Hard Rock Rotary Drill Bit and Method of Drilling Using Crowned Cutter Elements

Abstract

This rotary drill bit provides a plurality of spaced polycrystalline diamond compact cutter elements arranged at spaced 120° concentric rings around the face of the drill bit and a secondary, redundant deeper set polycrystalline diamond compact cutter elements placed to commence scuffing the face of a bore upon wear of the primary cutter element, thereby providing extended continuous service in hard rock drill applications previously unattainable with conventional PDC bits.

1 . A rotary drill bit comprising:
 a body having a proximal end adapted to connect to a drill string with a longitudinal passage accommodating a fluid flow through a face on a distal end of the drill bit;   a central PDC element providing a coating of PDC creating a composite crown on a hardened element connected on the face adjacent a longitudinal axis of the drill bit;   a first plurality of spaced PDC crowned elements connected on the face in concentric rings providing a single point of contact on each concentric ring; and,   at least three full-gauged PDC elements peripherally spaced around the face angled from the longitudinal axis of the drill bit for contacting a bore.   
     
     
         2 . The rotary drill bit of  claim 1  further comprising:
 a second redundant plurality of PDC elements spaced 180° from the first plurality of spaced PDC elements, and having a surface profile substantially equal to the depth of the surface thickness of the PDC crown on the hardened elements of the first plurality of spaced PDC elements. 
 
     
     
         3 . The rotary drill bit of  claim 1  wherein the spacing of each PDC element, from one concentric ring to the next outer concentric ring, is about 120°. 
     
     
         4 . The rotary drill bit of  claim 1  wherein the peripherally spaced full-gauged PDC crowned elements are angled at about 30°. 
     
     
         5 . The rotary drill bit of  claim 1  wherein the PDC elements are ballistic conical buttons providing a minimal radius point to contact a bore face with a scuffing motion. 
     
     
         6 . A method for rotary drilling of hard rock comprising:
 attaching a rotary bit having radially-spaced, longitudinally-aligned ballistic conical PDC crowned carbide elements arranged in a manner that permits only a single ballistic conical element to engage a borehole face at a radius from the central longitudinal axis of the drill bit;   turning the rotary bit to engage the borehole face at a central location scouring a central groove in the borehole face;   increasing the forward movement of the rotary drill bit to progressively advance the crowned carbide elements against the borehole face; and,   clearing borehole cuttings from the face of the borehole utilizing the hydraulic pressure from a plurality of jetting nozzles in the face of the rotary bit.   
     
     
         7 . The method of  claim 6  wherein the velocity of the longitudinal movement is increased after a desired borehole width is achieved.