NEW ORLEANS — A pivotal moment in the oil crisis hit an unexpected snag Tuesday night when officials announced they needed more time before they could begin choking off the geyser of crude at the bottom of the gulf.
BP and federal officials did not say what prompted the decision or when the testing would begin on a new, tighter-fitting cap it had just installed on the blown-out well. The oil giant had been scheduled to start slowly shutting off valves on the 75-ton cap, aiming to stop the flow of oil for the first time in three months.
It seemed BP was on track to start the test Tuesday afternoon. The cap, lowered over the blown-out well Monday night, is designed to be a temporary fix until the well is plugged underground.
A series of methodical, preliminary steps were completed before progress stalled. Engineers spent hours on a seismic survey, creating a map of the rock under the sea floor to spot potential dangers, like gas pockets. It also provides a baseline to compare with later surveys during and after the test to see if the pressure on the well is causing underground problems.
An unstable area around the wellbore could create bigger problems if the leak continued elsewhere in the well after the cap valves were shut, experts said.
"It's an incredibly big concern," said Don Van Nieuwenhuise, director of Professional Geoscience Programs at the University of Houston. "They need to get a scan of where things are, that way when they do pressure testing, they know to look out for ruptures or changes."
It was unclear whether there was something in the results of the mapping that prompted officials to delay. Earlier, BP vice president Kent Wells said he hadn't heard what the results were, but he felt "comfortable that they were good."
National Incident Commander Thad Allen met with the federal energy secretary and the head of the U.S. Geological Survey as well as BP officials and other scientists after the mapping was done.
"As a result of these discussions, we decided that the process may benefit from additional analysis," Allen said in a statement. He didn't specify what type of analysis would be done, but said work would continue until today.
Assuming BP gets the green light to do the cap testing after the extra analysis is finished, engineers can finally begin to shut the openings in the metal stack of pipes and valves gradually, one at a time, while watching pressure gauges to see if the cap holds or new leaks erupt.
The operation could last anywhere from six to 48 hours.
If the cap works, it will enable BP to stop the gushing, either by holding all the oil inside the well machinery like a stopper or, if the pressure is too great, channeling some through pipes to as many as four collection ships.
To end the leak for good, however, the well needs to be plugged at the source. BP is drilling two relief wells through the sea floor to reach the broken well, possibly by late July, and jam it permanently with heavy drilling mud and cement.
In Washington, White House spokesman Robert Gibbs said the effort to put the containment cap into operation "represents the best news that we've had in the preceding 85 days."
"We are approaching what we hope is the next phase in the gulf — understanding that that next phase is likely to take many years," he added.
PASSING THE TAB: The Obama administration says it has sent a fourth bill to BP and other parties seeking $99.7 million for costs related to the response and cleanup of the gulf oil spill. The administration says three earlier bills, totaling $122.2 million, have been paid in full.