Drill bit

Abstract

The invention relates to a rotary drill bit for drilling a borehole in an earth formation, the drill bit comprising a first and a second disc cutter, each disc cutter being arranged to roll along the borehole bottom during rotation of the drill bit and thereby to cut respective first and second substantially circular, radially spaced cuts in the borehole bottom so that a body of rock material is defined between said cuts. The second disc cutter is arranged to cut into the bottom of the borehole at a selected rotational interval of the drill bit behind the first disc cutter and to shear-off said body of rock material in the direction of the first cut. Each disc cutter includes a set of mutually spaced cutting members arranged to create, during a turn of the drill bit, a corresponding set of cut sections of the cut created by the disc cutter, and wherein the cutting members are arranged so that the sets of cut sections created during subsequent drill bit turns are staggered relative to each other.

1 . A rotary drill bit for drilling a borehole in an earth formation, the drill bit comprising a first and a second disc cutter, each disc cutter being arranged to roll along the borehole bottom during rotation of the drill bit and thereby to cut respective first and second substantially circular, radially spaced cuts in the borehole bottom so that a body of rock material is defined between said cuts, the second disc cutter being arranged to cut into the bottom of the borehole at a selected rotational interval of the drill bit behind the first disc cutter and to shear-off said body of rock material in the direction of the first cut, wherein each disc cutter includes a set of mutually spaced cutting members arranged to create, during a turn of the drill bit, a corresponding set of cut sections of the cut created by the disc cutter, and wherein the cutting members are arranged so that the sets of cut sections created during subsequent drill bit turns are staggered relative to each other.  
     
     
         2 . The rotary drill bit of  claim 1 , wherein the cutting members are substantially regularly spaced along the cutter, and wherein the drill bit is dimensioned so that 
         D/d =( i +f )/ n   
       in which 
 D=diameter of the cut created by the cutter;  
 n=number of cutting members of the cutter;  
 d=rolling diameter of the cutter;  
 i=integer number 1, 2, 3, . . . etc.;  
 0<f<1.  
 
     
     
         3 . The drill bit of  claim 2 , wherein 0.3<f<0.7  
     
     
         4 . The drill bit of  claim 2  or  3 , wherein f is about 0.5.  
     
     
         5 . The drill bit of any one of claims  2 - 4 , wherein 1.5<D/d<2.  
     
     
         6 . The drill bit of any one of claims  1 - 5 , wherein the drill bit includes a bit body and a plurality of roller cones rotatably connected to the bit body so as to substantially roll along the borehole bottom during rotation of the bit in the borehole and being oriented in different radial orientations, a first one of the roller cones being provided with the first disc cutter and a second one of the roller cones being provided with the second disc cutter.  
     
     
         7 . The drill bit of  claim 6 , wherein each roller cone is provided with a plurality of said disc cutters spaced along the axial direction of the roller cone, and wherein the sets of cutting members of adjacent disc cutters of the roller cone are arranged in a staggered relationship.  
     
     
         8 . The drill bit of any one of claims  1 - 7 , wherein for each disc cutter, each cutting member of the disc cutter extends along a section angle α of the disc cutter and each spacing between adjacent cutting members of the disc cutter extends along a section angle β of the disc cutter, and wherein α=β+δ and 0°<δ<4°.  
     
     
         9 . The drill bit of  claim 8 , wherein 1°<δ<3°, and preferably δ is about 2°.  
     
     
         10 . The drill bit of any one of claims  1 - 9 , wherein each set of cutting members is defined by a set of mutually spaced recesses formed in the disc cutter to which the set of cutting members pertains.  
     
     
         11 . The drill bit substantially as described hereinbefore with reference to the drawings.