TORQUE REDUCTION ASSEMBLY

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.

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 claim1. 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 claim14.

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.

DETAILED DESCRIPTION

FIGS.1and2show a torque reduction assembly100in an exploded view. The torque reduction assembly100is 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 assembly100comprises a mandrel10(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 inFIG.3.

The mandrel10is 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 mandrel10also defines a central longitudinal axis, with a first end10A and a second end10B at opposites ends of the mandrel10along this axis. An annular shoulder12is formed on an outer surface of the mandrel10. The shoulder12may be formed as a radial projection from the mandrel10. That is, the shoulder12may have a greater radius than the adjacent parts of the mandrel10.

The mandrel10further comprises a plurality of radial retention slots14. These retention slots14may be formed as notches cut into the outer surface of the mandrel10.

Alternatively, the retention slots14may be formed in any suitable manner including casting. The retention slots14are arranged circumferentially around the outer surface of the mandrel10. That is, the retention slots14may be arranged at generally the same location longitudinally along the mandrel10, but spaced apart in the circumferential direction. The mandrel10may include any suitable number of retention slots14.

The retention slots14may be arranged symmetrically. Particularly, when viewed in the longitudinal direction of the mandrel10the retention slots14may be arranged with N-fold rotational symmetry, where N is the number of retention slots. That is, each retention slot14may be spaced (360/N°) from adjacent retention slots14. For example, if there were 6 retention slots14there would be 60° between adjacent retention slots14.

The plurality of retention slots14include at least one first retention slot14and one second retention slot14.

The retention slots14may be generally identical to one another. Alternatively, the first retention slot(s)14may vary in depth compared to the second retention slot(s)14. This is discussed in detail below.

The mandrel10may further comprise an outer threaded section, which may be generally adjacent to the shoulder12. The outer threaded section may be used to attach a further component of the torque reduction assembly100.

The next component in the torque reduction assembly100is the bearing sleeve20. While the bearing sleeve20is shown in the embodiment of the present Figures, it may be omitted from the torque reduction assembly100. The bearing sleeve20is formed of a material showing high strength and lubricity. For example, the bearing sleeve20may have a strength of greater than 90,000 PSI, particularly in the region of at least 94,000 PSI. For example, the bearing sleeve20may be formed of aluminium bronze, such as those according to standard CCC333G. The bearing sleeve20may be formed from a machined cylinder of aluminium bronze. In embodiments of the torque reduction assembly100without the bearing sleeve20, a section of the mandrel10may be formed of such materials.

Installation of the bearing sleeve20onto the mandrel10is shown inFIGS.4and5. The bearing sleeve20is slid onto the mandrel10from the second end10B of the mandrel10towards the mandrel shoulder12. The bearing sleeve20may include a bearing sleeve shoulder22for abutting against the mandrel shoulder12. The bearing sleeve20may include an internal threaded surface. With the bearing sleeve20slid along the mandrel10, this internal threaded surface may engage with an external thread on the mandrel10. The bearing sleeve may be tightened to a specific torque against the shoulder12of the mandrel10. This partial assembly is shown inFIG.5.

The next component of the torque reduction assembly100is the outer sleeve30. The outer sleeve30is rotatably mounted on the mandrel10as shown inFIGS.5and6. The outer sleeve30is slid onto the mandrel10towards the mandrel shoulder12from the second end10B of the mandrel10.

In embodiments of the torque reduction assembly100including the bearing sleeve20, the outer sleeve30may be slid over the bearing sleeve20such that the bearing sleeve20is provided between the mandrel10and the outer sleeve30. This may include the shoulder22of the bearing sleeve20being between the shoulder12of the mandrel10and the outer sleeve30. In this position, as shown inFIG.6, the outer sleeve30is able to rotate relative to the mandrel10.

In use, the mandrel10will be driven to rotate by the top drive system. The outer sleeve30can contact the walls of the wellbore or the inside surface of any casing. As the outer sleeve30and the mandrel10are rotatable relative to one another, this reduces the torque required to drive the drill string.

A retaining ring40is provided to retain the outer sleeve30on the mandrel10. Particularly, the retaining ring40retains the outer sleeve30between the shoulder12of the mandrel10and the retaining ring40. In embodiments of the torque reduction assembly100including the bearing sleeve20, the retaining ring40may retain the outer sleeve30between the shoulder22of the bearing sleeve20and the retaining ring40.

The retaining ring40comprises at least one aperture44(known as a first aperture). The retaining ring40further comprises an inner circumferential groove46or slot formed on an inner surface of the retaining ring40. The inner surface faces the outer surface of the mandrel10. The inner circumferential groove46is aligned with the first aperture44. That is, the first aperture44opens into the inner circumferential groove46. The retaining ring40is shown inFIGS.7A and7B.FIG.7Bis an axial cross-section of the retaining ring40. In these Figures, the arrangement of the first aperture44and the inner circumferential groove46can be easily seen.

The retaining ring40is slid onto the mandrel10from the second end10B of the mandrel10until the first aperture44is at the same longitudinal position along the mandrel as the retention slots14. In this position, the retaining ring40is rotatable about the mandrel10.

The retaining ring40is then rotated about the mandrel10until the first aperture44is aligned with a first retention slot14of the plurality of retention slot14. A first retention element50S as shown inFIG.9Ais then inserted into the first retention slot14via the first aperture44. The first retention element50S may be any suitable component. In the depicted embodiment it is an elongate key. The first retention element50S has a length Ls. The first retention element50S may have a threaded bore52, which may be arranged centrally as shown inFIG.9A. This threaded bore52can be used to remove the first retention element50S from the first retention slot14. A corresponding threaded component can be screwed into the central threaded bore52, which is then pulled out of the first retention slot14.

The length Ls of the first retention element50S is between the depth of the first retention slot14and the combined depth of the first retention slot14and the circumferential groove46. Thus, when the first retention element50S is inserted in the first retention slot it protrudes therefrom into the circumferential groove46of the retaining ring40. As this protrusion is received in the circumferential groove46, the retaining ring40is fixed axially relative to the mandrel10. That is, the retaining ring40can no longer slide off of the mandrel10along its axial direction. However, because the first retention element50S does not extend beyond the circumferential groove46into the first aperture44, the retaining ring40is still able to rotate relative to the mandrel10. As the retaining ring40rotates the first retention element may slide along the circumferential groove46.

The retaining ring40can therefore be rotated until the first aperture44aligns with another retention slot14of the mandrel10. This retention slot14may be a second retention slot14. A second retention element50L as shown inFIG.9Bis then inserted into the second retention slot14via the first aperture44. The second retention element50L has a length LI. The length LI of the second retention element50L is greater than the combined depth of the second retention slot14and the circumferential groove46. Thus, when fully inserted into the second retention slot14the second retention element50L extends into the first aperture44. This insertion is shown inFIGS.8A and8B. As the second retention element50L extends into the first aperture44, this prevents the retaining ring40from rotating relative to the mandrel10. Thus, it rotationally fixes the retaining ring40relative to the mandrel10. As a result, the retaining ring40holds the outer sleeve30relative to the mandrel10. The outer sleeve30is still able to rotate relative to the mandrel10in this position.

The second retention element50L may have a threaded bore52in the same manner as the first retention element50S. The threaded bore52may function in the same manner as above for the first retention element50S so as to aid in the removal of the second retention element50L from the second retention slot14. The second retention element50L may not include the threaded bore52, even if the first retention element50S does. As the second retention element50L is longer and projects from the second retention slot14it is easier to remove than the first retention element50S is from the first retention slot14.

The second retention element50L may be welded in position to lock the retaining ring40to the mandrel10. To aid in this, the second retention element50L 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 slot14and the second retention slot14may be substantially the same, and the length Ls of the first retention element50S may be shorter than the length LI of the second retention element50L. Alternatively, the length Ls of the first retention element50smay be substantially the same as the length LI of the second retention element50L, and the depth of the second retention slot14may 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 element50L extends into the first aperture44and the first retention element does not, but does extend into the circumferential groove46.

Based upon the respective depths and lengths, any retention slot14of the plurality of retention slots14may be a first retention slot14or a second retention slot14. Particularly where the retention slots14are identical and the length of the retention elements50S,50L are varied. The type of retention slot14is essentially defined by the type of retention element50S,50L inserted therein. The same retention slot14may be a first retention slot14if a first retention element50S is inserted therein, or a second retention slot14if a second retention element50L is inserted therein.

In particular embodiments, the mandrel10may include more than two retention slots14. Particularly, there may be a plurality of first retention slots14. After the first retention element50sis inserted into the first retention slot14via the aperture44, the retaining ring40may be rotated to align with a further first retention slot14. A further first retention element50smay be then inserted into the first retention slot14via the first aperture44. This can be repeated until every first retention slot14has a first retention element50sinserted via the aperture44. Each additional first retention element50sincreases the strength of the lock between the retaining ring40and the mandrel10. The retaining ring40can then be rotated about the mandrel10to the second retention slot14, with the second retention element50L inserted to rotationally fix the retaining ring40.

Additionally, or alternatively, the mandrel10may include a plurality of second retention slots14. The retaining ring14may include a plurality of apertures44corresponding to the plurality of second retention slots14. The second retention slots14are spaced around the mandrel10the same distance as the plurality of apertures44are spaced around the retaining ring40. For example, with two second retention slots14these may be spaced 180° apart around the mandrel10. The retaining ring40would then have two apertures44, which are likewise spaced 180° from one another around the retaining ring40. Once all of the first retention slots14have been filled with first retention elements50svia the apertures44, the two apertures44are aligned simultaneously with the two second retention slots14. Two second retention elements50L (one for each aperture44) are then inserted into the mandrel10via the apertures44. Each second retention element50L extends into the respective aperture44, thereby rotationally fixing the retaining ring. Each second retention element50L may then be welded in place.

FIG.10shows a side view of the fully assembled torque reduction assembly100. A cross-section is taken along line X-X and shown inFIG.11. This torque reduction assembly100includes five first retention elements50S and one second retention element50L. The circumferential groove46can be seen in this cross-section. The first retention elements50S extend only as far as this circumferential groove46. Without the second retention element50L inserted, the retaining ring40would be able to rotate with the first retention elements50S in this circumferential groove46. The second retention element50L extends beyond the circumferential groove46into the first aperture44, thereby rotationally fixing the retaining ring40.

Thus, the retaining ring40is axially and rotationally fixed relative to the mandrel10so as to retain the outer sleeve30to form a torque reduction assembly100.

A method of assembling a torque reduction assembly100is further provided. The method comprising the following steps.

Firstly, a mandrel10is provided. The mandrel10is suitable for connecting two sections of drill pipe in a drill string. The mandrel10comprises a first annular shoulder12and a plurality of radial retention slots14arranged circumferentially around an outer surface of the mandrel10. The radial retention slots14include a first retention slot14and a second retention slot14. The mandrel10may be as described above in relation to the torque reduction assembly100ofFIGS.1to11and may include any variations discussed.

Next, an outer sleeve30is slid on the mandrel10. Again, the outer sleeve30may be as described above in relation to the torque reduction assembly100ofFIGS.1to11and may include any variations discussed. The outer sleeve30is rotatable relative to the mandrel10.

A retaining ring40is then slid on the mandrel10. The retaining ring40is arranged such that the outer sleeve30is between the first annular shoulder12of the mandrel10and the retaining ring40. The retaining ring40comprises a first aperture44and a circumferential groove46about an inner surface of the retaining ring40. The first aperture44is aligned with the circumferential groove46. Again, the retaining ring40may be as described above in relation to the torque reduction assembly100ofFIGS.1to11and may include any variations discussed. The retaining ring40is rotatable about the mandrel10so as to progressively align the first aperture44with each retention slot14. That is, the retaining ring40may be rotated about the mandrel10so as to align with one retention slot14at a time.

The retaining ring40is then rotated to align the first aperture44with the first retention slot14. By aligned, this means that the opening of the aperture44substantially lays above the first retention slot14.

Next, a first retention element50S is inserted into the first retention slot14via the first aperture44. This first retention element50S may be as described above in relation to the torque reduction assembly100ofFIGS.1to11and may include any variations discussed. Particularly, the first retention element50S may have a length Ls relative to the combined depth of the first retention slot14and circumferential groove46as discussed above. The first retention element50S axially fixes the retaining ring40relative to the mandrel10. That is, the retaining ring40cannot be slid off the mandrel10due to the contact between the circumferential groove and the first retention element50S. The retaining ring40is, however, still rotatable about the mandrel10.

Once the first retention element50S has been located in the first retention slot14, the retaining ring40is rotated about the mandrel10. This rotation continues until the first aperture44of the retaining ring40is aligned with the second retention slot14. As noted above, there may be one or more further first retention slots14which are filled with first retention elements50S in-between this step and the preceding step.

A second retention element50L is then inserted into the second retention slot14via the first aperture44. The second retention element50L may be as described above in relation to the torque reduction assembly100ofFIGS.1to11and may include any variations discussed. Particularly, the second retention element50L may have a length LI relative to the combined depth of the second retention slot14and circumferential groove46as discussed above. The second retention element50L rotationally fixes the retaining ring40relative to the mandrel10.

A bearing sleeve20may be slid onto the mandrel10before the outer sleeve30. If this is the case, the outer sleeve30is slid over the bearing sleeve20and the mandrel10. As a result, the bearing sleeve20is provided between the mandrel10and the outer sleeve30. The bearing sleeve20may be as described above in relation to the torque reduction assembly100ofFIGS.1to11and may include any variations discussed.

After the second retention element50L has been inserted into the second retention slot14, it may be welded in place to the retaining ring40.