HOUSTON — By injecting solid objects overnight as well as heavy drilling fluid into the stricken well leaking oil into the Gulf of Mexico, engineers appeared to have stemmed the flow of oil, Adm. Thad W. Allen of the Coast Guard, the leader of the government effort, said on Friday morning. But he stressed that the next 12 to 18 hours would be “very critical” in permanently stanching what is already the worst oil spill in United States history.
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“They’ve been able to push the hydrocarbons and the oil down with the mud,” he said, referring to the heavy drilling fluid. “The real challenge is to put enough mud into the well to keep the pressure where they can put a cement plug over the top.”
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He said that overnight, workers pumped what is known as “junk shot,” a mix of more substantial materials, like golf balls and shredded tires, into the well, and he said they would follow with more mud later Friday. The junk shot serves as a “bridge,” he said, for the mud injections, to strengthen their ability to counteract the leaking oil.
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While he was optimistic, Mr. Hayward gave the effort a 60 percent to 70 percent chance of success because it had never been tried in water this deep. On CNN Friday, Mr. Hayward said it would be at least 48 hours before the success of the effort could be fully assessed, but he acknowledged that much damage had already been done.
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“This is clearly an environmental catastrophe,” he said. “There is no two ways about it.” The effort to plug the well has proceeded in fits and starts. BP officials, who along with government officials created the impression early Thursday that the strategy was working, disclosed later that they had stopped pumping on Wednesday night when engineers saw that too much of the drilling fluid was escaping along with the oil. At a news conference in Washington on Thursday, the president said he was angry and frustrated about the catastrophe, and he shouldered much of the responsibility for the continuing crisis.
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In the top kill maneuver, a 30,000-horsepower engine aboard a ship injected heavy drill liquids through two narrow flow lines into the stack of pipes and other equipment above the well to push the escaping oil and gas back down below the sea floor.
As hour after hour passed after the top kill began early Wednesday afternoon, technicians along with millions of television and Internet viewers watched live video images showing that the dark oil escaping into the gulf waters was giving way to a mud-colored plume.
That seemed to be an indication that the heavy liquids known as “drilling mud” were filling the chambers of the blowout preventer, replacing the escaping oil.
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