The BP spill: What do the methane bubbles mean?

Adm. Thad Allen, the U.S. government's point man for the BP oil spill, said Monday that BP's apparently successful well cap could stay on for another 24 hours, since oil and gas leaks from the cap appear "inconsequential" and methane bubbles seeping from the sea floor two miles away are apparently unrelated. However, even as BP is talking about sealing the well early, Allen warned that he could order the well uncapped if oil or gas is discovered bubbling up from the damaged well. Why is he so worried about a few leaks? (Watch an MSNBC report about the methane bubbles)

What's the current prognosis?

Allen says that things currently look fine with the cap, but that the ongoing "integrity test" will be approved on a 24-hour basis. The methane gas bubbling up two miles from the wellhead is probably naturally occurring. And pressure in the well is slowly building, which is a good thing, but isn't at the level BP and U.S. scientists were expecting.

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Why is the pressure lower than expected?

There are conflicting theories. Some scientists and engineers think it's because the oil reservoir is becoming depleted, so the oil isn't under as much pressure. Others suspect that the well casing is damaged, and that if the currently seen seepage isn't from the busted well, we'll soon find some that is. That could be very bad.

What if the well casing is damaged?

That will be hard to determine "beyond a reasonable doubt," says geologist Dave Rensink. But if U.S. scientists become concerned, Allen will order the cap to be opened for a few days, letting the pressure abate to a level where ships on the surface can safely begin siphoning up the gushing oil.

What's the best-case scenario?

Obviously, a safely and permanently plugged well. BP officials and Allen agree that still means finishing the relief wells and cementing shut the well at its base — a so-called "bottom kill." But BP is also starting to sell the idea of a "static kill," which could choke the well weeks before the relief wells are ready.

How does a "static kill" work?

Much like BP's earlier failed "top kill" — engineers would pump heavy drilling "mud" into the capped well to force the oil and gas back down into the reservoir below. Except it would probably work this time, says BP Senior Vice President Kent Wells, because the mud wouldn't have to overcome the upward-gushing oil. Allen "seemed considerably less enthusiastic about the idea," says Bryan Walsh in Time, since he wants BP to be able to open the cap if things take a turn for the worse.

What's the worst-case scenario?

The sea floor above the oil reservoir crumbling. Oil or gas "seep could be the first sign that the ocean floor is breaking up," says Michael Reilly in Discovery News. The BP cap may be "like sticking your finger in a leaking dam," he adds, and "if another leak springs up nearby, you know the dam's about to crumble." But "does that mean it's time to panic that oil from the Macondo well... is set to burst open through the seafloor in a new, unstoppable gusher?" asks Christopher Hellman in Forbes. "Probably not."

Well, what are the odds of an unstoppable gusher?

"With this extensive monitoring we're having, we're in a good position to not have a catastrophic event," said BP's Kent Wells. And that statement, says Time's Walsh. "I think is meant to make us feel better."

Sources: Newsweek, New York Times, Discovery News, Bloomberg, Balloon Juice, USA Today, Forbes, Time