OHMSETT Assesses oil herders

In an effort to assess the use of chemical herding agents to thicken oil spills on open water that would allow the slicks to be more effectively treated with chemical dispersants during offshore operations, SL Ross Environmental Research, Ltd. of Ottawa, Canada conducted a week-long test in October 2009 at Ohmsett. This was the fifth experimental task in a multi-year program that was jointly funded by MMS and ExxonMobil.

“The objective was to determine if herders can be used in a spill situation for other than thickening oil slicks in broken ice for burning,” said Ian Buist of SL Ross Environmental Research, Ltd.

According to Buist, in the earlier experiments, they studied:

? If there are better surfactants or chemicals available than the original US Navy herder

? Different formulations of herders for application in cold weather

? Use of herders for improving mechanical recovery (skimmers) in broken ice

? Use of herders in salt marshes

“This experiment at Ohmsett was to see whether herders could thicken slicks from offshore platform blowouts and allow responders to apply dispersants more efficiently,” said Buist.

During the experiment a light crude oil was laid on the water and allowed to spread. A herding agent was then applied to thicken the slick, after which a dispersant was applied at a dosage that either simulated aircraft application, or a vessel spray system.

“We looked at dispersant effectiveness, operational efficiency, and how much dispersant would have to be applied.”

Buist explained that during dispersant operations, vessels can carry more dispersant and apply it to a targeted area of thick oil within the slick; however, it takes time for the vessel to get to the spill. Aircraft can cover a much greater area and spray dispersant on all the oil in the slick, but as a result of the application, overdosing thin sheen and under dosing thick oil can occur.

“So, we really need to answer the question; can herders be used to improve dispersant operational efficiency when responding to a spill?” said Buist

The next step in their research will be to develop the application system for herders incorporating a method to apply it in small doses.