Patent ID: 7370712
Filing Date: 2008-05-13
Classification: E21B

Abstract:
1. An under reamer for expanding a borehole through an earthen formation, the under reamer comprising: a mandrel including an end for connection into a drill string and an opposite end; a housing including an inner bore, telescopically disposed over the mandrel and axially moveable relative to the mandrel, the housing being rotationally moveable with the mandrel; a hydraulic pressure chamber between the housing and the mandrel for driving the housing axially relative to the mandrel; an under reamer arm carried on the housing, the under reamer arm formed as a block and including an outer facing surface, a rear surface and top, bottom and side surfaces extending between the outer facing surface and the rear surface; and a cutter-supporting portion on the under reamer arm outer facing surface in which poly-crystalline diamond compact cutters are mounted, the under reamer arm being moveable by driving the housing axially over the mandrel between a retracted position extending into the housing inner bore and an expanded position wherein the under reamer arm is pivoted out of the housing inner bore and supported by the mandrel such that the cutter-supporting portion is exposed for use to enlarge a borehole.