GB2385342A

GB2385342A - A downhole device eg a centraliser

Info

Publication number: GB2385342A
Application number: GB0302119A
Authority: GB
Inventors: Harry Whitelaw; Serena Arif
Original assignee: Polyoil Ltd
Current assignee: Polyoil Ltd
Priority date: 2002-02-05
Filing date: 2003-01-30
Publication date: 2003-08-20
Anticipated expiration: 2023-01-30
Also published as: GB0302119D0; GB2385342B

Abstract

A downhole device (10) is applicable as a casing centraliser to support the casing away from the well bore wall. It comprises an annular body (12a, 12b) formed of a polymer based material and a sheath (14), which is made from a metallic material. The polymeric nature of the annular body (12a, 12b) provides improved torque resistance and low friction characteristics to the device, and the sheath (14) provides increased structural strength to the device and reduces tendency to swage. The annular body may be moulded around the sheath, or the sheath moulded around the annular body. The annular body may be formed by two or more parts that are clipped together. Alternatively, two parts of the body may be hinged together. The sheath would then be similarly hinged. The blades 16 may be hollow and have openings therein to allow fluid to flow therethrough.

Description

1 2385342

1 Improved downhole device 3 The present invention relates to downhole devices, and in 4 particular to annular devices for assisting in the 5 support and location of casing or drill-strings.

7 It is conventional practice after drilling an oil or gas 8 well to run tubing, known as casing, into the wellbore to 9 act as a liner. The casing stabilises the bore and 10 prevents it from collapsing inwards. The casing is run 11 into the newly formed bore from the surface, and the 12 annular space between the casing and the bore is then 13 filled with cement. The cement acts as a sealant and 14 also to structurally support the casing.

16 It will be appreciated that before the casing is cemented 17 in position, it is important for the casing to be held 18 substantially central in the bore. This allows a strong 19 cement bond to be formed around the casing by ensuring 20 that an even thickness is placed around the casing.

22 It is known in the art to use centralisers to support the 23 casing or liner away from the wellbore wall. Although 24 there are several types of centralizer known in the art,

1 one commonly used type is known as a solid centraliser.

2 Solid centralisers are comprised of a hollow cylindrical 3 body, often with a plurality of blades around the body.

4 These blades are raised solid structures that extend 5 longitudinally around the centraliser body and abut the 6 wellbore wall to optimise stand off.

8 Conventionally, the centralisers are made from a strong 9 metal material. It will be appreciated that centralisers 10 are subject to large loads, such as impact and shear ll forces, and accordingly must be durable and hardy.

12 Although metal centralisers are able to withstand high 13 loads and the hostile downhole environments, they do have 14 certain limitations. These include a degree of 15 inflexibility, which can mean that the centraliser is 16 unable to yield to obstructions in the wellbore, 17 resulting in its progress being blocked. Furthermore, 18 metal centralisers are prone to corrosion, particularly 19 in acidic environments.

21 A further problem of metal centralisers is that of 22 friction between the centraliser and objects downhole.

23 This applies to casing centralisers which may contact the 24 wall of the wellbore causing friction, torque and drag.

25 In addition, it is desirable to reduce friction between a 26 tool string and the internal surface of wellbore casings.

27 Friction between the tool string and the casing, 28 particularly metalon-metal, hinders rotation of the 29 string and causes wear to the casing. Fitting a 30 protector to the tool string to reduce both tool and 31 casing wear is known in the art. Such protectors may be 32 comprised of an annular body which fits around the work

1 string and prevents damaging contact between the tool 2 string and casing wall.

4 Recent developments in polymer technology have led to the 5 creation of non-metallic centralizers and downhole 6 devices. For example, GB 2361019 discloses the casing 7 centraliser cast from a polyamide material. This casing 8 centraliser offers advantages in that it is hard wearing 9 but has sufficient compliance and resilience to negotiate 10 restrictions in the wall of the wellbore. Further, the 11 centraliser is resistant to corrosion and offers means 12 for reducing torque and friction as the centraliser is 13 advanced downhole.

15 Interest in non-metallic components has increased with 16 the prospect of "smart" or "intelligent well" designs, 17 which may in the future use the production tubular as an 18 electrical or signal conductor. The electrical 19 insulating properties of a non-metallic centralizer allow 20 the passage of electrical currents, and pulsed electrical 21 or radio signals. This would enable downhole tool power 22 supply, or signals to operate downhole equipment such as 23 valves or other downhole flow controlling devices.

24 Similarly, any downhole gauges or well monitoring 25 equipment can use either the casing wellbore or the 26 producing tubular within for information transmission to 27 the surface.

29 However, current polymer centralizers such as that 30 disclosed in GB 2361019 are limited in structural 31 strength. In order to provide a centralizer durable 32 enough to withstand hostile downhole environment, highly 33 specialized materials and production techniques must be

1 employed, which in some cases can be prohibitive. Even 2 then, the centraliser may not be able to withstand 3 particularly high forces. Indeed, some current polymer 4 centralizers are suspected of "swaying" over abutting 5 metal stop collars and other tubular couplings.

7 It would therefore be desirable to provide a downhole 8 device that obviates or at least mitigates some of the 9 drawbacks associated with the prior art.

11 It is one object of the invention to provide a downhole 12 device that is hardwearing, but that has sufficient 13 compliance and resilience to negotiate a restriction in 14 the wall of a wellbore. It is a second object of the 15 invention to provide the downhole device with low 16 friction characteristics.

18 It is a further aim of the invention to provide a 19 downhole device with improved structural strength and 20 reduce tendency to swage. It is also an aim of the 21 invention to provide a downhole device with improved 22 compressive load strength and lateral crush resistance, 23 and with minimal body distortion under highly compressed 24 or side- loaded situations.

26 Further aims and objects of the invention will become 27 apparent from reading the following description.

29 According to a first aspect of the present invention 30 there is provided a downhole device comprising an annular 31 body with a longitudinal bore extending therethrough, and 32 a sheath, wherein the annular body is formed of a polymer

1 based material, and the sheath extends along the majority 2 of the length of the annular body.

4 Preferably, the sheath is comprised of a metallic 5 material. More preferably the sheath is made from steel.

7 The annular body may comprise a main body portion and a 8 plurality of blades.

10 The sheath may be an external sheath surrounding the main 11 body portion of the annular body. The external sheath 12 may include a plurality of windows through which the 13 blades of the annular body extend.

15 The annular body may be made from a plurality of moulded 16 segments. Alternatively, the segments may be machined.

18 The segments may be part cylindrical. Two or more 19 segments of making up the annular body may be hinged 20 together. Additionally, the external sheath may be 21 hinged.

23 Alternatively, the annular body may be moulded around the 24 sheath. The annular body may comprise a main body 25 portion with an inner surface and an outer surface, and a 26 plurality of blades extending from said outer surface.

27 The sheath is preferably radially displaced outwardly 28 from the inner surface of the main body portion.

30 Optionally, the sheath surrounds the outer surface of the 31 main body portion.

1 The sheath may be provided with a plurality of windows 2 through which the blades of the annular body are moulded.

3 The annular body may partially surround the sheath to 4 provide additional bonding strength.

6 The blades on the annular body may be hollow.

7 Optionally, the blades may comprise conduction means.

8 Alternatively, or in addition, the blades may comprise 9 one or more integral ports for flow of fluid into, and 10 out of the hollow blade.

12 The downhole device may be a casing centralizer.

13 Alternatively, the downhole device may be run on a drill 14 string. As further alternatives, the downhole device may 15 be run on a liner, on sand screens, or on production 16 tubing.

18 According to a second aspect of the invention there is 19 provided a method of forming a downhole device comprising 20 the steps of: using a polymer-based material to provide 21 an annular body having a longitudinal bore extending 22 therethrough, andi providing a sheath around the majority 23 of the length of the annular body.

25 The annular body may comprise a main body portion and a 26 plurality of blades.

28 The sheath may be an external sheath surrounding the main 29 body portion of the annular body. The external sheath 30 may include a plurality of windows through which the 31 blades of the annular body extend.

1 The annular body may be made from a plurality of moulded 2 segments. Alternatively, the segments may be machined.

4 According to a third aspect of the invention there is 5 provided a method of forming a downhole device comprising 6 the steps of: placing a sheath within a mould tool, and; 7 moulding an annular body around the sheath.

9 The annular body may comprise a main body portion with an 10 inner surface and an outer surface, and a plurality of 11 blades extending from said outer surface. The sheath is 12 preferably radially displaced outwardly from the inner 13 surface of the main body portion.

15 The sheath may be provided with a plurality of windows 16 through which the blades of the annular body are moulded.

17 The annular body may partially surround the sheath to 18 provide additional bonding strength.

20 There will now be described by way of example only 21 various embodiments of the invention with reference to 22 the following figures in which: 24 Figure 1 is the perspective view showing a downhole 25 device in accordance with an embodiment of the invention; 27 Figure 2 is a perspective view of an annular body 28 component in isolation; 30 Figure 3 is a perspective view of an external sheath in 31 accordance with an embodiment of the invention;

1 Figures 4 and 5 show a perspective view of an annular 2 body component with alternative construction; 4 Figures 6 and 7 show downhole devices in accordance with 5 alternative embodiments of the invention.

7 Figure 8a shows an alternative annular body arrangement; 9 Figure 8b shows an alternative external sheath 10 arrangement, and; 12 Figure 9 shows a downhole device in accordance with an 13 alternative embodiment of the invention.

15 Figure 1 shows a downhole device, in this case being a 16 casing centralizer, generally depicted at 10. The casing 17 centralizer 10 comprises an annular body made up of part 18 cylindrical components 12a and 12b. The part-cylindrical 19 components are made from a polymer-based material, such 20 as nylon. Positioned on the external surface of the 21 annular body are a number of blades 16. Blades 16 22 protrude from the surface and extend in a substantially 23 longitudinal direction of the annular body. The blades 24 shown are positioned helically around the longitudinal 25 axis of the annular body, although alternative 26 arrangements may be used. The blades 16 provide the 27 necessary degree of clearance between the casing and the 28 wellbore wall.

30 Figure 2 shows more clearly the part cylindrical 31 components 12a and 12b making up the annular body. The 32 components are positioned adjacent one another such that 33 they abut along join 13.

2 By forming the annular body from more than one part 3 cylindrical component, the manufacturing process and 4 assembly of the annular body may be simplified.

6 The part cylindrical components 12a and 12b may be shaped 7 with clip profiles for attaching two or more of the part 8 cylindrical components together. This allows the 9 components to be retained in position during transport, 10 storage, or during fitting to the casing.

12 During use, the inner surface 17 of the annular body 13 abuts the outer surface of the casing. Depending on the 14 conditions of use, the annular body may be able to 15 rotate, or may remain stationary relative to the casing.

17 The casing centraliser TO is provided with an external 18 sheath 14, as shown in isolation in Figure 3. The 19 external sheath 14 is formed from steel or other suitable 20 metallic material, and is located around the outer 21 surface of the annular body. Apertures or windows 18 are 22 provided in the external sheath and are shaped and 23 positioned such that the blade 16 may extend 24 therethrough.

26 The external sheath is formed from steel plate and rolled 27 into a cylindrical form. The windows are formed by any 28 suitable technique, as would be known to one skilled in 29 the art. For example, the windows may be cut by laser 30 cutting, machining, punching, torch or plasma cutting, 31 sawing, electro-discharge machining (EDM) processes or 32 abrasive water jet cutting. It is envisaged that the 33 windows could be formed on the flat sheet, prior to

1 rolling into a cylindrical form. Alternatively, the 2 windows could be perforated into the pre-formed cylinder.

4 In one embodiment, the device can be manufactured by 5 positioning the part-cylindrical components on a mandrel 6 and forming the annular body. A pre-cut sheath 14 is 7 then wrapped around the annular body and spotwelded into 8 position, or fastened by other means.

10 Figures 4 and 5 show alternative embodiments of the 11 invention. Figure 4 shows an annular body cast or 12 machined as a unitary structure 12, as an alternative to 13 the two-part structure shown in Figures 1 to 3. A 14 unitary annular body may offer advantages in increased 15 structural strength.

17 Figure 5 shows a further alternative construction of the 18 annular body. The annular body comprises three-part 19 cylinders 12a, 12b, 12c. Once again, the part cylinders 20 abut at seams 13. Clips may be provided to hold the part 21 cylindrical components in position.

23 It will be evident that the annular body could be 24 constructed from any number of moulded or machined part 25 cylindrical components, depending on process costs and 26 other factors.

28 Figure 6 shows an alternative embodiment. An advantage 29 of this embodiment of the invention is that the blades 16 30 are hollow and have a number of ports 19 into and out of 31 which fluid can flow. The fluid may include drilling 32 fluid, cleaning fluid, carrier fluids or gels used for 33 gravel packing operations such as are continuously passed

1 through the section of well being bored to lubricate the 2 drilling apparatus and wash out the bore. The ports 19 3 may be positioned on the external surface of the blades.

4 In an alternative embodiment shown in Figure 7, the ports 5 are located at the ends of the blade 20.

7 Because the blades are hollow, they may be used as a 8 conduit or housing to protect conduction means such as 9 power lines, electrical cables or optical fibres. A 10 further advantage is that the plastic hollow blades have 11 a greater flexibility and compliance than convention 12 metal solid blades and can therefore negotiate any 13 obstructions encountered in the wall of the bore.

15 As before, an external sheath 14 is provided over the 16 annular body to increase the integral strength of the 17 device.

19 Figure 8a shows an alternative annular body. The body is 20 formed from two part cylindrical components, the two 21 components being hinged together at 22. This allows them 22 to be positioned on or removed from the casing easily and 23 quickly. Clips or other engaging means (not shown) may 24 be provided on the components 12a, 12b for securing the 25 body.

27 Figure 8b shows an external sheath formed from two 28 components 14a and 14b. The components are part 29 cylindrical, and are hinged together at 24. The sheath 30 may be provided with engaging means for securing around 31 the annular body, or alternatively may be welded in 32 position.

1 The annular body and sheath shown in Figures 8a and 8b 2 may be used in conjunction with one another, or with 3 alternative components described elsewhere in this 4 application.

6 Figure 9 shows an alternative embodiment of the 7 invention. In this example, the annular body is 8 partially moulded around the sheath.

10 The sheath 14 is placed within a mould tool prior to the 11 formation of the annular body 12. The annular body is 12 then moulded around the sheath to form a polymeric 13 structure with an embedded sheath for providing 14 additional rigidity and strength. This embedded 15 structure reduces the likelihood of distortion of the 16 annular body in a radial direction during high load 17 situations, such as running tubing, casing, liner or well 18 screen.

20 In this example, the sheath is provided with windows 21 through which the blades are moulded. The annular body 22 is partially moulded over the sheath such that the two 23 are securely bonded to one another. However, the sheath 24 14 is disposed at the outer surface of the main 25 cylindrical body portion, such that parts of it 22 remain 26 visible from the exterior of the device. The main 27 cylindrical body is thus moulded flush, or near flush 28 with the sheath 14.

30 The annular body is moulded over the sheath at the root 31 of the blades, and at either end of the sheath.

32 Accordingly, the windows within the sheath may be formed 33 to a width that is less than the desired width of the

1 blades. Further perforations or apertures are optionally 2 included at parts of the sheath 14 in order to improve 3 bonding between the polymer body 12 and the sheath as required. 6 The degree of overmoulding can be increased to provide 7 greater integration between the sheath and the body.

8 Indeed, the sheath could be entirely encapsulated by an 9 overmoulded annular body. In such an embodiment the 10 sheath would be positioned between the inner surface and 11 the outer surface of the main cylindrical body. It 12 should be noted that the sheath would retain a degree of 13 radial displacement from the inner surface of the annular 14 body. This would maintain the low-friction 15 characteristics of the device. It is preferred that the 16 sheath is moulded at, or close to, the outer surface of 17 the main cylindrical body. This arrangement optimises 18 the containment of the polymer component under conditions 19 of axial compression or lateral crush.

21 It will also be appreciated that the annular body could 22 be partially pre-formed, with the sheath 14 moulded 23 thereto as a subsequent step.

25 As before, the embodiment described with reference to 26 Figure 9 could be supplemented with various other 27 features, such as the ported/hollow blade configuration 28 of Figures 6 and 7.

30 The downhole device in accordance with the invention 31 offers several advantages over the prior art. For

32 example, the device offers the benefits of polymer-based

1 devices, including corrosion resistance, and improved 2 flexibility in use.

4 However, the sheath provides increased structural 5 strength to the device. The sheath effectively 6 eliminates the risk of swaging, whereby conventional 7 polymer based centralisers ride up over stop collars or 8 tubular couplings positioned adjacent on the tool or 9 casings. This is achieved by the sheath providing 10 increased rigidity and reducing the tendency of the 11 annular body to flex in a radial direction.

13 In addition, the sheath provides strength in the 14 longitudinal direction. The sheath effectively acts as a 15 strengthened spine and increases the resistance to 16 compressive forces in the longitudinal direction of a 17 tool string or casing assembly.

19 Furthermore, the polymeric nature of the annular body 20 provides improved torque resistance and low friction 21 characteristics. The polymer based annular body is in 22 contact with the metal downhole components on both the 23 inner surface and outer surface of the blades. That is, 24 although the device has structural strength comparable 25 with metal centralizers, the problems of torque, drag, 26 and wear associated with metal-on-metal movement are 27 avoided.

29 Although the above-described embodiments relate primarily 30 to a casing centralizer, it will be appreciated that the 31 above principles also apply to downhole devices for 32 running on a drill string. For example, the arrangement 33 shown can be used to locate a tool within a liner,

1 thereby reducing the drag between the tool and the liner 2 casing. The low-friction characteristics of the device 3 make it ideal for this purpose. In addition, the device 4 may be used on the outside of a liner, or could be 5 applied to sand screens.

7 A further advantage of a polymer centraliser is in the 8 application of the device to a production tubing string, 9 where tubing stand-off and the natural heat-insulating 10 properties of the material allow the well fluids to 11 maintain higher temperatures. This has positive benefits 12 in certain field developments where there can be problems

13 with the formation of waxes or viscous crudes slowing 14 down or blocking production. These problems arise from 15 solid formation on cooling and/or the viscous drag 16 created by an increase in fluid viscosity due to cooling 17 nearer the surface. A device in accordance with the 18 invention could be run on the outside of the production 19 tubulars over the entire length of the tubing.

20 Alternatively, where the tubular suffers from chilling in 21 certain well locations, the device could be selectively 22 run. For example, where the production tubular traverses 23 the area inside a marine riser, the device may be run 24 over the upper section only.

26 Further improvements and modifications may be made within 27 the scope of the invention herein intended.

Claims

1 Claims

3 1. A downhole device comprising an annular body with a 4 longitudinal bore extending therethrough, and a 5 sheath, wherein the annular body is formed of a 6 polymer based material, and the sheath extends along 7 the majority of the length of the annular body.

9

2. A downhole device as claimed in Claim 1 wherein the 10 sheath is comprised of a metallic material.

12

3. A downhole device as claimed in Claim 2 wherein the 13 sheath is made from steel.

15

4. A downhole device as claimed in any preceding Claim 16 wherein the annular body comprises a main body 17 portion and a plurality of blades.

19

5. A downhole device as claimed in Claim 4 wherein the 20 sheath is an external sheath surrounding the main 21 body portion of the annular body.

23

6. A downhole device as claimed in Claim 5 wherein the 24 external sheath includes a plurality of windows 25 through which the blades of the annular body extend.

27

7. A downhole device as claimed in any preceding Claim 28 wherein the annular body is made from a plurality of 29 moulded segments.

31

8. A downhole device as claimed in any of Claims 1 to 6 32 wherein the annular body is made from a plurality of 33 machined segments.

2

9. A downhole device as claimed in Claim 7 or Claim 8 3 wherein the segments are part cylindrical.

5

10. A downhole device as claimed in any of Claims 7 to 9 6 wherein two or more segments of making up the 7 annular body is hinged together.

9

11. A downhole device as claimed in any of Claims 5 to 10 10 wherein the external sheath is made from a 11 plurality of segments, and two or more segments of 12 making up the external sheath is hinged together.

14

12. A downhole device as claimed in any of Claims 1 to 3 15 wherein the annular body is moulded around the 16 sheath.

18

13. A downhole device as claimed in Claim 12 wherein the 19 annular body comprises a main body portion with an 20 inner surface and an outer surface, and a plurality 21 of blades extending from said outer surface.

23

14. A downhole device as claimed in Claim 13 wherein the 24 sheath is radially displaced outwardly from the 25 inner surface of the main body portion.

27

15. A downhole device as claimed in Claim 14 wherein the 28 sheath surrounds the outer surface of the main body 29 portion.

31

16. A downhole device as claimed in any of Claims 13 to 32 15 wherein the sheath is provided with a plurality

1 of windows through which the blades of the annular 2 body are moulded.

4

17. A downhole device as claimed in any of Claims 12 to 5 16 wherein the annular body is partially surround 6 the sheath to provide additional bonding strength.

8

18. A downhole device as claimed in Claim 4 or Claim 13 9 wherein the blades on the annular body is hollow.

11

19. A downhole device as claimed in Claim 18 wherein the 12 blades comprise conduction means.

14

20. A downhole device as claimed in Claim 18 or Claim 19 15 wherein the blades comprise one or more integral 16 ports for flow of fluid into, and out of the hollow 17 blade. 19

21. A downhole device as claimed in any preceding Claim 20 wherein the downhole device is a casing centralizer.

22

22. A downhole device as claimed in any preceding Claim 23 wherein the downhole device is run on a drill 24 string.

26

23. A downhole device as claimed in any preceding Claim 27 wherein the downhole device is run on a liner, on 28 sand screens, or on production tubing.

30

24. A method of forming a downhole device comprising the 31 steps of:

1 using a polymer-based material to provide an annular 2 body having a longitudinal bore extending 3 therethrough, andi 4 providing a sheath around the majority of the length 5 of the annular body.

7

25. A method of forming a downhole device as claimed in 8 Claim 24 wherein the annular body comprises a main 9 body portion and a plurality of blades.

11

26. A method of forming a downhole device as claimed in 12 Claim 25 wherein the sheath is an external sheath 13 surrounding the main body portion of the annular 14 body.

16

27. A method of forming a downhole device as claimed in 17 Claim 26 wherein the external sheath includes a 18 plurality of windows through which the blades of the 19 annular body extend.

21

28. A method of forming a downhole device as claimed in 22 any of Claims 24 to 27 wherein the annular body is 23 made from a plurality of moulded segments.

25

29. A method of forming a downhole device as claimed in 26 any of Claims 24 to 27 wherein the annular body is 27 made from a plurality of machined segments.

29

30. A method of forming a downhole device comprising the 30 steps of: 31 placing a sheath within a mould tool, and; 32 moulding an annular body around the sheath.

1

31. A method of forming a downhole device as claimed in 2 Claim 30 wherein the annular body comprises a main 3 body portion with an inner surface and an outer 4 surface, and a plurality of blades extending from 5 said outer surface.

7

32. A method of forming a downhole device as claimed in 8 Claim 31 wherein the sheath is radially displaced 9 outwardly from the inner surface of the main body 10 portion.

12

33. A method of forming a downhole device as claimed in 13 any of Claims 30 to 32 wherein the sheath is 14 provided with a plurality of windows through which 15 the blades of the annular body are moulded.

17

34. A method of forming a downhole device as claimed in 18 any of Claims 30 to 33 wherein the annular body 19 partially surrounds the sheath to provide additional 20 bonding strength.