hubris: it's because of the basalt that they invented this type of reverse circulation... fascinating how they solved the basalt problem... would love to have lunch with the guy who came up with the idea below.
I have not read any additional info, nor am I an expert on this particular rig, but I think that your answer lies in this part:
"The problem we have with basalt, it's like swiss cheese," Delahoussaye explained. "Real porous. It's got avenues to go through. The problem that causes is what we call lost circulation. In other words, if you drill with a conventional rig and when your cuttings come up outside the drill pipe, and you have lost circulation, you have no way to get the cuttings up to the surface, because it's going through the basalt, the holes or caverns. When that happens, your cuttings start piling up, they'll stick your pipe and then you have a lot of problems there."
(snip)
"What makes this company so unique, they love lost circulation," Delahoussaye said of Lang. "They can drill with lost circulation, because what they do is fill in the backside up with a drilling fluid -- that's water plus clay-type additives, which we call 'mud' --and makes it thicker. So if you have any cuttings and you stop circulating, they'll suspend the cuttings and they won't fall down on top of you."
For flood reverse air drilling, Delahoussaye said his team keeps the backside as full as it wants to level out at, using a dual wall pipe -- a 4-inch outside diameter pipe within a 65/8 outside diameter pipe -- and pumping air in between the two pipes at 1,170 cubic feet per minute.
A crossover (jim's note: the crossover is 3,000 feet above the bit, but the doublewalled pipe goes all the way down, as implied in the above paragraph -- this is the key to the whole system... the air switches to outside the pipe 3,000 feet above the bit and pushes all the mud, cuttings and everything else INTO the inside pipe where it gets sucked to the surface) where the air comes out is located about 3,000 feet from the drill bit. As the air goes down and back up, the least resistant air goes back up the inside of the 4-inch pipe and causes a vortex of suction, like a vacuum cleaner. (jim's note: that is the genius of this system, IMO)
"What's happening now is all the cuttings we're making now come inside the pipe, instead of outside," Delahoussaye explained. "Once it gets up inside the pipe, then the air that we're pumping pushes it up the rest of the way. So we're pushing the cuttings, the mud and any gas or anything else that's with it."
The cuttings and company come out over a centrifuge, which breaks the air out the top and the cuttings and mud over a shaker with a screen. The cuttings go off onto the ground and the mud goes through the screen into a pit, and then back down into the backside of the drilling. |
