How did they drill the hole that allowed the Chilean miners to escape?
There are a couple different methods I can think of. The fundamental problem with drilling a deep hole down is how do you remove the chips of rock ground ahead of the bit from the hole? Usually drillers use some kind of media like water, heavy drilling mud or even high pressure air to float or blow the chips out.
If there is a column of mud or water a few thousand feet high, the pressure on the escape cavern (which housed the miners) is tremendously high and could either flood the cavern with liquid or overpressure the tunnel if it broke through. My guess is that they calculated how far they could drill on water and then pumped the hole down and then dry drilled the remaining segment. This would be inefficient drilling but might be the easiest way to not kill the surviving miners.
I'm also thinking that they drilled numerous holes to feed water and food to the guys trapped for 69 days. Smaller diameter holes are easier and faster to drill and I imagine they could have burned through bits and blew out chips in the rush to get that first hole sunk. I remember at the beginning they could only send a small video camera to communicate with the miners by recording messages. This suggests to me that the first hole was only a few inches in diameter.
I have not been following the news in detail and the story might be out there. It would be slick to get the story linked or get some expertise from my geo friends who have spent more time on a drill rig.
This is an amazing recovery story and I'm happy for the survivors. Props to the brave medics who went down first and presumably came up last.
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