UNDERREAMER

摘要

An underreamer for expanding a borehole through an earthen formation. The underreamer may include a housing including an outer surface, a top end for the connection into a drill string and an opposite end for attaching a pilot bit; an inner bore through the housing to allow for the passage of the drilling fluid and a cavity in the housing with an opening to the housing outer surface, the cavity being in fluid communication with the inner bore and a cutter arm slidably moveable in the cavity and drivable from a retracted position to an expanded position by fluid pressure applied to the cavity.