ECCENTRIC CONES FOR ROCK CUTTING

Abstract

A backreaming assembly having an elongate rotatable tool shaft and a plurality of cutting elements. The tool shaft is disposed on a tool axis and has a first end and a second end. Each cutting element is supported on the shaft in side-to-side relationship. Each cutting element is rotatable with respect to the shaft and with respect to each other. Each cutting element has a center offset from the tool axis.

Description

FIELD

This invention relates generally to a tool for backreaming and pulling a product pipe into a bore.

SUMMARY

A backreaming or hole-opening tool that provides radial force to widen a bore. The tool comprises an elongate rotatable tool shaft and a plurality of cutting elements. The tool shaft is disposed on a tool axis and has a first end and a second end. The cutting elements are supported on the shaft in side-to-side relationship. Each cutting element is rotatable with respect to the shaft and with respect to each other and has a center offset from the tool axis. An underground drill stem may be attached to the tool adjacent the first end of the shaft and a product pipe may be attached to the tool adjacent the second end of the shaft. Thus, the tool may be used to widen a bore and tow a product pipe into the bore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a backreaming tool.

FIG. 2 is a side view of the backreaming tool of FIG. 1.

FIG. 3 is a sectional view of the tool of FIG. 2, taken along line 3-3.

FIG. 4 is a close-up view of detail B of FIG. 3.

FIG. 5 is a perspective exploded view of a cutting element used in the backreaming tool.

FIG. 6 is a front end view of the backreaming tool of FIG. 1.

FIG. 7 is a side view of the backreaming tool of FIG. 6, taken along line 7-7.

FIG. 8 is a side view of the backreaming tool of FIG. 6, taken along line 8-8.

FIG. 9 is a side view of the backreaming tool of FIG. 6, taken along line 9-9.

FIG. 10 is a diagram of a backreaming operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Horizontal Directional Drilling (hereinafter “HDD”) systems commonly deploy pneumatic hammers and/or rock drill bits to cut a bore through difficult subsurface conditions such as solid rock or cobble. Such operations are undertaken to install underground utilities without the need to cut an open trench. Because the initial cutting operation may be difficult to accomplish, the hammer and/or rock drill bit will have a small cutting dimension. However, many underground utilities intended to carry natural gas, water or telecom lines require a bore larger than the bore cut by the drill bit. Therefore, it may be necessary to enlarge the bore by pulling a backreamer, having a cutting dimension larger than the drill bit, through the ground along the path of the bore to increase the size of the bore.

Backreaming is the process of increasing the size of the bore in order to allow the installation of the underground utility. As used herein, the term “backreaming” is intended to designate such a process carried out in any terrestrial environment, whether solid rock, or otherwise. The downhole tool used increase the bore's diameter may be referred to herein as a “backreaming tool,” “tool,” or “backreamer.”

Turning now to the figures in general and FIGS. 1 and 2 in particular, shown therein is a backreaming assembly 10. The backreaming assembly 10 comprises a stub shaft 12, a swivel 14, a towing connection 16, and a plurality of cutting elements 20A-F. Each cutting element 20A-F is of substantially similar construction and supported side-to-side from element 20A to 20F. Each cutting element 20A to 20F is rotatable with respect to each other and has a center offset from a tool axis 30. The tool axis 30 is defined generally by the center of rotation of the tool shaft 40 and extends from a first end 26 of the tool to a second end 28 of the tool. Each cutting element 20A-F is angularly offset about the tool axis 30 relative to its adjacent cutting elements. Such angular offset may be uniform about the tool axis 30.

As shown in FIG. 2, each cutting element 20A-20F is shaped as a conical frustum and has a plurality of cutters 24 formed on the side wall of the frustum. Cutters 24 mechanically spall material from a rock face or wall 200 (FIG. 10) of the bore when the cutting elements are rotated and pulled through the bore. The cutters 24 may comprise tungsten carbide or other suitable hardened material.

Each cutting element 20A-F has its maximum cross-sectional dimension adjacent the swivel 14. Thus, the diameter of each cutting element 20A-20F gets progressively larger from front (nearer to stub shaft 12) to back (nearer to swivel 14). Cutting element 20A may have a smaller maximum cross-sectional dimension than the minimum cross-sectional dimension of cutting element 20B, which may be smaller than maximum cross-sectional dimension of cutting element 20C, etc. As shown in FIG. 2, the minimum cross-section dimension of cutting element 20A is less than the minimum cross-sectional dimension of 20B. However, the maximum cross-sectional dimension of 20A is larger than the minimum cross-sectional dimension of 20B.

The stub shaft 12 is disposed at a first end of the tool 10 and may comprise a threaded connection 22. The rotational axis of the stub shaft 12 is not centered with the tool axis 30. Rather, it is offset from the tool axis 30 but generally parallel thereto. The threaded connection 22 may comprise a box formed to receive a threaded end of an underground drill stem 202 (FIG. 10).

Swivel 14 is supported at the second end of the tool 10 and its axis of rotation is generally aligned with the tool axis 30. However, it may also be slightly laterally offset form the tool axis 30. The swivel has a towing connection 16 which may be a towing eye 18 formed on the swivel. The swivel 14 maintains the towing eye 18 in a non-rotating configuration when the tool is under rotation. The towing eye 18 allows for the attachment of a product pipe 208 (FIG. 10) to the tool. The swivel allows the drill stem 202 to rotate the tool shaft 40 (FIG. 3) as the tool 10 is pulled through the ground while maintaining the non-rotating configuration of the product pipe. The towing eye 18 is a cross hole that is used to attach the product pipe to the tool 10 with a clevis or similar coupling device.

Turning now to FIG. 3, a sectional view of the tool 10 of FIG. 2 is shown along line 3-3. FIG. 3, shows the tool 10 has an elongate rotatable tool shaft 40 disposed on the tool axis 30. The tool shaft 40 has a first end 36 and a second end 38. Each of the plurality of cutting elements 20A-F is supported on the shaft 40 in side-to-side relationship intermediate the first 36 and second 38 ends of the tool shaft. Each cutting element 20A-F is rotatable with respect to the shaft 40 and with respect to each other. Each cutting element 20A-F has a center of rotation that is laterally offset from the tool axis 30. Stub shaft 12 having threaded connection 22 is formed at the first end 36 of the tool shaft 40 and towing connection 16 is formed at the second end 38 of the shaft.

The threaded connection 22 comprises tapered internal threads 50 formed in the stub shaft 12 to connect the tool to a downhole end of the drill stem 202 (FIG. 10). The stub shaft 12 may have an outer profile that is frustoconical and a hollow region 52 that extends for the entire length of the stub shaft. The hollow region 52 allows fluid to pass from the drill stem 202 and into central bore 54 of the tool shaft 40. The stub shaft 12 is connected to the tool shaft 40 using a threaded connection 44 located within a counter bore 46 formed at the end of the stub shaft that opposes the threaded connection 22. The stub shaft 12 may be threaded onto the tool shaft using a tool that fits into an internal hex drive feature 48. The stub shaft 12 and tool shaft 40 are connected such that hollow regions 52 and central bore 54 are in fluid communication and torque is transmitted from the stub shaft 12 to the tool shaft 40 through the threaded connection 44.

The swivel 14 is connected to the second end 38 of the tool shaft. The swivel 14 comprises a housing 32 having a hole that is formed to fit around the second end 38 of the tool shaft 40. A nut 60 having a cross-sectional dimension larger than the hole formed in the housing 32 may be threaded onto a collar 62 formed on the second end 38 of the tool shaft 40 to secure the housing 32 to the tool shaft. As nut 60 is threaded onto the collar 62 the cutting elements are compacted and secured on the shaft 40 between stub shaft 12 and housing 32. The collar 62 may be a portion of the tool shaft 40 that extends through the housing 32 into a swivel hollow region 63.

A portion of the towing connection 16 is supported within the housing 32 and a second portion protrudes from the housing at an end opposite the end at which the housing 32 is connected to the tool shaft 40. The towing connection 16 may comprise the towing eye 18 and a shaft 68. The shaft 68 is mounted in a bearing stack 64 to permit relative rotation between the towing connection 16 and the swivel housing 32 when the housing is rotated with the tool shaft 40. This arrangement maintains the towing connection 16 in a non-rotating configuration when the tool shaft 40 is under rotation. A nut 66 and threaded flange 72 may be used to secure the bearing stack 64 within the swivel hollow region 63.

With reference now to FIGS. 3, 4, and 5 each cutting element 20A-F comprises an eccentric puck 80, a bushing 82, and a bit roller 84. Each puck 80 has a central passage 128 through which the tool shaft 40 passes and on which the puck is supported for rotation with the shaft. Each puck 80 is generally cylindrical and has an outer groove 100 formed on an outer surface of the puck. The outer groove 100 generally extends around the entire circumference of the puck 80 and has a passage 122 that connects the central passage 128 and the outer groove 100. The end of the puck 80 disposed towards the second end 38 of the tool shaft 40 has a groove 94 that extends from the central passage 128 toward an outer edge of the puck. When assembled on the tool shaft 40, groove 94 is aligned with port 90 formed in the tool shaft. A pin bore 142 is towed in puck 80 to receive a pin 140. The puck 80 also has an inner groove 98 formed on an inner surface of the puck and aligned with port 92 when the puck is supported on the tool shaft 40.

The puck 80 is press-fit into a bushing 82. The bushing 82 is generally cylindrical having a flange 102 at one end. The bushing 82 has a port 101 that aligns with the outer groove 100 when the puck 80 and bushing are assembled. The bushing 82 is supported on the puck 80 to rotate with the puck. A longitudinal groove 124 is formed in the outer surface of the bushing 82 and communicates with the port 101. The bushing 82 and puck 80 are supported within the bit roller 84 and inserted so that flange 102 is disposed within the counter bore 120. The bit roller 84 is supported on the bushing 82 and puck 80 so that it may rotate independently of the bushing and puck.

When assembled a fluid flow path is formed that allows the injection of fluid into the cutting element from the tool shaft 40 through port 92. The fluid passes through port 92 into inner groove 98. The fluid then flows into passage 122, which connects the inner groove 98 to the outer groove 100. The fluid in outer groove 100 lubricates and cools the puck 80 and bushing 82. Fluid may then pass through the port 101 formed in the bushing 82 and spread along the longitudinal groove 124 to lubricate rotation of the bit roller 84 relative to the bushing 82.

As discussed above, the puck 80 has a pin bore 142. The pin bore 142 is offset from a bit axis 130 and the tool axis 30. As used herein, each bit axis 130 is defined by the center of its related cutting element and is not parallel to the tool axis 30. The bit rollers 84 are symmetric about their respective bit axes 130. As shown in FIG. 8, the bit axis 130 is tilted relative to the tool axis 30. Each bit axis 130 may be tilted by an angle of less than 30 degrees from parallel relationship to the tool axis 30. In a preferred embodiment the bit axis 130 is tilted by an angle of about 3 degrees from a parallel relationship to the tool axis. Each cutting element 20A-F is rotatable about its respective bit axis 130.

Each cutting element 20A-F has a shield 95. A shaft bore 144 and a nozzle 96 are formed in each shield 95. The shield 95 is positioned to cover the groove 94 and align the shaft bore 144 with the central passage 128. The pin bore 146 of the shield 95 is positioned to align with pin 140. A second shield 195 abuts the shield 95 and is positioned on a leading side of an adjacent cutting element 20. A pin 140 fits through a pin bore 146 into the pin bore 142 of the puck 80 and an adjacent puck, aiding in torque transmission between adjacent cutting elements and to maintain the angular offset relationship about the tool axis 30 between cutting elements. The shaft bore 144 allows passage of the tool shaft 40 between adjacent cutting elements. A second shield 195 having a pin bore 146 and shaft bore 144 may be used with shield 95 to provide protection from cuttings and soil and to shield the pucks 80 bushings 82 from contamination. The nozzle 96 is shown in shield 95 and positioned to communicate with groove 94 to provide lubrication to outer surfaces of cutting elements 20A-F.

In operation, lubricant comprising an air-foam-oil mixture or bentonite drilling mud is pumped down the drill stem 202 (FIG. 10) into the hollow region 52 of the stub shaft 12. In cases where an air hammer is used during pilot boring, the entire backreaming operation can be completed using only air-foam-oil mixture, thereby eliminating any need for mud cleanup. The lubricant flows through the hollow region 52 and into the central bore 54 through the first end 36 of the tool shaft. The lubricant is forced out through ports 90 and 92 because the second end 38 of the tool shaft is closed off by the collar 62. The lubricant that passes through port 90 is directed into the groove 94 and through nozzle 96 to lubricate and clean the cutting element adjacent the nozzle 96. Lubricant ejected from nozzle 96 also clears cuttings generated by the cutting elements from the surface of the cutting elements and may float the cuttings to the surface.

Lubricant that is ejected from the tool shaft 40 through port 92 is used to lubricate and cool the puck 80, bushing 82, and bit roller 84. The lubricant enters the inner groove 98 to lubricate the area between the puck 80 and shaft 40. The lubricant then travels through passage 122 to outer groove 100 to lubricate relative movement of the puck 80, bushing 82, and bit roller 84. Lubricant injected into this region promotes cooling of the bushing 82 and bit roller 84. The injected lubricant also promotes sliding between the bushing 82 and bit roller 84, and flushes away debris.

As shown in FIG. 4, the cross-sectional area of nozzle 96 may be greater than the cross-sectional dimension of port 101 and the end of the fluid path 124 through the bushing 82. Therefore, in this embodiment, more lubricant may be ejected through the hole 96 than via the bushing port 101. The relative amounts of lubricant supplied to the bushing 82 and to the outside of the cutting elements may be adjusted as needed. Adjustment is performed by increasing the relative cross-sectional dimensions of the lubricant passage serving the component in need of greater lubrication.

With reference to FIG. 6, the backreamer tool 10 is shown in a front view. Cutting elements 20A, 20B, 20C, 20D, 20E, and 20F are each shown disposed head-to-tail behind stub shaft 12. The cutting elements 20A-F are each disposed generally in one of three “clock” positions when the tool 10 is stationary in the orientation shown. Proceeding counterclockwise, cutting element 20A is in the twelve o'clock position, cutting element 20B is in the eight o'clock position, and cutting element 20C is in the four o'clock position, and so on. This angular offset about the tool axis 30 is preferred for some applications but other orientations and dispositions of the cutting elements 20A-F about the shaft 40 are possible without departing from the spirit of the invention. In a preferred embodiment, the cutting elements 20A-F are evenly and sequentially distributed in angular positions about the center shaft 40 to generate roughly even radial forces on the backreamer tool 10 during backreaming.

The offset orientation of the cutting elements 20A-F and the progressively larger diameters of the cutting elements from front to back allow the backreamer tool 10 to enlarge the bore as the backreamer is rotated and pulled through the ground. Cutting element 20A will rotate about the bit axis 30 to enlarge the bore. Cutting element 20B will follow and rotate about its bit axis 130 to provide a slightly larger dimension to enlarge the bore a bit more, and so on.

FIG. 7 shows the tool 10 from the side such that cutting elements 20C and 20F contact a bore wall 200. FIGS. 8 and 9 are additional side views of the tool 10 from different positions. FIG. 8 shows cutting elements 20A and 20D contacting bore wall 200 while FIG. 9 shows cutting elements 20B and 20E contacting bore wall 200. Thus, FIGS. 7, 8, and 9 show the tool 10 at one moment in time, such that each of the cutting elements 20A-F are contacting the bore wall 200 at different points to enlarge the bore for pulling a product pipe 204 (FIG. 10) into the bore with the towing connection 16. The points of contact between the tool 10 and the wall 200 of the bore are distributed about the wall and will move together as the tool is rotated and pulled through the bore.

An exemplary offset angle between the tool axis 30 and the bit axis 130 is shown in FIG. 8 with reference to cutting element 20B. The offset angle may be between zero and thirty degrees. Preferably, this offset angle is three degrees though other angles may be used. Each cutting element 20A-F will have a distinct bit axis with a similar offset angle.

With reference now to FIG. 10, shown therein is a representation of a backreaming operation. A drill machine 201 is attached to a drill stem 202. The drill stem 202 is located in an unwidened portion 206 of the bore. The drill stem 202 is attached to the backreaming tool 10 and transfers pullback and rotational forces imparted by the drill machine 201 to the backreaming tool 10. Where the backreaming tool 10 has been pulled through the ground to engage the bore wall 200, a widened portion 208 of the bore has been formed. A product pipe 204 connected to the towing connection 16 (FIG. 1) is pulled through the widened portion 208 of the bore.

The maximum cross-sectional dimension of the cutting elements will be less than its adjacent bore dimension. Preferably, the cutting elements 20A-F cross-sectional dimensions are approximately 77% of their adjacent bore dimension. In this configuration, they will perform approximately 1.3 revolutions about their bit axis 130 for every revolution the tool 10 makes around tool axis 30. The radial forces on each cutting element 20A-F may meet or exceed 8,000 lbs. This radial force preferably causes the cutters 24 (FIG. 1) to spall material from the bore wall 200. Summed up over six cutting elements, this is 48,000 lb of radial force. The forces are preferably balanced by the uniform angular distribution of the cutting elements about axis 30. Radial forces result from the towing forces applied to stub shaft 12 by the drill stem 202. More cuffing elements may be utilized to provide more force. However, the addition of cutting elements may require additional towing force. The shallow offset angle of the bit axes 130 relative to the tool axis 30 creates a wedging effect. In the absence of friction between the tool and the wall 200, an offset angle of three degrees per side multiplies the towing forces by a factor of 38. Since the cutting elements 20A-F with their cutters 24 are not frictionless, the multiplication is lower. However, it may be that for a towing force of 20,000 lb at the drill stem, the multiplication factor need only be on the order of 2.4 to achieve the suggested radial forces. Preferred performance of the tool 10 at 90 RPM about axis 30 is 22.5 inches of axial progress requiring 1,800 fl-lb of torque.

While the force calculations given herein are representative, they should not be construed as limiting in any way. One skilled in the art will appreciate the variations that may be effective in this invention. For example, while backreaming through rock is one possible use, the backreaming tool 10 may be used in various types of drilling conditions. Six cutting elements are used as one preferred embodiment, but other numbers, such as four or eight, and other angular offsets may be contemplated without departing from the spirit of the claimed invention.

Claims

1. A tool, comprising: an elongate rotatable tool shaft disposed on a tool axis and having a first end and a second end; anda plurality of cutting elements supported on the shaft in side-to-side relationship, each cutting element rotatable with respect to the shaft and with respect to each other and having a center offset from the tool axis.

2. The tool of claim 1 in which each cutting element is rotatable about a bit axis that is not parallel to the tool axis.

3. The tool of claim 2 in which each bit axis is tilted by an angle of less than about 30 degrees from parallel relationship to the tool axis.

4. The tool of claim 2 in which each bit axis is tilted by an angle of about 3 degrees from parallel relationship to the tool axis.

5. The tool of claim 1 in which each cutting element is shaped as a conical frustum and in which cutters are formed on the side walls of the frustum.

6. The tool of claim 4, in which each cutting element has its maximum cross-sectional dimension adjacent the second end of the tool shaft.

7. The tool of claim 1 in which the cutting elements are situated intermediate the first and second ends of the tool shaft and in which a threaded connection is formed at the first end of the tool shaft and a towing connection is formed at the second end of the tool shaft.

8. The tool of claim 7 in which the towing connection is a towing eye formed on a swivel that is maintained in a non-rotating configuration when the tool shaft is under rotation.

9. The tool of claim 1 in which each cutting element is angularly offset about the tool axis relative to its adjacent cutting elements.

10. The tool of claim 9 in which the angular spacing of adjacent cutting elements is uniform.

11. A system comprising: the tool of claim 1;an underground drill stem attached to the tool adjacent the first end of the shaft; anda product pipe attached to the tool adjacent the second end of the shaft.

12. A tool, comprising: an elongate rotatable tool shaft disposed on a tool axis and having a first end and a second end; anda plurality of cutting elements supported on the shaft in side-to-side relationship, each cutting element rotatable with respect to the shaft and with respect to each other and having a center offset from the tool axis; anda product pipe towing connection formed at the second end of the elongate rotatable tool shaft.

13. The tool of claim 12 in which the towing connection is maintained in a non-rotating configuration when the tool shaft is under rotation.

14. The tool of claim 12 in which each cutting element is shaped as a conical frustum and in which cutters are formed on the side walls of the frustum

15. The tool of claim 12 in which each cutting element is angularly offset about the tool axis relative to its adjacent cutting elements.

16. The tool of claim 15 in which the angular spacing of adjacent cutting elements is uniform.

17. The tool of claim 12 in which each cutting element is rotatable about a bit axis that is not parallel to the tool axis.

18. The tool of claim 17 in which each bit axis is tilted by an angle of less than about 30 degrees from parallel relationship to the tool axis.

19. The system of claim 12 having a central bore formed in the tool shaft and a radial fluid passage in fluid communication with the central bore formed in each of the cutting elements.