The Oil Spill's Worst-Case Scenario?

A timeline of the BP oil spill. In the photo above, the well gushes on June 23 after the containment cap was removed following an accident. BP via MSNBC

The grim video feed of oil pouring into the Gulf of Mexico got even worse on Wednesday after BP had to remove the containment cap because a robotic submarine collided with a vent. Even before this setback to contain the massive flow of oil into the gulf, online speculation has fueled fears that the leaks could be much greater than what's been shown. According to these theories, such leaks at the bottom—that is, below the sea floor—could present a new "worst-case scenario" for the disaster, which has now stretched past its second month.

It's possible that hydrocarbons are leaking out the bottom or sides of the well. If so, they might erode surrounding sediments and undermine the foundation upon which the 450-ton blowout preventer sits. If such leaks aren't sealed off in time, the entire structure could topple over. "After that, it goes into the realm of 'the worst things you can think of,'" writes a commenter on the oil- and energy-focused website The Oil Drum. It was this commenter's post that has become the subject of wider speculation. "The well may come completely apart as the inner liners fail. There is still a very long drill string in the well that could literally come flying out … at the very least we are stuck with a wide open gusher blowing out 150,000 barrels a day of raw oil or more."

This comment has since spread online, causing widespread fear and speculation. But not everyone is convinced that such a scenario is probable, or even possible. "The BOP is rigidly connected to all the pipe below," says Roger Anderson, an oil geophysicist at Columbia University. "It would be like knocking the top off a coke bottle, except the bottle top has already been fully breached." Other experts have agreed with him, but point out that the pipe below may have been significantly compromised by initial recovery efforts. "The blowout preventer should be well anchored, with about 2,900 feet of full string casing and cement," says Don Van Nieuwenhuise, director of geosciences at the University of Houston. "However, the well has received some exceptional pressure jolts or kicks, and that has been a concern to BP from the very start."

The likelihood of a complete collapse is difficult to assess, in part, engineers and legislators say, because BP hasn't shared enough information to evaluate the situation. But a handful of clues suggest that the company is concerned. On Friday, BP spokesperson Toby Odone acknowledged that the 45-ton stack of the blowout preventer was tilting noticeably, but said the company could not attribute it to down-hole leaks. "We don't know anything about the underground portion of the well," he said. But, the stack "is tilting and has been tilting since the rig went down. We believe that it was caused by the collapse of the riser." The company is monitoring the degree of leaning but has not announced any plans to run additional supports to the structure.

Photo Gallery: View images of road signs highlighting the rage against the oil spill. SAUL LOEB

As many have speculated, and as the New Orleans Times Picayune reported Friday, concerns over structural integrity are what led BP to halt "top kill" efforts late last month. When it was digging this particular well, the company ran out of casing–the pipe that engineers send down the hole–and switched to a less durable material called liner. This may have created several weak spots along the well that would be particularly vulnerable to excessive pressure or erosion. So instead of sealing the well, the company has been focused on trying to capture the oil as it flows out the top.

At this point, some experts say, additional leaks wouldn't matter much. "It's very possible that there are subfloor leaks," says Anderson. "But that doesn't change the strategy moving forward." The linchpin of that strategy involves drilling relief wells that would absorb all possible leaks, both at the top and the bottom of the hulking, teetering structure. Relief wells are drilled straight down into the sea bottom. After running parallel to the existing well for a few thousand meters, they cut in and intersect the original well bore. BP is drilling two such wells, one on either side of the main well. Once they are complete, the company will use them to pump heavy fluid and cement into the main well, stopping the oil at its source. The approach usually has a 95 percent success rate.

But to work, the well must be sealed as far down as possible–if it's sealed too high, oil could still escape through any leaks beneath the seal. In this case, relief wells will have to drill down to 5,500 meters, and that takes time, at least until August. The real question now is whether the entire structure can hold out long enough.

–Additional reporting by Ian Yarett