WO2021255494A1

WO2021255494A1 - Wireline drill rod

Info

Publication number: WO2021255494A1
Application number: PCT/IB2020/055587
Authority: WO
Inventors: Peixue LU; Michael John Duffy
Original assignee: Epiroc Canada Inc.
Priority date: 2020-06-15
Filing date: 2020-06-15
Publication date: 2021-12-23

Abstract

A drill rod (10) having tapered pin and box sections (12 and14) at opposite ends of a body (16). The pin and box sections (12 and 14) are provided with multi-start tapered threads (38 and 40) The pin and box sections (12 and 14) are devoid of undercut at the junction between the pin and box sections (12 and 14) and the body (16).

Description

TITLE OF THE INVENTION

Wireline Drill Rod

FIELD OF THE INVENTION

[001] This invention relates to components used in core drilling. More particularly, the invention relates to a wireline drill rod.

BACKGROUND OF THE INVENTION

[002] During drilling, the threaded joints of wireline drill rods receive and transfer the torque from drill rigs to twist the drill string and turn the diamond bit used to drill at the bottom of the bore hole. These joints also have to support the pullback tension load required at the end of the drill string opposed to the drill bit to maintain the desired drilling thrust force at the drill bit. Also, the threaded joint must be leak-proof since the wireline drill rod often serves as a channel through which a flushing medium is transported.

[003] Additionally, the threaded joints must withstand numerous cycles of make-up and break-down (coupling and uncoupling) during their life span. Indeed, in addition to be used on many different sites during their lifetime, the wireline drill rods are installed in and removed regularly from a drill string while drilling a bore hole to change the drill bit when the latter is worn down. The rod joint time is one important factor for productivity, so the make-up and break-down of the joint is preferably easy and fast to perform.

[004] Furthermore, some bore holes are not completely straight, either by being purposely deviated from a straight line direction to explore an ore body, or through undesired deviations that need to be corrected while drilling. These deviations may cause bending at the threaded joints and the latter may be subjected to alternating and fatigue stresses.

[005] Many existing drill rods may be cross-threaded relatively easily when assembled, which can greatly increase the time required to make a joint, and which may eventually damage the threads of the drill rods. Also, in many existing drill rods, stresses are distributed asymmetrically around the threads. This can cause stress concentrations and limits the radius of curvature of deviations.

[006] Against this background, there exists a need in the industry to provide an improved wireline drill rod.

[007] An object of the present invention is therefore to provide an improved wireline drill rod.

SUMMARY OF THE INVENTION

[008] In a broad aspect, the invention provides a drill rod, comprising: a pin section, a box section and an elongated body extending therebetween, the pin section, box section and body being hollow, the body defining a longitudinal axis, the box and pin sections being threaded and complementarily shaped so that the pin section of the drill rod is screwable in the box section of a similar drill rod, the box section and body together defining a cylindrical radially outwardmost surface and the pin section and body defining together a cylindrical radially inwardmost surface, the radially inwardmost and outwardmost surfaces being distanced by a body thickness in the body; the pin and box sections defining respectively pin and box nose portions respectively at pin and box free ends thereof, the pin and box sections also defining respectively pin and box end portions opposed respectively to the pin and a box nose portions and adjacent the body, pin and box threads extending respectively between the pin and box nose portions and respectively the pin and box end portions, the pin and box threads being multi-start and defining alternating crests and roots, each crest being joined to adjacent roots through substantially flat pressure and clearance flank surfaces, the pressure flank surfaces defining a pressure flank angle relative to a plane perpendicular to the longitudinal axis and the clearance flank surfaces defining a clearance flank angle relative to the longitudinal axis; the pin and box nose portions, threads and end portions being tapered, the pin nose and end portions defining respectively substantially frusto-conical pin nose and end mating surfaces opposed to the radially inwardmost surface and the box nose and end portions defining respectively substantially frusto-conical box nose and end mating surfaces opposed to the radially outwardmost surface, the crests and roots being truncated and delimited respectively by substantially frusto-conical crest and root envelopes, the crest and root envelopes being angled at respectively crest and root taper angles relative to the longitudinal axis; the pin section extending between a pin leading face at the pin free end and a pin end shoulder face defined by the body opposed to the pin free end and extending between the pin end mating surface and the radially outwardmost surface, the box section extending between a box leading face at the box free end and a box end shoulder face defined by the body opposed to the box leading face and extending between the box end mating face and the radially inwardmost surface, the pin leading face and the box end shoulder face being complementarily shaped and the box leading face and the pin end shoulder face being complementarily shaped; then pin and box end sections being devoid of undercuts at their respective junctions with the body so that a pin end portion thickness of the pin end portion between the radially inwardmost surface and the pin end mating surface increases monotonically from the pin thread to the pin end shoulder face and a box end portion thickness of the box end portion between the radially outwardmost surface and the box end mating surface increases monotonically from the box thread to the box end shoulder face.

[009] There may also be provided a drill rod wherein the pin leading face and the box end shoulder face are complementarily filleted; and the box leading face and the pin end shoulder face are complementarily filleted.

[0010] There may also be provided a drill rod wherein the pin section and the box section are configured and sized to ensure sealing between the box leading face and the pin end shoulder face when two of the drill rods are screwed together.

[0011] There may also be provided a drill rod wherein the crest and root taper angles are substantially equal to each other, the crest and root envelopes defining a crest height equal to a distance therebetween.

[0012] There may also be provided a drill rod wherein the crest height is larger in the pin thread than in the box thread.

[0013] There may also be provided a drill rod wherein the crest height is between about 12.5% to about 20% of the body thickness.

[0014] There may also be provided a drill rod wherein the pin nose and end mating surfaces and the box nose and end mating surfaces all taper at a mating surface taper angle substantially equal to the crest taper angle. [0015] There may also be provided a drill rod wherein the crest and root taper angles are between 0.5° and 1.05° the pressure flank angle is between 0.5° and 8.55° and the clearance flank angle is between 83° and 91.5°.

[0016] There may also be provided a drill rod wherein a box nose thickness of the box nose portion at the box free end between the radially outwardmost surface and the box nose mating surface is larger than a pin nose thickness of the pin nose portion at the pin free end between the radially inwardmost surface and the pin nose mating surface.

[0017] There may also be provided a drill rod wherein the pin and box nose thicknesses are from about 21% to about 35% of the body thickness.

[0018] There may also be provided a drill rod wherein the pin leading face and the box end shoulder face are angled at an inner nose mating angle relative to the plane perpendicular to the longitudinal axis and the box leading face and the pin end shoulder face are angled at an outer nose mating angle relative to the plane perpendicular to the longitudinal axis, the inner and outer nose mating angles being between 10° and 20°, for example between 13° and 17°, and in a more specific example, about 15°.

[0019] There may also be provided a drill rod wherein the pressure and clearance flank surfaces are angled at a thread flank angle relative to each other, the thread flank angle being between 0° and 15°, for example between 8° and 12°, and in a more specific example, about 10°.

[0020] There may also be provided a drill rod wherein a thread root length of the roots between opposed pressure and clearance flank surfaces is between 45% to about 51% of a thread pitch of the pin and box threads.

[0021] There may also be provided a drill rod wherein the pin and box threads are filleted at intersections of pressure and clearance flank surfaces with the roots and crests.

[0022] There may also be provided a drill rod wherein the pin and box threads define a thread pitch, the thread pitch being between 2.5 to 3.5 per inch, for example 3 per inch.

[0023] There may also be provided a drill rod wherein the pin nose portion is about 20% to about 30% longer than the pin end portion, for example about 25%.

[0024] There may also be provided a drill rod wherein the pin section is from about 0.002" to about 0.003" shorter than the box section, for example about 0.002” or about 0.0025” shorter than the box section.

[0025] There may also be provided a drill rod wherein the pin and box threads are double-start.

[0026] There may also be provided a drill rod wherein the pin and box nose portions have similar nose lengths, the pin and box end portions have similar end lengths and the pin and box nose portions are about 20% to about 30% longer than the pin and box end portions, for example about 25% longer than the pin and box end portions. [0027] There may also be provided a drill rod wherein the pin and box threads have chamfered thread starts such that the pin and box threads start at an angle relative to a radius of the pin and box sections intersecting the thread starts.

[0028] Advantageously, the proposed drill rod has features that synergistically create drill rods that are simultaneously relatively easy to rapidly screw to each other and unscrew from each other in difficult outdoors drilling conditions, while having the ability to be deviated around curves in bore holes that have relatively small radii of curvature.

[0029] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In the appended drawings:

[0031] Figure 1A, in a longitudinal side view, illustrates a drill rod in accordance with an embodiment of the present invention;

[0032] Figure 1 B, in a longitudinal cross-sectional view midway therethrough, illustrates the drill rod of FIG. 1 A;

[0033] Figure 2, in a combined longitudinal elevational and longitudinal cross- sectional view, illustrates a box section of the drill rod and a pin section of another one of the drill rod of FIG. 1 ;

[0034] Figure 3, in a longitudinal cross-sectional view, illustrates a wall profile of the pin section of FIG. 2;

[0035] Figure 4, in a longitudinal cross-sectional view, illustrates a wall profile of the box section of FIG. 2;

[0036] Figure 5, in a longitudinal cross-sectional view, illustrates a wall profile of the box and pin sections of FIG. 2 screwed to each other;

[0037] Figure 6, in a transverse cross-sectional view, illustrates the joined pin and box sections of FIG. 5 along section line VI-VI of FIG. 5.

[0038] Figure 7, in a longitudinal cross-sectional view, illustrates a box section of a blank used to manufacture the drill rod of FIG. 1 ;

[0039] Figure 8, in a longitudinal elevation view, illustrates a pin section of a blank used to manufacture the drill rod of FIG. 1 ;

[0040] Figure 9, in a front elevation view with parts removed, illustrates the box section of FIG. 4; and

[0041] Figure 10, in a front elevation view with parts removed, illustrates the pin section of FIG. 4; and. DETAILED DESCRIPTION

[0042] Referring to FIGS. 1A and 1 B, there is shown a wireline drill rod 10 in accordance with an embodiment of the present invention, referred to simply as “the drill rod 10” hereinbelow. The drill rod 10 includes a pin section 12, a box section 14 and an elongated body 16 extending therebetween. The pin section 12, box section 14 and body 16 are hollow. Referring to FIG. 2, the body 16 defines a longitudinal axis 18. The box and pin sections 14 and 12 are threaded and complementarily shaped so that the pin section 12 of the drill rod 10 is screwable in the box section 14 of a similar drill rod 10. The drill rod 10 is usable, for example, in a drill string used to support and rotate a drill bit at the distal end of a bore hole.

[0043] The box section 14 and the body 16 together define a cylindrical radially outwardmost surface 20. The pin section 12 and the body 16 define together a cylindrical radially inwardmost surface 22, the radially inwardmost and outwardmost surfaces 22 and 20 being distanced by a body thickness 24 in the body 16. The pin section 12 extends from the body 16 and is radially inwardly recessed relative to the radially outwardmost surface 20. The box section 14 extends from the body 16 and is radially outwardly recessed relative to the radially inwardmost surface 22.

[0044] The pin and box sections 12 and 14 define respectively pin and box nose portions 26 and 28 respectively at pin and box free ends 30 and 32 thereof. The pin and box sections 12 and 14 also define respectively pin and box end portions 34 and 36 opposed respectively to the pin and box nose portions 26 and 28 and adjacent the body 16. Pin and box threads 38 and 40 extend respectively between the pin and box nose portions 26 and 28 and respectively the pin and box end portions 34 and 36 and each include a plurality of helical turns extending respectively along the pin and box sections 12 and 14. The pin and box threads 38 and 40 are multi-start, for example double-start, and define alternating crests 42 and roots 44. Referring for example to FIGS. 3 and 4, each crest 42 is joined to adjacent roots 44 through substantially flat pressure and clearance flank surfaces 46 and 48. The pressure flank surfaces 46 define a pressure flank angle 50 relative to a plane 52 perpendicular to the longitudinal axis 18 and the clearance flank surfaces 48 define a clearance flank angle 56 relative to the longitudinal axis 18, as seen in FIG. 5. The drill rods 10 are typically circumferentially symmetrical, except for the pin and box threads 38 and 40 which are helical.

[0045] The pin and box nose portions, end portions and threads 26, 28, 34, 36, 38 and 40 are tapered in a direction leading away from the body 16 in the pin section 12 and towards the body in the box section 14. The pin nose and end portions 26 and 34 define respectively substantially frusto-conical pin nose and end mating surfaces 58 and 60 opposed to the radially inwardmost surface 22, as seen in FIG. 3. The box nose and end portions 28 and 36 define respectively substantially frusto-conical box nose and end mating surfaces 62 and 64 opposed to the radially outwardmost surface 20, as seen in FIG. 4. When the drill rods 10 are operatively screwed to each other, the pin nose mating surfaces 58 of the drill rods 10 face the box end mating surfaces 64 of adjacent drill rods, and the pin end mating surfaces 60 of the drill rods 10 face the box nose mating surfaces 62 of adjacent drill rods. The crests and roots 42 and 44 are truncated so as to be substantially flat and are delimited respectively by substantially frusto-conical crest and root envelopes 68 and 70, identified in FIG. 2. The crest and root envelopes are angled at respectively crest and root taper angles 73 and 75 relative to the longitudinal axis 18, as seen in FIG. 4. Typically, the crest and root taper angles 73 and 75 are substantially equal to each other, the crest and root envelopes 68 and 70 defining a crest height 90, better seen for example in FIG. 4, equal to a distance therebetween.

[0046] The pin section 12 extends between a pin leading face 72 at the pin free end 30 and a pin end shoulder face 74 defined by the body 16 opposed to the pin free end 30 and extending between the pin end mating surface 60 and the radially outwardmost surface 20. The box section 14 extends between a box leading face 76 at the box free end 32 and a box end shoulder face 78 defined by the body 16 opposed to the box leading face 76 and extending between the box end mating face 64 and the radially inwardmost surface 22. The pin leading face 72 and the box end shoulder face 78 are complementarily shaped and the box leading face 76 and the pin end shoulder face 64 are complementarily shaped so that when drill rods 10 are screwed to each other, the pin and box sections 12 and 14 of adjacent drill rods 10 mate with each other closely.

[0047] Typically, the pin and box end sections 12 and 14 are devoid of undercuts at their respective junctions with the body 16 so that a pin end portion thickness 82 of the pin end portion 34 between the radially inwardmost surface 22 and the pin end mating surface 60 increases monotonically from the pin threads 38 to the pin end shoulder face 74 and a box end portion thickness 86 of the box end portion 36 between the radially outwardmost surface 20 and the box end mating surface 64 increases monotonically from the box thread 40 to the box end shoulder face 78. Such undercuts are popular in the industry as it is believed that they help in management of impurities in drill rod junctions, but it has been found that drill rods 10 in which this undercut is absent are not significantly disadvantaged by this absence while they benefit from the increased strength provided by the corresponding thicker ends of the pin and box sections 12 and 14.

[0048] The combination of a tapered configuration of the pin and box sections 12 and 14 with multi-start pin and box threads 38 and 40 greatly facilitates assembly and disassembly of drill strings as cross-threading and jamming is greatly reduced or eliminated, and junction of the drill rods 10 is guided by their tapered shape. In addition, multi-start threads distribute stress more uniformly around the drill rods 10, which allow tighter deviations in the borehole and reduces the risk of damaging the drill rods 10 in operation.

[0049] Typically, to ensure proper seal between joined drill rods 10, the pin section 12 and the box section 14 are configured and sized to ensure sealing between the box leading face 76 and the pin end shoulder face 74 when two of the drill rods 10 are screwed together. To that effect the pin end shoulder face 74 and the box leading face 76 are shaped such that they may contact each other along most of their surface, due to their complementary shape and dimensions. Also, the pin and box sections 12 and 14 are sized such that a relatively large pressure can be exerted between the box leading face 76 and the pin end shoulder face 74. Typically, this is achieved by having a pin section 12 that is slightly shorter, for example by 0.002" to about 0.003", such as 0.002” or 0.0025”, than the box section 14. Therefore, in some embodiments, when two drill rods 10 are joined to each other, a very small gap 115 remains between the pin leading face 72 and the box end shoulder face 78.

[0050] In some embodiments, the pin and box leading faces 72 and 76 and the pin and box end shoulder faces 74 and 78 are not completely perpendicular to the longitudinal axis 18 but instead make an angle with the plane 52 perpendicular to the longitudinal axis 18. More specifically the pin leading face 72 and the box end shoulder face 78 are angled at an inner nose mating angle 98 relative to the plane 52 perpendicular to the longitudinal axis 18 and the box nose face 76 and the pin end shoulder face 74 are angled at an outer nose mating angle 100 relative to the plane 52 perpendicular to the longitudinal axis 18. The inner and outer nose mating angles 98 and 100 are better seen in FIG. 5. The inner and outer nose mating angles 98 and 100 are typically substantially similar to each other and have in some embodiments a value of between 10° and 20 °, for example between 13° and 17° and in a very specific example, about 15°. The inner and outer nose mating angles 98 and 100 are typically such that the radially inwardmost and outwardmost surfaces 22 and 20 overlap longitudinally respectively the box and pin end mating surfaces 64 and 62. In addition to providing a proper seal, this configuration helps in preventing overlapping while drilling occurs.

[0051] Overlapping can further be prevented or reduced by having a box nose thickness 102 of the box nose portion 28 at the box free end 32 between the radially outwardmost surface 20 and the box nose mating surface 62 being larger than a pin nose thickness 104 of the pin nose portion 26 at the pin free end 30 between the radially inwardmost surface 22 and the pin nose mating surface 58.

[0052] Furthermore, to ensure that the crest 42 of the pin threads 38 properly engage the roots 44 of the box threads 40, in some embodiments, the crest height 90 is slightly larger in the pin thread 38 than in the box thread 42. This improves the seal between joined drill rods and ensure proper load transfer therebetween. Also, this will create a small gap between the roots 44 of the pin threads 38 and the crests 42 of the box threads 40, which allow storage of impurities to facilitate assembly of the drill rods 10 in the field, in which dust particles and other impurities may be found.

[0053] To further ensure proper mating between pin and box sections 12 and 14, typically, the pin nose and end mating surfaces 58 and 60 and the box nose and end mating surfaces 62 and 64 all taper at a mating surface taper angle 92 substantially equal to the crest taper angle 73. Also, as seen respectively from FIGS. 8 and 7, this allows to conveniently manufacture the pin and box sections 12 and 14 from pin and box section blanks 94 and 96 including two frusto-conical tiers.

[0054] Stress concentration at the intersection of the many surfaces of the drill rod 10 may be reduced through filleting of such intersections. In various embodiments, one or more of the following may be included in the drill rod 10. Example of fillet radii are given that have been found advantageous, but other values may be used where suitable. In some embodiments, the pin leading face 72 and the box end shoulder face 78 are complementarily filleted (for example 0.01” to 0.02”) and the box leading face 76 and the pin end shoulder face 74 are complementarily filleted (for example 0.01 ” to 0.02”). In some embodiments, the pin and box threads 38 and 40 are filleted at intersections of pressure and clearance flank surfaces 46 and 48 with the crests 42 (for example 0.003" to 0.008") and the roots 44 (for example 0.002" to 0.007"). with a need to optimize the compromise between stronger joints (smaller fillet) and smaller stress concentration (larger fillet).

[0055] FIGS. 9 and 10 respectively illustrate the pin and box threads 38 and 40. The number of threads has been reduced to better illustrate the pin and box thread starts 116 and 118. The pin and box thread starts 116 and 118 are chamfered such that the pin and box threads 38 and 40 start at a start angle 120 relative to a radius 122 of the pin and box sections 12 and 14 intersecting the thread starts 116 and 118. In some embodiments, the start angle 120 is for example about 45 degrees. FIG. 6 illustrates also mating of the pin and box threads 38 and 40 in a cross-sectional view.

[0056] Example of values of the various parameters defining the pin and box sections 12 and 14 are as detailed herein below. These values have been found particularly advantageous, when combined together to provide a drill rod 10 well suited for core drilling in many different rock formations. However, in alternative embodiments, other values for these parameters may be used.

[0057] In some embodiments, the crest height 90 is between about 10% to about 20% of the body thickness 24 and is for example between 0.027" and 0.050". In some embodiments, the crest and root taper angles 73 and 75 are between 0.5° and 1.05°. This range of angles has been found to facilitate coaxial alignment of drill rods 10 during assembly while ensuring that the pin and box sections 12 and 14 remain thick enough to be strong enough to not be easily damaged in use.

[0058] In some embodiments, the pressure flank angle 50 is between 0.5° and 8.55° and the clearance flank angle 56 is one of between 83° and 91 .5°, between 85° and 91.5°or larger than 90°. These angles have been found to allow relatively large pullback force during drilling while facilitating disassembly of attached pin and box sections 12 and 14. In some embodiments, the pressure and clearance flank surfaces 46 and 48 are angled at a thread flank angle 106 relative to each other, the thread flank angle 106 being between 0° and 15°, for example between 8° and 12°, and in a very specific example about 10°. [0059] In some embodiments, the pin and box nose thicknesses 104 and 102 are from about 21% to about 35% of the body thickness.

[0060] In some embodiments, a thread root length 110 of the roots 44 between opposed pressure and clearance flank surfaces 46 and 48 is between 45% to about 51% of a thread pitch 112 of the pin and box threads 38 and 40. These values provide a good compromise for a small clearance gap 114 between clearance flank surfaces 48 on pin and box sections 12 and 14 after making as small clearance gaps 114 can cause joint problem if there is any tinny impurity and and can make them hard to break-down, but large clearance gap 114 decrease the strength of the joint. The thread pitch 112 is typically constant along the pin and box sections 12 and 14, but in some embodiments, variable thread pitches 112 may be used. The thread pitch 112 is for example between 2.5 to 3.5 per inch, for example about 3 per inch.

[0061] In some embodiments, the pin and box nose portions 26 and 28 have similar lengths and are about 20% to about 30% longer (for example about 25% longer) than the pin end and box end portions 34 and 36, which also have similar lengths.

[0062] The above-described pin and box sections 12 and 14 have been described as being part of a drill rod 10. Other drill string components that are attached to these pin and box sections 12 and 14 can either have similar threads, or be joined to the drill rods 10 using adapters having threads similar to those of the pin and box sections 12 and 14 at one end and industry standard threads at the opposed end, so that the drill rods 10 may be used with existing equipment. [0063] Although the present invention has been described hereinabove by way of exemplary embodiments thereof, it will be readily appreciated that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, the scope of the claims should not be limited by the exemplary embodiments, but should be given the broadest interpretation consistent with the description as a whole. The present invention can thus be modified without departing from the spirit and nature of the subject invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A drill rod, comprising:

- a pin section, a box section and an elongated body extending therebetween, the pin section, box section and body being hollow, the body defining a longitudinal axis, the box and pin sections being threaded and complementarily shaped so that the pin section of the drill rod is screwable in the box section of a similar drill rod, the box section and body together defining a cylindrical radially outwardmost surface and the pin section and body defining together a cylindrical radially inwardmost surface, the radially inwardmost and outwardmost surfaces being distanced by a body thickness in the body;

- the pin and box sections defining respectively pin and box nose portions respectively at pin and box free ends thereof, the pin and box sections also defining respectively pin and box end portions opposed respectively to the pin and a box nose portions and adjacent the body, pin and box threads extending respectively between the pin and box nose portions and respectively the pin and box end portions, the pin and box threads being multi-start and defining alternating crests and roots, each crest being joined to adjacent roots through substantially flat pressure and clearance flank surfaces, the pressure flank surfaces defining a pressure flank angle relative to a plane perpendicular to the longitudinal axis and the clearance flank surfaces defining a clearance flank angle relative to the longitudinal axis;

- the pin and box nose portions, threads and end portions being tapered, the pin nose and end portions defining respectively substantially frusto-conical pin nose and end mating surfaces opposed to the radially inwardmost surface and the box nose and end portions defining respectively substantially frusto-conical box nose and end mating surfaces opposed to the radially outwardmost surface, the crests and roots being truncated and delimited respectively by substantially frusto-conical crest and root envelopes, the crest and root envelopes being angled at respectively crest and root taper angles relative to the longitudinal axis;

- the pin section extending between a pin leading face at the pin free end and a pin end shoulder face defined by the body opposed to the pin free end and extending between the pin end mating surface and the radially outwardmost surface, the box section extending between a box leading face at the box free end and a box end shoulder face defined by the body opposed to the box leading face and extending between the box end mating face and the radially inwardmost surface, the pin leading face and the box end shoulder face being complementarily shaped and the box leading face and the pin end shoulder face being complementarily shaped;

- the pin and box end sections being devoid of undercuts at their respective junctions with the body so that a pin end portion thickness of the pin end portion between the radially inwardmost surface and the pin end mating surface increases monotonically from the pin thread to the pin end shoulder face and a box end portion thickness of the box end portion between the radially outwardmost surface and the box end mating surface increases monotonically from the box thread to the box end shoulder face.

2. The drill rod as defined in claim 1 , wherein

- the pin leading face and the box end shoulder face are complementarily filleted; and

- the box leading face and the pin end shoulder face are complementarily filleted.

3. The drill rod as defined in claim 1 or 2, wherein the pin section and the box section are configured and sized to ensure sealing between the box leading face and the pin end shoulder face when two of the drill rods are screwed together.

4. The drill rod as defined in any one of claims 1 to 3, wherein the crest and root taper angles are substantially equal to each other, the crest and root envelopes defining a crest height equal to a distance therebetween.

5. The drill rod as defined in claim 4, wherein the crest height is larger in the pin thread than in the box thread.

6. The drill rod as defined in claim 4 or 5, wherein the crest height is between about 12.5% to about 20% of the body thickness.

7. The drill rod as defined in claim 4, 5 or 6, wherein the pin nose and end mating surfaces and the box nose and end mating surfaces all taper at a mating surface taper angle substantially equal to the crest taper angle.

8. The drill rod as defined in any one of claims 1 to 7, wherein the crest and root taper angles are between 0.5 ° and 1.05 °, the pressure flank angle is between 0.5° and 8.55° and the clearance flank angle is between 83° and 91.5°.

9. The drill rod as defined in any one of claims 1 to 8, wherein a box nose thickness of the box nose portion at the box free end between the radially outwardmost surface and the box nose mating surface is larger than a pin nose thickness of the pin nose portion at the pin free end between the radially inwardmost surface and the pin nose mating surface.

10. The drill rod as defined in claim 9, wherein the pin and box nose thicknesses are from about 21% to about 35% of the body thickness.

11. The drill rod as defined in any one of claims 1 to 10, wherein the pin leading face and the box end shoulder face are angled at an inner nose mating angle relative to the plane perpendicular to the longitudinal axis and the box leading face and the pin end shoulder face are angled at an outer nose mating angle relative to the plane perpendicular to the longitudinal axis, the inner and outer nose mating angles being between 10° and 20°.

12. The drill rod as defined in claim 11 , wherein the inner and outer nose mating angles are between 13° and 17°.

13. The drill rod as defined in claim 12, wherein the inner and outer nose mating angles is about 15°.

14. The drill rod as defined in any one of claims 1 to 13, wherein the pressure and clearance flank surfaces are angled at a thread flank angle relative to each other, the thread flank angle being between 0°and 15°.

15. The drill rod as defined in claim 14, wherein the thread flank angle is between 8° and 12°.

16. The drill rod as defined in claim 15, wherein the thread flank angle is about 10°.

17. The drill rod as defined in any one of claims 1 to 16, wherein a thread root length of the roots between opposed pressure and clearance flank surfaces is between 45% to about 51% of a thread pitch of the pin and box threads.

18. The drill rod as defined in any one of claims 1 to 17, wherein the pin and box threads are filleted at intersections of pressure and clearance flank surfaces with the roots and crests.

19. The drill rod as defined in any one of claims 1 to 18, wherein the pin and box threads define a thread pitch, the thread pitch being between 2.5 to 3.5 per inch.

20. The drill rod as defined in claim 19, wherein the thread pitch is about 3 per inch.

21. The drill rod as defined in any one of claims 1 to 20, wherein the pin and box nose portions have similar nose lengths, the pin and box end portions have similar end lengths and the pin and box nose portions are about 20% to about 30% longer than the pin and box end portions.

22. The drill rod as defined in claim 21 , wherein the pin and box nose portions are about 25% longer than the pin and box end portions.

23. The drill rod as defined in any one of claims 1 to 22, wherein the pin section is from about 0.002" to about 0.003" shorter than the box section.

24. The drill rod as defined claim 23, wherein the pin section is about 0.002" shorter than the box section.

25. The drill rod as defined claim 23, wherein the pin section is about 0.0025" shorter than the box section.

26. The drill rod as defined in any one of claims 1 to 25, wherein the pin and box threads are double-start.

27. The drill rod as defined in any one of claims 1 to 26, wherein the pin and box threads have chamfered thread starts such that the pin and box threads start at an angle relative to a radius of the pin and box sections intersecting the thread starts.