WASHINGTON — The Obama administration late Wednesday told BP that it can pour cement into its Deepwater Horizon well, a step that could seal the well permanently.

Moments later, BP announced that the cementing would begin Thursday. There was no word on how long the procedure would last.

"Based on the successful completion of the static kill procedure and a positive evaluation of the test results, I have authorized BP to cement its damaged well," retired Coast Guard Adm. Thad Allen said. "I made it clear that implementation of this procedure shall in no way delay the completion of the relief well."

What role the relief well will actually play in the final demise of the Deepwater Horizon well is uncertain, however.

BP reported earlier Wednesday that a "static kill" had succeeded in forcing what oil remained in the Deepwater Horizon's well bore back into rock formations 13,000 feet below the sea floor and that oil was no longer flowing into the well. If that's true, then the cementing Allen authorized on Wednesday should seal the well — weeks before the relief well will be in a position to try to do the same thing.

BP Vice President Kent Wells said BP was committed to finishing the relief well, which has been underway since May 2, but he was less emphatic than Allen about the need to do so. He said the relief well would be ready to intercept the Deepwater Horizon well in mid August.

"We have always said that we will move forward with the relief well," Wells told reporters in a briefing before Allen's announcement. "If we choose to pump (cement) in from the top, then that might alter what we do with the relief well."

Wells declined to say that BP and the government disagreed. "I wouldn't put it government versus BP," he said. "This is just about some really smart people debating about what's the best way to do things."

Wells said the "static kill" had gone as smoothly as engineers could have hoped. The procedure, which began at about 4 p.m. Eastern time Tuesday, lasted eight hours and required, Wells said, 2,300 barrels — 96,600 gallons — of drilling mud. At a weight of 13.2 pounds per gallon, the mud weighed nearly 1.3 million pounds or more than 637 tons.

At the beginning of the procedure, technicians added the mud at a rate of five barrels per minute, Wells said, but doubled, then tripled that rate to 15 barrels a minute as they gained confidence that the oil was in fact being forced into the reservoir below and being kept there by the mud's weight alone.

He said there was no evidence that the mud had gone anywhere but straight down the drill pipe — suggesting that oil was not flowing in the well's annulus, the empty space between the outside of the pipe and the rock wall of the bore. Allen has said sealing the annulus is the primary reason for completing the relief well.

"Yesterday was a very encouraging day," Wells said.