Environmental

Gulf oil sheens coming from Deepwater Horizon rig debris, study finds

BP 435x292 Gulf oil sheens coming from Deepwater Horizon rig debris, study findsBP’s 2010 Deepwater Horizon oil spill has been making encore appearances ever since it erupted in the Gulf of Mexico a few dozen miles off the Louisiana coast, a group of researchers has concluded in a recent report.

In the fall of 2012, many Gulf Coast residents were alarmed by news that more mysterious oil sheens were being found in the vicinity of BP’s Macondo well, which blew out more than three years ago, killing 11 workers and toppling the Deepwater Horizon rig.

The new oil elevated concerns that BP’s well, which company engineers and contractors had capped and plugged from below, could be leaking oil again. Different sheens were found in that region of the Gulf throughout the following winter. Documented flyovers showed that the trajectory of the new sheens were consistent with Gulf currents and trajectory of the oil’s path from the well.

Fortunately, scientists from Woods Hole Oceanographic Institution (WHOI) and the University of California, Santa Barbara (UCSB) found that the oil has been escaping from the Deepwater Horizon wreckage at the bottom of the Gulf, not the Macondo well itself.

“It was important to determine where the oil was coming from because of the environmental and legal concerns around those sheens,” WHOI chemist Chris Reddy explained. “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.”

Tests conducted on fourteen samples skimmed from the Gulf determined first that the oil’s chemical fingerprint was identical to that of Macondo well crude. But the researchers also found trace amounts of industrial oil-drilling chemical called “olefins” in the oil. Those chemicals are not present in oil samples taken directly from the Macondo well.

“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,” said David Valentine of UCSB, another of the study’s lead scientists. “This pointed us to the wreckage of the rig, which was known to have both, as the most likely source for the sheens.”

The question of how long the wreckage will continue to release significant amounts of oil into the Gulf largely remains unanswered for now. Finding out that answer depends on how much oil is left in the ruins of the rig and its riser pipe. But one thing is nearly certain: BP’s Macondo well oil will continue to make encore appearnces in the Gulf for decades to come, whether it’s in the form of fresh crude or tar mats and oil dredged up by the Gulf’s frequent storm surges.

Source:

Woods Hole Oceanographic Institution