Peer-reviewed report confirms budget estimates on gulf oil spill

A peer-reviewed report released Nov. 23 reaffirmed most of the estimates released Aug. 4 by a collaboration of federal and independent scientists regarding what happened to the oil released into the Gulf of Mexico from Apr. 20 through July 14 by BP PLC’s deepwater Macondo well.

Paula Dittrick
OGJ Senior Staff Writer

HOUSTON, Nov. 23 -- A peer-reviewed report released Nov. 23 reaffirmed most of the estimates released Aug. 4 by a collaboration of federal and independent scientists regarding what happened to the oil released into the Gulf of Mexico from Apr. 20 through July 14 by BP PLC’s deepwater Macondo well.

The most significant change between the August oil budget calculator and the November peer-review report was a doubling of the amount of oil classified as chemically dispersed. This was revised from an estimated 8% to an estimated 16% with a possible range of 10-29%.

Oil spill response crews capped the well on July 15 following the April blowout of the Macondo well, which resulted in an explosion and fire on Transocean Ltd.’s Deepwater Horizon semisubmersible, killing 11 people.

A flow rate technical team estimated 4.9 million bbl of oil was released, of which BP captured 800,000 bbl. Chemical dispersant was used at both the gulf’s surface and at the wellhead to break up the oil so it would degrade faster. Macondo was in 5,000 ft of water on Mississippi Canyon Block 252.

Separate from the flow rate technical team, scientists from the US Geological Survey, Department of the Interior, and National Oceanic and Atmospheric Administration developed an oil budget calculator to try and explain what happened to the oil that had been spilled.

In August, NOAA reported 74% of the oil spilled from Macondo well had evaporated or been burned, skimmed, diluted, dispersed, and recovered. NOAA’s report called for more research (OGJ, Aug. 9, 2010, p. 28).

NOAA’s report prompted inquiries from many observers who questioned the rate of the oil’s biodegradation. Federal officials responded by saying the oil budget calculator’s purpose was to describe the short-term fate of the spilled oil and to guide response efforts. Meanwhile, extensive subsea oil monitoring efforts continue.

“I cannot emphasize enough that it does not tell us today where the oil is or its impact,” National Oceanic and Atmospheric Administration Administrator Jane Lubchenco said during a Nov. 23 conference call in which she described the peer-reviewed report that refined the findings of the first oil budget calculator report.

“The oil budget was not created to draw conclusions about the long-term environmental impact,” of the spilled oil, Lubchenco said. The oil budget calculator was intended to provide clarity on how much oil could be captured or mitigated and how much was not recoverable, she said.

“Fully understanding the damages and impacts of the spill on the Gulf of Mexico ecosystem is something that will take time and continued monitoring and research by federal and academic scientists,” she said.

The early estimate of the percentage of residual oil was 26% in August. The peer-reviewed report revised that figure to 23%, and qualifies that estimate, saying it could be in the range of 11-30%.

“Today’s report is a validation of the original numbers,” Lubchenco said, adding the original estimates in the oil budget calculator were done during an emergency. “We were communicating them to the public simply to share what we knew…in an effort to be as transparent as possible.”

The oil budget calculator used reports about the amount of oil and natural gas captured at the well, combined with model-projected estimates based on historical oil spill data for similar types of oil. Government agencies, academia, and the energy industry devised the oil budget calculator.

Contact Paula Dittrick at paulad@ogjonline.com.

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