GB2431664A

GB2431664A - Wear resistant downhole tool

Info

Publication number: GB2431664A
Application number: GB0620922A
Authority: GB
Inventors: Grant Stewart; Craig Stewart
Original assignee: Stable Services Ltd
Current assignee: Stable Services Ltd
Priority date: 2005-10-21
Filing date: 2006-10-23
Publication date: 2007-05-02
Also published as: GB0521478D0; GB2431664A8; GB0620922D0

Abstract

A method and apparatus for forming a wear resistant surface on a tool is described. The method comprises the steps of combining a bonding agent with an abrasive grit and curing the bonding agent about a support structure to form the wear resistant surface. The bonding agent may be a curable epoxy resin, and the support structure may comprise a woven fibre material and/or a plurality of tungsten carbide bricks. The method has particular application to downhole apparatus such as drill pipe section 14 or stabilisers.

Description

1 Improvements to wear resistance 3 The present invention relates to

improvements to wear 4 resistance. In particular, the invention relates to a method of forming a wear resistant surface suitable for 6 downhole tooJs used in the drilling and construction of 7 oil and gas wells. In another of its aspects, the 8 invention relates to tools with wear resistance surfaces 9 formed thereon. :10

11 Apparatus and equipment used downhole, such as drilling 12 equipment, is subject to wear during running and 13 operation. The wear is caused by frictional contact with 14 casing, liner or the borehole itself. it is known to provide welibore equipment with wear resistant portions 16 to increase the working lifetime of the equipment. On 17 drill pipe, these wear resistant regions are referred to 18 as hard-banding, and typically comprise strips extending 19 around the circumference of parts of the drill pipe. The hard-banding is built up from chromium-based material 21 welded onto portions of the drill pipe, which will 22 typically the box section of the drill pipe joint.

1 There are a number of problems associated with the 2 welding of hard-bandings on to downhole equipment. The 3 process is relatively time consuming and therefore 4 expensive, and associated with a number of practical and technical difficulties. For example, the drill pipe will 6 require requires pre-welding heat treatment and post- 7 welding heat treatment.

9 welding processes can in addition cause damage to the welibore apparatus. For example, the internal bore of 11 drill pipe will typically be provided with a coating of a 12 protective plastic material. It is necessary for this 13 plastic material to be applied to the apparatus after the 14 welding stages of the manufacturing process, as subsequent welding can affect the properties of the 1 1 2'- 18 Heating of the apparatus can have an effect on the 19 mechanical properties of the parent material. The heat :20 treatment can cause spalling or cracking of the 21 apparatus, making non-destructive testing (NDT) of the 22 apparatus necessary in many cases. The welding process 23 may also affect the magnetic properties of the apparatus.

24 This is particularly significant when providing hard-banding on non-magnetic drill collars, which need to 26 retain their non-magnetic properties during use.

28 Furthermore, the welding process will also produce rough 29 weld beads and band ends. These rough surfaces must be machined or ground post-application to ensure that the 31 equipment does not damage casing or equipment used in 32 under-balanced drilling (UBD) snubbing operations.

1 Furthermore, some apparatus is non-weldable due to the 2 grades of materials used or structure of the apparatus.

3 For example, mother pipe extending between box and pin 4 sections of drill pipe will typically be made of. non-weldable material, such as S135 grade steel, precluding 6 the application of hard-banding to the mother pipe by 7 welding. Mother pipe of drill pipe can itself be subject 8 to wear, particularly when being run in deviated wells.

Hard-bandings on downhole equipment will wear during use 11 and will need to be repaired or reconditioned to extend 12 the working lifetime of the equipment. Wear on the 13 equipment will usually not be concentric with the 14 internal bore of the equipment and worn drill pipe will often have an eccentric outer surface. Welding processes 16 require careful delivery of welding materials at 17 controlled radial heights, and effective welding of the 18 hard banding onto an outer, eccentric surface is not 19 difficult due to variation in the radial height of the outer diameter of the equipment to be welded as it is 21 rotated on a chuck. Often, this will not permit welding 22 of a new layer of hard-banding without preliminary 23 machining or grinding of the outer surface to make it 24 concentric with the inner bore of the equipment. This introduces an additional processing step, and moreover 26 reduces the thickness, and thus mechanical strength, of 27 the equipment as the outer diameter is machined down.

29 Welding processes must be carried out in a specialised welding facility, by skilled technicians. Fumes and 31 chromium particles produced during the welding process 32 have a negative impact on the health and safety of 33 personnel in and around the welding facility, and have a 1 detrimental effect on the environment. Appropriate fume 2 extraction equipment is therefore necessary to meet 3 health and safety requirements.

welding units themselves are expensive pieces of 6 equipment, and the welding facilities will need to have 7 appropriate heating zones for pre-and post-weld 8 treatments. Where it is necessary to apply hard-bandings 9 to sections of heavy weight drill pipe (HWDP) intermediate to the box and pin sections, the welding 11 equipment and/or drill pipe can be difficult to 12 manipulate.

14 It is not practical to have such facilities at the drilling rig itself, and typically worn apparatus such as i drill pipe that requires reconditioning Will need to be 17 transported to a specific re-conditioning site onshore.

18 This causes significant time delays and expense as the 19 equipment is shipped to and from the repair workshop.

21 It is one aim of the invention toprovide a method of 22 applying a wear-resistant layer that obviates or 23 mitigates the disadvantages of prior art methods.

It is a further aim of the invention to provide an 26 alternative wear-resistant layer or material suitable for 27 application to downhole equipment.

29 It is a further aim of the invention to provide a method of applying a wear resistant layer to downhole equipment 31 without welding.

1 It is an aim of an embodiment of the invention to provide 2 a method of applying a wear resistant layer to downhole 3 equipment without heat treatment.

According to a first aspect of the invention there is 6 provided a method of forming a wear resistant surface on 7 a downhole apparatus, the method comprising the steps of: 8 -Combining a bonding agent with an abrasive grit; 9 -Curing the resin material about a support structure to form a wear resistant surface on the downhole 11 apparatus.

13 Preferably, the bonding agent is a curable resin material 14 such as an epoxy resin. More preferably, the curable resin material is a phenyl epoxy resin.

17 Preferably, the abrasive grit is selected from silicon 18 carbide, boron carbide and diamond.

Preferably, the support structure comprises plurality of 21 components and a plurality of interspaces. In one 22 embodiment, the support structure comprises a woven layer 23 of high strength fibre material. The high strength fibre 24 material may be a para-aramid fibre material. The high strength fibre material may be KEVLIAR .

27 Alternatively, or in addition, the support structure may 28 comprise a plurality of bricks of a material harder than 29 the material of the downhole tool. The support structure may comprise an arrangement of tungsten carbide bricks.

1 The bonding agent may encapsulate the support structure.

2 The resin material may form a network about and between 3 components of the support structure, via the interspaces.

The method may include the steps of: 6 -Applying the bonding agent to an area of the 7 downhole apparatus; 8 -Locating the support structure on the area of the 9 downhole apparatus.

11 The method may include the steps of: 12 -Applying the bonding agent to the high strength 13 fibre material; 14 -Applying the bonding agent to an area of the downhole apparatus; 16 -Locating the high strength fibre material on the 17 area of the downhole apparatus.

19 Preferably, the step of applying the bonding agent to the high strength fibre material involves saturating the high 21 strength fibre material with the curable resin.

23 The method may include the additional step of wrapping 24 the high strength fibre material around the downhole apparatus. The downhole apparatus may be rotated during 26 wrapping.

28 The method may include the step of providing multiple 29 layers of the high strength fibre material on the downhole apparatus. The method may include the step of 31 wrapping a length of the high strength fibre material 32 which exceeds the circumferential length of the downhole 1 apparatus such that multiple layers of the high strength 2 fibre material are provided on the downhole apparatus.

4 In an embodiment, the method includes the step of locating a plurality of bricks of a material harder than 6 the material of the downhole apparatus on the area to 7 which the resin has been applied.

9 The method may include the steps of: -Locating a layer of the high strength fibre material 11 on an area of the downhole apparatus; 12 -Locating bricks of a material harder than the 13 material of the downhole apparatus on the layer of 14 the high strength fibre material.

IC m1-.-. 1. i-i-..... j.... _.... t. ...i, J L.JL. LJ.LL LJ AL LL.L LLA.).L 1LIQLL.Li ILty 17 formed from discrete sections, smaller than the wear 18 resistant surface. The layer of the high strength fibre 19 material may be saturated with curable resin material prior to location of the bricks.

22 The method may include the step of applying curable resin 23 material to the layer of bricks.

In one embodiment, the method includes the step of 26 combining abrasive grit with the resin after it is 27 applied to the support structure.

29 Alternatively, or in addition, the method includes the step of premixing the abrasive grit with the curable 31 resin.

1 The method may include the additional step of applying a 2 force to the support structure.

4 The method may include the additional step of embedding abrasive grit into the support structure.

7 The method may include the additional step of curing the 8 resin by the application of heat. Alternatively the 9 resin may cure at room temperature.

11 According to a second aspect of the invention there is 12 provided downhole apparatus having a body and a wear 13 resistant surface formed on the body, wherein the wear 14 resistant surface is provided by the method of the first aspect of the invention.

17 According to a third aspect of the invention there is 18 provided downhole apparatus having a body and a wear 19 resistant portion formed on the body, wherein the wear resistant portion comprises a resin material combined 21 with an abrasive grit, and cured about a support 22 structure.

24 Preferably, the curable resin material is an epoxy resin.

More preferably, the curable resin material is a phenyl 26 epoxy resin.

28 Preferably, the abrasive grit is selected from silicon 29 carbide, boron carbide and diamond.

31 Preferably, the support structure comprises plurality of 32 components and a plurality of interspaces. In one 33 embodiment, the support structure comprises a woven layer 1 of high strength fibre material. The high strength fibre 2 material may be a para-aramid fibre material. The high 3 strength fibre material may be KEVLAR .

Alternatively, or in addition, the support structure may 6 comprise a plurality of bricks of a material harder than 7 the material of the downhole tool. The support structure 8 may comprise an arrangement of tungsten carbide bricks.

The resin material may encapsulate the support structure.

11 The resin material may form a network about and between 12 components of the support structure, via the interspaces.

14 The downhole apparatus may be drill pipe. The wear resistant portion may be formed on a box section of the 16 drill pipe. Alternatively, the wear resistant portion 17 may be formed on a mother pipe section of the drill pipe.

18 In a further alternative, the wear resistant portion is 19 formed on a stabiliser.

21 According to a fourth aspect of the invention, there is 22 provided a method of forming a wear resistant surface on 23 a tool, the method comprising the steps of: 24 -combining a curable resin material with an abrasive grit; 26 -Curing the resin material about a support structure *27 to form the wear resistant surface on the tool.

29 Although the present invention has particular application to the oil and gas industry, the tool need not be a 31 downhole tool.

1 According to a fifth aspect of the invention there is 2 provided apparatus for forming a wear resistant surface 3 on a tool, the apparatus comprising means for rotating 4 the tool to facilitate application of a support structure to the tool, means for applying an abrasive grit to the 6 support structure, and means for applying a force to the 7 support structure.

9 There will now be described, by way of example only, various embodiments of the invention with reference to 11 the following drawings, of which: 13 Figure 1 is a perspective view of a drill pipe box 14 section having a wear-resistant surface provided thereon in accordance with an embodiment of the 16 invention; 18 Figures 2a and 2b show schematically a method of 19 application of the wear-resistant surface to a drill pipe section; 22 Figure 3 shows a wear surface of a stabiliser on a 23 drill pipe section in a side view; Figure 4 shows schematically a support structure of 26 a wear resistant material on a blade of the 27 stabiliser in a plan view; 29 Figure 5 shows schematically the wear resistant material on the blade of the stabiliser in a cross- 31 sectional view.

1 Referring firstly to Figure 1, there is shown a drill 2 pipe section generally depicted at 10, comprising a box 3 section 11 and a mother pipe section 12. The box section 4 11 is provided with a band of wear-resistant material 14 extending circumferentially around the outer diameter of 6 the drill pipe 10. In this embodiment, the thickness of 7 the band is approximately 5-6mm and the width of the 8 strip is approximately 50 mm. The band of wear-resistant 9 material is formed from a combination of a cured phenyl epoxy resin material, mixed with a silicon carbide 11 abrasive grit material. The wear-resistant material also 12 includes a support structure in the form of a woven strip 13 of KEVLAR material, which is a high strength para-aramid 14 fibre material marketed by the DuPont companies. The resin is cured to encapsulate the strip. In addition, 16 the resin fills interspaces between fibres of the woven 17 strip.

19 In combination, the support structure, the resin and the abrasive grit form a hard, wear-resistant material which 21 protects the drill pipe from wear during running and 22 operation.

24 Figure 2 shows schematically how the wear-resistant material is applied to the drill pipe in an embodiment of 26 the invention. The drill pipe 10 is shown in cross- 27 section, and is mounted on a chuck 16 which allows 28 rotation of the drill pipe about its longitudinal axis.

29 The area to which the wear-resistant material is to be applied is cleaned to remove contaminants such as grit, 31 dust or grease, and is dried before the materials are 32 applied.

1 The phenyl epoxy resin is applied to the surface of the 2 drill pipe in the bonding area, about the entire 3 circumference of the drill pipe to form a coated layer 4 17.

6 A strip 18 of woven KEVLAR material, formed to pre- 7 determined size, is soaked in phenyl epoxy resin until 8 the strip is saturated. The properties of the material 9 are such that it is advantageous if the strip is woven to the size required, so that cutting is not required.

11 Typically, the strip will have a width of approximately 12 25mm, 50mm or 75mm, although the size will be selected 13 depending on the application. The length of the strip 14 will be selected to form a pre-determined number of layers of material on the drill pipe as the material is 16 wound or wrapped on. Typically, the length will be 17 selected such that a single strip can be wound around the 18 drill pipe 2 to 5 times, but in a preferred embodiment 3 19 to 4 wraps are provided.

21 The strip 18 is fed manually onto the coated area 17 and 22 the drill pipe is rotated (clockwise in this example) on 23 the chuck 14. As the drill pipe rotates, the strip 18 is 24 wound onto the drill pipe. A compression wheel 20 applies a pressure to the outer surface of the strip 18 26 to assist in fixing to the drill pipe. The compression 27 wheel provides a pressure of approximately 50 to 60 PSI.

29 As the strip passes around the drill pipe, the abrasive grit 22 is gravity fed from an applicator 23 onto the 31 outer surface of the first wound layer of the strip. The 32 drill pipe continues to rotate as the strip is manually 33 fed, until the strip begins to form a second layer 24 of 1 material on top of the first. The compression wheel 20 2 applies pressure to the second layer of the strip 18, 3 forcing the layers of the strip together and embedding 4 the abrasive grit 22 therebetween. The woven structure of the KEVLAR material is such that the compression 6 wheel 20 forces the grit into the interspaces between 7 fibres, thus impregnating the support structure.

9 The process continues until the entire length of the strip is bonded to the drill pipe. A final layer of 11 phenyl epoxy resin is applied to the outer surface of the 12 strip and the resulting band of material is allowed to 13 cure.

Variations to the above described methoi envisaged, 16 and are within the scope of the invention.

18 For example, the positions of the compression wheel and 19 grit applicator can be interchanged, such that the compression wheel provides a pressure to the surface of 21 the strip to which grit has been applied. That is, the 22 compression wheel provides a force direct on the grit, 23 embedding it into the woven material. Multiple grit 24 applicators in different positions could be provided.

26 The abrasive grit may be mixed with the bonding agent 27 prior to its application to the drill pipe or the woven 28 strip. Additional abrasive grit may be combined with the 29 bonding agent during application of the material to the drill pipe.

32 It will be appreciated that the method described above is 33 applicable to tools other than drill pipe.

2 Figures 3 to 5 show an alternative embodiment of the 3 invention, wherein the support structure of the wear- 4 resistant layer differs from that in Figure 2.

6 Figure 3 is a perspective view of a drill pipe stabiliser 7 30 having a wear surface 31 on a stabiliser blade 32.

8 Figure 4 is a plan view of the wear surface 31, showing a 9 wear resistance layer in schematic form. Figure 5 is a cross-sectional view through the same blade 32.

12 The wear-resistant layer comprises a bonding agent 33 and 13 a support structure made up of sections 34 of KEVLAR 14 material. By providing the KEVLAR material in discrete sections, in the event that a corner of one of the 16 sections is caught and begins to peel away from the 17 downhole tool, the entire wear resistant portion will not 18 be removed. Rather, only the portion directly above and 19 around the discrete section of KEVLAR material will be at risk.

22 As with the previous embodiments, the bonding agent is a 23 curable phenyl epoxy resin, and is combined with an 24 abrasive grit such as silicon carbide.

26 The support structure also comprises a plurality of 27 substantially cuboidal bricks 36 of hard material, which 28 in this example is tungsten carbide. The tungsten 29 carbide bricks 36 are arranged in a two-dimensional array, which need not be ordered. The bricks 36 are 31 provided over the sections of KEVLAR material, although 32 in Figure 4, not all of the bricks are shown in order to 33 reveal other components. The bricks in this example have 1 dimensions of approximately 13mm length, 5mm width and 2 3mm depth.

4 To apply the wear resistant layer, the following method can be used. Firstly, the surface of the stabiliser 6 blades is cleaned, and a coating of the bonding agent 33 7 is applied to an area 37 of the blade. Sections 34 are 8 saturated with the bonding agent 33, and located on the 9 coated area 37. A further layer of bonding agent is applied over the sections 34, and the bricks 36 are 11 arranged over the sections 34. Further coatings of the 12 bonding agent are applied over the bricks 36 to 13 encapsulate the structure.

The combination of a support structure in the form of 16 sections of KEVLAR material and bricks of tungsten 17 carbide with the bonding agent and abrasive material 18 provides a wear resistant coating suitable for 19 application to a wide variety of tools, not restricted to downhole tools for the oil and gas industry.

22 In an alternative embodiment to the one shown in Figures 23 3 to 5, the support structure does not contain a layer of 24 KEVLAR material, and the tungsten carbide bricks form the support structure on the bonding agent layer 37.

27 Various different abrasive grits could be used for the 28 methods and applications described above. For example, 29 the grit could be silicon carbide, boron carbide or industrial diamond granules with a density, grade 31 dependant on the level of wear resistance required.

32 Typical densities of application will be 3 to 5 grains per 33 square inch. Particle sizes may be in the range of 15 to 1 100 microns. The particles could be applied by an air 2 blowing or high velocity oxygen fuel (HVOF) process.

3 Mixtures and combinations of particles of different 4 sizes, types and grades could be used.

6 The bonding agent, described in the embodiments as being 7 phenyl epoxy resins, could be other curable compounds 8 selected according to their physical, thermal and curing 9 properties. In some examples, the bonding agent may be cured by application of heat or ultraviolet light.

12 Although the above-described embodiments relate to drill 13 pipe and drill pipe stabilisers, the present invention 14 has application to any downhole tools which are subject to wear. These include centralisers, stabilisers, 16 packers, clamps, bottom hole assemblies and drilling 17 equipment. The present invention is applicable to tools 18 and equipment made of materials other than steel. It 19 will also be appreciated that the invention could be applied to tools and equipment other than downhole tools 21 for the oil and gas industry.

23 The invention provides improved wear resistant layers for 24 tools such as downhole tools, and a method of application thereof. The method of application may be carried out 26 without heating of the equipment and other disadvantages 27 associated with welding techniques. Of particular 28 significance is that method may be carried out with 29 little specialised equipment on a drilling rig.

31 Various modifications and improvements may be made within 32 the scope of the invention herein intended.

Claims

1 Claims 3 1. A method of forming a wear resistant surface on a 4

downhole apparatus, the method comprising the steps of: 6 -Combining a bonding agent with an abrasive 7 grit; 8 -Curing the bonding agent about a support 9 structure to form a wear resistant surface on the downhole apparatus.

12
2. The method as claimed in Claim 1 wherein the 13 bonding agent is a curable resin material.

3. The method as claimed in Claim 2 wherein the 16 bonding agent is an epoxy resin.

18 4. The method as claimed in Claim 3 wherein the 19 curable resin material is a phenyl epoxy resin.

21 5. The method as claimed in any preceding claim 22 wherein the abrasive grit is selected from silicon 23 carbide, boron carbide and diamond.

6. The method as claimed in any preceding claim 26 wherein the support structure comprises plurality 27 of components and a plurality of interspaces.

29 7. The method as claimed in any preceding claim wherein the bonding agent encapsulates the support 31 structure.

1 8. The method as claimed in any preceding claim 2 wherein the bonding agent forms a network about 3 and between components of the support structure, 4 via the interspaces.

S

6 9. The method as claimed in any preceding claim 7 further comprising the steps of: 8 -Applying the bonding agent to an area of the 9 downhole apparatus; -Locating the support structure on the area of 11 the downhole apparatus.

13 10. The method as claimed in any preceding claim 14 wherein the support structure comprises a woven layer of high strength fibre material.

17 11. The method as claimed in Claim 10 wherein the high 18 strength fibre material is a para-aramid fibre 19 material.

21 12. The method as claimed in Claim 11 wherein high 22 strength fibre material is KEVLAR .

24 13. The method as claimed in any of Claims 10 to 12 further comprising the steps of: 26 -Applying the bonding agent to the high 27 strength fibre material; 28 -Applying the bonding agent to an area of the 29 downhole apparatus; -Locating the high strength fibre material on 31 the area of the downhole apparatus.

1 14. The method as claimed in Claim 13 wherein the step 2 of applying the bonding agent to the high strength 3 fibre material involves saturating the high 4 strength fibre material with the bonding agent.

6 15. The method as claimed in any of Claims 10 to 14 7 including the additional step of wrapping the high 8 strength fibre material around the downhole 9 apparatus.

11 16. The method as claimed in Claim 15 including the 12 additional step of rotating the downhole apparatus 13 during wrapping.

17. The method as claimed in any of Claims 10 to 16 __1.. a.L.. .-. _.__-1...-.-...-. .-.4 U iliL L. ULLL11 L1L aLLLL.L. LLLALJ. L.C.I L'4 U V 17 multiple layers of the high strength fibre 18 material on the downhole apparatus.

18. The method as claimed in Claim 17 including the 21 additional step of wrapping a length of the high 22 strength fibre material which exceeds the 23 circumferential length of the downhole apparatus 24 such that multiple layers of the high strength fibre material are provided on the downhole 26 apparatus.

28 19. The method as claimed in any preceding claim 29 wherein the support structure comprises a plurality of bricks of a material harder than the 31 material of the downhole tool.

1 20. The method as claimed in Claim 19 wherein the 2 support structure comprises an arrangement of 3 tungsten carbide bricks.

21. The method as claimed in Claim 19 or Claim 20 6 including the additional step of locating a 7 plurality of bricks of a material harder than the 8 material of the downhole apparatus on the area to 9 which the bonding agent has been applied.

11 22. The method as claimed in any of Claims 19 to 21 12 including the additional steps of: 13 -Locating a layer of the high strength fibre 14 material on an area of the downhole apparatus; 16 -Locating bricks of a material harder than the 17 material of the downhole apparatus on the 18 layer of the high strength fibre material.

23. The method as claimed in Claim 22 including the 21 additional step of forming the layer of the high 22 strength fibre material from discrete sections, 23 smaller than the wear resistant surface.

24. The method as claimed in Claim 22 or Claim 23 26 including the additional step of saturating the 27 layer of the high strength fibre material with the 28 bonding agent prior to locating the bricks.

25. The method as claimed in any of Claims 22 to 24 31 including the additional step of applying the 32 bonding agent to the layer of bricks.

1 26. The method as claimed in any preceding claim 2 including the additional step of combining 3 abrasive grit with the bonding agent after it is 4 applied to the support structure.

6 27. The method as claimed in any preceding claim 7 including the additional step of premixing the 8 abrasive grit with the bonding agent.

28. The method as claimed in any preceding claim 11 including the additional step of applying a force 12 to the support structure.

14 29. The method as claimed in any preceding claim including the additional step of embedding 16 abrasive grit into the support structure.

18 30. The method as claimed in any preceding claim 19 including the additional step of curing the bonding agent by the application of heat.

22 31. The method as claimed in any of claims 1 to 29 23 including the additional step of curing the 24 bonding agent at room temperature.

26 32. A downhole apparatus having a body and a wear 27 resistant portion formed on the body, wherein the 28 wear resistant portion comprises a resin material 29 combined with an abrasive grit, and cured about a support structure.

1 33. The downhole apparatus as claimed in Claim 32 2 wherein the curable resin material is an epoxy 3 resin.

34. The downhole apparatus as claimed in Claim 33 6 wherein the curable resin material is a phenyl 7 epoxy resin.

9 35. The downhole apparatus as claimed in any of Claims 32 to 34 wherein the abrasive grit is selected 11 from silicon carbide, boron carbide and diamond.

13 36. The downhole apparatus as claimed in any of Claims 14 32 to 35 wherein the support structure comprises plurality of components and a plurality of 16 interspaces.

18 37. The downhole apparatus as claimed in any of Claims 19 32 to 36 wherein the support structure comprises a woven layer of high strength fibre material.

22 38. The downhole apparatus as claimed in Claim 37 23 wherein the high strength fibre material is a 24 para-aramid fibre material.

26 39. The downhole apparatus as claimed in Claim 38 27 wherein the high strength fibre material is 28 KEVLAR .

40. The downhole apparatus as claimed in any of Claims 31 32 to 39 wherein the support structure comprises a 32 plurality of bricks of a material harder than the 33 material of the downhole tool.

2 41. The downhole apparatus as claimed in Claim 40 3 wherein the support structure comprises an 4 arrangement of tungsten carbide bricks.

6 42. The downhole apparatus as claimed in any of Claims 7 32 to 41 wherein the bonding agent encapsulates 8 the support structure.

43. The downhole apparatus as claimed in any of Claims 11 32 to 42 wherein the bonding agent forms a network 12 about and between components of the support 13 structure, via the interspaces.

44. The downhole apparatus as claimed in any of Claims 16 32 to 43 wherein the dowiihole apparatus is drill 17 pipe.

19 45. The downhole apparatus as claimed in Claim 44 wherein the wear resistant portion is formed on a 21 box section of the drill pipe.

23 46. The downhole apparatus as claimed in Claim 44 24 wherein the wear resistant portion is formed on a mother pipe section of the drill pipe.

27 47. The downhole apparatus as claimed in any of Claims 28 32 to 44 wherein the wear resistant portion is 29 formed on a stabiliser.

31 48. Apparatus for forming a wear resistant surface on 32 a tool, the apparatus comprising means for 33 rotating the tool to facilitate application of a 1 support structure to the tool, means for applying 2 an abrasive grit to the support structure, and 3 means for applying a force to the support 4 structure.