Reporting from Atlanta — BP engineers began a crucial test of their leaking Gulf of Mexico oil well Wednesday evening in an effort to determine whether the pipes were structurally sound enough to allow them to seal off the gushing crude.
The test will measure the pressure inside the well. High-pressure readings for at least 48 hours may suggest that the well casings are relatively undamaged, which could mean it is safe to leave the well capped from above.
And that, of course, would mean the incessant gush of oil, which has already despoiled ecosystems, livelihoods and lives, may finally stop, perhaps by the end of the week.
But the test itself is risky business. It requires that the well be sealed off temporarily with a snug, specially constructed capping stack, which was latched on to the top of the well Monday. And much like a thumb in a hole-studded garden hose, the cap could force oil out of any cracks that might exist in the well.
That scenario, in turn, could cause oil to seep upward and begin gushing from the seabed, potentially turning the well into a ragged crater.
"That is the worst-case scenario," said Iraj Ershaghi, a petroleum engineering expert at USC. "Nobody has the technology to handle that."
Late Wednesday, BP reported on its website that it had closed a ram in its capping device, which is similar to a blowout preventer, but was working to repair a leak on a choke line that would be used to seal the well.
BP officials maintained that the chance was remote that new oil leaks could cause craters in the seafloor around the wellhead. BP Senior Vice President Kent Wells promised that if the test showed very low pressure in the well, a sign that oil could be seeping out underground, the company would move quickly to reopen the gusher and revert to trying to collect as much of the spewing oil as possible.
"We'll immediately look to open up the well, because that would be a very strong indicator that we don't have integrity in the well," Wells said at an afternoon news conference.
Such concerns were a key factor in the federal government's decision Tuesday to delay the start of the test for 24 hours. Wells said in a Wednesday morning news briefing that experts wanted to use that time to consider whether leaks, if they existed, were in the shallow or deep parts of the well.
"What we want to do is avoid that oil is being put out in the shallow environment," Wells said. "There's always the potential, remote as it might be, that it could breach up to the surface."
Thad Allen, the former Coast Guard admiral heading the federal response, announced about 2 p.m. Pacific time Wednesday that he was giving BP the green light to conduct the test, even though much remained unknown about the troublesome hole that reaches 13,000 feet below the ocean bottom, about 5,000 feet below the water's surface.
"We gave them some additional direction, and we did this to make sure we were taking due care — in some cases, maybe an overabundance of caution — to make sure we didn't do any irreversible harm to the well bore as we proceeded," Allen said.
In that spirit of caution, Wells said, BP planned to increase the monitoring of the seafloor by robot submarines, and agreed to consult every six hours with the federal science team, headed by Energy Secretary Steven Chu.
"We spent the last 24 hours addressing all the questions that were raised as we're going forward," Wells said. "The test will proceed as planned with some additional monitoring and consultation along the way."
Wells added that results of a recent seismic test were studied during the 24 hours, but said they "gave us nothing to be concerned about."
The company plans to shut the well off gradually and methodically. By the early evening, they had shut valves leading to two ships collecting some of the oil. Then they used a massive hydraulic ram in the new capping stack to shut off the billowing flow of oil, an ugly icon of the disaster that has been beamed 24 hours a day by underwater cameras to cable news and websites. After that, a so-called kill line will be closed off. Then, slowly, over two hours, with constant monitoring, a final choke line will close. Engineers were working on a leak in that line, according to BP's website.
With that, the runaway well from Mississippi Canyon Block 252, known as Macondo, will be shut, at least for a while.
If the pressure readings are low, the well could be reopened within three hours, and BP could begin collecting some of the oil with two of its containment ships. The company says that with the new capping mechanism, it can eventually use four ships to take up all of the oil, now estimated to be 60,000 barrels a day.
Those ships would have to disconnect in the event of a hurricane, which is possible in the gulf in late summer.
Even if the cap is fully sealed, BP officials say that the permanent fix for the well will only be achieved when it is intersected far beneath the earth's surface by one of two relief wells now being drilled. The closest of those wells, now 17,840 feet in length, is scheduled to plug the faulty well with mud and concrete sometime in mid-August.
Wells said that work on that well was delayed until the integrity test could be completed.