Steerable Downhole Hammer Bit

Abstract

A drill bit for use with a pneumatic hammer used in horizontal directional drilling operations. A compact forward face is formed on the first end of the drill bit. The forward face reciprocates against a face of a borehole. A steering face is disposed behind the forward face and is concave adjacent its first end and convex adjacent its second end, with a smooth transition between the two regions. The body has a circular profile at its second end. The drill bit displaces cobble and small rocks encountered, rather than breaking them, enhancing steering in mixed conditions.

1 . A method comprising:
 providing a drill bit comprising a body having opposed first and second ends and opposed steering and external faces formed between the first and second end, in which the steering face has a concave portion that transitions into a convex portion, in which the concave portion starts at the first end and the convex portion terminates at the second end;   attaching the drill bit to an end of a downhole tool comprising a fluid driven hammer;   positioning the drill bit within an underground zone;   thrusting the drill bit forward in a first direction while rotating the drill bit;   thrusting the drill bit forward in a second direction without rotation; and   thrusting the drill bit forward in the second direction while rotating the drill bit.   
     
     
         2 . The method of  claim 1  in which the underground zone contains cobblestones. 
     
     
         3 . The method of  claim 1  further comprising reciprocating the drill bit against a face of the underground zone using the fluid driven hammer. 
     
     
         4 . The method of  claim 1  further comprising venting air from the drill bit into the underground zone. 
     
     
         5 . The method of  claim 1  further comprising venting an air-foam mixture from the drill bit into the underground zone. 
     
     
         6 . A system comprising:
 a fluid driven hammer; and   a drill bit disposed in force-transmitted relationship to the hammer, comprising:
 a body having opposed first and second ends and opposed steering and external faces formed between the first and second end, in which the steering face has a concave portion that transitions into a convex portion, in which the concave portion starts at the first end and the convex portion terminates at the second end. 
   
     
     
         7 . The system of  claim 6  further comprising a drilling machine and a drill string having opposed first and second ends, the first end being operatively connected to the drilling machine and the second end being connected to the hammer. 
     
     
         8 . The system of  claim 6  further comprising a magnetic dipole transmitter installed within a housing connected to the hammer. 
     
     
         9 . The system of  claim 6  in which a chuck is positioned between the hammer and the drill bit. 
     
     
         10 . The system of  claim 6  in which the second end of the body is symmetric about a longitudinal axis of the drill bit and the first end is asymmetric with respect to that axis. 
     
     
         11 . The system of  claim 6  in which the steering face is positioned at a non-zero angle relative a longitudinal axis of the drill bit. 
     
     
         12 . The system of  claim 6  in which at least one fluid port is formed on the external face. 
     
     
         13 . The system of  claim 12  in which a flow passage is formed along a longitudinal axis of the drill bit, in which the flow passage is connected to at least one passage that extends at a non-zero angle to at least one fluid port formed on the external face. 
     
     
         14 . The system of  claim 12  in which the at least one fluid port is formed in a channel that extends from the first end to the second end of the body. 
     
     
         15 . The system of  claim 6  further comprising a shank joined to the second end of the body. 
     
     
         16 . The system of  claim 15  in which the second end of the body has a maximum cross-sectional dimension that exceeds the maximum cross-sectional dimension of the shank. 
     
     
         17 . The system of  claim 6  in which a rectilinear passage within the body interconnects the external face and the steering face. 
     
     
         18 . The system of  claim 17  in which the rectilinear passage opens on the steering face proximate the zone of transition between the convex portion and the concave portion. 
     
     
         19 . The system of  claim 6  in which a forward face is positioned at the first end of the body, in which the forward face is bounded by a leading edge and a trailing edge, wherein the leading edge has a width less than a width of the trailing edge. 
     
     
         20 . The system of  claim 19  in which the leading edge and the trailing edge extend at a non-zero angle between the first end and the second end of the drill bit. 
     
     
         21 . The system of  claim 6  in which the second end of the body has a circular profile. 
     
     
         22 . The system of  claim 6  further comprising an underground terrain containing cobblestones and having a borehole formed therethrough, in which the hammer and drill bit are situated within the borehole. 
     
     
         23 . The system of  claim 6  in which the transition from the concave portion to the convex portion is made closer to the first end than the second end.