Sorry folks, but there is no comparison between drilling for cores and drilling for oil. In the case of oil, they just keep adding lengths of pipe as the drilling goes down. The only reason to pull up the entire rig is to change the bit. Core drills have to be pulled up more often to remove th contents of the hollow shafts.

At least, this is what makes sense to me; I could be off base, so correct me if I am missing something.

Shortty