Shear cutter drill bit

Abstract

A shear cutter drill bit for drilling a subterranean formation is provided having a bit body; a bit face on the bit body having at least a center zone, an efficiency zone, and an outer zone, the efficiency zone being located between the center zone and the outer zone; and a plurality of cutters having a backrake angle located on the bit face; wherein a majority of the cutters located in the efficiency zone of the bit face have a more aggressive backrake angle than a majority of the cutters located in the center zone of the bit face and a majority of the cutter located in the outer zone of the bit face.

1 . A shear cutter drill bit for drilling a subterranean formation, comprising:
 a bit body;   a bit face on the bit body having at least a center zone, an efficiency zone and an outer zone, the efficiency zone being located between the center zone and the outer zone; and   a plurality of cutters having a backrake angle located on the bit face;   
     wherein a majority of the cutters located in the efficiency zone of the bit face have a more aggressive backrake angle than a majority of the cutters located in the center zone of the bit face and a majority of the cutters located in the outer zone of the bit face. 
   
   
       2 . The drill bit as claimed in  claim 1 , wherein the majority of the cutters located in the efficiency zone have a backrake angle less than 20°. 
   
   
       3 . The drill bit as claimed in  claim 1 , wherein the majority of the cutters located in the efficiency zone have a backrake angle less than 15°. 
   
   
       4 . The drill bit as claimed in  claim 1 , wherein the majority of the cutters located in the efficiency zone have a backrake angle less than 10°. 
   
   
       5 . The drill bit as claimed in  claim 1 , wherein the majority of the cutters located in the efficiency zone have a backrake angle less than 5°. 
   
   
       6 . The drill bit as claimed in  claim 1 , wherein the majority of the cutters located in the efficiency zone have the most aggressive backrake angles, the majority of the cutters located in the center zone have intermediately aggressive backrake angles, and the majority of the cutters located in the outer zone have the least aggressive backrake angles. 
   
   
       7 . The drill bit as claimed in  claim 1 , wherein the majority of the cutters located in the efficiency zone have a backrake angle in the range of about 5° to about 15°, the majority of the cutters located in the center zone have a backrake angle in the range of about 15° to about 20°, and the majority of the cutters located in the outer zone have a backrake angle in the range of about 15° to about 30°. 
   
   
       8 . The drill bit as claimed in  claim 1 , wherein the majority of the cutters located in the efficiency zone have a backrake angle in the range of about 5° to about 15°, the majority of the cutters located in the center zone have a backrake angle in the range of about 15° to about 20°, and the majority of the cutters located in the outer zone have a backrake angle in the range of about 20° to about 30°. 
   
   
       9 . The drill bit as claimed in  claim 1 , wherein the majority of the cutters located in the efficiency zone have a backrake angle in the range of about 10°, the majority of the cutters located in the center zone have a backrake angle of about 15°, and the majority of the cutters located in the outer zone have a backrake angle in the range of about 15° to about 30°. 
   
   
       10 . The drill bit as claimed in  claim 1 , the bit face comprising at least one blade, wherein the cutters are located on the at least one blade. 
   
   
       11 . A method for drilling a subterranean formation, comprising:
 providing a shear cutter drill bit for drilling a subterranean formation, the shear cutter drill bit comprising:   a bit body;   a bit face on the bit body having at least a center zone, an efficiency zone and an outer zone, the efficiency zone being located between the center zone and the outer zone; and   a plurality of cutters having a backrake angle located on the bit face;   wherein a majority of the cutters located in the efficiency zone of the bit face have a more aggressive backrake angle than a majority of the cutters located in the center zone of the bit face and a majority of the cutters located in the outer zone of the bit face;   positioning the face of the drill bit towards the subterranean formation so that at least one of the center zone, efficiency zone and outer zone contacts the subterranean formation;   rotating the drill bit while applying a weight on the drill bit so as to penetrate the subterranean formation;   
     wherein the weight applied to the drill bit is less that the weight needed to be applied to a conventional shear cutter drill bit for obtaining the same rate of penetration. 
   
   
       12 . The method as claimed in  claim 11 , wherein the majority of the cutters located in the efficiency zone have a backrake angle less than 20°. 
   
   
       13 . The method as claimed in  claim 11 , wherein the majority of the cutters located in the efficiency zone have a backrake angle less than 15°. 
   
   
       14 . The method as claimed in  claim 11 , wherein the majority of the cutters located in the efficiency zone have a backrake angle less than 10°. 
   
   
       15 . The method as claimed in  claim 11 , wherein the majority of the cutters located in the efficiency zone have a backrake angle less than 5°. 
   
   
       16 . The method as claimed in  claim 11 , wherein the majority of the cutters located in the efficiency zone have the most aggressive backrake angles, the majority of the cutters located in the center zone have intermediately aggressive backrake angles, and the majority of the cutters located in the outer zone have the least aggressive backrake angles. 
   
   
       17 . The method as claimed in  claim 11 , wherein the majority of the cutters located in the efficiency zone have a backrake angle in the range of about 5° to about 15°, the majority of the cutters located in the center zone have a backrake angle in the range of about 15° to about 20°, and the majority of the cutters located in the outer zone have a backrake angle in the range of about 15° to about 30°. 
   
   
       18 . The method as claimed in  claim 11 , wherein the majority of the cutters located in the efficiency zone have a backrake angle in the range of about 5° to about 15°, the majority of the cutters located in the center zone have a backrake angle in the range of about 15° to about 20°, and the majority of the cutters located in the outer zone have a backrake angle in the range of about 20° to about 30°. 
   
   
       19 . The method as claimed in  claim 11 , wherein the majority of the cutters located in the efficiency zone have a backrake angle in the range of about 10°, the majority of the cutters located in the center zone have a backrake angle of about 15°, and the majority of the cutters located in the outer zone have a backrake angle in the range of about 15° to about 30°. 
   
   
       20 . The method as claimed in  claim 11 , wherein the bit face comprising at least one blade and the cutters are located on the at least one blade.