New data show Gulf oil spill is largest of kind

4.9 million barrels tops in world; study discounts dispersants’ peril

 Admiral Thad Allen, U.S. Coast Guard National Incident Commander, left, and Robert Gibbs, White House press secretary, speak to the media in the briefing room of the White House in Washington, D.C., U.S., on Wednesday.
Admiral Thad Allen, U.S. Coast Guard National Incident Commander, left, and Robert Gibbs, White House press secretary, speak to the media in the briefing room of the White House in Washington, D.C., U.S., on Wednesday.

— The BP spill is by far the world’s largest accidental release of oil into marine waters, according to the most precise estimates yet of the well’s flow rate, announced by federal scientists Monday.

Meanwhile, both retired Adm. Thad Allen, the top federal official in charge of the spill response, and the Environmental Protection Agency on Monday defended the safety of chemicals credited with breaking up the oil into tiny droplets and dispersing it into the Gulf. The EPA said Monday that those dispersants hastened the decomposition of the oil, a process that may also have kept vast quantities of oil from fouling the shoreline.

Nearly 5 million barrels of oil have gushed from BP’s well since the Deepwater Horizon rig exploded April 20, according to the latest data. That amount outstrips the estimated 3.3 million barrels spilled into the Bay of Campeche by the Mexican rig Ixtoc I in 1979, previously believed to be the world’s largest accidental release.

The BP spill was already thought to be the largest spill in U.S. waters, but it was unclear whether it had eclipsed Ixtoc.

“We’ve never had a spill of this magnitude in the deep ocean,” said Ian MacDonald, a professor of oceanography at Florida State University.

“These things reverberate through the ecosystem,” he said. “It is an ecological echo chamber, and I think we’ll be hearing the echoes of this, ecologically, for the rest of my life.”

Federal science and engineering teams, citing data that are “the most accurate to date,” estimated that 53,000 barrels of oil a day were pouring from the well just before BP was able to cap it July 15. They also estimated that the daily flow rate had diminished ove r t i m e , starting at about 62,000 barrels a day and decreasing as the reservoir of hydrocarbons feeding the gusher was gradually depleted.

The teams believe that the estimates are accurate to within 10 percent. They also reported that of the roughly 4.9 million barrels that had been released from the well, about 800,000 had been captured by BP’s containment efforts. That leaves more than 4 million barrels that gushed into the Gulf of Mexico from April 20 to July 15.

The amount of oil estimated to be pouring from the well has been a matter of dispute from the earliest days of the spill. Federal and BP officials initially announced that no oil appeared to be leaking, then 1,000 barrels a day, then 5,000 barrels a day, frequently repeating that spill estimates are rough at best and that the main goal was to stop the well. But criticism mounted that no effort was being made to measure the leak with more certainty.

The Obama administration announced the creation of a scientific group dedicated to analyzing the flow rate, which came up with a new estimate of 12,000 to 19,000 barrels a day in late May, a figure that was met with skepticism.That, too, was later revised upward several times before Monday’s announcement. Previous estimates came from analysis of videos from remote-controlled vehicles at the wellhead, modeling of the reservoir and measurements of the oil that was collected by surface ships in the response effort.

After BP capped the well, these measurements could be reinforced by pressure readings within the well. Those pressure readings were compared with pressure estimates when the well was first drilled to determine whether the rate had changed over time, which it apparently had.

The government is continuing to study the data and may refine the estimate.

‘STATIC KILL’ EFFORTS

Meanwhile, BP continued efforts Monday to permanently seal the well. It said it was preparing to conduct final testing today to determine whether to go ahead with a plan to pump heavy drilling mud into the Macondo well in hopes of permanently sealing it by the end of the week.

During the tests, a surface ship will slowly inject small amounts of mud into the well to make sure the mud will reach the oil reservoir from the column of pipes and valves that sit atop it. If that is accomplished, BP will pump higher volumes of mud, and possibly cement, into the well, in an operation known as a “static kill” or bullheading.

BP executives said Monday that they expected positive results from the tests, which will also check the pressure of the well to ensure that it is safe to pump the mud.


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The tests come 18 days after BP placed a tight-fitting cap on the well that put a temporary end to months of leaking. Engineers had planned to begin the tests Monday but had to delay when they found a small hydraulic leak in the capping control system above the well.

Kent Wells, senior vice president for exploration and production at BP, said Monday that a day or two after the pumping of mud begins, engineers would consider pumping cement into the well, which could permanently plug it. Engineers might also decide to wait for a relief well to be completed before pumping cement in. There is also a chance that they will pump cement during the static kill and later through the reliefwell, to make sure the runaway well is sealed.

“We want to end up with cement in the bottom of the hole, completely filling the entire Macondo well,” Wells said Monday. “Whether that comes from the top or whether it comes from the relief well, those will be decisions made along the way.”

An estimated 2,000 pounds of mud is to be flooded into the well this week.

Allen, leader of the federal response to the spill, cautioned against rushing to declare the static kill a final victory over the well. “I don’t think we can see this as the end-all, be-all, until we actually get the relief wells done,” he said.

Wells said the last 100 feet of the first of two relief wells should be completed by Aug. 15. A final killing of the well by pouring mud and cement just above the reservoir could take a few days or as much as a few weeks. If the first relief well somehow misses its target, a second one is being drilled for insurance.

STUDY ON DISPERSED OIL

Also on Monday, a new federal study of chemical dispersants used to breakup oil in the Gulf of Mexico shows that when mixed with oil, the dispersant is no more toxic to aquatic life than oil alone.

The study also shows that when mixed with oil, the dispersant used in the Gulf, Corexit 9500A, is no more or less toxic than oil mixtures with other chemical dispersants approved for use in oil spills.

The Environmental Protection Agency released the study results Monday as the Obama administration defended itself against assertions that officials allowed oil giant BP to use excessive amounts of chemical dispersants whose threat to sea life remains unknown.

Congressional investigators charge that the Coast Guard routinely approved BP requests to use thousands of gallons per day of Corexit despite a federal directive to use the chemical sparingly.

The Coast Guard approved 74 waivers over a 48-day period after the EPA order, according to documents reviewed by the investigators.

Only in a small number of cases did the government scale back BP’s request.

Often, Allen said, the government was making decisions “without complete information, and sometimes under conditions of uncertainty, because we have never used dispersants at this level before.”

“That was done, and to the extent there’s an issue about it, I’m the national incident commander, and I’m accountable,” he said.

While the chemical dispersant was effective at breaking up the oil into small droplets so that it could be more easily consumed by bacteria, the long-term effects to aquatic life are unknown.

That environmental uncertainty has led to several spats between BP and the government over the use of dispersants on the water’s surface and deep underwater when oil was spewing out of the well.

Information for this article was contributed by Campbell Robertson, Clifford Krauss and Catrin Einhorn of The New York Times; by Matthew Daly of The Associated Press; and by Erika Bolstad and Lesley Clark of McClatchy Newspapers.

Front Section, Pages 1 on 08/03/2010

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