Deepwater Horizon Rig Wreckage Oil Sheens
July 17, 2013

Deepwater Horizon Rig Wreckage Responsible For Recent Oil Sheens

redOrbit Staff & Wire Reports - Your Universe Online

Oil sheens recently discovered floating at the ocean's surface near the site of the 2010 Deepwater Horizon disaster were caused by pockets of oil trapped within the wreckage of the sunken rig, according to the results of a new chemical analysis.

The sheens, which were first reported to the US Coast Guard by BP last September, had led to some concern that the capped Macondo Well that played a key role in the largest offshore oil spill in US history could be leaking.

However, that possibility has been ruled out, thanks to the efforts of researchers from the University of California, Santa Barbara (UCSB) and Woods Hole Oceanographic Institution (WHOI) in Massachusetts. Their findings have been published in the journal Environmental Science & Technology.

In addition, the UCSB/WHOI team managed to rule out the natural oil seeps common to the Gulf of Mexico by using a recently-patented method. That method determines the chemical makeup of the sheens and estimated the location of the source of the sheens based on the amount of gasoline-like compounds that evaporate from them.

According to the researchers, every oil sample contains chemical clues that help indicate what reservoir it originated from. That information allows scientists to compare them to other samples in order to determine whether or not multiple samples originated from the same source.

"This appears to be a slow leak from the wreckage of the rig, not another catastrophic discharge from a deep oil reservoir," said UCSB geochemist and co-lead scientist David Valentine. "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."

"It was important to determine where the oil was coming from because of the environmental and legal concerns around these sheens. First, the public needed to be certain the leak was not coming from the Macondo Well, but beyond that we needed to know the source of these sheens and how much oil is supplying them so we could define the magnitude of the problem," added WHOI chemist and co-lead author Chris Reddy.

Valentine and Reddy have each been working on issues related to the Deepwater Horizon incident for much of the past three years. They have investigated the oil's composition and biodegradation, the detection of subsurface plumes, the fate of the dispersants, and the chemical transition from floating oil slicks to sunken tar balls.

They used a technique known as comprehensive two-dimensional gas chromatography (GCxGC) to analyze 14 different sheen samples obtained from the surface during two different trips to the Gulf of Mexico. Their research revealed that the sheens contained oil from the Macondo Well but also contained trace amounts of industrial chemicals known as olefins, which are not found in crude oil.

The presence of the man-made olefins, which are used in drilling operations, indicates that the Macondo Well was most likely not the source of the sheens, the researchers said. They determined the sheens were probably caused by equipment exposed to the chemicals during drilling operations.

"The occurrence of these man-made olefins in all of 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," Valentine said. "This pointed us to the wreckage of the rig, which was known to have both, as the most likely source for the sheens."