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"Relief well" is actually a misnomer

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charlesg Donating Member (311 posts) Send PM | Profile | Ignore Sun May-30-10 01:12 PM
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"Relief well" is actually a misnomer

BP says crude may continue flowing into gulf until August
By David S. Hilzenrath and Matt DeLong
Washington Post Staff Writers
Sunday, May 30, 2010; 12:59 PM

... The administration and the oil company say the flow ultimately can be stopped by drilling relief wells, a slow but proven process that is intended to relieve the pressure from the vast undersea oil field. Despite recent setbacks, Browner expressed confidence that the relief wells will work, saying the worst case scenario is that the spill continues until their expected completion in mid-August...

"Relief well" is actually a bit of a confusing misnomer. A relief well is not designed to "relieve pressure" from the existing blowout wellbore. Quite the opposite actually. A relief well is drilled in a similar way to a conventional well but it targets to intercept the blowout wellbore above the producing formation (using directional drilling techniques). In this case the blowout well is roughly 15,000 feet deep (measured from the wellhead on the ocean floor) so the relief well will be targetted to intercept at perhaps 8,000 - 10,000 feet sub-seafloor depth. As the relief well is drilled the crew will have to carry out substantially the same procedures as during the drilling of the original well...for example setting and cementing intermediate steel casing at intervals on the way down. Until they get near the intercept point there normally won't be any significant differences in the drilling procedures.

A little dissertation on drilling mud might be worthwhile here. The "mud" isn't a mixture of soil and water like the stuff we played with in the back yard as kids. It's actually a complex chemical soup that has a specific gravity greater than one (e.g. it is denser than fresh water) that can be controlled by changing the chemical mixture and water content. It serves several purposes. In addition to holding back the formation pressure as the well is being drilled the drilling mud also cools and lubricates the drill bit, and picks up and holds the rock cuttings from the bit in suspension to carry them back to the surface during drilling operations (the drill cuttings have to continuously be removed from the well or the bit risks being jammed in the bore). The higher the density of drilling mud the greater the margin of safety over formation pressure but also the greater the viscosity. The greater the viscosity the slower the rate of drilling (think of it as turning the long drill string and bit in a thicker "sludge"). This is one dilemma facing BP now - do something quick dammit, but make sure you don't have another screw up.

For this reason normal mud weights will be used to drill most of the depth of the relief well (contrary to some reports BP really would like this nightmare to end sooner rather than later). I do not know the details of BP's relief well drilling program, but typically a relief well is not drilled all the way into the blowout wellbore. As it approaches the intercept point, but before actually hitting that target, drilling is often suspended and the relief wellbore is circulated to the "kill fluid", which in this case is likely to be a "weighted up" mud (sometimes in shallow, lower pressure wells, salt water alone is enough to kill the well). The combination of the hydrostatic head from the heavy kill fluid and hydraulic pressure applied to the relief wellbore from surface is used to fracture the rock creating a pathway from the end of the relief well to the blowout wellbore, through which the kill fluid is forced at high rate in an effort to overcome the blowout formation. This is seriously complicated by the fact that the original wellbore is cased and cemented all the way they may have to use shaped explosive charges to make the connection from the relief well to the blowout bore.

A relief well is the only reasonably high-probability-of-success way to kill a blowout like this one. That is the reason that starting the first relief well was done as quickly as possible by BP. So reliant are they on the success of this technique that for back-up a second relief well is drilling about one week behind the first one...just in case something goes wrong with the first relief well (stuck drill bit, hole collapse, etc.). They simply cannot afford to wait to start a second relief well until after they have any sort of problem with the first one. If the first attempt with a relief well fails, then there will be a second attempt, and if necessary a third and a fourth...because there is no other better option to stop the blowout...

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dipsydoodle Donating Member (1000+ posts) Send PM | Profile | Ignore Sun May-30-10 01:18 PM
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1. And as will find elsewhere on DU
they've got to hit a pipe only 7" in diameter a couple of miles under the sea floor. No easy task.
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gristy Donating Member (1000+ posts) Send PM | Profile | Ignore Sun May-30-10 01:22 PM
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2. last I heard they stopped drilling the 2nd relief well
So reliant are they on the success of this technique that for back-up a second relief well is drilling about one week behind the first one

Anybody have a recent update on that?
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Junkdrawer Donating Member (1000+ posts) Send PM | Profile | Ignore Sun May-30-10 01:28 PM
Response to Reply #2
5. Here you go...(not surprisingly, not getting a lot of corporate press)....
Edited on Sun May-30-10 01:29 PM by Junkdrawer

BP has stopped drilling one of the relief wells to intercept the blown out Macondo bore so it can ready the rig's blowout preventer (BOP) to go on top of the crippled Macondo BOP.

Transocean boss Steve Newman told analysts today that Transocean semi-submersible rig Development Driller II had stopped drilling while BP tries a top kill to try to halt the flow of the Macondo well.

BP spokesman David Nicholas told UpstreamOnline that the rig was stopped so its BOP would be ready if needed.

"The (Developmen Driller II) has temporarily suspended drilling operations in preparation for the possible future deployment of its BOP on top of the (Macondo) BOP," he told UpstreamOnline in an email response.

"This is a possible future option for stopping flow from the well and, as throughout, we are advancing options in parallel."

BP operations boss Doug Suttles confirmed that the BOP was being prepped to be deployed but said that it had been at the ready since the beginning of the top kill operation and it was not a sign that BP thought the top kill would not work.

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On the Road Donating Member (1000+ posts) Send PM | Profile | Ignore Sun May-30-10 01:23 PM
Response to Original message
3. What Hasn't Been Clear to Me
is why the relief well has to be drilled so far away and intercept the pipe so far down. Since the leak is at the ocean floor, you would think a hundred feet would be more than enough to do the job, possibly much less.

I guess it must have to do with the geology, which BP is not releasing.
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gristy Donating Member (1000+ posts) Send PM | Profile | Ignore Sun May-30-10 01:49 PM
Response to Reply #3
7. Maybe to make it a "bottom kill". If they intercept too high, the well pressure
forces the mud right out the top of the broken BOP, just like in the top kill effort.
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Urban Prairie Donating Member (1000+ posts) Send PM | Profile | Ignore Sun May-30-10 01:25 PM
Response to Original message
4. Absolutely correct...
Edited on Sun May-30-10 01:34 PM by Urban Prairie
However, the second article fails to point out that if the first relief well fails, the second has now been temporarily halted in order to put a second BOP on top of the damaged original. This will stop drilling for the second relief well, and if (more likely "when ") drilling resumes, the second relief well will probably not be completed until sometime during the very peak of the hurricane season...Yikes!!!
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drm604 Donating Member (1000+ posts) Send PM | Profile | Ignore Sun May-30-10 01:46 PM
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6. I've actually been concerned about whether or not the "relief well" will work.
They say that it's a "proven technique", but has it been proven at these depths and pressures? They keep saying that this is new territory and they've never had to deal with something like this under these circumstances. What if there's some factor that will make a relief well either unworkable or much more difficult than usual? :scared:
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