Starter rod for use in back reaming

Abstract

An improved starter rod connects a back reamer to the distal end of a drill string. The starter rod is an elongated body having a front end portion which has a first connecting portion configured for connecting the starter rod to the back reamer, a rear end portion having a second connecting portion configured for connecting the starter rod to the drill string, a fluid passage configured for conveying fluid from the drill string through the starter rod from the rear end to the front end, and a branch passage extending from the fluid passage to a side surface of the starter rod configured to pass part of the fluid in the fluid passage outside the starter rod. Generally, the front end portion of the starter rod is also used to connect to a drill head and thus has an outer diameter greater than the rear end which connects to the drill string. In a preferred embodiment, the branch passage opens rearwardly of the large diameter front end portion so that the lubricating fluid is injected in the hole ahead of it. The lubricant provided ahead of the large diameter portion of the starter rod reduces wear and the chance of breakage at this location during back reaming.

Description

TECHNICAL FIELD

[0001] The invention relates to a starter rod used in a directional boring apparatus that has been connected to a back reamer for widening an existing hole.

BACKGROUND OF THE INVENTION

[0002] Wentworth et al. U.S. Pat. No. 6,148,935, Nov. 21, 2000, describes a starter rod for use in connecting a horizontal directional drilling string with a drill head including a bit and sonde housing. The illustrated embodiments of the Wentworth et al. joint use a projection and socket connection to secure the front end of the starter rod to the rear end of the sonde housing (FIG. 22). Splines are provided to pass torque. The projection and socket are mechanically interlocked by retainers such as roll pins inserted through transverse holes. The front end of the starter rod has a tapered threaded hole that receives the threaded male end of a standard drill rod. The rear end of the starter rod has an enlarged diameter or upset so that it matches the diameter of the drill head, which is generally greater than the diameter of the drill string.

[0003] As shown in FIGS. 28-30 of U.S. Pat. No. 6,148,935, it is common practice to remove the drill head and replace it with a back reamer during a backward run through a pilot hole drilled by the drill head. The starter rod is connected to the front of the back reamer and pulls and spins it through the ground while lubricating drilling fluid is injected though the center of the starter rod into the back reamer and then out through a series of holes in the outer surface of the back reamer. These outlet holes are most commonly located in grooves on the tapered portion of the back reamer for the purpose of carrying away cuttings. In one known back reamer design, the grooves are spiral-shaped and a series of fluid outlets are provided along the center of each groove.

[0004] When backreaming with a starter rod such as the one shown in the foregoing U.S. patent, cuttings tend to collect at the upset or large diameter portion of the starter rod. Wentworth et al. PCT Publication WO 00/11303, published Mar. 2, 2000, teaches providing the enlarged front end portion 206 of the starter rod with a number of carbide studs 68D in order to reduce wear on the starter rod during back reaming. This has proven helpful, but does not solve the problem of accumulation of cuttings around the starter rod. The present invention addresses this problem.

SUMMARY OF THE INVENTION

[0005] The present invention provides a starter rod for connecting a back reamer to the distal end of a drill string. The starter rod is an elongated body having a front end portion which has a first connecting portion configured for connecting the starter rod to a back reamer, a rear end portion having a second connecting portion configured for connecting the starter rod to a drill string, a fluid passage configured for conveying fluid from the drill string through the starter rod from the rear end to the front end, and a branch passage extending from the fluid passage to a side surface of the starter rod configured to pass part of the fluid in the fluid passage outside the starter rod. Generally, the front end portion of the starter rod is also used to connect to a drill head and thus has an outer diameter greater than the rear end which connects to the drill string. In a preferred embodiment, the branch passage opens rearwardly of the large diameter front end portion so that the lubricating fluid is injected in the hole ahead of it. The first and second connecting portions are each one half of a coupling needed to connect to an adjacent component, and may be of the same or different types.

[0006] The invention further provides a method for back reaming using a back reamer mounted on a drill string driven by a directional boring machine. The back reamer is connected to the drill string by a starter rod of the invention. The method includes the steps of connecting the back reamer to the starter rod, and pulling the back reamer through an existing hole through which the drill string extends while rotating the back reamer with the drill string and injecting a fluid through the drill string so that fluid is ejected through the branch passage and lubricates the outer surface of the starter rod. In preferred embodiments, about 5 to 50 percent of the drill fluid entering the starter rod through the drill string is ejected through the branch passage. A nozzle may be installed in the branch passage to regulate the amount of fluid ejected from the branch passage, and a solid plug may be installed in the branch passage prior to using the starter rod for forward drilling of a pilot hole, or on other occasions where no fluid flow through the branch passage is desired.

[0007] These and other aspects of the invention are set forth in the detailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In the accompanying drawings, wherein like numerals denote like elements:

[0009] FIG. 1 is a side view of a starter rod according to the invention connected to a back reamer;

[0010] FIG. 2 is an exploded view of the starter rod and back reamer of FIG. 1;

[0011] FIG. 3 is a partial, lengthwise sectional view of the starter rod and back reamer of FIG. 1;

[0012] FIG. 4 is a partial perspective view of a starter rod of the invention, with internal passages shown in phantom lines; and

[0013] FIG. 5 is a partial, lengthwise sectional view of a starter rod equipped with a nozzle according to the invention.

DETAILED DESCRIPTION

[0014] Referring now to FIGS. 1 to 3, a starter rod 203 according to the invention is a generally cylindrical steel body configured at one end for connection to a sonde housing (during drilling of the pilot hole) or back reamer 240 by means of a splined joint described in Wentworth et al. U.S. Pat. No. 6,148,935, Nov. 21, 2000, and Wentworth et al. PCT Publication WO 00/11303, published Mar. 2, 2000, the entire contents of which are hereby incorporated by reference herein for all purposes. References hereafter to “front” and “rear” refer to the original orientation of the starter rod as it is used to drill the pilot hole prior to back reaming. As will be appreciated by those skilled in the art, during back reaming, the orientation of the starter rod is reversed.

[0015] A rear end portion 204 of starter rod 203 has a threaded, tapered recess 205 for securing a threaded male end of a drill rod so that starter rod 203 is at the distal end of the drill string. A cylindrical projection 210 coaxial with a lengthwise axis of starter rod 203 extends from a enlarged diameter front end portion 206 of starter rod 203. Projection 210 has four transverse holes 212 extending therethrough at spaced positions, preferably offset from the lengthwise axis of starter rod 203 as shown. A pair of annular grooves 218, 220 are provided on the outer periphery of projection 210 near its front and rear ends. Groove 220 receives an elastomeric O-ring 221 or other suitable seal to prevent leakage from the front end of projection 210. Rear groove 218 is a stress relief undercut. The interlock mechanism of which the starter rod forms part includes an annular, frontwardly-facing portion 222 of the front end of starter rod 203. Annular portion 222 is located radially outwardly of projection 210 to provide maximum strength to the connection. Portion 222 has a series of arcuate, spaced, frontwardly-extending splines 224 including a master spline having a greater width which performs a keying function.

[0016] An axial mud flow passage 214 extends the length of starter rod 203 for feeding drilling mud to the drill head or back reamer. A branch passage 300 runs from passage 214 to an outer side of starter rod 203, most preferably opening on a rearwardly tapering, frustoconical shoulder 301 which adjoins enlarged diameter portion 206 and forms part of a reduced diameter midportion 302. Midportion 302 has a minimum outer diameter smaller than either of the end portions 204, 206. Passage 300 is preferably angled away from enlarged diameter portion 206 for the purpose of directing the lubricating fluid in front of portion 206 as the starter rod and back reamer advance through the ground.

[0017] FIG. 4 illustrates a cone-shaped spray 305 of lubricant ejected from passage 300. The lubricant, which may be water or conventional drilling fluid, lubricates the hole and helps reduce accumulation of cuttings ahead of enlarged diameter end portion 206, reducing the amount of wear on the joint. Passage 300 is sized so that about 5 to 50 percent of the fluid entering the starter rod passes into the bore through passage 300, and the remainder (50-95%) continues to the rear and exits through the holes in the back reamer in a manner well known in the art.

[0018] Several holes 300 may be provided at spaced locations on should 301 as needed, for example, two holes 300 that are 180° apart, three that are 120° apart, and the like. It is also possible to locate the hole(s) at other locations along the length of the starter rod, such as on the outer surface of the large diameter portion 206 (300A, FIG. 3) or on the midportion 302 (300B, FIG. 3). The location and arrangement of the radial passage(s) 300 is not critical as long as drilling fluid is introduced at or ahead of the large diameter portion 206 of starter rod 203 during back reaming.

[0019] Since the starter rod is also used for drilling the pilot hole with a drill bit and sonde housing, it may be desirable to close passage 300 during the forward drilling process and then open it during back reaming. For this purpose, as shown in FIG. 5, passage 300 may be provided with internal threads 311 ending at a step 312. A threaded plug 310 is installed in passage 300 into engagement with step 312 by means of threads 311. Any suitable means can be used for installing plug 310, for example, a polygonal recess 313 that fits the head of an Allen wrench. A central hole 314 through the center of plug 310 permits fluid to pass out of starter rod 203 and by its diameter regulates the amount of fluid that is ejected from the side of the starter rod. A set of interchangeable plugs with holes 314 of varying diameters can be provided to permit the user to adjust the flow, and a solid plug with no hole 314 is provided so that passage 300 can be sealed during forward drilling.

[0020] Starter rod 203 of the invention can be used as follows. Upon completion of a first boring run, the boring head emerges into an exit pit or trench at a location far removed from the directional boring machine. At this point, a worker may manually remove roll pins 120 with a hammer and chisel, and then remove the boring head including the bit and sonde housing. Back reamer 240 having a front end configuration substantially matching the rear end of the sonde housing is then mounted on starter rod 203 in place of housing 32. The solid plug in passage 300 is removed while the drill head is exposed in the exit pit and replaced with a nozzle (plug with central hole 314). Back reamer 240 has an enlarged diameter rear portion 242 that is pulled or spun and pulled through the ground to widen the initial borehole during the second run. The forwardly tapering midportion 244 of reamer 240 may have a radially spaced series of longitudinal grooves 246 therein which have edges useful in grinding away rock if the borehole extends through a rock formation. Grooves 246 conduct material back from the cutting area when reamer 240 functions as a drill bit in this manner. Fluid is injected ahead of the starter rod 203 through passage 300 and at the same time out through the holes provided in the surface of back reamer 240.

[0021] When back reamer 240 emerges into the original entrance pit, it is removed from starter rod 203, and a drill head can be reattached if another borehole needs to be made at a nearby location.

[0022] While certain embodiments of the invention have been illustrated for the purposes of this disclosure, numerous changes in the method and apparatus of the invention presented herein may be made by those skilled in the art, such changes being embodied within the scope and spirit of the present invention as defined in the appended claims. In particular, the improvement of the invention is not limited by the specific starter rod connecting mechanism discussed above, and applies generally to all known starter rod designs currently used in horizontal directional drilling wherein the starter rod has a larger diameter end with a connecting portion that couples to a drill head/back reamer and a smaller diameter end with a connecting portion that couples to the drill string. Other styles of connection include, for example, starter rods that are threadedly connected to adjacent parts at both ends, and starter rods wherein the front end is a polygonal shank that is coupled to the drill head or back reamer by a sleeve that slides over the shank and is secured to the starter rod with a bolt or other fastener.

Claims

1. A starter rod for connecting a back reamer to the distal end of a drill string, comprising an elongated body having:

a front end portion having a first connecting portion configured for connecting the starter rod to a back reamer;

a rear end portion having a second connecting portion configured for connecting the starter rod to a drill string;

a fluid passage configured for conveying fluid from the drill string through the starter rod from the rear end to the front end;

a branch passage extending from the fluid passage to a side surface of the starter rod configured to pass part of the fluid in the fluid passage outside the starter rod.

2. The starter rod of claim 1, wherein the front end portion has an outer diameter greater than the outer diameter of the rear end portion.

3. The starter rod of claim 2, wherein the branch passage opens rearwardly of the front end portion.

4. The starter rod of claim 3, wherein the branch passage opens on a midportion of the starter rod that spans the front and rear end portions.

5. The starter rod of claim 4, wherein the branch passage opens on a rearwardly tapering shoulder of the midportion of the starter rod.

6. The starter rod of claim 1, further comprising a removable plug that fits into the branch passage.

7. The starter rod of claim 6, wherein the plug is solid and blocks the flow of fluid through the branch passage.

8. The starter rod of claim 6, wherein the plug comprises a nozzle having a hole therethough through which the fluid passes.

9. The starter rod of claim 1, further comprising:

a first removable plug that fits into the branch passage, which plug is solid and blocks the flow of fluid through the branch passage; and

a second removable plug that fits into the branch passage, which plug comprises a nozzle having a hole therethough through which the fluid passes, wherein the first and second plugs are interchangeable.

10. The starter rod of claim 1, wherein the branch passage is angled away from the front end of the starter rod so that it ejects fluid towards the rear end of the starter rod.

11. A method for back reaming using a back reamer mounted on a drill string driven by a directional boring machine, wherein the back reamer is connected to the drill string by a starter rod, the starter rod including an elongated body having a front end portion having a first connecting portion configured for connecting the starter rod to the back reamer, a rear end portion having a second connecting portion configured for connecting the starter rod to the drill string, a fluid passage configured for conveying fluid from the drill string through the starter rod from the rear end to the front end, and a branch passage extending from the fluid passage to a side surface of the starter rod configured to pass part of the fluid in the fluid passage outside the starter rod, comprising the steps of:

connecting the back reamer to the front end portion of the starter rod and connecting the drill string to the rear end portion of the starter rod; and

pulling the back reamer through an existing hole through which the drill string extends while rotating the back reamer with the drill string and injecting a fluid through the drill string so that fluid is ejected through the branch passage and lubricates the outer surface of the starter rod.

12. The method of claim 11, further comprising ejecting about 5 to 50 percent of the drill fluid entering the starter rod through the drill string through the branch passage.

13. The method of claim 11, further comprising installing a nozzle in the branch passage, which nozzle has a hole therethrough which regulates the amount of fluid ejected from the branch passage.

14. The method of claim 11, further comprising installing a solid plug in the branch passage prior to using the starter rod for forward drilling.