On Wed, Apr 28, 2010 at 11:42 AM, Don McCumber <woodkayaker_at_yahoo.com>wrote: > > Well, Brad... those of us who live near the Gulf Coast are wondering the > same things..... > Brad wanted to know if a wellhead in 5000 feet of water can be capped off. The answer is, "yes". Even much deeper wellheads can be capped. But there seems to be an issue with the Blow Out Preventer (also called the "BOP Stack"). I spent a half decade working on dynamically positioned drill rigs in deep water; and half of that on a semi-submersible (Sedco 709) that differs from the one that sank only in that the Sedco 709 was not anchored. An anchored semi in water that deep suffers from a few problem areas; one of which is the inability to get out of the way quickly. The details of this are a little murky but I can make an educated guess as to what may have happened. The drill floor is connected to the wellhead via a "riser" which effectively extends the "well" right up to where the men are working. This riser is tensioned to keep it stiff and the drill string goes down the middle of it. As the men drill they pump "mud" through the center of the drill string and out the bit at the bottom. This keeps the bit clear and carries the tailings back up to the drill floor for examination by the geologists. The "mud" is a chemical balance of materials designed to keep any high pressure encountered by the drill bit under control. At the bottom of the riser is the BOP stack which is designed to close off the well in the event of a "blow out". The BOP has several huge valves which can close around the drill string plus a set of shears that can actually cut the drill string in two. Once the well is sealed in the BOP can often be separated into two pieces so that the drill rig can move away from any problems with the riser (and what's left of the drill string) dangling beneath it. With an anchored rig moving away takes much more time. There can be many gas pockets in the geological strata that they drill through and so the drill crew has to be aware of any bubbles of gas that might be moving up the well bore and through the riser. As the gas moves up the well bore it expands because the pressure goes down. One of the main things they look at is the weight of the drill string because a gas bubble will tend to float the drill string and reduce its apparent weight on the block. They also look closely at how the "mud" is flowing through the drill string and up the riser because the expanding bubble of gas displaces the mud which suddenly can vastly increase the flow rate into the "mud" room on the rig.. A sudden increase in mud flow coming up combined with a sudden reduction of drill string weight can spell problems and might cause the driller to hang off the drill string and shut off the well with the BOP. In essence, everything is designed so that the "gusher" you see in old movies never actually happens. It appears that in this case it did happen and it happened so quickly that the drilling crew had no time to close the well in with the BOP stack. That's what those Remote Operated Vehicles (ROV) you see on TV are trying to do manually. The remote controls, obviously, went down with the drill rig. Unfortunately they are having problems. My guess is that when the drill rig sank the riser and drill string inside it damaged the BOP when it all collapsed downwards. At any rate it appears that the well is leaking crude oil. If they cannot get the BOP to close in the well they probably can't use another drill rig to reconnect to it and cement in the wellhead. Remember that the BOP can separate into two pieces. Under a normal disconnect the rig waits out the problem and then comes back to the well head, sends down an ROV for eyes, and then reconnects the top half of the BOP to the bottom half and then recovers the drill string left in the well bore and just keeps on working. A couple of million bucks down the tubes but no big deal. This, however, might be more of a big deal. For one thing the drill string is still in the well bore making a simple cement job more difficult (the drill string would be like a "straw" through the cement). For another thing, there is nearly a mile of riser and drill pipe scattered around the wellhead cluttering up the place and making it more difficult for the work to continue. They may have to slant drill down into the well bore from a distance away using another drill rig and then use that bore to cement in the one that's problematic. At that point they'll slant drill an entirely new bore into the pocket of oil from where they set up for the recovery of the first. None of this can be done quickly. For one thing most drill rigs are booked up long in advance. For another this is deep water and not many rigs are able to carry out such operations in water this deep. Twenty years ago I was part of the crew that set a deep water drilling record of just over 6,000 feet while working on the Discoverer Seven Seas. Today they drill in water 10,000 or 12,000 feet deep. There are rigs and personnel who specialize in fixing these sorts of problems and I'm sure they are on their way now. Til then it's a matter of holding what you've got and hoping for no bad weather. Glad it's not winter... and not quite hurricane season. Not quite. All of this is conjecture, mind you. It's quite possible that someone just dropped a match in the wrong spot and blew the rig up. Craig Jungers Moses Lake, WA www.nwkayaking.net *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Wed Apr 28 2010 - 21:21:35 PDT
This archive was generated by hypermail 2.4.0 : Thu Aug 21 2025 - 16:31:40 PDT