Over the last couple of weeks, I’ve been watching videos of the Joint Investigation by the Coast Guard and the MMS of the Horizon disaster, where many of the surviving BP and Transocean members of the Horizon crew were interviewed during May in Kenner, Louisiana. The information is detailed and very interesting, but have highlighted some inconsistencies with others’ accounts. Much of the conflict surrounds the condition of the BOP (blowout preventer) in the days leading up to the blowout. Remember, there are two real issues here: First and foremost are the bad decisions made by BP management and supervisors that contributed to conditions that allowed the well to come see them. It’s become clear that well design, short cuts, impatience, and bad judgment led to the blowout in the first place. The second issue is why the BOP did not close as designed and tested.
Let’s focus on the second issue today. Why did the BOP not close, sealing the well? There are a number of factors involved, but let’s do a little BOP 101 first. Blowout preventers are a stack of large valves designed to shut-in a well in the event of an emergency while it is being drilled or worked on. These valves have different types of closing devices, or rams, that can close around different sizes of pipe that may be in the hole, close off the hole if there is no pipe inside, or the ultimate failsafe, cut the pipe and seal off the well. These rams that cut pipe are called shear rams, or blind shears, and are designed to cut whatever pipe may be in the hole in the event of a well control situation. The weakness of these particular rams, though, is that they can’t necessarily cut all pipe that may be in the hole. They are usually unable to cut running tools or drillpipe tool joints (shown at left) that are heavier than the pipe itself. The BOP stack is usually set up so that, in a well control situation, the drillpipe rams are closed, the drill string dropped so that a tool joint lands at the pipe rams putting the shear rams opposite the body of the pipe that can be cut. All that assumes that there is time to do all that; in this particular case, we’re not even sure if the rig floor crew survived long enough to even know what hit them, much less go through the shear and shut-in sequence.
The blowout preventer is controlled by hydraulic pressure sourced from accumulator bottles on the surface or subsea. The subsea bottles can be seen at left on a BOP stack. (Notice the size of the stack compared to the men standing next to it.) The rams are in the bottom of the stack, and the two annular preventers, flex joint and riser connector are visible at the top. The BOP is activated by the operator opening a pilot valve on the surface that signals the control pod to activate a control valve that opens, releasing accumulator pressure to fire the rams, causing them to close with explosive force, as much as 5,000 psi. Redundancy is key to BOP control, so there are multiple panels, accumulators, and control pods. On a subsea stack, there are two control pods, always called the yellow pod and blue pod.
Which brings us back to the conflicting reports. During his testimony, Transocean’s Subsea Supervisor, Christopher Pleasant, testified that he had supervised the preventive maintenance of the Horizon’s BOP stack before it was “splashed” (run and set) on the Macondo well. He testified that it tested properly and that it had no leaks. However, he also testified that, at the time of the blowout, he attempted to close both the shear rams and separate from the well with the EDS (emergency disconnect system). He activated the shear rams from the panel on the bridge, and reported that, even though the panel electronically went through the appropriate sequence, the hydraulic gauges showed no fluid movement. When he activated the EDS, he got the same result. He abandoned ship with the rest of the crew a few minutes later after the BOP failed to operate. We know the rest of the story.
Last week, Tyrone Benton, an ROV technician with subcontractor Oceaneering gave an interview to CNN. He tells the story that he detected an hydraulic leak on the yellow control pod. He asserts that he reported the leak to his bosses, who reported it to BP and Transocean. He also asserts that, rather than shutting down, pulling the BOP and repairing the pod, it was merely shut down, eliminating half of the BOP’s redundancy. BP, of course, said that this wasn’t the case; however, it’s well known that, after the rig sank, BP pulled the yellow pod with ROVs and made repairs, later acknowledging a leak. Here’s Benton’s CNN interview:
So. Transocean and BP say the BOP was operable with no leaks. After the blowout, the BOP and EDS completely failed, directly causing the Horizon to burn down and ultimately sink. There are widespread reports of a hydraulic leak, and indeed the yellow pod was pulled for repairs after the blowout. We don’t know yet why the BOP failed. Did it close on a tool joint or the casing hanger? Was there not enough pressure to fire the blind shears? Or did it fail to close at all? Why did the EDS fail to separate? These are questions tthat BP and Transocean could clear up by just saying what the facts are.