Re: Sorry OT, but I have to ask


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Posted by Franz [209.86.226.24] on Friday, September 17, 2010 at 22:29:47 :

In Reply to: Sorry OT, but I have to ask posted by Paul(in NY) [12.64.140.42] on Friday, September 17, 2010 at 16:00:44 :

Downhole on a straight line lies primarily in the hands of the drillpusher knowing his craft. Doing it in solid rock of a single type rock is a walk in the park according to old pushers.

Unfortunately in the rescue situation mud motors can't be used because the mudflow would fill the cavern before it could be stopped. It all becomes pressure on the cutter for the pilot hole, 6" in this case, and the pusher knowing his craft. Only minimal mud can flow the pilot due to chamber flooding possibilities, so more frequent withdrawls and cutting head changeouts are how the initial holes will be drilled. Dull cutters get replaced real fast in drilling rescue holes.

The second part of the operation is a pilot reaming job where a 5" pilot about 10 feet long will go downhole ahead of the cutter. Unless the pilot breaks off it's a fairly simple cut.
Unfortunately it is also a cut that dumps a lot of spoil downhole, so the guys in the chamber have work to do to keep the target area clean.

As depth increases rock compression also has to be compensated for. Rock freed from the weight of compression swells rapidly, and can choke a hole.

I believe they are now reaming a hole to 12" and will then ream a second time to provide clearance for the rescue device. The device resembles a 7 foot length of steel pipe with a sliding door on one side that pusehs up for entry. The man backs into the device in a seated position, wriggles his shoulders against the back and stands erect. The door is then slid shut and he's in for one hell of a ride. The hoist operator controls speed of up, and if the device hits a snag it can rocket when cable stretch comes out. Hoisting speed will generally be kept slow to avoid snagging because a device can overshoot the cable in the bore and become a near impossible to clear lashup.



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