Drill bit

Abstract

The present invention relates generally to drill bits used in drilling subterranean boreholes. More specifically, the invention relates to drill bits and cutting elements on the drill bits and the design of each. The invention utilizes a cutting element having a convex curved top portion with a shear face wherein said shear face is a plane formed by taking a planer slice from said convex curved top portion.

What is claimed is: 
     
         1 . A cutting element for use in a drill bit for drilling a borehole in earthen formations, the cutting element comprising:
 a substrate column comprising a first material, said substrate column having a convex curved top portion with a shear face wherein said shear face is a plane formed by taking a planer slice from said convex curved top portion;   an ultrahard material layer disposed on said hemispherical top portion.   
     
     
         2 . The cutting element of  claim 1  wherein said substrate column has a longitudinal axis and said shear face is at an inner angle of less than 80° from said longitudinal axis. 
     
     
         3 . The cutting element of  claim 1  wherein said shear face is comprised of said first material without any ultrahard material disposed thereon. 
     
     
         4 . The cutting element of  claim 1  wherein said shear face has said ultrahard material disposed thereon. 
     
     
         5 . The cutting element of  claim 1  wherein said convex curved top portion has a shape of either hemispheric or ballistic. 
     
     
         6 . The cutting element of  claim 5  wherein said shape of said convex curved top portion is hemispheric. 
     
     
         7 . The cutting element of  claim 6  wherein said substrate column has a longitudinal axis and said shear face is at an inner angle of from 40° to 80° from said longitudinal axis. 
     
     
         8 . The cutting element of  claim 7  wherein said inner angle is from 50° to 70°. 
     
     
         9 . A drill bit for drilling a borehole in earthen formations, the drill bit comprising:
 a drill head having a plurality of cutting elements thereon, said cutting elements comprising:
 a substrate column comprising a first material and having a convex curved top portion with a shear face, wherein said shear face is a plane formed by taking a planer slice from said convex curved top portion; and 
 an ultrahard material layer disposed on said hemispherical top portion. 
   
     
     
         10 . The drill bit of  claim 9  wherein said drill bit is a rotary percussive drill bit. 
     
     
         11 . The drill bit of  claim 5  wherein said drill bit further comprises a longitudinal axis, an impact surface transverse to said longitudinal axis and a gage surface having an angle of from 35° to 42° degrees from said longitudinal axis, wherein said gage surface has a plurality of said cutting elements mounted thereon and configured such that upon use said cutting elements provide percussive and shear drilling functions. 
     
     
         12 . The cutting element of  claim 9  wherein said substrate column has a longitudinal axis and said shear face is at an inner angle of less than 80° from said longitudinal axis. 
     
     
         13 . The cutting element of  claim 9  wherein said shear face is comprised of said first material without any ultrahard material disposed thereon. 
     
     
         14 . The cutting element of  claim 9  wherein said shear face has said ultrahard material disposed thereon. 
     
     
         15 . The cutting element of  claim 9  wherein said convex curved top portion has a shape of either hemispheric or ballistic. 
     
     
         16 . The cutting element of  claim 9  wherein said shape of said convex curved top portion is hemispheric. 
     
     
         17 . The cutting element of  claim 16  wherein said substrate column has a longitudinal axis and said shear face is at an inner angle of from 40° to 80° from said longitudinal axis. 
     
     
         18 . The cutting element of  claim 17  wherein said inner angle is from 50° to 70°.