Patent ID: 6237702
Filing Date: 2001-05-29
Classification: E21B

Abstract:
A mill section for use in a hydraulic underreamer comprising:a tubular bit sub having an upper end and a lower end;a tubular primary mill having an upper end, removably connected to the bit sub lower end, and also an abrasive lower end; anda center assembly having a passageway therethrough and adapted to be received in a mill section central bore defined in the bit sub and primary mill, wherein the center assembly includes (i) a locking mandrel having an upper end and a lower end and being selectively lockable in the mill section central bore, (ii) a center mill having an upper end removably connected to the locking mandrel lower end and also having an abrasive lower end adjacent to the primary mill lower end when the locking mandrel is locked in the mill section central bore, and (iii) a mill nozzle connected to the center mill lower end so as to be in communication with the center assembly passageway.