil prevents it from being broken into smaller droplets," said Joe Mullin, program manager, BOEM Oil Spill Response Research.

The information gained from these experiments, when applied to the use of chemical dispersants, will significantly enhance the effectiveness of oil spill response countermeasures.