BP's ruptured well in the Gulf of Mexico released more than 200 million gallons of oil before it was capped, government officials said Monday, as the company was poised to stuff the well with dense mud in preparation for a final seal later this month.
The new figures, described as the most accurate to date, place the size of the BP spill in the upper range of earlier estimates, affirming the disaster's ranking as by far the worst offshore oil spill in U.S. history.
Based on pressure measurements from the capped well and new modeling, science teams believe that the deep-sea leak initially poured 62,000 barrels of oil a day into the gulf. As the leak depleted the underlying oil reservoir, the rate fell to a daily flow of 53,000 barrels just before the well was corked with a mechanical cap in mid-July.
All told, experts say, about 4.9 million barrels of oil, or 205.8 million gallons, gushed from the well. Not all of that tainted the gulf, as containment efforts captured about 33 million gallons and funneled it to ships.
With the cap in place, BP is embarking on a series of carefully calibrated steps this week to plug the well in advance of permanently sealing it with cement.
After detecting a small leak in the capping system, engineers postponed until Tuesday the start of a "static kill" procedure that involves pumping heavy drilling mud through the well top. If it works as planned, the dense material will shove the oil down the well's pipe system into the reservoir miles beneath the seabed.
Expected to take several days to complete, the process will fill the well with mud. But federal officials continued to say Monday that even then, they would probably not write the well's obituary.
"I don't think we can see this as the end-all, be-all until we actually get the relief wells done," said retired Coast Guard Adm. Thad Allen, who is overseeing the federal response effort.
It is possible that the final shot of cement could be pumped into the well from the top at the end of the static kill procedure. But it is more likely, Allen said, that the first of two relief wells being drilled will be used to inject cement into the bottom of the original well, smothering it sometime in the next week or two.
In the first phase of the static kill, now scheduled for Tuesday, BP will run an "injectivity test" to see how the well holds up when material is pumped into it. Pressure at the top of the well will be carefully monitored to make sure it does not rise to dangerous levels.
If that goes well, a surface ship will start slowly pumping dense mud, weighing 13.2 pounds per gallon, into the well. How long that process takes and how much mud is needed will depend on the oil's location in the well system.
Oil could have seeped up through the drill pipe, its casing, the space between the pipes and the edge of the drill hole — an area called the annulus — or all three. If oil is in all three places, it could take more than two days to fill them with mud, Allen said.
Engineers cannot be certain that all of the oil's upward paths have been blocked until the relief well bores into the lower portion of the original well, sometime between Aug. 10 and 15.
"We're going to need the final step of drilling into the annulus and making sure that the mud effort from the top got everything done. I don't think we will know that until we come in from the bottom," Allen said.
Controversy continues over one of the tools BP used to keep the oil offshore. Especially in the early stages of the three-month leak, the company made extensive use of chemical dispersants to break the oil into smaller bits that would rapidly dissolve and degrade.
That raised questions about the dispersant's toxicity and the degree to which it would speed the uptake of oil into the gulf's ecological webs.
On Monday, the Environmental Protection Agency released a second round of test results that the agency said showed that oil treated with dispersants was no more toxic than untreated oil.
"I think that probably shows us … the oil itself is the hazard we're concerned about," Paul Anastas, the EPA's assistant administrator for research and development, said in a news briefing.
In tests, researchers exposed juvenile mysid shrimp and an estuarine fish called the inland silverside to oil and dispersed oil.
Anastas said the EPA had not turned up any evidence that dispersants or their byproducts were traveling up the food chain.
Still, Robert Diaz, a marine scientist at the College of William & Mary, said the long-term effects of dispersants on marine life and the gulf environment remained unclear.
With some gulf waters reopening to commercial fishing, Louisiana Gov. Bobby Jindal and other state officials demanded Monday that BP fund a $173-million, long-term seafood safety and marketing plan that would include testing samples of shrimp, crab, oysters and fish each month in all coastal parishes.
"The key to consumer confidence is comprehensive testing," Jindal said during a news conference on a steamy fishing dock in Venice, La. "We need to be able to demonstrate, based on hundreds of samples every month, that this continues to be the safest seafood you can get anywhere in the country, anywhere in the world."
"The future of this industry is in peril," the officials wrote in a letter to BP executives. "The image of oil and dispersants will be difficult to overcome without science to back up our claims."
Times staff writers Louis Sahagun in Venice, La., and Amina Khan in Los Angeles contributed to this report.