Officials could know by early Friday if BP's broken oil well in the Gulf of Mexico has been sealed for good.
An analysis of tests on the well done Thursday was scheduled to be completed within 24 hours, letting the federal government and BP PLC know if work last month that was meant to be temporary had the unexpected effect of permanently plugging the gusher.
Retired Coast Guard Adm. Thad Allen, the Obama administration's point man on the oil spill, scheduled a news conference in Schriever, La. for 12:45 p.m. CDT to give an update on the operation.
On Thursday, Allen said it's possible that the long-discussed final fix, known as a "bottom kill," won't be necessary. After a temporary cap was placed on top of the well last month, heavy drilling mud and cement were pumped in from above in what's called a "static kill."
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Some of the cement may have gone down into the reservoir, come back up and plugged the space between the inner piping and the outer casing - which is what engineers were hoping to do with the bottom kill, Allen said.
"A bottom kill finishes this well. The question is whether it's already been done with the static kill," he said.
However, he cautioned it's more likely that drilling will continue on two relief wells, which have long been said to be the only way to ensure the blown-out well doesn't leak again. That work has been delayed because of bad weather and wouldn't resume for about another four days, if testing shows it's needed.
Calling off the drilling may be justified by the testing, but it would be a hard sell to a public that's heard for weeks that the bottom kill is the only way to ensure the well is no longer a danger to the region.
"That's been the mantra all along, that they wanted to do the bottom kill," said Eric Smith, associate director of the Tulane Energy Institute.
But work on the bottom kill would be largely pointless if the well is already sealed, he said.
"It doesn't make much sense to drill a hole into cement to pump more cement into it. But it's a public relations nightmare to explain that," Smith said.
On Thursday, officials tested pressure levels in the space between the inner piping and outer casing. Rising pressure means the bottom kill still needs to be done, Allen said. Steady pressure may mean cement already has plugged that space.
However, Allen said tests won't show how much cement is in the space, making the original plan for a bottom kill a better way to ensure the well is permanently plugged.
"What we hope we'll find is an immediate rise in pressure," he said. "It would be more problematic and quizzical if there were no immediate change in pressure."
A decision not to proceed with the relief well would bring an unexpected conclusion to the phase of the disaster that began on April 20 with an explosion on the Deepwater Horizon drilling rig. The federal government estimates that 206 million gallons of oil spilled into the Gulf, the worst offshore spill in U.S. history.