Cutting Structure for Casing Drilling Underreamer
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.
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This invention relates in general to earth-boring operations using the casing as a drill string, and in particular to a cutting structure of an underreamer.
BACKGROUND OF THE INVENTIONConventional drilling of wells involves using a drill bit with cutting elements, either fixed or roller cone, connected to a drill pipe. The drill pipe is rotated either by a top drive or a hex Kelly drive. The well bore is drilled to target depth, whereby the drill string and bit are removed and replaced with thin-walled casing, which is then cemented in place.
Casing drilling completes these two steps in one operation by simultaneously drilling and casing a well. A bottom hole assembly mounted to the casing protrudes from the lower end of the casing. The bottom hole assembly has a pilot bit on its lower end and an underreamer located above. The pilot bit drills the primary hole, which is enlarged by the underreamer to a larger diameter than the casing. The underreamer has arms that pivot between a retracted and extended position, enabling the underreamer to be retrieved along with the pilot bit and other portions of the bottom hole assembly. The arms may be pivoted out by hydraulic pressure from drilling fluid being pumped from the surface. The arms are equipped with a fixed cutting structure.
Many versions of underreamer tools have been designed, tested and utilized. The criteria for the success of the tool is most dependent on its ability to reliably enlarge the primary well bore by 40-50% at an acceptable rate of penetration (ROP) similar to that obtained by a bit drilled conventionally with drill pipe. Furthermore, the underreamer has to be able to retract and be successfully tripped to the surface after drilling potentially thousands of feet of formation. Current designs are proven and work well, however a demand exists for drilling harder formations with improved ROP's.
Most underreamers have three arms, each equipped with cutting elements arranged in a wedge orientation. Cutting elements typically have a tungsten carbide base with a polycrystalline diamond “PCD” face or layer on its end. The cutting elements are normally arranged so that a line extending from the axis of rotation through the centerline is straight and is about a 20-30 angle when viewing the cutting arm in a front elevational view. Initially, all of the cutting elements are loaded equally, however non-uniform loading may quickly develop because the outer cutting elements cut more formation and move faster than the inner cutting elements. The outer cutting elements may wear to a greater degree and are more prone to lateral impact damage before the inner or more slowly moving cutting elements. In some cases, this can result in the secondary hole being drilled by the underreamer becoming under-gauge. This wear requires the underreamer to be tripped to the surface and a new assembly dressed and sent back downhole.
SUMMARY OF THE INVENTIONThe underreamer of this invention has a tubular body with a longitudinal axis. Arms are pivotally mounted to the body and move relative to the body between a retracted and an extended position. 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.
Preferably, when viewed in a bottom view, each of the arrays defines a curved line from the inner cutting elements to the outer cutting elements. When viewed in a front view, each array preferably defines a curved line that extends outward and upward. To avoid tracking, preferably each of the cutting elements is located a different distance from the underreamer axis than all the other cutting elements. Preferably, at least the outermost cutting element is partially overlapped by the cutting element adjacent to it so as to reduce the load on the outermost cutting element.
Referring to
Underreamer 11 also has a lower threaded connector 17 for connection with a pilot bit (not shown). The pilot bit may be a conventional earth-boring bit of the fixed cutter type or of the rolling cone type. Body 13 has a longitudinal axis 19 through which a passage 21 extends. An orifice 20 may be located toward the lower end of passage 21 for creating a back pressure.
An actuator tube 23 is movably carried in passage 21 between an upper position shown in
Cutting arms 27, pivotally mounted to body 13, typically comprise three arms 27a, 27b, and 27c as shown in
Referring to
In this embodiment, each arm 27 has three cutting elements, but the number could differ. The array 37 includes an inner cutting element 49, an intermediate cutting element 51 and an outer cutting element 53. Inner cutting element 49 of each arm 27 is the one closest to axis 19. Outer cutting element 53 is the one farthest from axis 19. Because of swept back line 47, a radial line 55 extending from axis 19 to center point 45 of outer cutting element 53 does not pass through center points 45 of the other cutting elements 49, 51. Rather, radial line 55 for outer cutting element 53 lags radial line 55 extending through center point 45 of intermediate cutting element 51. Similarly, radial line 55 extending through center point 45 of intermediate cutting element 51 lags radial line 55 extending through center point 45 of inner cutting element 49. Radial line 55 of inner cutting element 49 leads radial line 55 for intermediate cutting element 51 by an acute angle 57. Radial line 55 for intermediate cutting element 51 leads radial line 55 for outer cutting element 53 by an acute angle 59. Acute angles 57, 59 can vary and need not be of the same degree.
In addition to array 37 being swept back along curve 47, in this example face 43 of each cutting element 49, 51, 53 points at a different angle into the direction of rotation.
Referring to
Also, in the preferred embodiment, the radius from axis 19 to the center point 45 of each cutting element 49, 51, 53 is unique. Radius r1 in
In this example, intermediate cutting element 51 and outer cutting element 53 for each arm 27a, 27b and 27c overlap each other. That is, outer cutting element 53 is slightly behind intermediate cutting element 51 of the same arm. Referring to
Also, although different, the path of inner cutting element 49 on arm 27a overlaps with the path of inner cutting element 49 of arm 27b, which in turn overlaps with the path of inner cutting element 49 of arm 27c. The same overlap exists for intermediate cutting elements 51 of the different arms 27a, 27b and 27c, and outer cutting elements 53 of the different arms 27a, 27b and 27c.
Another difference between arrays 37 of arms 27a, 27b and 27c concerns the axial placement of the various cutting elements 49, 51 and 53 along lines parallel to axis 19. Referring to
In operation, the BHA (not shown) will be assembled with underreamer 11 as shown in
A second embodiment, shown in
Inlet ports 85 extend through the sidewall of actuator tube 83 for registering with the outlet ports 81 when actuator tube 83 is in the lower position. As illustrated in
When drilling fluid is first pumped down the string, it causes actuator tube 83 to move downward, and inlet ports 85 and nozzles 87 move downward in unison. When actuator tube 83 is in the lower position, nozzles 87 will align with outlet ports 81. A portion of the drilling fluid will flow through inlet ports 85, nozzles 87 and outlet ports 81 across the cutting element arrays 79 for cleaning and cooling.
While the invention has been shown in only two of its forms, it should be apparent to those skilled in the art that it is not so limited but it is susceptible to various changes without departing from the scope of the invention. For example, a different number than three arms could be utilized. Other arrangements for moving the arms between the retracted and extended positions may be employed.
Claims
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.
Type: Application
Filed: Jan 30, 2009
Publication Date: Aug 5, 2010
Applicant: Tesco Corporation (Calgary)
Inventor: Kevin C. Graf (Calgary)
Application Number: 12/363,444
International Classification: E21B 10/32 (20060101);