Questions of the day

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Why was this not done with the big one?

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i have to imagine that there was a chemical injection / hydrate inhibition plan w/ the big one, but it was going to be run in association w/ the riser / casing from the rig that was going to engage the cofferdam. they must have thought they had time to do it in this manner.

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Also i know it would be hell trying to thread the needle to but another BOP on to of the 1st, but can it be done and would it work if they could?

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i understand they're aggressively pursuing the a second BOP option. the issue is the connectors that BOP's use to latch onto to something.

The BOP consists of 2 parts -- the lower BOP stack (the rams) and the Lower Marine Riser Package or LMRP (the annular and flex joint). The LMRP is designed to be unlatched and pulled to surface during evacuation activities (and during an emergency disconnect sequence), so when it's pulled there is a profile looking up from the lower stack to latch onto.

The top of the LMRP has no profile or anything, it's just the flex joint then on to riser joints. So in order to latch up a second BOP, the LMRP will have to unlatched using an ROV and recovered to surface along w/ some of the riser that is laid over. This will expose the connector at the top of the BOP stack, and potentially enable a second stack to be latched up on top to shut the well in.

Some special equipment would be required to do this as well. you would need some kind of landing joint on top of the 2nd BOP that would allow the well flow to come through the BOP then divert it out and away as the stack is being lowered, and i'm not aware of any such thing existing at the moment; however, i'm sure BP and TOI are working on it.

Another major concern is the total weight a second stack would put on top of the wellhead. subsea wellhead systems are made out of heavy duty mandrels w/ special profiles cut in them to enable BOP stacks to be latched up and casing hangers to be landed. a major design spec of the mandrel is its resistance to being loaded w/ a huge bending moment due to the weight of a 500k BOP stack sitting on top of it + the rig being pushed off location due to weather (keep in mind that the top of the wellhead system is usually 15' above the the mudline).

So a major question is this: was the wellhead system badly damaged when the rig began drifting off location and ultimately sunk? this question needs to be evaluated before an attempt is made to stack up another 500k BOP stack on top of the existing stuff, for fear that the additional weight + any movement of the rig at surface could result in the wellhead being laid over at the seafloor and breaking -- which would be a much worse situation.