Improvements Relating To Downhole Traction Apparatus & Methods

Abstract

A sleeve 40 for a downhole traction apparatus (14, Fig 1) comprises a body portion 44, head portion 46 and an alignment arrangement 48 integrally formed on the sleeve. The alignment arrangement compri

Description

In the oil and gas exploration and production industry, amongst others, a borehole (known in the oil and gas industry as a “wellbore” since it facilitates access to the hydrocarbon bearing formation) is drilled from surface, the borehole typically then being lined with metallic bore-lining tubing known as casing. Sections of casing are typically threaded together to form a casing string which is run into the borehole, the annulus between the casing string and the borehole then being filled with a settable material, typically cement, which amongst other things supports the casing string and the borehole and provides a seal which prevents uncontrolled fluid flow up the annulus between the outside of the casing string and the inside of the borehole. While traditionally boreholes were drilled vertically or substantially vertically, the development of directional drilling techniques and equipment has enabled boreholes to be drilled which extend away from vertical and it is now common for boreholes (commonly known as horizontal boreholes) to include a substantial portion which extends at a high angle from vertical or horizontally. In the oil and gas industry, for example, horizontal boreholes are able to maximise the surface area of the borehole in contact with the producing formation. In this way, the production rate of the oil and / or gas being produced may be enhanced. The drilling and / or completion of horizontal boreholes, however, presents a number of technical challenges. For example, when drilling a horizontal borehole section, the drill string will typically lie on the low side of the borehole wall, resulting in increased torque, drag and / or wear on the drill string and / or associated components, this in turn resulting in increased trips into the borehole and associated costs. Similarly, completion of a pre-drilled horizontal borehole section the tubulars forming the completion string tend to lie on the low side of the cased bore, resulting in increased torque, drag and / or wear on the completion string and / or associated components, this in turn resulting in increased trips into the borehole and associated costs. In both cases, increased torque, drag and / or wear increases the risk of damage to the borehole or bore-lining tubing (casing or liner). In extreme cases, severe wear to the wall of the casing increases the risk of the casing pressure integrity being compromised. This may require that the completion be withdrawn (where indeed this is possible) or other remedial work or workover carried out, resulting in significant expense and delay to the operator. The drilling of horizontal boreholes may also suffer from a number of further performance reducing factors. For example, in order to create any borehole, it is necessary to exert sufficient force on the drill bit to drive the drill bit through rock, this force commonly known as weight on bit. However, it will be recognised that for boreholes having a significant horizontal section, the drilling tubulars located in the horizontal borehole section do not contribute to the weight on bit. Alternatively or additionally, compression applied to a long string of rotating drilling tubulars in a borehole tends to cause a degree of buckling and pipe whirl, forcing the rotating tubulars against the bore wall and resulting in increased friction which inhibits (and in extreme cases prevents) progress of the drill string. Similar issues may also occur in running completion tools and assemblies into pre-drilled boreholes. Applicant’s Driver® tool comprises rollers configured for mounting on and around a body. The rollers are each mounted on the body so as to be offset and define a skew angle relative to a longitudinal axis of the body. In use, as the rollers engage a wall of a borehole or bore-lining tubular, by virtue of the offset and skew the apparatus and connected drilling or completion string is urged along the borehole or bore-lining tubular. SUMMARY Aspects of the present disclosure include a sleeve for a downhole traction apparatus; a traction member for a downhole traction apparatus comprising the sleeve; a downhole traction apparatus comprising a plurality of the traction members; and associated downhole traction methods and methods of manufacture. According to a first aspect, there is a provided a sleeve for a downhole traction apparatus, wherein the sleeve is configured for location on and around a body of the downhole traction apparatus, and comprises: a body portion; a head portion extending radially from said body portion; and an alignment arrangement integrally formed on the sleeve, wherein the alignment arrangement comprises at least one of: a first alignment profile formed on the body portion, wherein said first alignment profile is configured to engage a corresponding second alignment profile formed on an adjacent sleeve or on the body of the downhole traction apparatus; and a second alignment profile formed on the head portion, wherein said second alignment profile is configured to engage a corresponding first alignment profile formed on another adjacent sleeve or on the body of the downhole traction apparatus. In use, and as will be described further below, the sleeve may be configured to receive a roller, the roller being locatable on and around the body portion of the sleeve and configured to engage a wall of the borehole or bore-lining tubing (for brevity and unless specified otherwise, the borehole and bore-lining tubing will be referred to below simply as “the borehole”). The sleeve and roller may together form a traction member of the downhole traction apparatus, whereby engagement between the roller and the wall of the borehole generates an axial or longitudinal force on the sleeve which in turn is transmitted to the downhole traction apparatus, thereby urging the downhole traction apparatus along the borehole. Beneficially, the alignment arrangement permits the sleeve to be coupled to one or more other sleeves in the correct orientation, obviating the need for complex alignment mechanisms between the sleeves. The alignment arrangement also permits the sleeve to be located on the body, e.g. mandrel, of the downhole traction apparatus in the correct orientation, obviating the need for complex alignment mechanisms between the sleeve and the body of the downhole traction apparatus. Moreover, the alignment arrangement may also form a locking mechanism for rotationally securing a plurality of the sleeves together and / or for rotationally securing the sleeve to / relative to the body of the downhole traction apparatus. For example, by virtue of the alignment arrangement providing a single orientation at which the first alignment profile and the corresponding second alignment profile can be engaged, the alignment arrangement obviates the risk that the sleeve is assembled to the one or more other sleeves incorrectly and / or obviates the risk that the sleeve is assembled to the body of the downhole traction apparatus incorrectly. This in turn may facilitate more efficient manual assembly and / or facilitate automated, e.g. robotic, assembly. The sleeve facilitates the creation of a traction member with reduced complexity and / or number of parts in comparison to previous apparatus’. This reduced complexity and / or number of parts in turn simplifies manufacture, permitting the traction member to be formed using simpler and / or more cost effective conventional manufacturing techniques and / or facilitates the manufacture of the sleeve using advanced manufacturing techniques such as additive manufacturing. As described above, the alignment arrangement comprises a first alignment profile formed on the body portion, wherein said first alignment profile is configured to engage a corresponding second alignment profile formed on an adjacent sleeve or on the body of the downhole traction apparatus; and a second alignment profile formed on the head portion, wherein said second alignment profile is configured to engage a corresponding first alignment profile formed on another adjacent sleeve or on the body of the downhole traction apparatus. The first alignment profile and the second alignment profile may take any suitable form, provided they allow for co-operating engagement with the associated profiles of the adjacent sleeve or the body of the downhole traction apparatus. In particular embodiments, the first alignment profile comprises or takes the form of an alignment flat. In particular embodiments, the second alignment profile comprises or takes the form of an alignment recess. In particular embodiments, the sleeve comprises both the first alignment profile and the second alignment profile, the first alignment profile facilitating engagement between the sleeve and respective adjacent sleeves and / or facilitating engagement between the sleeve and the body of the downhole traction apparatus. Beneficially, this facilitates the installation of a plurality of the sleeves, with the alignment arrangement ensuring that each sleeve is oriented correctly relative to the adjacent sleeve or sleeves and / or the body of the downhole traction apparatus. Moreover, providing the sleeve with both the first alignment profile and the second alignment profile means that each sleeve is identical to its neighbour, the only difference being that the sleeves are oriented differently on the body of the downhole traction apparatus (the correct orientation being dictated by the alignment arrangement). This in turn simplifies manufacture and / or reduces the number of parts needed to form the downhole traction apparatus. Where the sleeve comprises both the first alignment profile and the second alignment profile, the first alignment profile and the second alignment profile may be circumferentially offset from each other. The first alignment profile and the second alignment profile may be circumferentially offset from each other by any suitable angle, for example but not exclusively 45 degrees, 60 degrees, 90 degrees, 120 degrees, 135 degrees, 180 degrees. In particular embodiments, the first alignment profile and the second alignment profile may be circumferentially offset from each other by 120 degrees. Beneficially, the alignment arrangement permits a plurality of the sleeves to be located on the body of the downhole traction apparatus, the circumferential offset between the second alignment profile (and thus when coupled the first alignment profile of the adjacent sleeve) and the first alignment profile (and thus, when coupled the second alignment profile of the other adjacent sleeve) permitting the sleeves to be accurately oriented relative to each other on the body of the downhole traction apparatus, so as to generate the desired axial traction force. As described above, the sleeve is configured for location on and around a body, e.g. a mandrel, of the downhole traction apparatus. The sleeve may comprise a throughbore configured, e.g. sized and / or shaped, to facilitate location of the sleeve on and around the body of the downhole traction apparatus. The sleeve may be configured for location on an outer circumferential surface of the body of the downhole traction apparatus. For example, and as will be described further below, the body of the downhole traction apparatus may comprise or define a journal portion and the body portion of the sleeve may be configured, e.g. sized and / or shaped, for location on the journal portion. More particularly, the journal portion may comprise or take the form of a recessed journal portion and the sleeve may be configured, e.g. sized and / or shaped, for location on the recessed journal portion. It will be recognised that, in use, a first sleeve can be located on the body, e.g. mandrel, of the downhole traction apparatus and engaged with the body (e.g. the end wall of the recessed journal or end ring) to orient and rotationally lock said first sleeve to the body of the downhole traction apparatus. Additional sleeves can be located on the body, e.g. mandrel, of the downhole traction apparatus and engaged with the adjacent sleeves, the alignment arrangements ensuring that the sleeves are oriented correctly. A final sleeve can be located on the body, e.g. mandrel, of the downhole traction apparatus and engage the body (e.g. the opposite end wall of the recessed journal or other end ring) to orient and rotationally lock said final sleeve to the body of the downhole traction apparatus. The sleeve may be configured to be offset and / or define a skew angle with respect to a central longitudinal axis of the body of the downhole traction apparatus, and in particular embodiments the sleeve may be configured to be both offset and define a skew angle with respect to the central longitudinal axis of the body of the downhole traction apparatus. In use, and as will be described further below, the sleeve may be configured to receive a roller, the roller being locatable on and around the body portion of the sleeve and configured to engage a wall of the borehole or bore-lining tubing (for brevity and unless specified otherwise, the borehole and bore-lining tubing will be referred to below simply as “the borehole”). The sleeve and roller may together form a traction member of the downhole traction apparatus, whereby engagement between the roller and the wall of the borehole generates Beneficially, the provision of the offset ensures that each roller will engage the wall of the borehole e.g. the low side of the borehole, whereas the skew angle facilitates the creation of the axial or longitudinal force on the sleeve which in turn is transmitted to the downhole traction apparatus, thereby urging the downhole traction apparatus along the borehole. It will be recognised that when a plurality of sleeves are provided, the alignment arrangement ensures that each sleeve is oriented to engage the borehole wall, i.e. the low side of the borehole, and generate the axial or longitudinal force in the desired sequence and / or with the desired timing, this providing the desired traction force urging the downhole apparatus and associated downhole tool along the borehole. The body portion of the sleeve may comprise a portion, e.g. circumferential portion, arc portion or segment, having a greater wall thickness than a remaining portion, e.g. circumferential portion, arc portion or segment, of the body portion of the sleeve. The body portion of the sleeve may be configured, e.g. sized and / or dimensioned, so that the when the portion of the body portion having said greater wall thickness is oriented towards the low side of the borehole, the associated roller provided on the body portion will engage the borehole wall. Beneficially, this provides a simple and effective mechanism for providing the sleeve and associated traction member with a radial offset. The alignment arrangement may be provided on or in, e.g. formed on or in, the portion of the body portion having said greater wall thickness. Beneficially, the portion of the body portion with greater wall thickness thus, in addition to providing the offset functionality, also provides space for the alignment arrangement without the requirement for additional components and / or complex mechanisms; thereby simplifying construction and reducing the risk of failure modes associated with the introduction of additional components and / or complex mechanisms. The portion of the body portion with greater wall thickness may alternatively or additionally provide a robust construction of loads through the sleeve, which may again simplify construction and reduce the risk of failure modes associated with the introduction of additional components and / or complex mechanisms. The sleeve may be configured so that a central longitudinal axis of the body portion of the sleeve is offset from the central longitudinal axis of the body of the downhole traction apparatus. The sleeve may be configured so that a central longitudinal axis of the body portion of the sleeve is offset from the central longitudinal axis of the head portion of the sleeve. The sleeve may be configured so that a central longitudinal axis of the body portion of the sleeve defines a skew angle relative to the central longitudinal axis of the body of the downhole traction apparatus. The sleeve may be configured so that a central longitudinal axis of the body portion of the sleeve defines a skew angle relative to the central longitudinal axis of the head portion of the sleeve. As described above, the sleeve comprises a body portion. The body portion may comprise or take the form of a shank portion of the sleeve. The first alignment profile may be provided, e.g. formed, on an outer surface, e.g. outer circumferential surface, of the body portion. The first alignment profile may be provided, e.g. formed, at a distal end of the body portion. As described above, the sleeve comprises a head portion. The head portion may comprise or take the form of a flange portion. The second alignment profile may be provided, e.g. formed, on an inner surface, e.g. inner circumferential surface, of the head portion. The second alignment profile may be provided, e.g. formed, at a proximal end of the head portion. The head portion may comprise a first, e.g. proximal, end surface. The first, e.g. proximal, end surface may be oriented transverse to the central longitudinal axis of the downhole traction apparatus. Beneficially, the provision of an end surface which is oriented transverse to the central longitudinal axis of the downhole traction apparatus provides a datum point / plane for manufacture and / or assembly of the sleeve and downhole traction apparatus, since this is known to be oriented at 90 degrees to the body of the downhole traction apparatus, e.g. mandrel. The first, e.g. proximal, end surface may define a thrust bearing surface. The first, e.g. proximal, end surface may define or may be provided with a honed and / or hard faced surface or material capable of withstanding the thrust loads exerted thereon. In use, the first, e.g. proximal, end surface may provide a thrust bearing surface abutting, in the case of the first sleeve, the body of the downhole traction apparatus (e.g. the end wall of the recessed journal or end ring) or, in the case of adjacent sleeves, the roller of the preceding sleeve. The head portion may comprise a second, distal, end surface. The second, e.g. distal, end surface may define a thrust bearing surface. The second, e.g. distal, end surface may define or may be provided with a honed and / or hard faced surface or material capable of withstanding the thrust loads exerted thereon. In use, the second, e.g. distal, end surface may provide a thrust bearing surface abutting the roller of the sleeve. The sleeve may comprise an abutment surface. The abutment surface may be provided, e.g. formed, inside the sleeve. The abutment surface may extend radially inwards, i.e. into the throughbore of the sleeve. The abutment surface may be oriented transverse to the central longitudinal axis. The abutment surface may be formed inside the head portion of the sleeve. In use, the abutment surface may be configured and / or operable to receive the distal end surface of the body portion of the adjacent sleeve. Likewise, the distal end surface of the body portion of the present sleeve may be configured and / or operable to engage an abutment surface of the adjacent sleeve. Beneficially, the abutment surface(s) may function to control the axial arrangement, e.g. spacing, of the sleeves, while also permitting a degree of float, e.g. due to thermal effects downhole. According to a second aspect, there is a provided a downhole traction member for a downhole traction apparatus, the traction member comprising: the sleeve of the first aspect; and a roller configured for location on and around the sleeve. In use, and as will be described further below, the sleeve may be configured to receive the roller, the roller being locatable on and around the body portion of the sleeve and configured to engage a wall of the borehole. The sleeve and roller may together form the traction member of the downhole traction apparatus, whereby engagement between the roller and the wall of the borehole generates an axial or longitudinal force on the sleeve which in turn is transmitted to the downhole traction apparatus, thereby urging the downhole traction apparatus along the borehole. As described above, the roller is configured for location on and around the sleeve. The roller may comprise a throughbore configured, e.g. sized and / or shaped, to facilitate location of the roller on and around the body portion of the sleeve. The roller may be configured for location on an outer circumferential surface of the body portion. For example, the body portion of the sleeve may comprise or define a journal portion and the roller may be configured, e.g. sized and / or shaped, for location on the journal portion. The roller may comprise a body portion. The body portion may be annular. The roller may comprise one or more blade portions. In particular embodiments, the roller comprises a plurality of the blade portions. The blade portions may be circumferentially arranged and / or spaced. Beneficially, the spacing between the blade portions facilitate flow of fluid bypass around the outside of the roller / between the roller and the borehole. At least one of the blade portions may extend axially and / or at least partially circumferentially with respect to the body portion and / or a central longitudinal axis of the roller. In use, the one or more blade portions may be configured and / or operable to engage the borehole on rotation of the roller around the sleeve. The roller may be constructed from a polymeric material. In particular, the roller may be constructed from an elastomeric material, e.g. HNBR. In particular embodiments, the body portion of the roller and the one or more blade portions may be integrally formed, i.e. form a unitary construction. At least one of the blade portions may comprise or may be provided with a hard facing material. The roller may comprise a fluid lubricated bearing. An inner circumferential surface of the body portion of the roller may comprise or define flutes and pads to create the fluid lubricated bearing. The pads may be sized to make a clearance running fit on the body portion of the sleeve. Beneficially, the pads may provide a bearing surface between the inside of the roller and the outside of the body portion of the sleeve. The flutes may facilitate flow of fluid, e.g. drilling mud or the like, to lubricate the bearing surface between the inside of the roller and the outside of the body portion of the sleeve. The roller may comprise one or more ports provided, e.g. formed, therein. The roller may comprise at least one port at a proximal end of the roller. This may facilitate entry of fluid, e.g. drilling mud or the like, to the flutes. In particular embodiments, the roller may comprise a plurality of ports at the proximal end of the roller. The ports may be circumferentially arranged and / or spaced. The roller may comprise at least one port at a distal end of the roller. This may facilitate exit of fluid, e.g. drilling mud or the like, from the flutes. In particular embodiments, the roller may comprise a plurality of ports at the distal end of the roller. The ports may be circumferentially arranged and / or spaced. The roller may comprise a first, e.g. proximal, end surface. The first, e.g. proximal, end surface may define a thrust bearing surface. The first, e.g. proximal, end surface may define or may be provided with a honed and / or hard faced surface or material capable of withstanding the thrust loads exerted thereon. The roller may comprise a second, e.g. distal, end surface. The second, e.g. distal, end surface may define a thrust bearing surface. The second, e.g. distal, end surface may define or may be provided with a honed and / or hard faced surface or material capable of withstanding the thrust loads exerted thereon. According to a third aspect, there is a provided a downhole traction apparatus comprising: a body; one or more of the downhole traction members of the second aspect. In particular embodiments, the downhole traction apparatus may comprise a plurality of the traction members, e.g. 6 traction members. The body of the downhole traction apparatus may comprise a first alignment profile for engaging in the second alignment profile of the sleeve. The first alignment profile of the body of the downhole traction apparatus may be formed in an end wall of the recessed journal or in an end ring coupled or formed on the body of the downhole traction apparatus. The body of the downhole traction apparatus may comprise a second alignment profile for receiving the first alignment profile of the sleeve. The second alignment profile of the body of the downhole traction apparatus may be formed in an end wall of the recessed journal or in an end ring coupled or formed on the body of the downhole traction apparatus. The first alignment profile of the body of the downhole traction apparatus and the second alignment profile of the body of the downhole traction apparatus may take any suitable form, provided they allow for co-operating engagement with the associated profiles of the adjacent sleeve. In particular embodiments, the first alignment profile of the body of the downhole traction apparatus comprises or takes the form of an alignment flat. In particular embodiments, the second alignment profile of the body of the downhole traction apparatus comprises or takes the form of an alignment recess. According to a fourth aspect, there is provided a downhole tool comprising one or more of the downhole traction apparatus according to the third aspect. According to a fifth aspect, there is provided a method of downhole traction using the downhole traction apparatus of the third aspect. As described above, the sleeve facilitates the creation of a traction member with reduced complexity and / or number of parts in comparison to previous apparatus’. This reduced complexity and / or number of parts in turn simplifies manufacture, permitting the traction member to be formed using simpler and / or more cost effective conventional manufacturing techniques and / or facilitates the manufacture of the sleeve using advanced manufacturing techniques such as additive manufacturing. According to a sixth aspect, there is provided a sleeve according to the first aspect, a downhole traction member according to the second aspect, a downhole traction apparatus according to the third aspect, or a downhole tool according to the fourth aspect, wherein at least part of one of the sleeve, traction member, traction apparatus or downhole tool is manufactured using a casting process, in particular investment casting. According to a seventh aspect, there is provided a sleeve according to the first aspect, a downhole traction member according to the second aspect, a downhole traction apparatus according to the third aspect, or a downhole tool according to the fourth aspect, wherein at least part of one of the sleeve, traction member, traction apparatus or downhole tool is manufactured using an additive manufacturing process. The sleeve, traction member or downhole traction apparatus, or any aspect defined herein, or any individual component or groups of components, may be manufactured in any suitable manner. In some examples the disclosed sleeve, traction member or downhole traction apparatus, or any individual component or groups of components may be manufactured by additive manufacturing. Such described additive manufacturing typically involves processes in which components are fabricated based on three-dimensional (3D) information, for example a three-dimensional computer model (or design file), of the component. Accordingly, examples described herein not only include the sleeve, traction member or downhole traction apparatus and associated components, but also methods of manufacturing the apparatus or associated components via additive manufacturing and computer software, firmware or hardware for controlling the manufacture of the apparatus and associated components via additive manufacturing. All future reference to “product” are understood to include the described sleeve, traction member or downhole traction apparatus and all associated components. The structure of the product may be represented digitally in the form of a design file. A design file, or computer aided design (CAD) file, is a configuration file that encodes one or more of the surface or volumetric configuration of the shape of the product. That is, a design file represents the geometrical arrangement or shape of the product. Design files may take any now known or later developed file format. For example, design files may be in the Stereolithography or “Standard Tessellation Language” (.stl) format which was created for stereolithography CAD programs of 3D Systems, or the Additive Manufacturing File (.amf) format, which is an American Society of Mechanical Engineers (ASME) standard that is an extensible markuplanguage (XML) based format designed to allow any CAD software to describe the shape and composition of any three-dimensional object to be fabricated on any additive manufacturing printer. Further examples of design file formats include AutoCAD (.dwg) files, Blender (.blend) files, Parasolid (,x_t) files, 3D Manufacturing Format (,3mf) files, Autodesk (3ds) files, Collada (.dae) files and Wavefront (.obj) files, although many other file formats exist. Design files may be produced using modelling (e.g. CAD modelling) software and / or through scanning the surface of a product to measure the surface configuration of the product. Once obtained, a design file may be converted into a set of computer executable instructions that, once executed by a processer, cause the processor to control an additive manufacturing apparatus to produce a product according to the geometrical arrangement specified in the design file. The conversion may convert the design file into slices or layers that are to be formed sequentially by the additive manufacturing apparatus. The instructions (otherwise known as geometric code or “G-code”) may be calibrated to the specific additive manufacturing apparatus and may specify the precise location and amount of material that is to be formed at each stage in the manufacturing process. The formation may be through deposition, through sintering, or through any other form of additive manufacturing method. The code or instructions may be translated between different formats, converted into a set of data signals and transmitted, received as a set of data signals and converted to code, stored, etc., as necessary. The instructions may be an input to the additive manufacturing system and may come from a part designer, an intellectual property (IP) provider, a design company, the operator or owner of the additive manufacturing system, or from other sources. An additive manufacturing system may execute the instructions to fabricate the product using any of the technologies or methods disclosed herein. Design files or computer executable instructions may be stored in a (transitory or non-transitory) computer readable storage medium (e.g., memory, storage system, etc.) storing code, or computer readable instructions, representative of the product to be produced. As noted, the code or computer readable instructions defining the product that may be used to physically generate the object, upon execution of the code or instructions by an additive manufacturing system. For example, the instructions may include a precisely defined 3D model of the product and may be generated from any of a large variety of well-known computer aided design (CAD) software systems such as AutoCAD®, TurboCAD®, DesignCAD 3D Max, etc. Alternatively, a model or prototype of the component may be scanned to determine the three-dimensional information of the component. Accordingly, by controlling an additive manufacturing apparatus according to the computer executable instructions, the additive manufacturing apparatus may be instructed to print out the product. In light of the above, embodiments include methods of manufacture via additive manufacturing. This includes the steps of obtaining a design file representing the product and instructing an additive manufacturing apparatus to manufacture the product in assembled or unassembled form according to the design file. The additive manufacturing apparatus may include a processor that is configured to automatically convert the design file into computer executable instructions for controlling the manufacture of the product. In these embodiments, the design file itself may automatically cause the production of the product once input into the additive manufacturing device. Accordingly, in this embodiment, the design file itself may be considered computer executable instructions that cause the additive manufacturing apparatus to manufacture the product. Alternatively, the design file may be converted into instructions by an external computing system, with the resulting computer executable instructions being provided to the additive manufacturing device. Given the above, the design and manufacture of implementations of the subject matter and the operations described in this specification may be realised using digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. For instance, hardware may include processors, microprocessors, electronic circuitry, electronic components, integrated circuits, etc. Implementations of the subject matter described in this disclosure may be realised using one or more computer programs, i.e., one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions may be encoded on an artificially generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium may be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium may be a source or destination of computer program instructions encoded in an artificially generated propagated signal. The computer storage medium may also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices). Although additive manufacturing technology is described herein as enabling fabrication of complex objects by building objects point-by-point, layer-by-layer, typically in a vertical direction, other methods of fabrication are possible and within the scope of the present subject matter. For example, although the discussion herein refers to the addition of material to form successive layers, one skilled in the art will appreciate that the methods and structures disclosed herein may be practiced with any additive manufacturing technique or other manufacturing technology. The invention is defined by the appended claims. However, for the purposes of the present disclosure it will be understood that any of the features defined above or described below may be utilised in isolation or in combination. For example, features described above in relation to one of the above aspects or below in relation to the detailed description may be utilised in any other aspect, or together form a new aspect. BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects will now be described with reference to the accompanying drawings, of which: Figure 1 shows a perspective view of a downhole tool according to the present disclosure; Figure 2 shows a perspective view of a downhole traction apparatus shown in Figure 1; Figure 3 shows a perspective view of the downhole traction apparatus shown in Figure 2, with several traction members removed for clarity; Figure 4 shows a perspective view of a traction member of the downhole traction apparatus shown in Figure 2; Figures 5 to 12 show a sleeve of the downhole traction member shown in Figure 4; and Figure 13 shows a roller of the downhole traction member shown in Figure 4. DETAILED DESCRIPTION OF THE DRAWINGS Referring first to Figure 1 of the accompanying drawings, there is shown a downhole tool, generally denoted 10. The downhole tool 10 forms part of a downhole tubing string S (such as a drill string for drilling a borehole or a downhole completion string for completing a pre-drilled borehole) and is configured for running into a borehole B. As shown in Figure 1, the downhole tool 10 comprises a top sub 12 and a downhole traction apparatus 14. The downhole traction apparatus 14 is configured and / or operable to provide downhole traction, torque reduction, thrust and / or wear protection in the drilling and / or completion of horizontal boreholes. Figures 2 and 3 of the accompanying drawings shows the downhole traction apparatus 14 in isolation. As shown in Figures 2 and 3, the apparatus 14 comprises a body 16 which in the illustrated apparatus 14 comprises or take the form of a mandrel. A threaded pin connector 18 is provided at a first end 20 of the body 16 (which in use defines an uphole end of the apparatus 14) and a threaded box connector 22 is provided at a second end 24 of the body 16 (which in use defines a downhole end of the apparatus 14). The threaded pin connector 18 and threaded box connector 22 facilitate connection between the ends 20, 24 of the body 16 and the tubing string S. It will be understood that the apparatus 14 may alternatively comprise at a box connector at its uphole end and a pin connector at its downhole end, pin connectors at both ends, box connectors at both ends, or other suitable connectors. A central throughbore 26 is provided in the body 16 and, in use, the throughbore 26 facilitates the flow of fluid and / or tooling through the apparatus 14. As shown in Figures 2 and 3, and referring also to Figure 4 of the accompanying drawings, the body 16 is configured to receive a plurality of traction members 28, the traction members 28 locatable on and around the body 16. An outer circumferential surface of the body 16 defines a journal portion 30 for receiving the traction members 28. In the illustrated apparatus 14, the journal portion 30 comprises or takes the form of a recessed journal portion, the body 16 comprising end rings 32, 34 at respective ends of the journal portion 30. The end rings 32, 34 defines thrust bearing surfaces 36,38 against which the tractions members 28 abut and through which thrust loads from the traction members 28 may be transmitted to the body 16. As shown, each traction member 28 comprises a sleeve 40 (shown and described below with reference in particular to Figures 4 to 11) and a roller 42 (shown and described below with reference in particular to Figure 12). As shown in Figures 4 to 11, the sleeve 40 is configured for location on and around the body 16 of the downhole traction apparatus 14, and comprises a body portion 44 and a head portion 46. The head portion 46 extends radially from said body portion 44. In the illustrated sleeve 40, the body portion 44 and the head portion 46 are integrally formed, i.e. form a unitary construction. The sleeve 40 further comprises an alignment arrangement, generally denoted 48. The alignment arrangement 48 comprises a first alignment profile 50 formed on the body portion 44 and a second alignment profile 52 formed on the head portion 46. In the illustrated sleeve 40, the first alignment profile 50 comprises or takes the form of an alignment flat, and the second alignment profile 52 comprises or takes the form of an alignment recess. The first alignment profile 50 is configured to engage a corresponding second alignment profile formed on an adjacent sleeve. The second alignment profile 52 is configured to engage a corresponding first alignment profile formed on another adjacent sleeve. Beneficially, the alignment arrangement 48 obviating the need for complex alignment mechanisms. The alignment arrangement 48 also permits the sleeve 40 to be located on the body 16, e.g. mandrel, of the downhole traction apparatus 14 in the correct orientation, obviating the need for complex alignment mechanisms between the sleeve 40 and the body 16. Moreover, the alignment arrangement 48 may also form a locking mechanism for rotationally securing the sleeves together. For example, by virtue of the alignment arrangement 48 providing a single orientation at which the first alignment profile 50 and the corresponding second alignment profile can be engaged, the alignment arrangement 48 obviates the risk that the sleeve 40 is assembled incorrectly. This in turn may facilitate more efficient manual assembly and / or facilitate automated, e.g. robotic, assembly. The sleeve 40 facilitates the creation of a traction member 28 with reduced complexity and / or number of parts in comparison to previous apparatus’. This reduced complexity and / or number of parts in turn simplifies manufacture, permitting the traction member 28 to be formed using simpler and / or more cost effective conventional manufacturing techniques and / or facilitates the manufacture of the sleeve 40 using advanced manufacturing techniques such as additive manufacturing. The illustrated sleeve 40 comprises both the first alignment profile 50 and the second alignment profile 52. Beneficially, this facilitates the installation of a plurality of the sleeves 40, with the alignment arrangement 48 ensuring that each sleeve 40 is oriented correctly. Moreover, providing the sleeve 40 with both the first alignment profile 50 and the second alignment profile 52 means that each sleeve 40 is identical to its neighbour, the only difference being that the sleeves 40 are oriented differently on the body 16 of the downhole traction apparatus 14 (the correct orientation being dictated by the alignment arrangement 48). This in turn simplifies manufacture and / or reduces the number of parts needed to form the downhole traction apparatus 14. As shown most clearly in Figure 4, the first alignment profile 50 and the second alignment profile 52 are circumferentially offset from each other. In the illustrated sleeve 40, the first alignment profile 50 and the second alignment profile 52 circumferentially offset from each other by 120 degrees. Beneficially, the alignment arrangement 48 permits a plurality of the sleeves 40 to be located on the body 16 of the downhole traction apparatus 14, the circumferential offset between the second alignment profile 52 (and thus when coupled to the first alignment profile of the adjacent sleeve) and the first alignment profile 50 (and thus, when coupled to the second alignment profile of the adjacent sleeve) permit the sleeves 40 to be accurately oriented relative to each other, so as to generate the desired axial traction force. As described above, the sleeve 40 is configured for location on and around a body 16, e.g. mandrel, of the downhole traction apparatus 14. The sleeve 40 comprises a throughbore 54 configured, e.g. sized and / or shaped, to facilitate location of the sleeve 40 on and around the body 16 of the downhole traction apparatus 14, more particularly around the journal portion 28. The body 16 of the downhole traction apparatus 14 comprises a first alignment profile for receiving the second alignment profile of the sleeve 40. The first alignment profile of the body 16 is formed in the end ring 32. The body 16 of the downhole traction apparatus 14 comprises a second alignment profile for engaging the first alignment profile 50 of the sleeve 40. The second alignment profile of the body 16 is formed in the end ring 34. It will be recognised that, in use, a first sleeve can be located on the body 16, e.g. mandrel, of the downhole traction apparatus 14 and engaged with the end ring 32 to orient and rotationally lock said first sleeve 40. Additional sleeves 40 can then be located on the body 16, the alignment arrangements 48 of each ensuring that the sleeves 40 are oriented correctly. A final sleeve 40 can be located on the body 16, and engage the end ring 34 to orient and rotationally lock said final sleeve 40 to the body 16. As shown, the sleeve 40 is configured to be offset and define a skew angle with respect to a central longitudinal axis X of the body 16. Beneficially, the provision of the offset ensures that each roller 40 will engage the wall of the borehole B e.g. the low side of the borehole B, whereas the skew angle facilitates the creation of the axial or longitudinal force on the sleeve 40 which in turn is transmitted to the body 16 of the downhole traction apparatus 14, thereby urging the downhole traction apparatus 14 along the borehole B. It will be recognised that when a plurality of sleeves 38 are provided, the alignment arrangement 48 ensures that each sleeve 40 is oriented to engage the wall of the borehole B and generate the axial or longitudinal force in the desired sequence. As described above, the sleeve 40 comprises body portion 44 and head portion 46. The body portion 44 comprises or takes the form of a shank portion of the sleeve 40. The first alignment profile 50 is formed on an outer circumferential surface of the body portion 44. The first alignment profile 50 is formed at a distal end of the body portion 44. The head portion 46 comprises or takes the form of a flange portion 44. The second alignment profile 52 is formed on an inner circumferential surface of the head portion. The second alignment profile 52 is formed at a proximal end of the head portion 46. As shown most clearly in Figures 7 and 8, the head portion 46 comprises a first, e.g. proximal, end surface 56. The first, e.g. proximal, end surface 56 is oriented transverse to the central longitudinal axis X of the downhole traction apparatus 14. Beneficially, the provision of an end surface 56 which is oriented transverse to the central longitudinal axis X of the downhole traction apparatus 14 provides a datum point / plane for manufacture and / or assembly of the sleeve 40 and downhole traction apparatus 14, since this is known to be orthogonal to the body 16, e.g. mandrel. The first, e.g. proximal, end surface 56 defines a thrust bearing surface. In the illustrated sleeve 40, the first, e.g. proximal, end surface 56 defines or is provided with a honed and / or hard faced surface or material capable of withstanding the thrust loads exerted thereon. The head portion 46 comprises a second, distal, end surface 58. The second, e.g. distal, end surface 58 defines a thrust bearing surface. The second, e.g. distal, end surface 58 defines or is provided with a honed and / or hard faced surface or material capable of withstanding the thrust loads exerted thereon. Referring again to Figures 5 &6, for example, the sleeve 40 further comprises an abutment surface 57. The abutment surface 57 is provided, e.g. formed, inside the sleeve 40, more particularly the head portion 46 of the sleeve 40. The abutment surface 57 extends radially inwards, i.e. into the throughbore 54 of the sleeve 40. In the illustrated sleeve 40, the abutment surface 57 is oriented transverse to the central longitudinal axis X. In use, the abutment surface 57 is configured and / or operable to receive the distal end surface of the body portion 44 of the adjacent sleeve 40. Likewise, the distal end surface of the body portion 44 of the present sleeve 40 is configured and / or operable to engage an abutment surface 57 of the adjacent sleeve 40. Beneficially, the abutment surface(s) 57 may function to control the axial arrangement, e.g. spacing, of the sleeves 40, while also permitting a degree of float, e.g. due to thermal effects downhole. As described above, and referring now in particular to Figure 13 of the accompanying drawings, the roller 42 comprises a throughbore 58 configured, e.g. sized and / or shaped, to facilitate location of the roller 42 on and around the body portion 44 of the sleeve 40. The roller 42 is configured for location on an outer circumferential surface of the body portion 44. The body portion 44 of the sleeve 40 comprises or defines a journal portion 60 and the roller 42 is configured, e.g. sized and / or shaped, for location on the journal portion 60. As shown in Figure 12, the roller 42 comprises an annular body portion 62 and a plurality of blade portions 64. The blade portions 64 are circumferentially arranged and / or spaced around the body portion 62. Beneficially, the spacing between the blade portions 64 facilitates flow of fluid bypass around the outside of the roller 42 / between the roller 42 and the borehole B. The blade portions 64 extend axially and partially circumferentially with respect to the body portion 62 and / or a central longitudinal axis of the roller 42. In use, the blade portions 64 are configured and / or operable to engage the borehole B on rotation of the roller 42 around the sleeve 40. The roller 42 is constructed from a polymeric material. In particular, the roller 42 is constructed from an elastomeric material, and the illustrated roller 42 is constructed from HNBR. The body portion 62 of the roller 42 and the blade portions 64 are integrally formed, i.e. form a unitary construction. In the illustrated roller 42, the blade portions 64 comprise or are provided with a hard facing material. As shown in Figure 12, the roller 42 comprises a fluid lubricated bearing, generally denoted 66. An inner circumferential surface of the body portion 62 of the roller 42 comprises or define flutes 68 and pads 70 to create the fluid lubricated bearing 66. The pads 68 are sized to make a clearance running fit on the body portion 44 of the sleeve 40. Beneficially, the pads 70 provide a bearing surface between the inside of the roller 42 and the outside of the body portion 44 of the sleeve 40. The flutes 68 facilitate flow of fluid, e.g. drilling mud or the like, to lubricate the bearing surface between the inside of the roller 42 and the outside of the body portion 44 of the sleeve 40. The roller 42 further comprises ports 72 formed therein for facilitating entry of fluid, e.g. drilling mud or the like, to the flutes 68 and ports 74 formed therein for facilitating exit of the fluid, e.g. drilling mud or the like, from the flutes 68. 5 The roller 42 comprises a first, e.g. proximal, end surface 76 and a second, e.g. distal, end surface 78, the end surfaces 76, 78 defining thrust bearing surfaces. In the illustrated roller 42, the end surfaces 76, 78 define or are provided with a honed and / or hard faced surface or material capable of withstanding the thrust loads exerted thereon. 0 It will be understood that various modifications may be made without departing from the scope of the invention as defined in the claims.

Claims

1. A sleeve for a downhole traction apparatus, wherein the sleeve is configured for location on and around a body of the downhole traction apparatus, and comprises:a body portion;a head portion extending radially from said body portion; andan alignment arrangement integrally formed on the sleeve,wherein the alignment arrangement comprises at least one of:a first alignment profile formed on the body portion, wherein said first alignment profile is configured to engage a corresponding second alignment profile formed on an adjacent sleeve or on the body of the downhole traction apparatus; anda second alignment profile formed on the head portion, wherein said second alignment profile is configured to engage a corresponding first alignment profile formed on another adjacent sleeve or on the body of the downhole traction apparatus.

2. The sleeve of claim 1, wherein:the first alignment profile of the sleeve comprises or takes the form of an alignment flat; and / orthe second alignment profile of the sleeve comprises or takes the form of an alignment recess.

3. The sleeve of claim 1 or 2, wherein the first alignment profile and the second alignment profile are circumferentially offset from each other, e.g. 45 degrees, 60 degrees, 90 degrees, 120 degrees, 135 degrees, 180 degrees.

4. The sleeve of claim 3, wherein the first alignment profile and the second alignment profile are circumferentially offset from each other by 120 degrees.

5. The sleeve of any one of claims 1 to 4, wherein the sleeve is configured to be offset and / or define a skew angle with respect to a central longitudinal axis of the body of the downhole traction apparatus.

6. The sleeve of any preceding claim, wherein the first alignment profile is provided, e.g. formed, on an outer surface of the body portion.

7. The sleeve of any preceding claim, wherein the first alignment profile is provided, e.g. formed, at a distal end of the body portion.

8. The sleeve of any preceding claim, wherein the second alignment profile is provided, e.g. formed, on an inner surface of the head portion.

9. The sleeve of any preceding claim, wherein the second alignment profile is provided, e.g. formed, at a proximal end of the head portion.

10. The sleeve of any preceding claim, wherein the head portion comprises a first, proximal, end surface.

11. The sleeve of claim 10, wherein the first end surface is oriented transverse to the central longitudinal axis of the downhole traction apparatus.

12. The sleeve of claim 10 or 11, wherein the head portion comprises a second, distal, end surface and at least one of the first end surface and the second end surface defines a thrust bearing surface.

13. The sleeve of any preceding claim, wherein the sleeve comprises an abutment surface extend radially inwards, wherein the abutment surface is configured and / or operable to receive the distal end surface of the body portion of the adjacent sleeve.

14. The sleeve of claim 13, wherein the abutment surface is oriented transverse to the central longitudinal axis.

15. A downhole traction member for a downhole traction apparatus, the traction member comprising:the sleeve of any preceding claim; anda roller configured for location on and around the sleeve.

16. The traction member of claim 15, wherein the roller is configured for location on and around an outer circumferential surface of the body portion, the body portion of the roller being annular.

17. The traction member of claim 15 or 16, wherein the roller comprises a body portion and one or more blade portions.

18. The traction member of claim 17, wherein the body portion of the roller and the one or more blade portions are integrally formed.

19. The traction member of any one of claims 17 or 18, wherein the roller comprises a plurality of the blade portions.

20. The traction member of claim 19, wherein at least one of:the blade portions are circumferentially arranged and / or spaced;at least one of the blade portions extend axially and / or at least partially circumferentially with respect to the body portion and / or a central longitudinal axis of the roller.

21. The traction member of any one of claims 15 to 20, wherein the roller is constructed from a polymeric material.

22. The traction member of claim 21, wherein the roller may be constructed from an elastomeric material, e.g. HNBR.

23. The traction member of claim 17 to 22, wherein the roller comprises a fluid lubricated bearing, wherein an inner circumferential surface of the body portion of the roller comprise or defines flutes and pads to create the fluid lubricated bearing.

24. A downhole traction apparatus comprising:a body;one or more of the downhole traction members of any one of claims 15 to 23.

25. The traction apparatus of claim 24, comprising a plurality of the traction members.

26. The traction apparatus of claim 24 or 25, wherein at least one of:the body of the downhole traction apparatus comprises a second alignment profile for receiving the first alignment profile of a sleeve; andthe body of the downhole traction apparatus comprises a first alignment profile for engaging in the second alignment profile of a sleeve.

27. A downhole tool comprising one or more of the downhole traction apparatus of claim 24, 25 or 26.

28. A method of downhole traction using the downhole traction apparatus of claim 24 or the downhole tool of claim 27.

29. A sleeve according to any one of claims 1 to 14; a downhole traction member according to any one of claims 15 to 23; a downhole traction apparatus according to any one of claims 24 to 26; or a downhole tool according to claim 27,wherein at least part of one of the sleeve, traction member, traction apparatus or downhole tool is manufactured using a casting process, in particular an investment casting process.

30. A sleeve according to any one of claims 1 to 14; a downhole traction member according to any one of claims 15 to 23; a downhole traction apparatus according to any one of claims 24 to 26; or a downhole tool according to claim 27,wherein at least part of one of the sleeve, traction member, traction apparatus or downhole tool is manufactured using an additive manufacturing process.

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