http://www.theoildrum.com/node/6879
How do you remove the drill pipe and replace the missing mass with mud at the same time ?
If the the pressure in the wellbore is currently at an equalibrium, nothings leaking, when they pull the pipe out, wouldn't seawater start to go down the wellbore ?
How do you pump mud and guarantee it will go down and not up ?
...also...is it possible for gas to drift from the reservoir, up through the strata, and back into the wellbore at a higher point ? I understand that if it's at an equilibrium, nothing can move either way...but if the bore does not have 100% structural integrity of the outer cement and casings, and the inside of the bore were to become underpressured against the surrounding formation by removing said mass (DP)...'looks at floor'....
...I'm gonna go tighten my neck-bolts for a spell.
If the the pressure in the wellbore is currently at an equalibrium, nothings leaking, when they pull the pipe out, wouldn't seawater start to go down the wellbore ?
How do you pump mud and guarantee it will go down and not up ?
...also...is it possible for gas to drift from the reservoir, up through the strata, and back into the wellbore at a higher point ? I understand that if it's at an equilibrium, nothing can move either way...but if the bore does not have 100% structural integrity of the outer cement and casings, and the inside of the bore were to become underpressured against the surrounding formation by removing said mass (DP)...'looks at floor'....
...I'm gonna go tighten my neck-bolts for a spell.
Isaac,
The well is open to the sea at the moment - it is not balanced with mud but sealed with 5000 feet of cement.
"it is not balanced with mud but sealed with 5000 feet of cement."
Yes, I understand that( I was under the impression that there is a leg of mud on top of that as well 5k' of seawater :), what I don't understand is how you remove mass from an area and add it at the same time without causing a differential in pressure. Are they going to remove the stuck pipe at the same time they are pumping mud..? I know it's a completely different scenario, but pulling a pipe stuck in mud creates suction/vacuum energy, the Casimir effect, which creates a negative pressure . Then there is the question of the mud and if its gelled inside the DP, wouldn't pulling that up also create negative pressure downhole( unless the force exerted by the water column above was sufficient to break the mud free when they started to pull up ) ? This is all very interesting in terms of fluid dynamics. Thanks again TOD, for taking the time to answer my " whacko" questions.
Yes, I understand that( I was under the impression that there is a leg of mud on top of that as well 5k' of seawater :), what I don't understand is how you remove mass from an area and add it at the same time without causing a differential in pressure. Are they going to remove the stuck pipe at the same time they are pumping mud..? I know it's a completely different scenario, but pulling a pipe stuck in mud creates suction/vacuum energy, the Casimir effect, which creates a negative pressure . Then there is the question of the mud and if its gelled inside the DP, wouldn't pulling that up also create negative pressure downhole( unless the force exerted by the water column above was sufficient to break the mud free when they started to pull up ) ? This is all very interesting in terms of fluid dynamics. Thanks again TOD, for taking the time to answer my " whacko" questions.
They slowly dropped the pressure during the negative test. When they initially had the well balanced that was with the column of mud up to sea-level and BOP was at about 4200psi but they are now right down to ambient at 2188 psi with the well open to seawater. If there was an open flow path then we would know fairly quickly :)
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That's not what I am asking about, but thank you anyway.
Isaac:
Yes, the mud level in the well will go down as the pipe is pulled, and that volume will be replaced by seawater, since the well is currently open to the sea at the top.
The key is, it doesn't matter. You could replace the entire 8000' down to the cement with seawater, and even then no oil would flow because the 5000' of cement would hold it in, as it has been for several days now ever since they started that near-ambient testing stuff.
Gas drifting "up through the strata, and back into the wellbore"? Anything's possible, I guess. Well, up to when they started the near-ambient testing, anyway. But the pressure DECREASE observed (due to leakage out of the stack) pretty well put that scenario out of the picture. Then when they went to exactly ambient and closed all the valves, they had no pressure change for 48 hours.
Frank
I'm not a expert, but I think I have an explanation:
The fishing tool is put down into the top of the second, new BOP that was kludged onto the top of the BOP that is wanted for evidence. To do this 'put down into ...' the tool is attached to the bottom end of a new string of drill pipe. This attachment is sturdy enough that the 'bad, broken' drill pipe can be lifted out of the well once the fishing tool is firmly connected to it. The strength of this attachment can be tested by pulling on the top end of new string of drill pipe from up on the drill ship. There, they can measure force of lifting of the crane that is holding the new drill pipe. If they can't develop enough force to lift an extra 3000' of drill pipe, they huddle and come up with a planB, otherwise they are ready to try to open the shear rams in the BOP (that they think are what is holding the bad, broken drill pipe and keeping it from falling deep into the well). If the get the shear ram open, which they should do --slowly-- so that
the weight of the bad broken drill pipe shifts from the shear ram over to the new string gradually, THEN they can start drawing the bad, broken drill pipe out of the well --SLOWLY--. This is the first time in the process when they have to start replacing the volume of the bad, broken drill pipe with something that is heavier than seawater.
This replacement material is, I think, what concerns you:
What to use as replacement material? Solid, liquid, or gas? I guess a liquid. A solid would get in the way of pulling the bad, broken pipe up and out. A gas is an option that a physicist, like me, would even mention. So their only option is a liquid, like mud. It is heavy and it can be made to flow downward by suitable application of gravity.
The fishing tool is mechanically connected to both the good new pipe string and the bad, broken pipe, BUT it is not a pipe fitting. Mud can be pumped down from the drill ship inside the the good new pipe string. Enough new mud can be pumped to flood the region around the fish tool so that it is immersed in mud. (Now they can't any longer see what they are doing, because mud is opaque. But they are probably doing this without downhole cameras, anyway.) They an determine the depth of mud in this flooding by measuring the pressure differential between the inside of the BOP and the surrounding seawater. They pull the string of bad, broken pipe and good, new pipe up. As they do this, the level of the top of the mud should go down to replace the volume of pipe that is coming up out of the mud. This should be done during the first few inches of upward motion of the combined pipe string. If there is numerical agreement of pipe string upward motion with mud level downward motion, they can continue --- add mud to keep the mud level above the top of the BOP, but not spilling out of the top and the top the top of that that other, now structure that they stacked on top of the BOP. AND keep track of mud volume pumped. And plot the data as they gather it. Make sure mud level and volume track the upward motion of drill string, psi by psi and cuft by cuft against pipe travel inch by inch.
My major problem with this is that I am convinced that BP managers are intellectually incapable of handling this level of sophistication in process. Or if they are capable, they perceive that it is to their advantage to pretend otherwise.
Not covered are issues relating to the possibility that bad, broken pipe is stuck in the cement that is being used to kill the well. Pulling it out of the cement would introduce cracks. Mud would have had no problems with cracking. Also, I have ignored all complications having to do with elastic nature of pipe, steel cable, etc.
The fishing tool is put down into the top of the second, new BOP that was kludged onto the top of the BOP that is wanted for evidence. To do this 'put down into ...' the tool is attached to the bottom end of a new string of drill pipe. This attachment is sturdy enough that the 'bad, broken' drill pipe can be lifted out of the well once the fishing tool is firmly connected to it. The strength of this attachment can be tested by pulling on the top end of new string of drill pipe from up on the drill ship. There, they can measure force of lifting of the crane that is holding the new drill pipe. If they can't develop enough force to lift an extra 3000' of drill pipe, they huddle and come up with a planB, otherwise they are ready to try to open the shear rams in the BOP (that they think are what is holding the bad, broken drill pipe and keeping it from falling deep into the well). If the get the shear ram open, which they should do --slowly-- so that
the weight of the bad broken drill pipe shifts from the shear ram over to the new string gradually, THEN they can start drawing the bad, broken drill pipe out of the well --SLOWLY--. This is the first time in the process when they have to start replacing the volume of the bad, broken drill pipe with something that is heavier than seawater.
This replacement material is, I think, what concerns you:
What to use as replacement material? Solid, liquid, or gas? I guess a liquid. A solid would get in the way of pulling the bad, broken pipe up and out. A gas is an option that a physicist, like me, would even mention. So their only option is a liquid, like mud. It is heavy and it can be made to flow downward by suitable application of gravity.
The fishing tool is mechanically connected to both the good new pipe string and the bad, broken pipe, BUT it is not a pipe fitting. Mud can be pumped down from the drill ship inside the the good new pipe string. Enough new mud can be pumped to flood the region around the fish tool so that it is immersed in mud. (Now they can't any longer see what they are doing, because mud is opaque. But they are probably doing this without downhole cameras, anyway.) They an determine the depth of mud in this flooding by measuring the pressure differential between the inside of the BOP and the surrounding seawater. They pull the string of bad, broken pipe and good, new pipe up. As they do this, the level of the top of the mud should go down to replace the volume of pipe that is coming up out of the mud. This should be done during the first few inches of upward motion of the combined pipe string. If there is numerical agreement of pipe string upward motion with mud level downward motion, they can continue --- add mud to keep the mud level above the top of the BOP, but not spilling out of the top and the top the top of that that other, now structure that they stacked on top of the BOP. AND keep track of mud volume pumped. And plot the data as they gather it. Make sure mud level and volume track the upward motion of drill string, psi by psi and cuft by cuft against pipe travel inch by inch.
My major problem with this is that I am convinced that BP managers are intellectually incapable of handling this level of sophistication in process. Or if they are capable, they perceive that it is to their advantage to pretend otherwise.
Not covered are issues relating to the possibility that bad, broken pipe is stuck in the cement that is being used to kill the well. Pulling it out of the cement would introduce cracks. Mud would have had no problems with cracking. Also, I have ignored all complications having to do with elastic nature of pipe, steel cable, etc.
Thanks Geek, jes' what I was thimking. I would pump mud INTO the top of the DP to provide the replaced mass at the bottom, but I am looking at this with the eyes of an industry outsider, so it's probably not even possible. I still don't understand how you pump mud into the BOP stack through the choke line(?)with the valves in the top of the cap open ( to remove the DP at the same time ) don't they have to have the system closed in order to pump the mud...? Usually in this event the path of least resistance for the mud would be down the bore, as it has no other place to flow.
...................at that point in the thread, there were no more responses....but it seems I got some people thinking about some things........so....further down the thread, somebody poses the same question I had asked earlier .....
ROCKMAN, wondering if you could field a couple questions before this thread closes? Already posted upthread, but no responses yet:
1) Following up on the thread you started about the suspect positive pressure test: would it have been possible for a bad cement job (and lax mud return monitoring) to result in the original bottom hole cement plugs getting slowly pushed up the 7 inch casing during the seawater displacement until they hit the 9 7/8 transition at which point all h*ll started breaking loose?
2) regarding the question about the effect of pulling the old drill pipe out of the WW, if the drill pipe is hanging, it isn't contributing any weight to the mud column, so nothing needs to be replaced as it is removed, right?
Thanks, I'll eat some BB for you this week, butter pecan maybe.
1) Following up on the thread you started about the suspect positive pressure test: would it have been possible for a bad cement job (and lax mud return monitoring) to result in the original bottom hole cement plugs getting slowly pushed up the 7 inch casing during the seawater displacement until they hit the 9 7/8 transition at which point all h*ll started breaking loose?
2) regarding the question about the effect of pulling the old drill pipe out of the WW, if the drill pipe is hanging, it isn't contributing any weight to the mud column, so nothing needs to be replaced as it is removed, right?
Thanks, I'll eat some BB for you this week, butter pecan maybe.
2) The DP is displacing mud. AS the DP is raised the mud level will fall so the pressure created by the mud will fall. If they want to keep the well balanced they need to add mud.
Mixed up some Gatorade the other day. I do it with weighed powder then stir it in. I had the jug of water on the scale and I got curious as to what effect raising or lowering the spoon, in the liquid, would have (you can try this at home). Lower the spoon without touching the bottom or sides the weight increased, lift the spoon and the weight decreased. Now anyone tell me why? ;) I guess the DP will act the same as well as the change in mud level.
NAOM, thanks. For no good reason I forgot about displacement and the difference between mud weight and mud pressure.
What I didn't think of at all was the buoyancy of the drill pipe in the mud, or of a spoon in Gatorade. The weight of the pipe hanging from the BOP is reduced by the buoyancy of the steel in liquid mud. So if you put a scale in the bottom of your Gatorade jug and set the spoon on it, it would read less than it would in air. Nice riddle, thanks again.
Mixed up some Gatorade the other day. I do it with weighed powder then stir it in. I had the jug of water on the scale and I got curious as to what effect raising or lowering the spoon, in the liquid, would have (you can try this at home). Lower the spoon without touching the bottom or sides the weight increased, lift the spoon and the weight decreased. Now anyone tell me why? ;) I guess the DP will act the same as well as the change in mud level.
NAOM, thanks. For no good reason I forgot about displacement and the difference between mud weight and mud pressure.
What I didn't think of at all was the buoyancy of the drill pipe in the mud, or of a spoon in Gatorade. The weight of the pipe hanging from the BOP is reduced by the buoyancy of the steel in liquid mud. So if you put a scale in the bottom of your Gatorade jug and set the spoon on it, it would read less than it would in air. Nice riddle, thanks again.
Didn't we conclude that for the well to be balanced, the mud column had to continue some distance up the choke/kill line above the BOP?
Why are people still talking about balance when there's a 5000' cement plug in place? It's not the mud, it's the PLUG that is controlling the well now, isn't it?
Frank
Why are people still talking about balance when there's a 5000' cement plug in place? It's not the mud, it's the PLUG that is controlling the well now, isn't it?
Frank
..............actually...." We "...didn't conclude anything, white man.
..........at this point, one of the Oil Drum posters , David E. Brown, was nice enough to have typed up a nice little synopsis....and included this little gem :
" While drawing our the old drill string, which is hollow, and therefore will be less likely to create any significant suction effect, at the speeds at which they will extract it, they can replace its weight with mud via the choke and/or kill lines which are attached below the rams. "
...........at this point, I began to start to question reality, let's check out some of the responses.
David, very good synopsis. There is one technical blooper, however.
"While drawing our the old drill string, which is hollow, and therefore will be less likely to create any significant suction effect, at the speeds at which they will extract it, they can replace its weight with mud via the choke and/or kill lines which are attached below the rams."
Actually, as the drill pipe is removed, it will be an equivalent volume of the pipe that is replaced rather than the weight of the pipe. Normally, the density of the replaced fluid is equivalent to that which is already in the well and which has demonstrated to be sufficient to hold back the pressure from below.
Good summary though.
Thanks.
That's an oops, big time - physics .00001- Archimedes, if I remember correctly.
Unfortunately I've forgotten more of my two years of engineering than I ever knew.
Now why did I switch to liberal studies (whatever that is - I've never been too sure)?
Thanks again.
That's an oops, big time - physics .00001- Archimedes, if I remember correctly.
Unfortunately I've forgotten more of my two years of engineering than I ever knew.
Now why did I switch to liberal studies (whatever that is - I've never been too sure)?
Thanks again.
If the pipe is well crimped it may lift mud up inside it as well.
EDM, if the drill pipe is hanging, it isn't contributing any weight to the mud column, so nothing needs to be replaced, right?
OB, you still have to replace the volume of the steel in the drill pipe as you pull it out of the hole. Otherwise the level of mud in the hole would decrease and the hydrostatic head would be reduced.
If you can remember back in the day when you went to the rigs with your dad, every few stands tripping out of the hole the driller would kick the pump in to fill the hole though what is called the fillup line. Before starting out of the hole they would close the standpipe valve and open the fillup line valve..
If you can remember back in the day when you went to the rigs with your dad, every few stands tripping out of the hole the driller would kick the pump in to fill the hole though what is called the fillup line. Before starting out of the hole they would close the standpipe valve and open the fillup line valve..
...........so then the thread closed..........but then, today's thread.....
brat - Just my guess but with an 11,900 psi pressure on the bottom side of the plug/shoe and a bad cmt job between it and the reservoir it would seem very possible to blow the plug/shoe out once they displaced and lost the head. I believe they tested the plug/shoe to 8,500 psi but that was pushing down from the top so I don't think that tells us anything about the stability of the system being pushed from the bottom.
I think the DP wouldn't add anything to the effective mud weight. Just like hanging a lead weight in a glass of water: doesn't make the glass any heavier. The weight of the DP is being transferred to the BOP and not the bottom of the hole IMHO.
As naom says the DP removal will require that volume to be replaced. If they pull the DP the cap will have to be open so I suspect it will be done with sea water.
As far as being balanced others have noted that with the cmt in place a balanced mud colume is required to keep the well from flowing. OTOH that's also what BP thought when they displaced the mud with sea water.
And they were wrong.
I think the DP wouldn't add anything to the effective mud weight. Just like hanging a lead weight in a glass of water: doesn't make the glass any heavier. The weight of the DP is being transferred to the BOP and not the bottom of the hole IMHO.
As naom says the DP removal will require that volume to be replaced. If they pull the DP the cap will have to be open so I suspect it will be done with sea water.
As far as being balanced others have noted that with the cmt in place a balanced mud colume is required to keep the well from flowing. OTOH that's also what BP thought when they displaced the mud with sea water.
And they were wrong.
.....well....interesting,.....I like the fact that the "Rockman" is willing to think a little...I'd like to examine the statement from his last post, not to drag him through the mud either.
" I think the DP wouldn't add anything to the effective mud weight. Just like hanging a lead weight in a glass of water: doesn't make the glass any heavier. The weight of the DP is being transferred to the BOP and not the bottom of the hole IMHO. "
.........actually, just for a simple experiment, because I doubt the truth of that statement , I took a digital scale, and a small plastic container filled with water, weighed the total, and displaced some fluid by immersing the end of an X-acto knife.
What I observe.....actually, once the mass is added, it becomes part of the total weight in the fluid.
........so again that leaves me with the question I originally asked.
" How do you remove the drill pipe and replace the missing mass with mud at the same time ? "
.....In my little brain, I see an easy way to remove the drillpipe, simply by pumping the mud down through the top of the pipe so the mud mass will be deposited at the bottom and will replace the mass removed (drillpipe) at exactly the same time.
.......that's if they can actually get the new cap to function correctly....>facepalm<
....that's all for now, I'm off to do some math-n-sh*t.
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