Fixed-cutter drill bits generating cores

Abstract

A drill bit includes a bit head having a front face, a plurality of blades extending along at least a portion of the front face, the blades comprising cutters, a cavity for forming a core, the cavity being approximately centrally located in the front face of the bit between adjacent end portions of the plurality of blades, and a removable core breaking device disposed within the cavity. The core breaking device is configured to project toward the front face a distance to engage and destroy the so formed core into multiple smaller fragments prior to a core length exceeding a core diameter, or project toward the front face a distance to engage and break the so formed core into a substantially unitary core sample.

What is claimed is: 
     
         1 . A drill bit comprising:
 a bit head having a front face;   a plurality of blades extending along at least a portion of the front face, the blades comprising cutters;   a cavity for forming a core, the cavity being approximately centrally located in the front face of the bit between adjacent end portions of the plurality of blades; and   a removable core breaking device disposed within the cavity and configured to project toward the front face a distance to engage and destroy the so formed core into multiple smaller fragments prior to a core length exceeding a core diameter, or   a removable core breaking device disposed within the cavity and configured to project toward the front face a distance to engage and break the so formed core into a substantially unitary core sample.   
     
     
         2 . The drill bit of  claim 1 , wherein the core breaking device comprises a cutter configured to extend toward the front face a distance to expose an edge on a distal end of the cutter to engage and destroy the so formed core into multiple smaller fragments. 
     
     
         3 . The drill bit of  claim 1 , wherein the core breaking device comprises a cutter configured to extend toward the front face a distance to expose a substantially flat surface at an angle with respect to a core axis to engage and break the so formed core into a substantially unitary core sample. 
     
     
         4 . The drill bit of  claim 1 , wherein the core breaking device comprises a nozzle having an exit orifice at a distal end of the nozzle configured to direct fluid to impinge upon and destroy the so formed core into multiple smaller fragments. 
     
     
         5 . The drill bit of  claim 4 , wherein the nozzle is configured to direct fluid to impinge upon the core at a distance from the distal end of approximately eight times a diameter of the exit orifice or less. 
     
     
         6 . The drill bit of  claim 1 , further comprising a number of nozzles that extend through the front face of the bit for dispensing fluid and carrying away drilling debris. 
     
     
         7 . The drill bit of  claim 1 , wherein the core breaking device threadably engages the bit head. 
     
     
         8 . The drill bit of  claim 1 , the cavity comprising an opening towards an evacuation channel, the opening having a width greater than or equal to a diameter of the so formed core. 
     
     
         9 . A method of using a drill bit comprising:
 providing a drill bit comprising:
 a bit head having a front face; 
 a plurality of blades extending along at least a portion of the front face, the blades comprising cutters; 
 a cavity for forming a core, the cavity being approximately centrally located in the front face of the bit between adjacent end portions of the plurality of blades; and 
 a removable core breaking device disposed within the cavity and configured to project toward the front face a distance to engage and destroy the so formed core into multiple smaller fragments prior to a core length exceeding a core diameter, or 
 a removable core breaking device disposed within the cavity and configured to project toward the front face a distance to engage and break the so formed core into a substantially unitary core sample; 
   operating a drillstring having the drill bit on a distal end for a first period of time, the drill bit having the removable core breaking device disposed within the cavity configured to project a distance toward the front face for destroying the so formed core into multiple smaller fragments, or   operating the drillstring having the drill bit for a second period of time, the drill bit having the removable core breaking device disposed within the cavity configured to project a distance toward the front face for breaking the so formed core into a substantially unitary core sample.   
     
     
         10 . The method of  claim 9 , further comprising operating the drill bit with the core breaking device and impinging upon the core with a fluid stream from a nozzle. 
     
     
         11 . The method of  claim 9 , further comprising operating the drill bit with the core breaking device and engaging the so formed core proximate to a base of the so formed core with an exposed edge on a distal end of the device. 
     
     
         12 . The method of  claim 9 , further comprising operating the drill bit with the core breaking device and engaging a distal end of the so formed core with an exposed substantially flat surface angled relative to a core axis on a distal end of the device.