Hybrid drill bit

Abstract

A drill bit for coupling in use downhole drilling apparatus, the drill bit comprising: an annular coring drill bit that is rotatable to cut a formation bore face to create a core plug, a concentric drill bit that can be repeatedly axially moved (such as by oscillation (such as a vibration) and/or impact) to break the core plug.

1 . A RC drilling apparatus comprising:
 drill string,   fluid driven force generator, and   a drill bit comprising:
 a diamond impregnated annular coring drill bit that is rotatable to cut a formation bore face to create a core plug, and 
 a concentric drill bit with aggressively shaped bit inserts that can be repeatedly axially moved by oscillation including a vibration, and/or impact by a force generator to apply a force to the drill bit to break the core plug. 
   
     
     
         2 . The RC drilling apparatus according to  claim 1 , wherein the drill string is coupled to and operable to rotate the annular coring bit. 
     
     
         3 . The RC drilling apparatus according to  claim 1 , wherein the fluid driven force generator is coupled to and operable to repeatedly axially move the concentric drill bit. 
     
     
         4 . A drill bit for coupling in use to a downhole reverse circulation drilling apparatus with a fluid driven force generator for drilling in hard rock formations, the drill bit comprising:
 a diamond impregnated annular coring drill bit that is rotatable to cut a formation bore face to create a core plug, and   a concentric drill bit with aggressively shaped bit inserts that can be repeatedly axially moved by oscillation including a vibration, and/or impact by a force generator to apply a force to the drill bit to break the core plug.   
     
     
         5 . The drill bit according to  claim 4 , wherein the concentric drill bit is axially setback from the annular coring bit to create a recess such that in use the core plug is unconfined by the surrounding formation. 
     
     
         6 . The drill bit according to  claim 4 , wherein the drill bit is for use in a reverse circulation drilling apparatus to create chip samples for return to surface by breaking the core plug. 
     
     
         7 . The drill bit according to  claim 4 , wherein in use:
 the annular coring drill bit is or can be coupled to and rotated by a rotational drive of a drilling apparatus, and   the concentric drill bit is or can be coupled to a repeatable force generating apparatus that can repeatedly axially move the concentric drill bit.   
     
     
         8 . The drill bit according to  claim 7 , wherein the rotational drive is a drillstring casing of the drilling apparatus. 
     
     
         9 . The drill bit according to  claim 7 , wherein the repeatable force generating apparatus is an impact apparatus or an oscillation apparatus configured to repeatedly axially move the concentric drill bit by impact or oscillation. 
     
     
         10 . The drill bit according to  claim 9 , wherein the force generating apparatus includes:
 a. an impact apparatus including a hammer to provide impact force to the concentric bit to break the core plug, or   b. an oscillation apparatus to provide oscillatory force including a vibration force to the concentric bit to break the core plug.   
     
     
         11 . The drill bit according to  claim 4 , wherein the annular coring bit comprises: a body with a hollow core, a bit face with a cutting structure around an end of the body, the cutting structure comprising: an inner ring of inner spaced apart teeth and an outer ring of outer spaced apart teeth, the inner and outer teeth being slanted such that: a) one or more inner teeth overlap one or more outer teeth to provide mutual bracing, and b) there is pathway for fluid flow where the spaces between inner and outer teeth overlap. 
     
     
         12 . The drill bit according to  claim 4 , wherein the bit inserts are ballistic bits or PDC bits and/or the bit inserts are tapered to increase point loading and promote core plug breaking. 
     
     
         13 . The drill bit according to  claim 4 , wherein the concentric drill bit is splined to or relative to the annular coring bit such that it can move axially relative to the annular coring bit but can rotate with the annular coring bit. 
     
     
         14 . The drilling apparatus with the drill bit according to  claim 1 , and configured to rotate the annular coring bit and repeatedly axially move the concentric drill bit. 
     
     
         15 . The drilling apparatus according to  claim 14 , comprising:
 a drillstring casing coupled to and operable to rotate the annular coring bit, and   a repeatable force generating apparatus coupled to and operable to repeatedly axially move the concentric drill bit.   
     
     
         16 . The drilling apparatus according to  claim 15 , wherein the repeatable force generating apparatus is splined to the drillstring casing. 
     
     
         17 . The drilling apparatus according to  claim 15 , wherein the repeatable force generating apparatus provides a vibration to the annular coring bit sufficient to enhance the performance of the coring bit. 
     
     
         18 . The drill bit according to  claim 5 , wherein the recess height, the number of bit inserts on the concentric drill bit and the force applied to the drill bit can be configured to generate a desired size of chip sample when breaking the core plug. 
     
     
         19 . The drilling apparatus according to  claim 1 , wherein breaking the core plug produces fractures in the formation to assist drilling. 
     
     
         20 . The drill bit according to  claim 12 , wherein the bit inserts are at right angles to the concentric drill bit face.