NEW ORLEANS -- Robotic submarines removed the cap from the gushing well in the Gulf of Mexico on Saturday, beginning a period of at least two days when oil will flow freely into the sea.
It's the first step in placing a tighter dome that is supposed to funnel more oil to collection ships on the surface a mile above. If all goes according to plan, the tandem of the tighter cap and the surface ships could keep all the oil from polluting the fragile Gulf as soon as Monday.
BP spokesman Mark Proegler said the old cap was removed at 12:37 p.m. Saturday.
"Over the next four to seven days, depending on how things go, we should get that sealing cap on. That's our plan," said Kent Wells, a BP senior vice president.
It would be only a temporary solution to the catastrophe unleashed by a drilling rig explosion nearly 12 weeks ago. It won't plug the busted well and it remains uncertain that it will succeed.
The oil is flowing mostly unabated into the water for about 48 hours -- long enough for as much as 5 million gallons to gush out -- until the new cap is installed.
The hope for a permanent solution remains with two relief wells intended to plug it completely far beneath the seafloor.
Engineers now begin removing a bolted flange below the dome. The flange has to be taken off so another piece of equipment called a flange spool can go over the drill pipe, where the sealing cap will be connected.
The work could spill over into today, Wells said, depending on how hard it is to pull off the flange. BP has a backup plan in case that doesn't work: A piece of machinery will pry the top and the bottom of the flange apart.
On Friday, National Incident Commander Thad Allen had said the cap could be in place by Monday. That's still possible, given the timeline BP submitted to the federal government, but officials say it could take up to a week of tests before it's clear whether the new cap is working.
The cap now in use was installed June 4, but because it had to be fitted over a jagged cut in the well pipe, it allows some crude to escape. The new cap -- dubbed "Top Hat Number 10" -- follows 80 days of failures to contain or plug the leak.
BP PLC first tried a huge containment box also referred to as a top hat, but icelike crystals quickly clogged the contraption in the cold depths. Then it tried to shoot heavy drilling mud into the hole to hold down the flow so it could then insert a cement plug. After the so-called "top kill," engineers tried a "junk shot" -- using the undersea robots to try to stuff carefully selected golf balls and other debris to plug the leak. That also met failure.
The company is also working to hook up another containment ship called the Helix Producer to a different part of the leaking well. The ship, which will be capable of sucking up more than 1 million gallons a day when it is fully operating, should be working by Sunday, Allen said.
The plan had originally been to change the cap and hook up the Helix Producer separately, but the favorable weather convinced officials the time was right for both operations. They have a window of seven to 10 days.
The government estimates 1.5 million to 2.5 million gallons of oil a day are spewing from the well, and the existing cap is collecting about 1 million gallons of that. With the new cap and the new containment vessel, the system will be capable of capturing 2.5 million to 3.4 million gallons -- essentially all the leaking oil, officials said.
In a response late Friday to Allen's request for detailed plans, BP managing director Bob Dudley confirmed that the leak could be contained by Monday. But Dudley included plans for another scenario, which includes possible problems and missteps that could push the installment of the cap back to Thursday.
And the latest effort is far from a sure thing, warned Louisiana State University environmental sciences professor Ed Overton.
"Everything done at that site is very much harder than anyone expects," he said. Overton said putting on the new cap carries risks: "Is replacing the cap going to do more damage than leaving it in place, or are you going to cause problems that you can't take care of?"
Containing the leak will not end the crisis that began when the Deepwater Horizon drilling platform exploded April 20, killing 11 workers.
The relief wells are still being drilled so they can inject heavy mud and cement into the leaking well to stop the flow, which is expected to be done by mid-August. Then a monumental cleanup and restoration project lies ahead.
Some people on Louisiana's oil-soaked coast were skeptical that BP can contain the oil so soon.
"This is probably the sixth or seventh method they've tried, so, no, I'm not optimistic," said Deano Bonano, director of emergency preparedness for Jefferson Parish.
He inspected beaches at Grand Isle lined with protective boom and bustling with heavy equipment used to scoop up and clean sand.
"Even if they turn it off today, we'll still be here at least another six weeks, on watch for the oil," he said.