By Washington's Blog
Recently-retired Shell Oil President John Hofmeister told MSNBC yesterday:
The question is whether there is enough mechanical structure left at the base of the reservoir to hold the cement when they start pouring cement in [from the relief well].
The more oil we some coming out, the more it tells you that the whole casing system is deteriorating. The fact that more oil would be coming out rather than less oil, would suggest that the construction within the pipe is offering no resistance whatsoever, and we’re just getting a gusher.
Newsweek gives a balanced view regarding the risk of a total 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 against 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 Think Progress points out:
In a press teleconference Monday, National Incident Commander Thad Allen announced that the riser package is tilting “10 or 12 degrees off perpendicular,” twice the 5.5 degree tilt of the Leaning Tower of Pisa:
The entire arrangement is kind of listed a little bit. I think it’s 10 or 12 degrees off perpendicular so it’s not quite straight up.
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.
Bea said BP isn't sharing enough information for others to know. If there is oil and gas escaping from the sides of the well, it could erode the sediments around the well and eat away at the support for all the heavy equipment that sits above. Bea said reports that BP is using an inclinometer is significant news. "It tells me that they are also concerned," he said.
Here are videos of BP measuring the tilt of the BOP.
While the BOP weighs 40 tons, the riser package as a whole weighs over 450 tons. If the BOP and riser package fell over, it would inflict severe damage to the attached well casing. The Houston Chronicle reports:
Money-saving measures BP took while designing the Macondo well in the Gulf of Mexico appear to have dogged efforts to bring the massive oil spill under control. Documents released by congressional investigators show that modifications to the well design BP made last year included a reduction in the thickness of a section of the casing — steel piping in the wellbore The modification included a slight reduction in the specified thickness for the wall of a 16-inch-diameter section of pipe toward the bottom of the well, according to a May 14, 2009, document.
The condition of the well also limits how much oil and gas can flow into containment systems now being used successfully to capture some of the flow. Even if a vessel could capture all the hydrocarbons gushing from the well, some would have to be released to keep well pressure under control.
Marvin Odum, president of Houston-based Shell Oil, the U.S. arm of Royal Dutch Shell, told the Houston Chronicle last week that the integrity of the well casing is a major concern. Odum and others from the industry regularly sit in on high-level meetings with BP and government officials about the spill.
If the well casing burst it could send oil and gas streaming through the strata to appear elsewhere on the sea floor, or create a crater underneath the wellhead - a device placed at the top of the well where the casing meets the seafloor - that would destabilize it and the blowout preventer.
The steel casing used in oil wells is strong, said Gene Beck, petroleum engineering professor at Texas A&M, but pressures deep in a well are powerful enough to split strong steel pipe or "crush it like a beer can."
The strength and thickness of casing walls are key decisions in well design, he said. If the BP well's casing wasn't strong enough, it may already be split or could split during a containment effort.
BP spokesman Toby Odone said the decision to reduce the pipe thickness was made after careful review. The company said it doesn't know the condition of the well casing and has no way of inspecting it.
BP is drilling two relief wells to intercept the Macondo well near the reservoir and plug it with cement. A rupture in the Macondo well casing probably wouldn't affect that effort, said Donald Van Nieuwenhuise, director of geoscience programs at the University of Houston.
"When they start the bottom kill the cement will try to follow oil wherever it's escaping, so it would actually hide a lot of sins in the well bore," Van Nieuwenhuise said.
So far there are no signs that the section of the pipe below the sea floor is leaking.
The blowout preventer has been listing slightly since the accident, but officials believe that may have happened when the Deepwater Horizon sank while still attached to the well via a pipe called a riser.
But the longer the well flows uncontrolled the more likely it is that the well casing could be damaged or the blowout preventer damaged further. Sand and other debris that flows through the pipes at high velocity can wear through metal over time, said Van Nieuwenhuise.
The chances of the well eroding from underneath and the blowout preventer tipping may seem unlikely.
"But everything about this well has been unlikely," said David Pursell, an analyst with Tudor Pickering Holt & Co
Indeed, oil industry expert Rob Cavner says that he wouldn't be surprised if the BOP ended up falling over entirely:
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