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Relief well explained....
Posted on 7/3/10 at 9:29 pm
Posted on 7/3/10 at 9:29 pm
Might be Germans but don't care to look back through the threads since I've been away.
Very interesting. I didn't know they were going to kill the well. Does that mean the relief well will be killed too in the process?
LINK
Very interesting. I didn't know they were going to kill the well. Does that mean the relief well will be killed too in the process?
LINK
3
Posted on 7/3/10 at 10:34 pm to Schwaaz
Thanks.
Posted on 7/4/10 at 12:06 am to Schwaaz
a well has to be killed when you experience a well control event -- a situation where the hydrostatic pressure exerted by the fluid in the hole is less than the pressure exerted by the formation that's been exposed.
so let's say you drilling w/ a 12 pound per gallon fluid at 5000' -- just made up #'s here -- the bottom hole pressure due to the mud is 12 x 5000 x 0.052 = 3120 psi. but let's say at 5000' you drilled into a formation that is at 3500 psi. shortly after that, you'll notice that the well will begin flowing, since 3120 < 3500 psi. furthermore, your situation gets worse the longer you don't recognize it, as the 12 ppg fluid is being replaced by a reservoir fluid like oil, gas, or salt water.
so in this case, you would shut the well in, and increase the weight of the fluid from 12 ppg to 13.5 ppg. at that point, the well would then be under control.
the rig team drilling the relief wells know exactly what the bottom hole pressure is -- it was measured prior to running casing. furthermore, they know how the formation behaved when it was drilled originally by the horizon.
based on this info, they know the mudweights required to enter the formation and the relief well should be under control throughout. after entering the blowout well, a heavier mud will be circulated up the blowout well. this mud from the formation to the mudline + the 5000' of sea water on top, will apply enough hydrostatic pressure on the formation to stop the flow, then they can move on to pumping cement to permanently isolate it.
so let's say you drilling w/ a 12 pound per gallon fluid at 5000' -- just made up #'s here -- the bottom hole pressure due to the mud is 12 x 5000 x 0.052 = 3120 psi. but let's say at 5000' you drilled into a formation that is at 3500 psi. shortly after that, you'll notice that the well will begin flowing, since 3120 < 3500 psi. furthermore, your situation gets worse the longer you don't recognize it, as the 12 ppg fluid is being replaced by a reservoir fluid like oil, gas, or salt water.
so in this case, you would shut the well in, and increase the weight of the fluid from 12 ppg to 13.5 ppg. at that point, the well would then be under control.
the rig team drilling the relief wells know exactly what the bottom hole pressure is -- it was measured prior to running casing. furthermore, they know how the formation behaved when it was drilled originally by the horizon.
based on this info, they know the mudweights required to enter the formation and the relief well should be under control throughout. after entering the blowout well, a heavier mud will be circulated up the blowout well. this mud from the formation to the mudline + the 5000' of sea water on top, will apply enough hydrostatic pressure on the formation to stop the flow, then they can move on to pumping cement to permanently isolate it.
Posted on 7/4/10 at 7:48 am to oilfieldtiger
Thanks for the detail. I understand the idea of pumping heavy mud to clog the main well that is leaking oil but I was surprised they are doing that. I just assumed (you know about assuming) they would use the relief well to reduce the pressure in the mail well and continue to capture the oil of the reservoir from the new well.
Why can't they top kill the Coronado once the pressure is reduced and just capture the oil from the relief well?
Why can't they top kill the Coronado once the pressure is reduced and just capture the oil from the relief well?
Posted on 7/4/10 at 10:49 am to Schwaaz
Wow that was a good explanation, thanks 
Posted on 7/4/10 at 11:26 am to oilfieldtiger
What are the potential success/failure %'s?
Posted on 7/4/10 at 1:32 pm to Schwaaz
quote:
Thanks for the detail. I understand the idea of pumping heavy mud to clog the main well that is leaking oil but I was surprised they are doing that. I just assumed (you know about assuming) they would use the relief well to reduce the pressure in the mail well and continue to capture the oil of the reservoir from the new well.
Why can't they top kill the Coronado once the pressure is reduced and just capture the oil from the relief well?
First of all, mud does not clog the wellbore. The hydrostatic pressure caused by the weight of the mud overbalances the pressure from the formation.
Secondly, the relief well does not reduce that pressure. It is what it is.
Imagine your 50' garden hose, one end hooked up to a faucet and the other end raised straight up into the air. You turn on the faucet and if your water pressure is high enough, water will flow out of the of the hose 50' up. Now replace that hose with a 100' hose. Now maybe your water pressure isn't high enough to overcome the weight of the water in the hose. No water flows.
OK, now go back to the 50' hose but this time there is a T a few feet above the faucet and on the tee there is a valve that connects to another hose. At first the valve is closed. You turn on the faucet and water flows out the top, just like before. But now you open the valve and inject mud that weighs twice as much as water into the hose. At first water continues to flow but as the hose fills up with heavy mud, the water pressure can't overcome the weight anymore. It's as if the hose was 100' long instead of 50'.
That's an oversimplified idea of what the relief well will do. They will come in from the side and penetrate the existing well (open the valve). Then they will push heavy mud into the well until the pressure of the formation can no longer push against the weight of the mud. At that point the flow stops.
Posted on 7/4/10 at 2:10 pm to MountainTiger
Sounds like the relief well should be renamed Kill Well.
Thanks for the info that was clear and concise.
Thanks for the info that was clear and concise.
Posted on 7/4/10 at 3:27 pm to MC123
quote:
What are the potential success/failure %'s?
It has the potential to succeed. It has the potential to fail. If you're asking about probabilities, assuming that they can intercept the well, a bottom kill should work every single time. Of course there's always a small chance of something very unusual going on. The difference between theory and practice is that in theory there is no difference between theory and practice but in practice there is.
Posted on 7/4/10 at 3:38 pm to MountainTiger
One other comment I'd like to make: I noticed on the graph of depth vs. time, (LINK ) after a couple of weeks of slow progress, there has been a sudden increase in drilling rate on DD III. If this continues for another day or two, I would conclude that they have aligned the relief well where they want it and now are simply drilling straight ahead until they feel the pressure from the original well. The slow progress during the last couple of weeks was them ranging to find the exact location of the casing and aligning the relief well to intersect with it.
This post was edited on 7/4/10 at 3:39 pm
Posted on 7/4/10 at 6:40 pm to MountainTiger
quote:
If you're asking about probabilities, assuming that they can intercept the well, a bottom kill should work every single time
i'd also add that when you regain the ability to circulate heavy mud in the hole from the bottom up, you have immensely more options in trying to kill the well by circulating around the appropriate density fluid than by trying to do anything top down. the big question is can you circulate the necessary volume fast enough.
Posted on 7/4/10 at 7:32 pm to oilfieldtiger
great post Mountain and Oilfield.
Posted on 7/6/10 at 7:50 am to TheEnglishman
quote:
i'd also add that when you regain the ability to circulate heavy mud in the hole from the bottom up, you have immensely more options in trying to kill the well by circulating around the appropriate density fluid than by trying to do anything top down.
Agreed and thats why i think it will take possibly a couple days to get to that point. Theres such an imbalance in pressures between the relief and original wells its gonna be a while before they get bottoms up in the relief well. Once they get to that point though, it should be all downhill..
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