Thursday, July 15, 2010

Bottom kill

This business of the relief wells as a way of stopping the gusher in the Gulf. I have to admit the whole idea left me gobsmacked.

First, you drop a drill string a mile deep into the ocean, then start drilling. You are going to drill another 2 miles into the sea floor and intersect a 16 centimeter (7 inch) pipe that's almost a kilometer off to the side. Whoa!

I'm sitting here looking out the window to Dingle Bay, two miles out there across the parish. And I'm trying to imagine that turning string of pipe worming through that much rock and hitting a soccer ball. How, I wonder, could the drillers possibly have that much control over where the drill bit is going?

Well, what do I know? That's why the BP engineers make the big bucks.

An article in last week's Science "explains" how it's done. They start with a navigation device invented for submarines and missiles, a set of 3-dimension accelerometers so tiny they can fit just above the drill bit. (Not unlike, I would imagine, the ones in your iPhone.) The device monitors the position of the bit within a few meters at all times. How the accelerometers are powered or communicate with the surface, Science doesn't say.

But a few meters isn't good enough. Once they are near the steel casing of the target well, they use an electromagnetic sensor to zero in on the pipe they are trying to intersect.

Remember, the three mile-long drill string is turned from the drilling platform. How can you steer it? By giving the drill bit an "extra bump" at the appropriate point in each revolution.

I'm impressed, even if I don't fully understand. And still I sit here looking out across the parish imagining that pipe chewing its way through two miles of rock looking for a soccer ball, with me here at my desk doing the turning, and with all that friction, and all that twisting of the pipe string, and it still seems impossible.

Apparently it's been tried 40 times before and hasn't missed yet.