TORQUE REDUCTION ASSEMBLY

Abstract

A torque reduction assembly for a drill string has a mandrel for connecting two sections of drill pipe, the mandrel comprising a first annular shoulder and a plurality of radial retention slots arranged circumferentially around an outer surface of the mandrel, including a first retention slot and a second retention slot; an outer sleeve for rotatably mounting on the mandrel; a retaining ring for retaining the outer sleeve between the retaining ring and the first annular shoulder, the retaining ring comprising a first aperture and a circumferential groove about an inner surface of the retaining ring, the first aperture aligned with the circumferential groove, the retaining ring being rotatable about the mandrel so as to progressively align the first aperture with each retention slot; a first retention element for locating in the first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel; and a second retention element for locating in the second retention slot via the first aperture to rotationally fix the retaining ring relative to the mandrel.

Description

BACKGROUND

The present specification relates to an improved torque reduction assembly, for use in a top drive drilling system.

In a top drive drilling system, a mechanical driver on the drilling rig provides torque to a drill string extending into a borehole in order to drill this borehole. As the borehole gets deeper and/or deviates from strictly vertical the torque required increases. This can be a problem as with deep boreholes the torque limit of the mechanical driver can be reached.

This increase in torque can be mitigated with chemical additives inserted into the drilling fluid (known as mud). However, these additives are relatively expensive and the extent of their benefit is not clear.

Alternatively, mechanical means to reduce torque may be used. These may be made of plastic and clamp on to the drill string, other means may be sub-based. Typically, many units are necessary along the length of the drill string, and clamp-on units may come lose in the borehole.

There is therefore a need for an improved torque reduction assembly.

CN 105 781 444 A discloses a torque reducing and resistance reducing stabilizer, which is provided with a tubular stabilizer body, wherein a position limiting ring, a rotatable centralizing body and a locking ring are sequentially arranged on an outer side of the stabilizer body from top to bottom; a female buckle and a male buckle are correspondingly formed in an upper end and an lower end of the stabilizer body; the two ends of the centralizing body, the position limiting ring and the locking ring are respectively sealed through an end surface sealing device; the locking ring is connected with the stabilizer body through screw threads.

US 2002/129976 A1 discloses a friction and/or torque reducing drill string component which has a one-piece mandrel body with a mandrel body recess smaller than mandrel upper neck and mandrel body lower neck, dressed with an outer sleeve which is interlocked with a two-piece inner bearing through several integral dove-tailed splines and grooves.

WO 2012/092985 A1 discloses a centralizer which comprises a centralizer body to be situated at an outer surface of a pipe string in the form of casing, liner, or the like used while drilling, the centralizer body being formed with a plurality of outer centralizer blades arranged in an inclined manner to a longitudinal axis thereof, wherein the centralizer body has an separate split inner tube secured to the pipe string by means of a press fit.

SUMMARY

A torque reduction assembly for a drill string is provided according to claim 1. This torque reduction assembly can be easily and robustly attached to a drill string.

The first retention element may be shorter than the second retention element. This allows the first retention element to not protrude into the aperture while the second retention element does.

The first retention slot may be the same depth as the second retention slot. This allows the height of the retention elements to be the determining factor for rotationally and/or axially fixing the retaining ring.

The first retention slot may be identical to the second retention slot. This allows for each retention element (whether it is a first retention element or a second retention element) to be used in each retention slot, thereby improving the ease and speed of manufacture.

The first retention element may be the same length as the second retention element. This may simplify the manufacturing of the retention elements.

The first retention element may be identical to the second retention element. This allows for the same retention elements to be used in assembly as both first and second retention elements, which can improve the ease and speed of manufacture.

The first retention slot may be deeper than the second retention slot. This allows for equal length first and second retention elements to selectively provide the axial and/or rotational fixing as appropriate.

The plurality of radial retention slots may further comprise a plurality of first retention slots; and the torque reduction assembly may further comprise a plurality of first retention elements, each first retention element for locating in a respective first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel. Increasing the number of first retention elements distributes the axial forces and thereby improves the strength of the connection.

The plurality of radial retention slots may further comprise a plurality of second retention slots; the retaining ring may further comprise a second aperture, the second aperture aligned with the circumferential groove, the retaining ring being rotatable about the mandrel so as to align the first aperture and the second aperture with respective second retention slots simultaneously; and the torque reduction assembly may further comprise a plurality of second retention elements, each second retention element for locating in a respective second retention slot via the first aperture and the second aperture to rotationally fix the retaining ring relative to the mandrel. Increasing the number of second retention elements distributes the rotational forces and thereby improves the strength of the connection.

The plurality of radial retention slots may be arranged with N-fold rotational symmetry, where N is the number of retention slots. This may distribute the retention elements around the assembly, thereby evenly distributing forces and improving the strength of the connection.

The torque reduction assembly may further comprise a bearing sleeve for mounting on the mandrel between the mandrel and the outer sleeve. The bearing sleeve may be a preferable surface for mounting a rotating element (the outer sleeve) on to protect the mandrel from wear.

The bearing sleeve may further comprise a second annular shoulder, wherein the second annular shoulder is positionable between the first annular shoulder and the outer sleeve. This may be a convenient way to locate the mandrel, bearing sleeve and outer sleeve.

The mandrel may comprise an external thread and the bearing sleeve may comprise an internal thread for screwing onto the external thread to mount the bearing sleeve on the mandrel. This may attach the bearing sleeve to the mandrel in a fixed manner, such that the outer sleeve can rotate relative thereto.

A method of assembling a torque reduction assembly is provided according to claim 14.

This method produces an torque reduction assembly which can be easily and robustly attached to a drill string.

The first retention element may be shorter than the second retention element. This allows the first retention element to not protrude into the aperture while the second retention element does.

The first retention slot may be the same depth as the second retention slot. This allows the height of the retention elements to be the determining factor for rotationally and/or axially fixing the retaining ring.

The first retention slot may be identical to the second retention slot. This allows for each retention element (whether it is a first retention element or a second retention element) to be used in each retention slot, thereby improving the ease and speed of manufacture.

The first retention element may be the same length as the second retention element. This may simplify the manufacturing of the retention elements.

The first retention element may be identical to the second retention element. This allows for the same retention elements to be used in assembly as both first and second retention elements, which can improve the ease and speed of manufacture.

The first retention slot may be deeper than the second retention slot. This allows for equal length first and second retention elements to selectively provide the axial and/or rotational fixing as appropriate.

The plurality of radial retention slots may further comprise a plurality of first retention slots; and the method may further comprise between steps (v) and (vi) the steps of: (v-1) rotating the retaining ring to align the first aperture with a further first retention slot; (v-2) inserting a further first retention element into the further first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel. Increasing the number of first retention elements distributes the axial forces and thereby improves the strength of the connection.

Steps (v-1) and (v-2) may be repeated until a first retention element is inserted into each first retention slot, before proceeding to step (vi). This means that each first retention slot is filled while the retaining ring is still rotatable, before the second retention element is inserted to rotationally fix the retaining ring.

The method may further comprise a step of sliding a bearing sleeve on the mandrel between steps (i) and (ii), wherein step (ii) further comprises sliding the outer sleeve over the bearing sleeve such that the bearing sleeve is between the mandrel and the outer sleeve. The bearing sleeve may be a preferable surface for mounting a rotating element (the outer sleeve) on to protect the mandrel from wear.

The method may further comprise the step of: (viii) welding the second retention element to the retaining ring. Welding the second retention element in place fixes the torque reduction assembly in place.

BRIEF DESCRIPTION OF THE FIGURES

The present specification will refer to the accompanying Figures in which:

FIG. 1 shows a perspective exploded view of a torque reduction assembly;

FIG. 2 shows a side exploded view of the torque reduction assembly of FIG. 1;

FIG. 3 shows a side view of a mandrel of the torque reduction assembly of FIG. 1;

FIG. 4 shows a side exploded view of a partial assembly showing the mandrel of FIG. 3 with a bearing sleeve;

FIG. 5 shows a side exploded view of a further partial assembly showing the bearing sleeve and mandrel of FIG. 4, with the bearing sleeve mounted on the mandrel and an outer sleeve;

FIG. 6 shows a side exploded view of a further partial assembly showing the bearing sleeve, mandrel and outer sleeve of FIG. 5, with the bearing sleeve and outer sleeve mounted on the mandrel and a retaining ring;

FIG. 7A shows a perspective view of the retaining ring of FIG. 6;

FIG. 7B shows a cross-section of the retaining ring of FIG. 6;

FIG. 8A shows a perspective view of a torque reduction assembly with a retention element to be inserted;

FIG. 8B shows a perspective view of the torque reduction assembly of FIG. 8A with the retention element inserted;

FIG. 9A shows a perspective view of a short retention element for use in the torque reduction assembly; and

FIG. 9B shows a perspective view of a long retention element for use in the torque reduction assembly as shown in FIGS. 8A and 8B;

FIG. 10 shows a side view of an assembled torque reduction assembly; and

FIG. 11 shows a cross-sectional view through the line X-X of FIG. 10.

DETAILED DESCRIPTION

FIGS. 1 and 2 show a torque reduction assembly 100 in an exploded view. The torque reduction assembly 100 is used to connect two sections of drill pipe. The two sections of drill pipe may each be one “stand”, formed of three joined 30 feet lengths of drill pipe.

The torque reduction assembly 100 comprises a mandrel 10 (or main body). The mandrel has threaded sections at either end for connecting to the sections of drill pipe. The mandrel is shown in isolation in FIG. 3.

The mandrel 10 is generally cylindrical for insertion into the borehole, and defines a cylindrical co-ordinate system with an axial direction along its length and a radial direction from its centre outwards. The mandrel 10 also defines a central longitudinal axis, with a first end 10A and a second end 10B at opposites ends of the mandrel 10 along this axis. An annular shoulder 12 is formed on an outer surface of the mandrel 10. The shoulder 12 may be formed as a radial projection from the mandrel 10. That is, the shoulder 12 may have a greater radius than the adjacent parts of the mandrel 10.

The mandrel 10 further comprises a plurality of radial retention slots 14. These retention slots 14 may be formed as notches cut into the outer surface of the mandrel 10.

Alternatively, the retention slots 14 may be formed in any suitable manner including casting. The retention slots 14 are arranged circumferentially around the outer surface of the mandrel 10. That is, the retention slots 14 may be arranged at generally the same location longitudinally along the mandrel 10, but spaced apart in the circumferential direction. The mandrel 10 may include any suitable number of retention slots 14.

The retention slots 14 may be arranged symmetrically. Particularly, when viewed in the longitudinal direction of the mandrel 10 the retention slots 14 may be arranged with N-fold rotational symmetry, where N is the number of retention slots. That is, each retention slot 14 may be spaced (360/N°) from adjacent retention slots 14. For example, if there were 6 retention slots 14 there would be 60° between adjacent retention slots 14.

The plurality of retention slots 14 include at least one first retention slot 14 and one second retention slot 14.

The retention slots 14 may be generally identical to one another. Alternatively, the first retention slot(s) 14 may vary in depth compared to the second retention slot(s) 14. This is discussed in detail below.

The mandrel 10 may further comprise an outer threaded section, which may be generally adjacent to the shoulder 12. The outer threaded section may be used to attach a further component of the torque reduction assembly 100.

The next component in the torque reduction assembly 100 is the bearing sleeve 20. While the bearing sleeve 20 is shown in the embodiment of the present Figures, it may be omitted from the torque reduction assembly 100. The bearing sleeve 20 is formed of a material showing high strength and lubricity. For example, the bearing sleeve 20 may have a strength of greater than 90,000 PSI, particularly in the region of at least 94,000 PSI. For example, the bearing sleeve 20 may be formed of aluminium bronze, such as those according to standard CCC333G. The bearing sleeve 20 may be formed from a machined cylinder of aluminium bronze. In embodiments of the torque reduction assembly 100 without the bearing sleeve 20, a section of the mandrel 10 may be formed of such materials.

Installation of the bearing sleeve 20 onto the mandrel 10 is shown in FIGS. 4 and 5. The bearing sleeve 20 is slid onto the mandrel 10 from the second end 10B of the mandrel 10 towards the mandrel shoulder 12. The bearing sleeve 20 may include a bearing sleeve shoulder 22 for abutting against the mandrel shoulder 12. The bearing sleeve 20 may include an internal threaded surface. With the bearing sleeve 20 slid along the mandrel 10, this internal threaded surface may engage with an external thread on the mandrel 10. The bearing sleeve may be tightened to a specific torque against the shoulder 12 of the mandrel 10. This partial assembly is shown in FIG. 5.

The next component of the torque reduction assembly 100 is the outer sleeve 30. The outer sleeve 30 is rotatably mounted on the mandrel 10 as shown in FIGS. 5 and 6. The outer sleeve 30 is slid onto the mandrel 10 towards the mandrel shoulder 12 from the second end 10B of the mandrel 10.

In embodiments of the torque reduction assembly 100 including the bearing sleeve 20, the outer sleeve 30 may be slid over the bearing sleeve 20 such that the bearing sleeve 20 is provided between the mandrel 10 and the outer sleeve 30. This may include the shoulder 22 of the bearing sleeve 20 being between the shoulder 12 of the mandrel 10 and the outer sleeve 30. In this position, as shown in FIG. 6, the outer sleeve 30 is able to rotate relative to the mandrel 10.

In use, the mandrel 10 will be driven to rotate by the top drive system. The outer sleeve 30 can contact the walls of the wellbore or the inside surface of any casing. As the outer sleeve 30 and the mandrel 10 are rotatable relative to one another, this reduces the torque required to drive the drill string.

A retaining ring 40 is provided to retain the outer sleeve 30 on the mandrel 10. Particularly, the retaining ring 40 retains the outer sleeve 30 between the shoulder 12 of the mandrel 10 and the retaining ring 40. In embodiments of the torque reduction assembly 100 including the bearing sleeve 20, the retaining ring 40 may retain the outer sleeve 30 between the shoulder 22 of the bearing sleeve 20 and the retaining ring 40.

The retaining ring 40 comprises at least one aperture 44 (known as a first aperture). The retaining ring 40 further comprises an inner circumferential groove 46 or slot formed on an inner surface of the retaining ring 40. The inner surface faces the outer surface of the mandrel 10. The inner circumferential groove 46 is aligned with the first aperture 44. That is, the first aperture 44 opens into the inner circumferential groove 46. The retaining ring 40 is shown in FIGS. 7A and 7B. FIG. 7B is an axial cross-section of the retaining ring 40. In these Figures, the arrangement of the first aperture 44 and the inner circumferential groove 46 can be easily seen.

The retaining ring 40 is slid onto the mandrel 10 from the second end 10B of the mandrel 10 until the first aperture 44 is at the same longitudinal position along the mandrel as the retention slots 14. In this position, the retaining ring 40 is rotatable about the mandrel 10.

The retaining ring 40 is then rotated about the mandrel 10 until the first aperture 44 is aligned with a first retention slot 14 of the plurality of retention slot 14. A first retention element 50S as shown in FIG. 9A is then inserted into the first retention slot 14 via the first aperture 44. The first retention element 50S may be any suitable component. In the depicted embodiment it is an elongate key. The first retention element 50S has a length Ls. The first retention element 50S may have a threaded bore 52, which may be arranged centrally as shown in FIG. 9A. This threaded bore 52 can be used to remove the first retention element 50S from the first retention slot 14. A corresponding threaded component can be screwed into the central threaded bore 52, which is then pulled out of the first retention slot 14.

The length Ls of the first retention element 50S is between the depth of the first retention slot 14 and the combined depth of the first retention slot 14 and the circumferential groove 46. Thus, when the first retention element 50S is inserted in the first retention slot it protrudes therefrom into the circumferential groove 46 of the retaining ring 40. As this protrusion is received in the circumferential groove 46, the retaining ring 40 is fixed axially relative to the mandrel 10. That is, the retaining ring 40 can no longer slide off of the mandrel 10 along its axial direction. However, because the first retention element 50S does not extend beyond the circumferential groove 46 into the first aperture 44, the retaining ring 40 is still able to rotate relative to the mandrel 10. As the retaining ring 40 rotates the first retention element may slide along the circumferential groove 46.

The retaining ring 40 can therefore be rotated until the first aperture 44 aligns with another retention slot 14 of the mandrel 10. This retention slot 14 may be a second retention slot 14. A second retention element 50L as shown in FIG. 9B is then inserted into the second retention slot 14 via the first aperture 44. The second retention element 50L has a length LI. The length LI of the second retention element 50L is greater than the combined depth of the second retention slot 14 and the circumferential groove 46. Thus, when fully inserted into the second retention slot 14 the second retention element 50L extends into the first aperture 44. This insertion is shown in FIGS. 8A and 8B. As the second retention element 50L extends into the first aperture 44, this prevents the retaining ring 40 from rotating relative to the mandrel 10. Thus, it rotationally fixes the retaining ring 40 relative to the mandrel 10. As a result, the retaining ring 40 holds the outer sleeve 30 relative to the mandrel 10. The outer sleeve 30 is still able to rotate relative to the mandrel 10 in this position.

The second retention element 50L may have a threaded bore 52 in the same manner as the first retention element 50S. The threaded bore 52 may function in the same manner as above for the first retention element 50S so as to aid in the removal of the second retention element 50L from the second retention slot 14. The second retention element 50L may not include the threaded bore 52, even if the first retention element 50S does. As the second retention element 50L is longer and projects from the second retention slot 14 it is easier to remove than the first retention element 50S is from the first retention slot 14.

The second retention element 50L may be welded in position to lock the retaining ring 40 to the mandrel 10. To aid in this, the second retention element 50L may be provided with weld preparation chamfers.

This arrangement may be achieved in two major embodiments. In the first, the depth of the first retention slot 14 and the second retention slot 14 may be substantially the same, and the length Ls of the first retention element 50S may be shorter than the length LI of the second retention element 50L. Alternatively, the length Ls of the first retention element 50s may be substantially the same as the length LI of the second retention element 50L, and the depth of the second retention slot 14 may be less than the depth of the first retention slot. Of course, other combinations of depths and lengths may be used, provided that the second retention element 50L extends into the first aperture 44 and the first retention element does not, but does extend into the circumferential groove 46.

Based upon the respective depths and lengths, any retention slot 14 of the plurality of retention slots 14 may be a first retention slot 14 or a second retention slot 14. Particularly where the retention slots 14 are identical and the length of the retention elements 50S, 50L are varied. The type of retention slot 14 is essentially defined by the type of retention element 50S, 50L inserted therein. The same retention slot 14 may be a first retention slot 14 if a first retention element 50S is inserted therein, or a second retention slot 14 if a second retention element 50L is inserted therein.

In particular embodiments, the mandrel 10 may include more than two retention slots 14. Particularly, there may be a plurality of first retention slots 14. After the first retention element 50s is inserted into the first retention slot 14 via the aperture 44, the retaining ring 40 may be rotated to align with a further first retention slot 14. A further first retention element 50s may be then inserted into the first retention slot 14 via the first aperture 44. This can be repeated until every first retention slot 14 has a first retention element 50s inserted via the aperture 44. Each additional first retention element 50s increases the strength of the lock between the retaining ring 40 and the mandrel 10. The retaining ring 40 can then be rotated about the mandrel 10 to the second retention slot 14, with the second retention element 50L inserted to rotationally fix the retaining ring 40.

Additionally, or alternatively, the mandrel 10 may include a plurality of second retention slots 14. The retaining ring 14 may include a plurality of apertures 44 corresponding to the plurality of second retention slots 14. The second retention slots 14 are spaced around the mandrel 10 the same distance as the plurality of apertures 44 are spaced around the retaining ring 40. For example, with two second retention slots 14 these may be spaced 180° apart around the mandrel 10. The retaining ring 40 would then have two apertures 44, which are likewise spaced 180° from one another around the retaining ring 40. Once all of the first retention slots 14 have been filled with first retention elements 50s via the apertures 44, the two apertures 44 are aligned simultaneously with the two second retention slots 14. Two second retention elements 50L (one for each aperture 44) are then inserted into the mandrel 10 via the apertures 44. Each second retention element 50L extends into the respective aperture 44, thereby rotationally fixing the retaining ring. Each second retention element 50L may then be welded in place.

FIG. 10 shows a side view of the fully assembled torque reduction assembly 100. A cross-section is taken along line X-X and shown in FIG. 11. This torque reduction assembly 100 includes five first retention elements 50S and one second retention element 50L. The circumferential groove 46 can be seen in this cross-section. The first retention elements 50S extend only as far as this circumferential groove 46. Without the second retention element 50L inserted, the retaining ring 40 would be able to rotate with the first retention elements 50S in this circumferential groove 46. The second retention element 50L extends beyond the circumferential groove 46 into the first aperture 44, thereby rotationally fixing the retaining ring 40.

Thus, the retaining ring 40 is axially and rotationally fixed relative to the mandrel 10 so as to retain the outer sleeve 30 to form a torque reduction assembly 100.

A method of assembling a torque reduction assembly 100 is further provided. The method comprising the following steps.

Firstly, a mandrel 10 is provided. The mandrel 10 is suitable for connecting two sections of drill pipe in a drill string. The mandrel 10 comprises a first annular shoulder 12 and a plurality of radial retention slots 14 arranged circumferentially around an outer surface of the mandrel 10. The radial retention slots 14 include a first retention slot 14 and a second retention slot 14. The mandrel 10 may be as described above in relation to the torque reduction assembly 100 of FIGS. 1 to 11 and may include any variations discussed.

Next, an outer sleeve 30 is slid on the mandrel 10. Again, the outer sleeve 30 may be as described above in relation to the torque reduction assembly 100 of FIGS. 1 to 11 and may include any variations discussed. The outer sleeve 30 is rotatable relative to the mandrel 10.

A retaining ring 40 is then slid on the mandrel 10. The retaining ring 40 is arranged such that the outer sleeve 30 is between the first annular shoulder 12 of the mandrel 10 and the retaining ring 40. The retaining ring 40 comprises a first aperture 44 and a circumferential groove 46 about an inner surface of the retaining ring 40. The first aperture 44 is aligned with the circumferential groove 46. Again, the retaining ring 40 may be as described above in relation to the torque reduction assembly 100 of FIGS. 1 to 11 and may include any variations discussed. The retaining ring 40 is rotatable about the mandrel 10 so as to progressively align the first aperture 44 with each retention slot 14. That is, the retaining ring 40 may be rotated about the mandrel 10 so as to align with one retention slot 14 at a time.

The retaining ring 40 is then rotated to align the first aperture 44 with the first retention slot 14. By aligned, this means that the opening of the aperture 44 substantially lays above the first retention slot 14.

Next, a first retention element 50S is inserted into the first retention slot 14 via the first aperture 44. This first retention element 50S may be as described above in relation to the torque reduction assembly 100 of FIGS. 1 to 11 and may include any variations discussed. Particularly, the first retention element 50S may have a length Ls relative to the combined depth of the first retention slot 14 and circumferential groove 46 as discussed above. The first retention element 50S axially fixes the retaining ring 40 relative to the mandrel 10. That is, the retaining ring 40 cannot be slid off the mandrel 10 due to the contact between the circumferential groove and the first retention element 50S. The retaining ring 40 is, however, still rotatable about the mandrel 10.

Once the first retention element 50S has been located in the first retention slot 14, the retaining ring 40 is rotated about the mandrel 10. This rotation continues until the first aperture 44 of the retaining ring 40 is aligned with the second retention slot 14. As noted above, there may be one or more further first retention slots 14 which are filled with first retention elements 50S in-between this step and the preceding step.

A second retention element 50L is then inserted into the second retention slot 14 via the first aperture 44. The second retention element 50L may be as described above in relation to the torque reduction assembly 100 of FIGS. 1 to 11 and may include any variations discussed. Particularly, the second retention element 50L may have a length LI relative to the combined depth of the second retention slot 14 and circumferential groove 46 as discussed above. The second retention element 50L rotationally fixes the retaining ring 40 relative to the mandrel 10.

A bearing sleeve 20 may be slid onto the mandrel 10 before the outer sleeve 30. If this is the case, the outer sleeve 30 is slid over the bearing sleeve 20 and the mandrel 10. As a result, the bearing sleeve 20 is provided between the mandrel 10 and the outer sleeve 30. The bearing sleeve 20 may be as described above in relation to the torque reduction assembly 100 of FIGS. 1 to 11 and may include any variations discussed.

After the second retention element 50L has been inserted into the second retention slot 14, it may be welded in place to the retaining ring 40.

Claims

1. A torque reduction assembly for a drill string, the torque reduction assembly comprising: a mandrel for connecting two sections of drill pipe, the mandrel comprising a first annular shoulder and a plurality of radial retention slots arranged circumferentially around an outer surface of the mandrel, including a first retention slot and a second retention slot;an outer sleeve for rotatably mounting on the mandrel;a retaining ring for retaining the outer sleeve between the retaining ring and the first annular shoulder, the retaining ring comprising a first aperture and a circumferential groove about an inner surface of the retaining ring, the first aperture aligned with the circumferential groove, the retaining ring being rotatable about the mandrel so as to progressively align the first aperture with each retention slot;a first retention element for locating in the first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel; anda second retention element for locating in the second retention slot via the first aperture to rotationally fix the retaining ring relative to the mandrel.

2. The torque reduction assembly of claim 1, wherein the first retention element is shorter than the second retention element.

3. The torque reduction assembly of claim 2, wherein the first retention slot is the same depth as the second retention slot.

4. The torque reduction assembly of claim 3, wherein the first retention slot is identical to the second retention slot.

5. The torque reduction assembly of claim 1, wherein the first retention element is the same length as the second retention element.

6. The torque reduction assembly of claim 1, wherein the first retention element is identical to the second retention element.

7. The torque reduction assembly of claim 5, wherein the first retention slot is deeper than the second retention slot.

8. The torque reduction assembly of claim 1, wherein: the plurality of radial retention slots further comprises a plurality of first retention slots; andthe torque reduction assembly further comprises a plurality of first retention elements, each first retention element for locating in a respective first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel.

9. The torque reduction assembly of claim 1, wherein: the plurality of radial retention slots further comprises a plurality of second retention slots;the retaining ring further comprises a second aperture, the second aperture aligned with the circumferential groove, the retaining ring being rotatable about the mandrel so as to align the first aperture and the second aperture with respective second retention slots simultaneously; andthe torque reduction assembly further comprises a plurality of second retention elements, each second retention element for locating in a respective second retention slot via the first aperture and the second aperture to rotationally fix the retaining ring relative to the mandrel.

10. The torque reduction assembly of claim 1, wherein the plurality of radial retention slots are arranged with N-fold rotational symmetry, where N is the number of retention slots.

11. The torque reduction assembly of claim 1, further comprising a bearing sleeve for mounting on the mandrel between the mandrel and the outer sleeve.

12. The torque reduction assembly of claim 11, wherein the bearing sleeve further comprises a second annular shoulder, wherein the second annular shoulder is positionable between the first annular shoulder and the outer sleeve.

13. The torque reduction assembly of claim 11, wherein the mandrel comprises an external thread and the bearing sleeve comprises an internal thread for screwing onto the external thread to mount the bearing sleeve on the mandrel.

14. A method of assembling a torque reduction assembly comprising the steps of: (i) providing a mandrel for connecting two sections of drill pipe, the mandrel comprising a first annular shoulder and a plurality of radial retention slots arranged circumferentially around an outer surface of the mandrel, including a first retention slot and a second retention slot;(ii) sliding an outer sleeve on the mandrel;(iii) sliding a retaining ring on the mandrel such that the outer sleeve is between the first annular shoulder and the retaining ring, the retaining ring comprising a first aperture and a circumferential groove about an inner surface of the retaining ring, the first aperture aligned with the circumferential groove, the retaining ring being rotatable about the mandrel so as to progressively align the first aperture with each retention slot;(iv) rotating the retaining ring to align the first aperture with the first retention slot;(v) inserting a first retention element into the first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel;(vi) rotating the retaining ring to align the first aperture with the second retention slot; and(vii) inserting a second retention element into the second retention slot via the first aperture to rotationally fix the retaining ring relative to the mandrel.

15. The method of claim 14, wherein the first retention element is shorter than the second retention element.

16. The method of claim 15, wherein the first retention slot is the same depth as the second retention slot.

17. The method of claim 16, wherein the first retention slot is identical to the second retention slot.

18. The method of claim 14, wherein the first retention element is the same length as the second retention element.

19. The method of claim 18, wherein the first retention element is identical to the second retention element.

20. The method of claim 18, wherein the first retention slot is deeper than the second retention slot.

21. The method of claim 14, wherein: the plurality of radial retention slots further comprises a plurality of first retention slots; andthe method further comprises between steps (v) and (vi) the steps of:(v-1) rotating the retaining ring to align the first aperture with a further first retention slot;(v-2) inserting a further first retention element into the further first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel.

22. The method of claim 21, wherein steps (v-1) and (v-2) are repeated until a first retention element is inserted into each first retention slot, before proceeding to step (vi).

23. The method of claim 14, further comprising a step of sliding a bearing sleeve on the mandrel between steps (i) and (ii), wherein step (ii) further comprises sliding the outer sleeve over the bearing sleeve such that the bearing sleeve is between the mandrel and the outer sleeve.

24. The method of claim 14, further comprising the step of: (viii) welding the second retention element to the retaining ring.