Probably "Twisted Off" Drill collars and drill pipe will...

Probably "Twisted Off" Drill collars and drill pipe will fracture and crack due to high pressures and high torques used to drill these depths.

My guess is, they twisted off and left some of the drill string down the hole.

Usually there is a preventative maintenance program where everything that goes in the hole is crack tested, but this doesnt guarantee no stuff ups.

Good news is, it's been fished. Was the most recent Casing run in program or is it there to help overcome hole probs??

This will mean a smaller bit and should result in faster drilling.....