A two-volume draft investigation report on what the U.S. Chemical Safety Board (CSB) claimed caused the drillpipe to buckle and jam the Deepwater Horizon’s BOP was released June 5. The CSB, which is an independent federal agency investigating chemical accidents, has been very proactive in pursuing its own investigation of the incident.
Now the agency has come out with its own explanation of how and when the pipe buckled. The report concluded that the buckling occurred in the first few minutes of the blowout. According to a press release, the identification of the new buckling mechanism for the drillpipe, called effective compression, was a central technical finding of the report.
CSB stated effective compression occurs when there is a large pressure differential between the inside and the outside of the pipe. The release continued, saying that condition likely occurred when the pipe rams were closed, temporarily sealing the well. This unfortunately established a large pressure differential that buckled the steel drillpipe inside the BOP.
The agency even created an 11-minute animated video to illustrate its theory. You can see it on its website at csb.gov. The CSB claimed its model differs from industry buckling theories due to “insufficient supporting evidence” for earlier explanations. How is it that CSB evaluates one well blowout, and it is a model, while all the other explanations are theories?
Although I am not an engineer, I could see another cause for pipe bending—the pressure of the uncontrolled flow forcing the drillpipe upward into the BOP.
In an earlier report in 2011 by the National Academy of Engineering—Macondo Well-Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety—there was a different conclusion about why the shear rams didn’t cut the pipe. The study was sponsored by the U.S. Department of the Interior.
The report provided a detailed forensic analysis of the BOP. One finding was that when the blind-shear ram was activated, it was unable to center the drillpipe in its blades, which were a combination of straight and “V” blades. This combination has been shown to be inferior to the double-V blade geometry. Because the blind-shear rams did not fully span the BOP annulus, a mashed segment of pipe was caught between the rams and prevented the rams from closing.
I have only read the CSB press release. The blade geometry wasn’t mentioned, although it is shown in the animation.
It is probably good to have an outside agency provide another perspective. If it makes sense, include it.