So, the current oil leak in the Gulf is gushing like crazy, and all the talk is that the real solution will have to be the relief well. I get that the relief well will relieve some of the pressure on the existing, open well head, but how is it suppose to relieve all the pressure?
And, how certain are we that this is going to work? I understand that the Obama administration is making them drill 2 relief wells in case the first one doesn’t work, but what are things that would cause it not to work, and how does having a 2nd well fix the first one not working?
Maybe I’m missing something, but that link looks like it is describing what I think was called “top kill”, when they injected cement into the existing well to try and cap it off.
The relief well is actually for performing a bottom kill. In the top kill procedure, they tried to pump heavy mud into the blow-out-preventer, to counter the enormous pressure of the leaking oil, in the hopes that they could hold it down long enough to pump in cement and plug it up. That didn’t work, because too much mud was just being pumped straight out the leak.
The relief well(s) will intersect the original well far under the sea floor, just above the oil reservoir. They will then pump mud and cement down the relief well to do the bottom kill.
Here (PDF) is a clearer diagram, straight from the horse’s mouth.
From my understanding yes, it SHOULD work. They are actually drilling TWO relief wells, just in case. Usually just one is needed but Obama said make two
Basically they are trying to intersect the original well at a depth that the density of the mud in the relief well will cause a pressure greater then the reservoir pressure in the original well. The problem with a top kill is that you do not have the depth necessary to combat that pressure so it is necessary to use greater density mud.
I’m not certain of the exact pressures but if the reservoir is normally pressured and at 10,000 feet below the sea floor it would have approximately 6500 psi of reservoir pressure. In order to combat this pressure once it makes it to the BOP stack it would take mud at about 23.7 pounds per gallon (ppg). If the relief well is able to intersect the original well at even 5000 feet below the sea floor it would only take 12.5 ppg mud.
20.4 ppg is the highest density that I can find in any of my text books so the remaining 2100 psi would need to be made up with friction. On the other hand 12.5 ppg mud is quite easy to make and is common all over the world.
The trick with the relief well is that you are trying to hit a 12.25" diameter hole with another 12.25" diameter hole at a distance of two miles. Even the best surveys have a margin of error of 0.034% (15’ surveys along a North-South path) which it is unlikely that they have. That means that at 12,000’ the wellbore could be off by as much as 4’ from where they think it is or in 13 sqft they are looking for a 0.8 sqft circle with another 0.8 sqft circle from two miles away.
eta: After looking at the graphic I see my numbers are off. I can redo the calcs if any one cares.
I believe they also have the added benefit of sonar (?) probes which they can send down the well shafts to make minor course corrections as they get closer.
Friedo is right. They can also drill the relief well down a certain depth, check their location, and then back up and resume drilling on a corrected course. It’s not the blind, error-prone, barely-possible process it’s being made out to be.
Kind of. The survey for the existing well has these errors built in. Since they are trying to intersect it below the casing there is no way to tell where the wellbore is exactly unless they drill by it with an LWD capable of sensing where the gas/oil is moving through the hole.
While corrections are possible on the fly, typically surveys are only done every 93’ and there is an error on the path taken between each survey point. These survey points also have errors build in to them, like I said about 0.034%. It is very complicated to actually drill into an existing wellbore because of this. Most of the time it does take several attempt of plugging back and re-drilling. My single success was considered close enough by the BLM in that our surveys overlapped the original well and there was a slight increase in the rate of penetration that I believe was more due to some of the formation giving way as it was pushed into the original well. It is hopeful that once you get that close you can pump between the wells but it is very complicated.
If you count Oredigger77 as one, then then the answer is at least twice - on this board. I did one in the early 90s in Norway. We got within six feet of the original well - first time :D.
IIRC, we used a tool from these guys to get that close.
The “it’s not easy” part is getting reported out in a lot of different ways, though. Heart surgery is not easy, but it’s done all the time these days. There are interpretations these days, though, of “it’s not easy” meaning “pratically impossible, and therefore sure to fail”.
As I understand it, the success of one of the relief wells is as close to guaranteed as one can get given the situation.
I used this. I can see it being much easier if you have some way of locating the actual wellbore.
With all of that flow I would assume that a sonic log or a resistivity log might be able to locate it pretty easily. Neutron density should also work but I can’t imagine what would happen if they lost a radioactive source in the relief well.
Yep, but with magnetic interference it can be hard to tell where is is coming from. I’m not aware of any tool that can give the direction of the interference. I was thinking that at least with the others there are azimuthal tools that will allow you to figure out which direction you missed it in.