DOWNHOLE APPARATUS

Abstract

A downhole apparatus (10; 10) for reducing rotational and linear friction between a downhole tool (100; 100) and/or a downhole tool string and the wall of a wellbore (B) includes an annular body portion (12; 12′) configured for location on a mandrel (102; 102′) of the downhole tool (102; 102′) and one or more rib portions (16; 16′) extending radially from the annular body portion (12; 12′), and configured to engage a wall of the wellbore (B), the annular body portion (12; 12′) and the one or more rib portions (16; 16′) are integrally formed. The annular body portion (12; 12′) is elastically reconfigurable between a first configuration in which the annular body portion (12; 12) defines a first inner diameter and a second configuration in which the annular body portion (12; 12′) defines a second inner diameter configuration, the second inner diameter being larger than the first inner diameter. The annular body portion (12; 12′) is elastically or plastically reconfigurable between the second configuration and a third configuration in which the annular body portion (12; 12) defines a third inner diameter, the third inner diameter being smaller than the second inner diameter.

Claims

1. A downhole apparatus for reducing rotational and linear friction between a downhole tool and/or a downhole tool string and a wall of a wellbore, comprising: an annular body portion configured for location on a mandrel of the downhole tool; one or more rib portions extending radially from the annular body portion, and configured to engage a wall of the wellbore; wherein the annular body portion and the one or more rib portions are integrally formed; wherein the annular body portion is elastically reconfigurable between a first configuration in which the annular body portion defines a first inner diameter and a second configuration in which the annular body portion defines a second inner diameter configuration, the second inner diameter being larger than the first inner diameter; and and wherein the annular body portion is elastically or plastically reconfigurable between the second configuration and a third configuration in which the annular body portion defines a third inner diameter, the third inner diameter being smaller than the second inner diameter.

2. The apparatus of claim 1, wherein the annular body portion and the one or more rib portions are formed from an elastomeric material, the elastomeric material selected from a group consisting of: silicone rubber, hydrogenated nitrile butadiene rubber (HNBR), a thermoplastic material, PEEK, PTFE, a fibre reinforced polymer plastic, and a non-metallic material.

3. (canceled)

4. (canceled)

5. (canceled)

6. (canceled)

7. The apparatus of claim 1, wherein the annular body portion is generally tubular in construction, the annular body portion defining an axial throughbore.

8. The apparatus of claim 1, comprising wherein the one or more rib portions comprises a plurality of rib portions.

9. The apparatus of claim 8, wherein areas of the annular body portion disposed between the rib portions define stretch zones facilitating the reconfiguration of the apparatus between the first, second and third configurations.

10. The apparatus of claim 1, wherein at least one of: an inner circumferential surface of the annular body portion defines a radial bearing surface; and the annular body portion includes at least one end wall that defines a thrust bearing surface.

11. (canceled)

12. The apparatus of claim 1, further comprising a fluid lubrication arrangement.

13. The apparatus of claim 12, wherein the fluid lubrication arrangement comprises one or more flutes formed in an inner circumferential surface of the annular body portion.

14. (canceled)

15. The apparatus of claim 12, wherein the annular body portion includes two end walls; and the fluid lubrication arrangement comprises one or more slots formed in the end walls of the annular body portion.

16. The apparatus of claim 15, wherein the fluid lubrication arrangement comprises one or more flutes formed in an inner circumferential surface of the annular body portion, wherein the one or more slots communicates with the one or more flutes, so as to provide means for entry and exit of fluid into the one or more flutes.

17. (canceled)

18. The apparatus of claim 1, comprising a reinforcing arrangement, the reinforcing arrangement comprising one or more reinforcing members.

19. The apparatus of claim 18, wherein the one or more reinforcing members are formed in or applied onto the annular body portion.

20. (canceled)

21. The apparatus of claim 18, wherein the one or more reinforcing members are constructed from a resin fibre composite material.

22. The apparatus of claim 18, wherein the reinforcing arrangement comprises one or more recessed grooves formed in the annular body portion.

23. The apparatus of claim 18, wherein the reinforcing arrangement comprises one or more locking bands.

24. The apparatus of claim 23, wherein the reinforcing arrangement comprises one or more recessed grooves formed in the annular body portion, and wherein the one or more locking bands are configured for location in respective recessed grooves of the one or more recessed grooves.

25. The apparatus of claim 23, wherein the one or more locking bands are formed from a composite material, the composite material selected from a group consisting of: a fibre reinforced composite, a fibre reinforced composite including aramid fibres, a fibre reinforced composite including Kevlar fibres, and a fibre reinforced composite including carbon fibres.

26. (canceled)

27. A downhole tool comprising: a mandrel; and a downhole apparatus according to claim 1.

28. The downhole tool of claim 27, wherein one or more upsets extend radially from the mandrel.

29. (canceled)

30. A downhole tool string comprising one or more of the downhole tool according to claim 27.

31. (canceled)

32. A method comprising using the downhole apparatus of claim 1 to reduce friction between the downhole tool and/or the downhole tool string and the wall of the wellbore.

33. A method of construction of the downhole tool of claim 27, comprising: providing a downhole apparatus according to claim 27; using an expander tool to elastically reconfigure the downhole apparatus from the first configuration in which the annular body portion defines the first inner diameter to the second configuration in which the annular body portion defines the second diameter configuration, the second inner diameter being larger than the first inner diameter; translating the downhole apparatus along the mandrel of the downhole tool in the second configuration; and elastically or plastically reconfiguring the annular body portion of the apparatus from the second configuration to the third configuration in which the annular body portion defines a third inner diameter, the third inner diameter being smaller than the second inner diameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0105] These and other aspects will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0106] FIG. 1 shows a perspective view of a downhole apparatus for reducing friction between a downhole tool and/or downhole tool string and the wall of a wellbore;

[0107] FIG. 2 shows a perspective view of a downhole tool comprising the downhole apparatus shown in FIG. 1;

[0108] FIG. 3 shows a perspective view of a mandrel of the downhole tool shown in FIG. 2, with friction-reducing apparatus removed;

[0109] FIG. 4 shows an exploded view of an assembly jig for constructing the downhole tool shown in FIG. 2;

[0110] FIG. 5 shows the downhole tool located on the assembly jig shown in FIG. 4;

[0111] FIG. 6 shows a perspective view of an expander tool of the assembly jig shown in FIGS. 4 and 5;

[0112] FIG. 7 shows a pushing tool of the assembly jig;

[0113] FIG. 8 shows a part-sectional view of an alternative downhole apparatus for reducing friction between a downhole tool and/or downhole tool string and the wall of a wellbore

[0114] FIG. 9 shows a perspective view of a downhole tool comprising the downhole apparatus shown in FIG. 8;

[0115] FIG. 10 shows an arrangement for locating reinforcement members on the friction-reducing apparatus of the downhole tool shown in FIG. 9; and

[0116] FIG. 11 shows a tool string comprising a plurality of the downhole tools shown in FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS

[0117] Referring first to FIG. 1 of the accompanying drawings, there is shown a downhole apparatus 10 for reducing friction between a downhole tool 100 and/or downhole tool string and the wall of a well borehole (“wellbore”) B.

[0118] In use, the downhole apparatus 10 takes the form of a bearing sleeve configured for location on a body or mandrel 102 (shown in FIGS. 2 and 3) of the downhole tool 100, the apparatus 10 functioning to reduce friction between the downhole tool 100 and the wall of the wellbore B. The downhole tool 100 forms part of a downhole tool string, the apparatus 10 and downhole tool 100 functioning to reduce friction between the downhole tool string and the wall of the wellbore B during ingress into and/or egress out of the wellbore B. In particular, but not exclusively, the downhole tool string may take the form of a drill string used to drill the wellbore B, but may alternatively take the form of a completion string, work string or the like. It will be understood that in the context of the present disclosure the term wellbore B is used to mean either or both of a section of the wellbore B lined with bore-lining tubulars (“cased”) or an open hole section of the wellbore B.

[0119] The apparatus 10 is configured, amongst other things by virtue of its construction and materials, to reduce rotational friction effects between the tool string and the wall of the wellbore B during rotational movement of the apparatus 10, downhole tool 100 and/or downhole tool string are rotating but also reduce linear frictional effects during linear movement of the apparatus 10, downhole tool 100 and/or downhole tool string.

[0120] As shown in FIG. 1, the apparatus 10 comprises an annular body portion 12 which is generally tubular in construction, the body portion 12 defining an axial throughbore 14 which facilitates location of the body portion 12 on the mandrel 102 of the downhole tool 100.

[0121] As will be described further below, the apparatus 10 is elastically reconfigurable between a first configuration in which the annular body portion 12 defines a first inner diameter and a second configuration in which the annular body portion 12 defines a second inner diameter configuration, the second inner diameter being larger than the first inner diameter. The apparatus 10 is also elastically or plastically reconfigurable between the second configuration and a third configuration in which the annular body portion 12 defines a third inner diameter, the third inner diameter being smaller than the second inner diameter.

[0122] In use, elastic reconfiguration of the apparatus 10 from the first configuration to the second configuration facilitates location of the apparatus 10 around, and along, the mandrel 102 of the downhole tool 100 while reconfiguration of the apparatus 10 from the second configuration to the third configuration facilitates location of the apparatus 10 on the mandrel 102 of the downhole tool 100.

[0123] A plurality of rib portions 16 extend radially from the annular body portion 12. In use, the rib portions 16 form blades which offset the downhole tool 100 from the wellbore B and facilitate fluid bypass around the outside of the annular body portion 12 in the annulus A between the apparatus 10 and the wellbore B.

[0124] In the illustrated apparatus 10, the body portion 12 and the rib portions 16 are integrally formed as a single piece construction.

[0125] As shown in FIG. 1, the rib portions 16 are parallel or substantially parallel with the longitudinal axis X of the apparatus 10 and have a curved profile whereby a central part 18 of the rib portions 16 extend radially further than end parts 20 of the rib portions 16.

[0126] However, it will be understood that the rib portions 16 may have other forms. For example, whereas in the illustrated apparatus 1 the rib portions 16 are parallel or substantially parallel with the longitudinal axis X of the apparatus 10, the rib portions 16 may alternatively extend at least partially circumferentially around the annular body portion 12, in particular but not exclusively in a spiral configuration or the like. Beneficially, extending at least partially circumferentially around the annular body portion 12 provides greater circumferential contact area with the wellbore B. While in the illustrated apparatus 10, the rib portions 16 are curved, one or more of the rib portions 16 may alternatively have sloped end parts and a central part which is parallel or substantially parallel with the longitudinal axis X of the apparatus 10.

[0127] As shown in FIG. 1, the areas 22 between rib portions 16 are of constant or substantially constant wall thickness and are approximately matched to the outer body diameters of the mandrel 102 of the downhole tool 100 such that when located on the mandrel 102 the areas 22 are flush or substantially flush with the mandrel 102.

[0128] As well as functioning to facilitate fluid bypass around the outside of the apparatus 10, the areas 22 function as stretch zones facilitating the reconfiguration of the apparatus 10 between the first, second and third configurations.

[0129] The apparatus 10 provides a number of benefits over conventional tools and equipment. For example, in contrast to conventional tools the apparatus 10 obviates the requirement for split sleeve designs which add to complexity, cost and increased risk of failure downhole, and which require service breaks in order to install. The provision of the annular body portion 12 also obviates the requirement to provide associated clamps and threaded components to hold the split sleeves together. The provision of the annular body portion 12 and one or more ribs 16 integrally formed from a non-metallic material, in particular but not exclusively an elastomeric material such as HNBR, a thermoplastic material, such as PEEK or PTFE or a fibre reinforced polymer plastic, means that in the unlikely event of loss in the wellbore B, the apparatus or parts thereof are readily drillable; in contrast to conventional tools which require metallic components which cannot be easily drilled using conventional drill bits and so risk leaving “junk” in the wellbore B. Moreover, the relatively low coefficient of friction of the material used to form the integrally formed annular body portion 12 and rib portions 16 reduces both rotational and linear friction, amongst other things improving drilling efficiency, reducing casing wear and increasing the potential length of high angle or horizontal ERD wellbores. The relatively low density of the integrally formed annular body portion 12 and rib portions 16. As the density of the material used to form the integrally formed annular body portion 12 and the rib portions 16 is low compared to steel, any material loss from the apparatus 10, should it occur, can be readily circulated out of the wellbore B.

[0130] In the illustrated apparatus 10, an inner circumferential surface 24 of the annular body portion 12 forms a radial bearing surface between the apparatus 10 and the mandrel 102 of the downhole tool 100. End walls 26 of the annular body portion 12 form thrust bearing surfaces between the apparatus 10 and the body 102 of the downhole tool 100.

[0131] As shown in FIG. 1, the apparatus 10 comprises a fluid lubrication arrangement comprising flutes 28 and slots 30. The flutes 28 are formed in the inner circumferential surface 24 of the annular body portion 12. The slots 30 are formed in the end walls 26 of the annular body portion 12 and communicate with the flutes 28, so as to provide means for entry and exit of fluid into the flutes 28. In use, the flutes 28 and slots 30 receive fluid, in particular but not exclusively drilling fluid, so as to lubricate and cool the radial bearing surfaces formed by the inner circumferential surface 24 as the mandrel 102 rotates relative to the annular body portion 12 of the apparatus 10 and the thrust bearing surfaces formed by the end walls 26.

[0132] The annular body portion 12 and rib portions 16, which form the unitary construction, are constructed from an elastomeric material suitable for use in the downhole environment. In the illustrated apparatus 10, the annular body portion 12 is formed from hydrogenated nitrile rubber (HNBR). However, it will be understood that the annular body portion 12 may be constructed from other elastomeric materials, such as silicone rubber or other polymeric materials that have sufficient elastic modulus and/or wear resistance for use in the downhole environment.

[0133] Referring now also to FIGS. 2 and 3 of the accompanying drawings, there is shown a downhole tool 100 comprising the apparatus 10. FIG. 2 shows the downhole tool 100 with the apparatus 10 located on the mandrel 102. FIG. 3 shows the mandrel 102 of the downhole tool 100 in isolation for ease of reference.

[0134] As shown in FIGS. 2 and 3, the mandrel 102 is generally tubular in construction having an axial throughbore 104 extending therethrough. The throughbore 104 facilitates the flow of drilling fluid and/or tools through the downhole tool 100. The mandrel 102 is constructed from thick wall tubing such as drill pipe or the like. The mandrel 102 takes the form of a sub and has a connection arrangement, generally denoted 106, to facilitate connection of the downhole tool 100 to adjacent components of downhole tool string 1000. In the illustrated apparatus, the connection arrangement 106 comprises a threaded pin connector 108 at a downhole end and threaded box connector 110 at an uphole end. The threaded pin and box connectors 108, 110 take the form of API (American Petroleum Institute) connectors. However, it will be understood that the connection arrangement 106 may alternatively comprise threaded pin connectors at both ends, threaded box connectors at both ends, a threaded pin connector at an uphole end and a threaded box connector at the downhole end. Alternatively, the connection arrangement 106 may take any other suitable form, such as premium connectors or the like.

[0135] As shown most clearly in FIG. 3 of the accompanying drawings, the mandrel 102 comprises a recess 112. The base 114 of the recess 112 defines a recessed bearing journal for the apparatus 10, while end faces 116 of the recess 112 define thrust bearing surfaces for the apparatus 10.

[0136] In the illustrated downhole tool 100, upsets 118 extend radially from the mandrel 102. The upsets 118 are disposed at respective ends of the recess 112 and provide an increased bearing area for the thrust bearing surfaces for a given size of tool and body design.

[0137] It will be understood, however, the mandrel 102 may alternatively define a cylindrical or substantially cylindrical outer surface without upsets. Beneficially, this provides a flush or substantially flush mandrel outer surface, which maximises the flow by area and minimises the effect on ECD (Equivalent Circulating Density) when running large numbers of the downhole tools in the wellbore B simultaneously.

[0138] An assembly and method for construction of the downhole tool 100 will now be described with reference to FIGS. 4 to 7 of the accompanying drawings.

[0139] Referring first to FIGS. 4 and 5 of the accompanying drawings, an assembly jig, generally denoted 200, is provided. As shown in FIG. 4, the assembly jig 200 comprises a spigot assembly 202 including a base portion 204 and a spigot portion 206. The assembly jig 200 further comprises an expander tool in the form of a forcing cone 208.

[0140] As shown most clearly in FIG. 6, which shows an enlarged view of the forcing cone 208, the forcing cone 208 comprises a first portion 210, a second portion 212 and a third portion 214.

[0141] The first portion 210 is generally tubular in shape, having a throughbore 216. An end portion 218 (the lower end portion as shown in FIG. 5) of the throughbore 216 defines a female portion formed with a thread and/or enlarged bore to facilitate the coupling of the forcing cone 208 to the threaded pin connector 108 of the mandrel 102 as described further below. In the illustrated jig 200, the thread and/or enlarged bore is machined, although the thread and/or enlarged bore may alternatively be formed by any suitable process.

[0142] The second portion 212 of the forcing cone 208 is interposed between the first portion 210 and the third portion 214. As with the first portion 210, the second portion 212 has a throughbore 218. However, the second portion 212 is generally frusto-conical in shape. The second portion 212 facilitates the expansion of the apparatus 10 to the second configuration as will be described further below.

[0143] The third portion 214 is generally tubular in shape, having a throughbore 220. The outer diameter of the third portion 214 matches or is slightly greater in diameter than the outside diameter of the mandrel 102. The third portion 214 comprises cross drilled bores 222, which in the illustrated jig 200 is formed—in particular but not exclusively machined, at 90 degrees to the throughbore 220. The bores 222 facilitate the handling of the forcing cone 208 as will be described further below.

[0144] In use, the method of construction comprises locating the forcing cone 208 on the mandrel 102 of the downhole tool 100, and making up the connection between the threaded pin connector 108 of the mandrel 102 and the end portion 218 of the first portion 210 of the forcing cone 208. Once secured, the forcing cone 208 and mandrel 102 form an assembly which can be handled via the bores 222 using a lifting device 224 (shown in FIG. 7).

[0145] The forcing cone 208 and mandrel 102 are placed on the spigot portion 206 of the assembly jig 200.

[0146] The apparatus 10 in its first configuration is then located on the third portion 214 of the forcing cone 208. In the illustrated assembly jig 200, the forcing cone coated in a grease oil or a soap solution to ease the expansion of the apparatus 10 from its first configuration to its second configuration.

[0147] Referring now to FIG. 7 of the accompanying drawings, the assembly jig 200 further comprises a pushing tool 226. In the illustrated jig 200, the pushing tool 226 takes the form of a collet fingered pushing tool having a number of circumferentially arranged collet fingers 228, a mass 230 and a handle 232 to facilitate handling of the pushing tool 226 by the lifting device 224.

[0148] In use, the pushing tool 226 is manipulated into position above the forcing cone 208 and lowered into engagement with the apparatus 10, the weight force of the mass 230 urging the collet fingers 228 to translate the apparatus 10 along the forcing cone 208. As the apparatus 10 is translated up the frusto-conical second portion 212 of the forcing cone 208, the apparatus 10 is expanded from its first configuration to its second configuration of greater inner diameter than the first configuration.

[0149] As the forcing cone 208 is coupled to the mandrel 102, the pushing tool 226 translates the apparatus 10, now in its second, larger diameter, configuration, along the mandrel 102 and into the recess 112, as shown in FIG. 2.

[0150] On location on the recess 112, the apparatus 10 elastically recovers, contracting to its third configuration, the third configuration being the same or similar to that of the first configuration the apparatus 10 defined before being elastically expanded.

[0151] The throughbore 14 and the length of the annular body portion 12 of the apparatus 10 are configured so that in the third configuration the apparatus 10 has sufficient diametric and end float clearance to run effectively as a mud lubricated bearing.

[0152] It will be understood that various modifications may be made without departing from the scope of the invention as defined in the claims.

[0153] For example, referring now to FIG. 8 of the accompanying drawings, there is shown an alternative apparatus 10′ for reducing friction between a downhole tool 100′ and/or downhole tool string and the wall of a well borehole (“wellbore B”). The apparatus 10′ is similar to the apparatus 10 and like components are represented by like reference signs.

[0154] In use, the downhole apparatus 10′ takes the form of a bearing sleeve configured for location on a body or mandrel 102′ of the downhole tool 100′, the apparatus 10′ functioning to reduce friction between the downhole tool 100 and the wall of the wellbore B. The downhole tool 100′ forms part of a downhole tool string, the apparatus 10′ and downhole tool 100′ functioning to reduce friction between the downhole tool string and the wall of the wellbore B during ingress into and/or egress out of the wellbore B. In particular, but not exclusively, the downhole tool string may take the form of a drill string used to drill the wellbore B, but may alternatively take the form of a completion string, work string or the like. It will be understood that in the context of the present disclosure the term wellbore B is used to mean either or both of a cased section of the wellbore B or open hole section of the wellbore B.

[0155] As shown in FIG. 8, like the apparatus 10, the apparatus 10′ comprises an annular body portion 12′ which is generally tubular in construction, the body portion 12′ defining an axial throughbore 14′ which facilitates location of the body portion 12′ on the mandrel 102′ of the downhole tool 100′.

[0156] A plurality of rib portions 16′ extend radially from the annular body portion 12′. In use, the rib portions 16′ form blades which offset the downhole tool 100′ from the wellbore B and facilitate fluid bypass around the outside of the annular body portion 12′ in the annulus A between the apparatus 10′ and the wellbore B. The body portion 12′ and the rib portions 16′ are integrally formed as a single piece construction.

[0157] While the downhole tool 100 provides a robust and simple tool, fit for use in downhole oilfield conditions, the apparatus 10′ a secondary security and failsafe arrangement as will be described below.

[0158] In the apparatus 10′, the annular body portion 12′ comprises one or more stiffening or reinforcing members 32′ moulded therein. While in the illustrated apparatus 10′, the reinforcing members 32′ are moulded within the annular body portion 12, one or more of the reinforcing members 32′ may alternatively be applied onto the annular body portion 12′.

[0159] In the illustrated apparatus 10′, the one or more stiffening or reinforcing members 32′ take the form of resin fibre composite bars. However, it will be understood that the stiffening or reinforcing members 32′ may take other suitable forms and may be constructed from other suitable materials such as carbon fibre reinforced composite or basalt fibre reinforce composite.

[0160] In use, the reinforcing members 32′ prevent or at least mitigate the possibility of compressive buckling of the apparatus 10′ and/or swelling when being pulled through a wellbore B restriction.

[0161] As shown in FIG. 8, the annular body portion 12′ of the apparatus 10′ comprises recessed grooves 34′ for receiving locking bands 36′. In the illustrated apparatus 10′, the recessed grooves 34′ are formed into the top and bottom sections of the annular body portion 12′ at the moulding stage.

[0162] The locking bands 36′ are formed from a composite material. In the illustrated apparatus 10′ the locking bands 36′ are formed from a fibre reinforced composite including aramid fibres such as Kevlar. However, it will be understood that the locking bands 36′ may alternatively be formed from other suitable materials, such as a fibre reinforced composite including carbon fibres or other high strength fibre. The locking bands 36′ are bonded in place by a flexible elastomeric silicone, rubber or epoxy based resin or compound.

[0163] Referring now also to FIG. 9 of the accompanying drawings, there is shown a downhole 100′ comprising the apparatus 10′. FIG. 9 shows the downhole tool 100′ with the apparatus 10′ located on the mandrel 102′. FIG. 10 shows the mandrel 102′ of the downhole tool 100′ in isolation for ease of reference.

[0164] The mandrel 102′ is generally tubular in construction having an axial throughbore 104′ extending therethrough. The throughbore 104′ facilitates the flow of drilling fluid and/or tools through the downhole tool 100′. The mandrel 102′ is constructed from thick wall tubing such as drill pipe or the like. The mandrel 102′ takes the form of a sub and has a connection arrangement, generally denoted 106′, to facilitate connection of the downhole tool 100′ to adjacent components of downhole tool string 1000. In the illustrated downhole tool 100′, the connection arrangement 106′ comprises a threaded pin connector 108′ at a downhole end and threaded box connector 110′ (shown in hidden line) at an uphole end. The threaded pin and box connectors 108′, 110′ take the form of API (American Petroleum Institute) connectors. However, it will be understood that the connection arrangement 106′ may alternatively comprise threaded pin connectors at both ends, threaded box connectors at both ends, a threaded pin connector at an uphole end and a threaded box connector at the downhole end. Alternatively, the connection arrangement 106′ may take any other suitable form, such as premium connectors or the like.

[0165] The mandrel 102′ comprises a recess 112′. Although not shown, the base of the recess 112′ defines a recessed bearing journal for the apparatus 10′, while end faces of the recess 112 define thrust bearing surfaces for the apparatus 10′ in a similar manner to that shown and described above with respect to the apparatus 10.

[0166] An assembly and method for construction of the downhole tool 100′ will now be described with reference to FIG. 10 of the accompanying drawings.

[0167] As shown in FIG. 10, the downhole tool 100′ is located on a rotary base 234, the rotary base 234 providing a means of rotating the tool 100′ for the purpose of winding the pre-coated aramid fibre, e.g. Kevlar, yarn 236 from a reel or bobbin 238 via a resin or elastomer coating system 240 into the preformed recessed grooves 34′ to form the composite locking band 36′. It will be understood that this operation could alternatively be achieved with the use of a purpose built winding head or horizontally on a lathe or other similar rotating system. Where provided, the reinforcing members 32′ may be further locked in position by the application of the reinforcing members 32′.

[0168] As described above, various modifications may be made without departing from the scope of the invention as defined in the claims.

[0169] For example, while the assembly method described above is a mass based pushing system, it could also be achieved vertically or horizontally by means of hydraulic ram type pushing systems.

[0170] It should be noted that more than one apparatus per body could also be mounted in the same way and that these apparatus, though concentric to the axis of the mandrel may also be mounted in to recessed bearing journal or journals which may be offset and/or skewed with respect to the longitudinal axis of the mandrel 102.

[0171] As described above, the downhole tool may form part of a downhole tool string, the downhole tool functioning to reduce friction between the downhole tool string and the wall of the wellbore during ingress into and/or egress out of the wellbore. In particular, but not exclusively, the downhole tool string may take the form of a drill string used to drill the wellbore, but may alternatively take the form of a completion string, work string or the like. It will be understood that in the context of the present disclosure the term wellbore is used to mean either or both of a cased section of the wellbore or open hole section of the wellbore.

[0172] FIG. 11 shows a downhole tool string 1000 comprising a plurality of the downhole tools 100 shown in FIG. 2. While the illustrated downhole tool string 1000 comprises a number of the downhole tools 100, it will e recognised that the downhole tool string 1000 may alternatively or additionally comprise one or more of the downhole tools 100′.