Bit Cone With Hardfaced Nose

Abstract

A drill bit for drilling a wellbore, the drill bit having a cutter which has tungsten carbide inserts and a spear point. The spear point has a neck that joins a smooth portion of the cutter and blades that extend from the neck and converge to an apex. The blades define valleys or spaces between them. A layer of hardfacing is applied to the entire spear point including the interim spaces and the neck.

1 . An earth boring bit, comprising in combination:
 a body with a longitudinal bit axis;   three bit legs depending from the body;   first, second, and third cutters, each rotatably mounted to one of the bit legs;   at least one of the cutters having a metal shell with a nose section extending inward toward the bit axis from the metal shell, the nose section having compacts located thereon and protruding therefrom for disintegrating an earth formation, the nose section being free of hardfacing; and   at least one other of the cutters having a metal shell with a nose section extending toward the bit axis, the nose section of the at least one other of the cutters having hardfacing located thereon.   
   
   
       2 . The earth boring bit of  claim 1 , wherein the nose section having hardfacing located thereon further comprises:
 a spear point having a neck which joins the metal shell of the at least one other of the cutters, the spear point having a plurality of blades extending from the neck, the blades converging to an apex and being circumferentially separated from each other about a cutter axis of the at least one other of the cutters, defining a space between each of the blades; and   a layer of hardfacing formed on the neck, the blades and the spaces between each of the blades, the hardfacing being tungsten carbide particles in a matrix for protecting the neck and spaces from erosion.   
   
   
       3 . The earth boring bit of  claim 1 , wherein the nose section having hardfacing located thereon extends a desired distance toward the bit axis and is positioned closest to the bit axis than any of the other cutters: 
   
   
       4 . An earth boring bit, comprising in combination:
 a body with a bit axis;   three bit legs depending from the body;   first, second, and third cutters, each rotatably mounted to one of the bit legs;   the first cutter having a metal shell with at least one row of compacts located thereon and protruding from the metal shell for disintegrating an earth formation, the metal shell having a smooth conical surface extending inward from the at least one row of compacts, the smooth conical surface being free of hardfacing;   a spear point having a neck which joins the smooth conical surface of the first cutter, the spear point having a plurality of blades extending from the neck, the blades converging to an apex and being circumferentially separated from each other about a cutter axis of the first cutter, defining a space between each of the blades; and   a layer of hardfacing formed on the neck, the blades and the spaces between each of the blades, the hardfacing being tungsten carbide particles in a matrix for protecting the neck and spaces from erosion.   
   
   
       5 . The earth boring bit of  claim 4 , wherein the spear point extends axially along the cutter axis of the first cutter a select distance such that the apex of the spear is closer to the bit axis than any portion of the second and third cutters. 
   
   
       6 . The earth boring bit of  claim 4 , wherein said at least one row of compacts comprises:
 an outer row of compacts located thereon, an intermediate row of compacts located thereon at a lesser distance from the bit axis than the outer row, and an inner row of compacts located thereon at a lesser distance from the bit axis than the intermediate row.   
   
   
       7 . The earth boring bit of  claim 6 , wherein the first cutter is free of hardfacing from the outer row of compacts to the neck of the spear point. 
   
   
       8 . The earth boring bit of  claim 7 , wherein each of the second and third cutters further comprises:
 a metal shell with a nose section containing at least one compact that protrudes therefrom for disintegrating the earth formation.   
   
   
       9 . The earth boring bit of  claim 4 , further comprising:
 the second cutter having a metal shell with a nose section extending axially toward the longitudinal axis from the metal shell along the axis of the second cutter, the nose section of the second cutter having compacts protruding thereform, the nose section of the second cutter being free of hardfacing.   
   
   
       10 . The earth boring bit of  claim 9 , further comprising:
 the second cutter having an outer row of compacts protruding therefrom, an intermediate row of compacts protruding thereform and being at a lesser distance from the bit axis than the outer row of compacts of the second cutter and a farther distance from the bit axis than the compacts located on the nose section of the second cutter.   
   
   
       11 . The earth boring bit of  claim 4 , further comprising:
 the third cutter having a metal shell with a nose section extending axially toward the longitudinal axis from the metal shell along the axis of the second cutter, the nose section of the third cutter having compacts protruding therefrom, the nose section of the third cutter being free of hardfacing.   
   
   
       12 . The earth boring bit of  claim 11 , further comprising:
 the third cutter having an outer row of compacts protruding therefrom, an intermediate row of compacts protruding therefrom and at a lesser distance from the bit axis than the outer row of compacts of the third cutter.   
   
   
       13 . An earth boring bit comprising in combination:
 a body with a bit axis;   three bit legs depending from the body;   first, second, and third cutters, each rotatably mounted to one of the bit legs;   the first cutter having a metal shell with an outer row, an intermediate row, and an inner row of compacts located thereon and protruding therefrom, the intermediate row being at a lesser distance from the bit axis than the outer row, and the inner row being at a lesser distance from the bit axis than the intermediate row, the metal shell having a smooth conical surface extending inward from the inner row of compacts, the smooth conical surface being free of hardfacing;   a spear point having a neck which joins the smooth conical surface of the first cutter, the spear point having a plurality of blades extending from the neck, the blades converging to an apex and being circumferentially separated from each other about a first cutter axis of the first cutter, defining a space between each of the blades;   a layer of hardfacing formed on the neck, the blades and the spaces between each of the blades, the hardfacing being tungsten carbide particles in a matrix for protecting the neck and spaces from erosion; and   the second and third cutters each having a metal shell with at least one row of compacts located thereon and protruding therefrom.   
   
   
       14 . The earth boring bit of  claim 13 , wherein the metal shell of the first cutter is free of hardfacing between the outer row and the neck of the spear point. 
   
   
       15 . The earth boring bit of  claim 13 , wherein the second cutter further comprises:
 a metal shell with a nose section extending inward toward the bit axis, the nose section of the second cutter having compacts located thereon and protruding therefrom;   an outer row of compacts located on the metal shell of the second cutter and protruding therefrom outward from the compacts on the nose section of the second cutter; and   an intermediate row of compacts located on the metal shell of the second cutter and protruding therefrom between the compacts on the nose section and the outer row of compacts on the metal shell of the second cutter.   
   
   
       16 . The earth boring bit of  claim 15 , wherein the third cutter further comprises:
 a metal shell with a nose section extending inward toward the bit axis, the nose section of the third cutter having a row of compacts located thereon and protruding therefrom;   an outer row of compacts located on the metal shell of the third cutter and protruding therefrom; and   an intermediate row of compacts located on the metal shell of the third cutter between the compacts on the nose section and the outer row of compacts on the metal shell of the third cutter.   
   
   
       17 . The earth boring bit of  claim 16 , wherein:
 a distance between the outer row of compacts and the intermediate row of compacts on the first cutter, measured along the first cutter axis, is less than a distance between the outer row of compacts and the intermediate row of compacts on the second cutter, measured along a second cutter axis.   
   
   
       18 . The earth boring bit of  claim 17 , wherein:
 the distance between the outer row of compacts and the intermediate row of compacts on the second cutter is less than a distance between the outer row of compacts and the intermediate row of compacts on the third cutter, measured along a third cutter axis.