Sunday, June 27, 2010

Why the Macondo BOP failure was a good thing.

Originally I believed that the casing was cemented solid and had not failed. When that is the case, bolting a gate valve or BOP onto the stack is an appropriate method of solving the problem. Since then I have learned that the downhole casing is NOT intact. The 9-5/8" segment of the casing (casing is set like an inverted layer cake with the largest casing near the top and successively smaller casing set lower in the well to minimize the hung weight of the casing string while optimizing for tensile strength.) has been blown out of the well and the casing hanger (which has hardened gripper blocks to grip the side of the larger casing) is currently lodged in the BOP, which is one reason why the BOP shear rams were unable to close in the well, too much hardened steel in the way. This means that the lower section of the wellbore is no longer cased. It is "open hole" and that means that the oil and gas can migrate into the formation and concievably flow up around and past the wellbore casing. In this well control configuration, you need to keep the well flowing with as little back-pressure as possible to prevent the fluids from trying to seep out of the wellbore while you prepare a relief well to to a "bottom kill". Imagine you have a garden hose that the dog has been chewing on and it has a bunch of bite holes in it. As long as you don't screw the sprayer nozzle on the end, the water doesn't spray out the holes because there is an easier leak path, but once you screw the nozzle on and restrict the flow, it starts spraying out the holes. Same thing in this situation, the fluid wants to follow the path of least resistance and we need to keep that path inside the wellbore where we can control where it goes not bubbling up all over the seafloor where we can't collect any of it, so it is probably for the best that the BOP did not close because then it would have simply percolated up around the well and it would have been virtually uncontrollable then because once it starts flowing around the wellbore there is no way to stop it and it will only flow more and more as the flow path is eroded and opened up.

Many people have lamented and protested that BP should have closed int he well months ago and have come up with myriad off the wall ideas to close in the well. The problem is that there is no such thing as a one size fits all well control methodology, and even if there was, it would unlikely be something you could wave a magic wand and have it instantly be implemented, most of them take some amount of time to prepare and implement, some more, some less. Yes, the well is making one heluva ecological mess and hundreds of millions of dollars are being lost every day so it behooves everyone to work as fast as possible but in this situation you can't let that be the only consideration because if you do, you will invariably chose the wrong control strategy and make things worse instead of better. Cutting corners and taking risks is what got us into this mess, it is unlikely to get us out of it. There are times when you must allow things to proceed while you bide your time and prepare, this is one such time.

That said, the first relief well is almost in position. It has made one "ranging run" where the drill is run offset and past the wellbore to allow the magnetometers in the directional guidance package behind the bit to more accurately locate the wellbore. They will back off and drill two or three more bypasses to get an accurate picture of the location of the wellbore before they attempt to drill into the wellbore. Then they will set casing and pump cement to seal off the annular area around the relief well's casing before they make a final assault on the blown out wellbore. This is the most ticklish part of the relief well process and they must work slowly and carefully. I expect they will be preparing to make the final assault on the wellbore over the july 4th weekend, if not a bit sooner. They are well ahead of schedule, but again, you don't want to get too ahead of yourself or you'll make mistakes, we've had enough of those.

2 Comments:

Blogger The Dude said...

"Since then I have learned that the downhole casing is NOT intact."

Are you sure that is the case here? I'm asking because there has been some discussion back and forth about that:

http://www.theoildrum.com/node/6659

At first, I gave some consideration to DougR's comment, but the response seemed considerably more rational. I don't mean to dis your post by asking. I truly don't know.

Although I work in the energy industry I'm pretty far removed from the actual drilling ops. So long and short, I'm just as short on real information as the next guy.

That part of both the original comment and the response really rings true with me: the transparency in this situation completely sucks. The reasons for that lack of transparency may be any number of things, but the fact remains.

June 27, 2010 8:45 PM  
Blogger Rorschach said...

Am I sure? no, This was told to me by someone who in involved with the recovery ops. that I trust.

June 28, 2010 7:13 AM  

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