High shear roller cone drill bits

Abstract

A drill bit may include a bit body, comprising: at its upper end, a connection adapted to connect to a drill string; at its lower end, a plurality of journals extending downwardly and radially outward from a longitudinal axis of the bit; a plurality of roller cones rotatable mounted on the plurality of journals; and at least three rows of cutting elements disposed on each of the plurality of roller cones, wherein an outermost row has an extension height to diameter ratio greater than a mid row, and the mid has an extension height to diameter ratio greater than an innermost row.

1 . A drill bit, comprising:
 a bit body, comprising:
 at the upper end of the bit body, a connection adapted to connect to a drill string; and 
 at the lower end of the bit body, a plurality of journals extending downwardly and radially outward from a longitudinal axis of the bit; 
   a plurality of roller cones rotatably mounted on the plurality of journals,   wherein a ratio of a distance from the longitudinal axis to a greatest diameter of the cone and a bit radius is in a range of 0 to 0.25.   
     
     
         2 . The drill bit of  claim 1 , wherein the bit body is shaped to have its lowest diameter at an axial location below its greatest diameter. 
     
     
         3 . The drill bit of  claim 1 , wherein each angle φ between the longitudinal axis of the bit and each journal axis of the plurality of journals is an acute angle. 
     
     
         4 . A drill bit, comprising:
 a bit body, comprising:
 at the upper end of the bit body, a connection adapted to connect to a drill string; and 
 at the lower end of the bit body, a plurality of journals extending downwardly and radially outward from a longitudinal axis of the bit; 
   a plurality of roller cones rotatably mounted on the plurality of journals; and   at least one cutting element configured to engage earth formation proximate a bit centerline.   
     
     
         5 . The drill bit of  claim 4 , wherein the plurality of roller cones is oriented to form a center core spacing therebetween. 
     
     
         6 . The drill bit of  claim 5 , wherein the at least one cutting element comprises a center insert disposed in a center hole of the lower end of the bit body between the plurality of roller cones. 
     
     
         7 . The drill bit of  claim 6 , wherein the center insert is configured to assist in cutting of a center core of formation. 
     
     
         8 . The drill bit of  claim 6 , comprising:
 a plurality of ball passages;   a plurality of ball retainers each disposed in the plurality of ball passages; and   a center plug disposed in a center of the lower end of the bit body proximate the plurality of ball retainers.   
     
     
         9 . The drill bit of  claim 8 , wherein the center plug includes at least one groove formed therein configured to receive at least one of the plurality of ball retainers. 
     
     
         10 . The drill bit of  claim 8 , wherein at least two of the plurality of ball retainers have a different length. 
     
     
         11 . The drill bit of  claim 8 , comprising a back hole plug disposed in at least one of the plurality of ball passages. 
     
     
         12 . The drill bit of  claim 4 , comprising at least one grease hole and a plurality of lubrication passages for each cone, wherein the plurality of lubrication passages do not intersect. 
     
     
         13 . The drill bit of  claim 6 , wherein the center insert is secured in the center hole with an interference fit. 
     
     
         14 . The drill bit of  claim 4 , wherein each of the plurality of roller cones includes a plurality of cutting elements thereon, at least one cutting element on an outermost row of at least one roller cone comprising an extension height to diameter ratio ranging from 0.675 to 0.76. 
     
     
         15 . The drill bit of  claim 5 , wherein at least one cutting element configured to engage the formation proximate the bit centerline engages a center core of formation formed by the center core spacing. 
     
     
         16 . The drill bit of  claim 15 , wherein the at least one cutting element is on a core-facing surface of the at least one roller cone. 
     
     
         17 . The drill bit of  claim 4 , wherein at least one roller cone touches the bit centerline. 
     
     
         18 . A drill bit, comprising:
 a bit body, comprising:
 at the upper end of the bit body, a connection adapted to connect to a drill string; and 
 at the lower end of the bit body, a first cutting structure and a second, different type of cutting structure, the first cutting structure including a plurality of journals extending downwardly and radially outward from a longitudinal axis of the bit and a plurality of roller cones rotatably mounted on the plurality of journals. 
   
     
     
         19 . The drill bit of  claim 18 , wherein the second, different type of cutting structure includes a center insert disposed in a center hole of the lower end of the bit body. 
     
     
         20 . The drill bit of  claim 18 , wherein at least one nozzle is disposed between each pair of adjacent roller cones. 
     
     
         21 . A drill bit, comprising:
 a bit body, comprising:
 at the upper end of the bit body, a connection adapted to connect to a drill string; and 
 at the lower end of the bit body, a plurality of journals; 
   a plurality of roller cones rotatably mounted on the plurality of journals; and   a center insert disposed in a center hole of the lower end of the bit body between the plurality of roller cones configured to engage earth formation proximate a bit centerline.