Importance

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Abstract

A downhole hammer drill for use with a dual concentric tube drill pipe string is characterized by the use of pressurized air from the annular passageway of the pipe string to operate the hammer. The exhaust air from the hammer is conducted to the periphery of the bit face of the hammer drill, across the bit face, and then through one or more openings in the central portion of the bit face. The exhaust air with entrained cuttings and hole water is then channeled through the drill and into the central passageway of the pipe string, through which it is removed from the drilling area. In a preferred embodiment an injection sub is provided in the drill string uphole of the drill and a drill body which substantially fills the bore annulus is used to throttle the flow of water down the borehole annulus to the bit face. In this embodiment a head of water is maintained in the borehole annulus and this water cascades down around the hammer drill to prevent cuttings and fines from moving up the bore annulus.

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First Claim