reply to post by Cloudsinthesky
Check this out
Newsweek gives a balanced view on the danger on the potential of a complete structural failure of the well:
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.
As many have speculated ... 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 [Roger
Anderson - an oil geophysicist at Columbia University]. “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.
One of the dangers which the relief wells are racing to try to beat is that the blowout preventer (BOP) is leaning and might fall over.
The well casing itself is attached to the BOP. And - as discussed below - the BOP is very heavy. So if the BOP fell over, it would likely severely
damage the structural integrity of the casing.
As the Times-Picayune notes:
The integrity of the well has become a major topic of discussion among engineers and geologists.
"Everybody's worried about all of this. That's all people are talking about," said Don Van Nieuwenhuise, director of geoscience programs at
University of Houston. He said the things that BP has being doing to try to stop the oil or gain control of it have been tantamount to repeatedly
hitting the well with a hammer and sending shock waves down the pipe. "I don't think people realize how delicate it is."
"There is a very high level of concern for the integrity of the well," said Bob Bea, the University of California Berkeley engineering professor
known to New Orleanians for investigating the levee failures after Katrina, who now has organized the Deepwater Horizon Study Group. Bea and other
engineers say that BP hasn't released enough information publicly for people outside the company to evaluate the situation.
When wells are drilled, engineers send links of telescoping pipe down the hole, and those links are encased in cement. The telescoping pipe, called
casing, unfolds like a radio antenna, only upside down, so the width of pipe gets smaller as the well gets deeper.
The cement and layers of casing are normally quite strong, Van Nieuwenhuise said. But with the BP well, there are several weak spots that the highly
pressurized oil could exploit. BP ran out of casing sections before it hit the reservoir of oil, so it switched to using something called liner for
the remainder of the well, which isn't as strong. The joints between two sections of liner pipe and the joint where the liner pipe meets the casing
could be weak, Van Nieuwenhuise said.
Bill Gale, an engineer specializing in fires and explosions on oil rigs who is part of Bea's Deepwater Horizon Study Group, said the 16-inch wide
casing contains disks that are designed to relieve pressure if necessary. If any of those disks popped, it could create undesirable new avenues for
the oil to flow.
Bea said there are also concerns about the casing at the seabed right under the blowout preventer.
Van Nieuwenhuise said he's never actually heard of oil from a blown out well rupturing the casing and bubbling up through the ocean floor. He would
consider that an unlikely, worst-case scenario.
A more likely problem, he said, is that oil could find its way into open spaces in the casing string, known as the annulus, and travel up the well in
areas where it isn't supposed to be. This scenario could be one reason why more oil than expected is flowing at the containment cap that BP installed
earlier this month to collect the oil.
Bea is more concerned about the worst-case scenario than Van Nieuwnhuise. In an answer to a question, Bea said, "Yes," there is reason to think that
hydrocarbons are leaking from places in the well other than the containment cap.
"The likelihood of failure is extremely high," Bea said. "We could have multiple losses of containment, and that's going to provide much more
difficult time of trying to capture this (oil)."
Meanwhile, observers monitoring the video feeds from the robotic vehicles working on the sea floor have noticed BP measuring a tilt in the 40-ton
blowout preventer stack with a level and a device called an inclinometer.