From: Allison Winter, ENN
Published July 16, 2013 03:03 PM

Oil Sheens in Gulf of Mexico Traced Back to Deepwater Horizon Site

When the US Coast Guard was informed of oil sheens in the Gulf of Mexico in July 2012, there was concern over where this oil was coming from.

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In order to determine the source of the sheen, a research team assembled to use recently patented technology in order to fingerprint the chemical makeup of the sheens, compare them to potential sources, and estimate the location of the source based on the extend the gasoline-like compounds evaporated from the sheens.

"The results demonstrate a recently developed geochemical analytical method and may have real-world implications in environmental management strategies for future contamination incidents," says Deborah Aruguete, program director in NSF's Division of Earth Sciences, which co-funded the research.

Because every oil sample contains chemical clues pointing to the reservoir it came from, scientists can compare it to other samples to determine if they share a common source.

After analyzing 14 sheen samples skimmed from the Gulf of Mexico, the researchers confirmed that the sheens contained oil from the Macondo well. However, the samples also contained trace amounts of olefins, industrial chemicals used in drilling operations. 

The team surmised that the sheens must be coming from equipment exposed to olefins during drilling operations.

"The occurrence of these man-made olefins in all our sheen samples points to a single main source, which contains both Macondo oil and lesser amounts of the drilling fluids that harbor the olefins," said geochemist David Valentine of UCSB. "This appears to be a slow leak from the wreckage of the rig, not another catastrophic discharge from a deep oil reservoir."

"Continued oil discharge to the Gulf of Mexico from the wreckage of the Deepwater Horizon rig is not a good thing, but there is some comfort that the amount of leakage is limited to the pockets of oil trapped within the wreckage of the rig."

"The ability to fingerprint synthetic hydrocarbons allowed us to crack this case," Valentine said. "We were able to exclude a number of suspects and match the olefin fingerprint in the new oil slicks to that of the wreckage from the sunken rig."

Scientists note that when the Deepwater Horizon rig sank in 2010, it was holding tanks containing hundreds of barrels of a mixture of drilling mud and oil. Over time, corrosive seawater can create small holes through which oil can slowly escape to the surface. The researchers suspect that the containers on the rig holding trapped oil may be the source of the recent oil sheen.

The results are published this week in the journal Environmental Science & Technology.

For more information, see the National Science Foundation.

Oil sheen image via Shutterstock.

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