HOUSTON — After a government review concluded that pressure tests of a new containment cap would not make the Gulf oil spill worse, BP on Wednesday started the process to begin testing — raising hopes once again that the flow could be stopped nearly three months after the Deepwater Horizon rig explosion.
Kent Wells, a BP senior vice president, said at a Wednesday evening news briefing that the valve on the top portion of the cap had been shut, meaning the oil had stopped pouring out from there. Live video of the cap a mile below the Gulf surface confirmed a significantly reduced flow.
The full "integrity test" will begin when the flow of oil stops coming out of the cap, a BP spokesman told NBC News.
On its Twitter feed Wednesday, BP reported a leak was detected and isolated in a pipe on the cap and the test won't begin until that is repaired.
Retired Coast Guard Adm. Thad Allen, the Obama administration's point man on the disaster, said the government gave the go-ahead after carefully reviewing the risks.
"What we didn't want to do is compound that problem by making an irreversible mistake," he said at the end of a 24-hour roller-coaster of hopes raised, hopes dashed and hopes raised again along the Gulf Coast.
The cap — a 75-ton metal stack of pipes and valves — was lowered onto the well on Monday in hopes of either bottling up the oil inside the well machinery, or capturing it and funneling it to the surface. But before BP could test the equipment, the government intervened because of second thoughts about whether the buildup of pressure from the gushing oil could rupture the walls of the well and make the leak worse.
"We sat long and hard about delaying the tests," Allen said. He said that the pause was necessary in the interest of the public, the environment and safety, and that officials were convinced the test could go forward.
A prelude to the test began with BP shutting off pipes that were funneling some of the oil to ships on the surface so the full force of the gusher went up into the cap. Then deep-sea robots began slowly closing, one at a time, three openings in the cap that let oil pass through. Ultimately, the flow of crude will be blocked entirely. All along, engineers will be watching pressure readings to learn whether the well is intact.
Allen said BP will monitor the results every six hours and end the test after 48 hours to evaluate the findings
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BP has been directed to carry out "additional seismic testing and monitoring from ROVs (remotely operated vehicles) as well as acoustic and temperature monitoring throughout the duration of the well integrity test," the White House said in a statement. "The test will take up to 48 hours and will include periodic assessments in 6-hour increments."
Earlier, Doug Suttles, BP chief operating officer of exploration and production, told CNN that "there were a couple of other concerns around ways flow could escape and we needed to go examine those before we proceeded."
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."
Suttles said the government wanted to verify that the casing, or the piping in the well, is intact and that the oil would stay contained if BP caps the well with its 75-ton metal stack.
'A good precaution' to wait
Wells said earlier Wednesday that it was the government's call late Tuesday to re-evaluate plans for testing the new cap. "It's a good precaution for us to take at this time," Wells added. "We need to understand exactly what's going on."
The cap is a stopgap measure until a relief well can be drilled to then plug the blownout well. The relief well's timeframe has always been hazy, with company and federal officials giving estimates ranging from the end of July to the middle of August before it can be completed.
The test is designed to tell if oil leaking to the surface is coming from a single leak or if more leaks are present elsewhere in the well.
If it's the latter case, the company would leave the valves open on the cap and try to collect the oil with up to four vessels floating on the surface above. Allen said a bigger siphoning operation should be in place by Monday to collect all or most of the oil if it is not contained by the cap.
The oil giant had been scheduled to start slowly shutting off valves Tuesday on the cap, aiming to stop the flow of oil for the first time in three months.
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. The map 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.
Allen late Tuesday 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.
Marine food web altered
As attempts to stop the leak continued, scientists reported early signs that the spill was altering the marine food web by killing or tainting some creatures and spurring the growth of others more suited to a fouled environment.
Near the spill site, researchers have documented a massive die-off of pyrosomes — cucumber-shaped, gelatinous organisms fed on by endangered sea turtles.
Along the coast, droplets of oil are being found inside the shells of young crabs that are a mainstay in the diet of fish, turtles and shorebirds.
And at the base of the food web, tiny organisms that consume oil and gas are proliferating.
If such impacts continue, the scientists warn of a grim reshuffling of sealife that could over time cascade through the ecosystem and imperil the region's multibillion-dollar fishing industry.
Along the Gulf Coast, where the spill has heavily damaged the region's vital tourism and fishing industries, people anxiously awaited the outcome of the painstakingly slow work.
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"I don't know what's taking them so long. I just hope they take care of it," said Lanette Eder, a vacationing school nutritionist from Hoschton, Ga., who was walking on the white sand at Pensacola Beach, Fla.
"I can't say that I'm optimistic — It's been, what, 84 days now? — but I'm hopeful," said Nancy LaNasa, 56, who runs a yoga center in Pensacola.
In other developments Wednesday:
- Attorney General Eric Holder indicated that corporations other than BP could be held liable eventually for the devastating oil spill in the Gulf of Mexico.
- Environmentalists plan to file a lawsuit to seek more information about potential health hazards from oil dispersants and a Senate panel plans a Thursday hearing on the issue.
- BP's safety record would bar the company from getting new U.S. offshore oil and gas exploration leases for up to seven years under bill language passed by a U.S. House committee.
- The European Union might toughen rules covering accident prevention and liability for offshore oil drilling in response to BP's Gulf of Mexico spill.
The Associated Press contributed to this report.