Another thing that should be considered: how do you keep the hole open while drilling? At extreme P and T, the hole will close in on the drillstring. Also, fl

Another thing that should be considered: how do you keep the hole open while drilling? At extreme P and T, the hole will close in on the drillstring. Also, fluids turn very nasty in those conditions. You'll need some unobtanium and some of Superman's suit material.