And how do they manage the twist of a 7 mile drill. The torsional strain energy must be enormous; you can't just let it go. You would need to unwind that energy in a managed way. I suppose this is not a new situation for any oil drilling, even just a few hundred feet. This is one of those things a layperson thinks about in the first minute, and has been obviously been thought of and dealt with in a simple manner by experts.
You basically use the drilling mud that circulates through the hole anyway (providing counter pressure, cooling, lubricataion, bringing up cuttings) to run a motor that rotates the drill bit.
This way the drill string does not need to rotate & you can even change the direction by manipulating the angle of the drill attached to the mud motor.
