Borehole underreamers.

摘要

A sub-surface borehole underreamer (10) is disclosed having freely rotatable precessing diamond cutters attached to extendable arms (22) connected to the body (12) of the underreamer. The diamond cutting face is skewed to a degree that tangential contact of the peripheral edge of the diamond cutter (46) with a borehole wall (15) causes the rotating cutter (40) to precess as the underreamer body is rotated by a drill string.