BP’s stricken well in the Gulf of Mexico spilled an estimated 4.4 million barrels of oil into the ocean before it was capped, the first objective study of the disaster has concluded.
The quantity of oil that poured from the Deepwater Horizon well for three months was enough to fill 700,000 cubic metres.
The gushing well head was capped in July, but the full impact of the world’s worst oil catastrophe is still being unravelled.
Researchers yesterday reported the findings of an independent assessment of the size of the spill in the journal, Science.
By analysing underwater video images of the leak, they calculated that up to 58,000 barrels of oil – possibly more – escaped daily until the first effective cap was installed on July 15. One barrel of oil is equivalent to 42 gallons.
BP has been strongly criticised over the disaster, which occurred on April 20 when escaping methane triggered an explosion that ripped through the oil platform killing 11 workers and injuring 17 others.
The study divides the flow rate into two periods.
The first, from April 22 to June 3, saw 56,000 barrels of oil a day gush from a jagged break in the riser, the pipe extending from the drilling platform to the sea floor.
After June 3, the riser was cut and oil temporarily poured into the ocean unimpeded. At this stage the flow rate rose to around 68,000 barrels.
The authors subtracted 804,877 barrels collected by BP at the site to come up with their final figure of 4.4 million barrels.
Dr Timothy Crone, from Columbia University, New York, who co-led the study, said: “We wanted to do an independent estimate because people had the sense that the numbers out there were not necessarily accurate.”
The researchers pointed out that their conclusions rested on just a few clips of high-resolution video – all that had been released to the public so far by BP and the US government.
Co-author Dr Maya Tolstoy, also from Columbia University, said: “We clearly acknowledge the limits of our technique; we’re unlikely to ever know the exact figure. This is not the last word. It is the first peer-reviewed word. But we think it’s a really good ballpark.”
Dr Simon Boxall, from the National Oceanography Centre at the University of Southampton, said: “There has been criticism of BP, the US Coastguard and the rig operators for not issuing accurate measures of flow from the leaking well. The paper shows that such estimates are by no means straightforward and have taken some significant research to provide values.
“There is still a fundamental question. Is it the size of the spill or the fate of the oil that science needs to focus on?”
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