Cutting Structure for Casing Drilling Underreamer

Abstract

An underreamer earth-boring tool is connected to a bottom hole assembly for casing drilling applications. The underreamer has a tubular body with a longitudinal axis. Arms are pivotally mounted to the body and movable between retracted and extended positions. An array of cutting elements is mounted to each of the arms. Each of the arrays is swept back so that the cutting elements farther from the axis than others rotationally lag the others.

1 . An underreamer earth boring tool, comprising:
 a tubular body having a longitudinal axis;   a plurality of arms pivotally mounted to the body and movable relative to the body between a retracted position and an extended position;   an array of cutting elements mounted to each of the arms; and   each of the arrays being swept back so that cutting elements farther from the axis than others rotationally lag the others.   
   
   
       2 . The tool according to  claim 1  wherein when viewed in a bottom view, each of the arrays defines a curved line from the cutting elements closest to the axis to those farthest from the axis. 
   
   
       3 . The tool according to  claim 1 , wherein when viewed in a front view, each array defines a curved line from the cutting elements closest to the axis to those farthest from the axis. 
   
   
       4 . The tool according to  claim 1 , wherein each of the cutting elements is located a different radial distance from the axis than all of the other cutting elements in all of the arms. 
   
   
       5 . The tool according to  claim 1 , wherein a path of the outermost cutting element on each of the arms is overlapped by a path of an adjacent cutting element on the same arm. 
   
   
       6 . The tool according to  claim 1 , wherein each cutting element is located a different axial distance from a plane perpendicular to the axis than all of the other cutting elements in all of the arms. 
   
   
       7 . The tool according to  claim 1 , further comprising:
 a passage extending through the body for the delivery of drilling fluid; and   a plurality of nozzles in the body, each of the nozzles being in fluid communication with the passage and oriented to discharge a portion of the drilling fluid across one of the arrays.   
   
   
       8 . An underreamer earth boring tool, comprising:
 a tubular body having a longitudinal axis;   a plurality of arms pivotally mounted to the body and movable relative to the body between a retracted position and an extended position;   an inner and an outer cutting element mounted to each of the arms, each of the cutting elements having a face facing into a direction of rotation of the body, the face of the inner cutting element being closer to the axis than the face of the outer cutting element; and   the face of the inner cutting element on each of the arms rotationally leading the face of the outer cutting element on the same arm.   
   
   
       9 . The tool according to  claim 8 , further comprising:
 an intermediate cutting element mounted to each of the arms and having a face facing into a direction of rotation of the body, the face of the intermediate cutting element being closer to the axis than the face of the outer cutting element and farther from the axis than the face of the inner cutting element; and   the face of the intermediate cutting element on each of the arms rotationally leading the face of the outer cutting element and rotationally lagging the face of the inner cutting element on the same arm.   
   
   
       10 . The tool according to  claim 8 , wherein each of the cutting elements is oriented at a side rake angle, and wherein the side rake angle of the outer cutting element is greater than the side rake angle of the inner cutting element on the same arm. 
   
   
       11 . The tool according to  claim 8 , wherein:
 the face of each inner cutting element is at a different distance from the axis than the inner cutting elements on the other arms.   
   
   
       12 . The tool according to  claim 8 , wherein:
 each cutting element is located a different axial distance from a plane perpendicular to the axis than all of the other cutting elements on all of the arms.   
   
   
       13 . The tool according to  claim 8 , further comprising:
 an intermediate cutting element mounted to each of the arms and having a face facing into a direction of rotation of the body, the face of the intermediate cutting element being closer to the axis than the face of the outer cutting element and farther from the axis than the face of the inner cutting element; and   wherein a path of the outer cutting element on each of the arms is overlapped by a path of the intermediate cutting element on the same arm.   
   
   
       14 . The tool according to  claim 8 , further comprising:
 an intermediate cutting element mounted between the inner and the outer cutting elements on each of the arms, each intermediate cutting element having a face facing into a direction of rotation of the body; and   a line extending through a center point of each of the faces on each of the arms curves upward when viewed in a front view.   
   
   
       15 . The tool according to  claim 8 , further comprising:
 an intermediate cutting element mounted between the inner and the outer cutting elements on each of the arms, each intermediate cutting element having a face facing into a direction of rotation of the body; and   a line extending through a center point of each of the faces on each of the arms curves away from the direction of rotation when viewed in a bottom view.   
   
   
       16 . The tool according to  claim 8 , further comprising:
 a passage extending through the body for the delivery of drilling fluid;   an actuator tube carried in the passage for movement from an upper position to a lower position in response to drilling fluid pressure applied to the passage, the actuator tube being cooperatively coupled to the arms so as to place the arms in the retracted position while the actuator tube is in the upper position, and to place the arms in the extended position while the actuator tube is in the lower position;   a plurality of outlet ports formed in the body adjacent the arms; and   a plurality of nozzles mounted to the actuator tube for movement therewith and in fluid communication with the passage, the nozzles aligning with the outlet ports while the actuator tube is in the lower position to discharge a portion of the drilling fluid across the cutting elements.   
   
   
       17 . The tool according to  claim 16 , further comprising:
 a sleeve having a wear-resistant inner diameter mounted in the actuator tube, the sleeve having an inlet port for each of the nozzles.   
   
   
       18 . An underreamer earth boring tool, comprising:
 a tubular body having a longitudinal axis;   a plurality of arms pivotally mounted to the body and movable relative to the body between a retracted position and an extended position;   inner, intermediate and outer cutting elements mounted to each of the arms, each of the cutting elements having a circular flat face with a center point;   on each of the arms, the center point of the intermediate cutting element being farther from the axis than the center point of the inner cutting element and less than the center point of the outer cutting element;   on each of the arms, a first radial line extending radially from the axis and passing through the center point of the inner cutting element is at an acute angle relative to a second radial line extending radially from the axis and passing through the center point of the intermediate cutting element; and   on each of the arms, the second radial line is at an acute angle relative to a third radial line extending radially from the axis and passing through the center point of the outer cutting element.   
   
   
       19 . The tool according to  claim 18 , wherein each of the cutting elements is oriented at a side rake angle, and wherein the side rake angle of the outer cutting element is greater than the side rake angle of the inner cutting element on the same arm. 
   
   
       20 . The tool according to  claim 18 , wherein:
 the center point of each inner cutting element is at a different distance from the axis than the inner cutting elements on the other arms; and   the center point of each intermediate cutting element is at a different distances from the axis than the intermediate cutting elements on the other arms.   
   
   
       21 . The tool according to  claim 18 , wherein:
 when each arm is viewed in a front view, a line drawn through the center point each of the cutting elements on that arm curves upward.   
   
   
       22 . The tool according to  claim 18 , wherein:
 when each arm is viewed in a bottom view, a line drawn through the center point of each of the cutting elements on that arm curves away from a direction of rotation of the tool.   
   
   
       23 . The tool according to  claim 18 , wherein a path of the outer cutting element on each of the arms is overlapped by a path of the intermediate cutting element on the same arm.