GB2391570A

GB2391570A - Adjustable centraliser

Info

Publication number: GB2391570A
Application number: GB0318520A
Authority: GB
Inventors: David Goffin; Martin Bunn
Original assignee: PARAMODE Ltd
Current assignee: PARAMODE Ltd
Priority date: 2002-08-07
Filing date: 2003-08-07
Publication date: 2004-02-11
Anticipated expiration: 2023-08-07
Also published as: GB0218312D0; GB0318520D0; GB2391570B

Abstract

A centralising device (10, fig 2) for centralising a string within a bore or a second string has a body portion including clamps (13, 14A, 14B, fig 1) for attaching the body portion to the string to be centralised. A number of guide members (15) are mounted on and project radially from the body portion with at least two of the guide members (15) being adjustably mounted and extendable in a purely radial direction. The adjustment can be carried out by cam surfaces (60, fig 6) which rotate between the adjustable guide members (15) and the body portion, or by wedges (32), slidably moveable along the axis of the string which engage an inclined inner surface of the guide members (15). The body includes annular rings (16, fig 2) and a tubular body comprising two semicircular halves (12A, 12B, fig 1) bolted together.

Description

239 1 570

Field of the Invention

The present invention relates to an adjustable centralizing device which can be used in drilling and pumping operations particularly in the oil and gas drilling and 5 production industries. It will be readily appreciated by the skilled reader that the invention is applicable also in relation to other industries.

Bound of tlm Inyenti In many industrial processes, it is common for a first elongate article, such as a tube, to be passed inside or threaded through a second article which may itself be 10 elongate. Ideally, the first and second articles are co-axial. Cables, pipes, bore holes, drilling shafts, offshore well platform risers, etc., are all examples of such articles. In the description that follows particular reference will be made to the centralising

of one pipe or "string" within another. It should be noted that these references are 15 in no way intended to limit the intended scope of the invention which has application throughout a number of industries.

More generally, due to forces on a pipe from, for example, sea or air currents, an operator is faced with the problem of minimising motion in a direction perpendicular to that of the axis of the pipe. Such motion can cause damage and 20 lead either to release of gas or oil from a pipe.

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In order to restrict the lateral motion, a rigid tubular structure is often placed around the pipe and co-axial therewith. The tubular structure has a diameter such that lateral movement of the pipe is restricted but not completely inhibited.

Even where such tubular structures are employed, the remaining lateral motion of 5 the inner pipe can still cause problems such as vibration of the supporting structure. The vibrations can cause wear and tear and can produce considerable noise particularly in those supporting structures. It is particularly dangerous when harmonics of the vibrations concentrate energy and movement.

A number of solutions have been proposed to overcome the above problems. For 10 example fins, projecting radially from the inner string, have been clamped into position around the string. The diameter of circle described by each outer edge of the fins is set to be slightly less than or the same as the inner diameter of the outer string or bore around said inner string. Lateral motion is therefore substantially prevented and the inner pipe maintained in a relatively constant position. An IS array of fins can be clamped along the length of the string, especially at harmonic points where it is believed vibrational energy will be concentrated Centralisers commonly comprise upper and lower coUars having a plurality of spring elements or bows which are attached at their respective upper and lower ends to the collars. The collars are positioned about the string and one collar 20 clamps or is clamped to the string while the other is allowed to move a limited distance along the axial length of the string. Movement of the "free" collar with respect to the clamped collar dictates the radial projection of the spring bows which operably engage a string or bore wall and centralize the inner string with respect to the outer string or bore.

25 The use of adjustable radially extending fins as described above is the basis for the invention disclosed in United Kingdom Patent No 2 277 336. This document discloses a centraliser attached around a shaft, the centralizer having a number of fins projecting radially. Adjustment of the fins radially is always accompanied by a change in the axial direction. The fins are attached to a tubular body which

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clamps around a length of the shaft. This arrangement obviates the moving collar amngement and simplifies adjustable centraliser construction. Conversely, the structure can be heavy and the introduction of an axial component in the radial

adjustment brings with it the disadvantage that correct positioning of the 5 centralizer, in order that the required section of the outer string or guide bore is engaged, is subject to a certain amount of guesswork.

It is an object of the present invention to seek to address the above problems and provide a centralizer device to stabilise a string.

Summary of the entinn

10 According to the present invention there is provided a centralizing device suitable for centralizing a string within a bore or a second string, the device comprising: a body portion including clamp means for attaching the body to a string to be centralized; and a plurality of guide members mounted on said body and projecting radially 15 therefrom, two or more of said guide members being adjustably mounted on said body, each of said adjustable guide members being extensible in a purely radial direction.

The lack of any axial movement during the radial adjustment of the guide members means that the centralizing device can be positioned directly adjacent the 20 required section of a guide bore or second string. There is therefore no need to guess and/or calculate how far the guide members will move axially during the adjustment. The body portion comprises a pair of annular rings one adjacent each end of the centralizing device onto which the guide members are secured. Optionally, the 25 body portion comprises a tubular body defined by a cylindrical tube.

À..e ÀeÀeÀ Conveniently, the body portion is split into two equal semicircular halves which are bolted or otherwise fixed together so as to be secured to the string.

The or each guide member substantially eliminates lateral movement of the axis of the first string. Deviations in the lateral direction either bring a guide member 5 into contact with the inner surface of the second string or are prevented by established contact between a guide member and the inner surface and damage from said contact is minimised. Noise produced by vibration is also reduced. By restricting a guide member to move in a purely radial direction minimal force is introduced along the axis of either string which could cause damage or introduce 10 other forces or influences to a stung which could cause damage or alter allowable tolerances particularly at couplings.

Advantageously, the device includes one or more wedges engaging an inclined inner surface of a guide, movement of the or each wedge changing the radial projection of the corresponding guide member.

15 This arrangement obviates the prior art requirement to move the radially

projecting guides in an axial direction to achieve radial adjustment. Accordingly, there is no requirement for the radial projection of the guides to depend on the position of the guides along the axis of the body.

Optionally, the or each wedge is slidably moveable in a direction parallel to the 20 main axis of the first string.

Conveniently, the radial projection of a guide member is controlled by two sliding wedges, both wedges being threadably engaged on separate threads on a control screw, the threads on the control screw having opposite orientations. The radial projection of a guide member can therefore be easily and precisely controlled.

25 Altematively, two or more wedges are mounted on one or more screw threads on a control screw, the screw threads having the same orientation.

Be;- In an alternative embodiment of the invention there is provided a centralising device suitable for centralising a string within a bore or a second string, the device comprising: a body portion including clamp means for attaching the body to a string to be 5 centralized; and a plurality of guide members mounted on said body and projecting radially therefrom, two or more of said guides being adjustably mounted on said body, each of said adjustable guide members being extensible in a purely radial direction by cam 10 surfaces rotating between said adjustable guide members and the body.

Advantageously, the cam surfaces are of involute form so as to ensure that radial loads on the centraliser cannot force the cam surfaces to rotate and drive the guide members radially inwardly.

Preferably, rotation of the cam surfaces is achieved by extension of a link member 15 which is coupled to the cam surfaces via crank shafts. The extension of the linlc member is effected by a threaded adjustment bolt.

Optionally, rotation of the cam surfaces is achieved by rotation of a link member, the extension member being threadably engaged to the device. A crank shaft disposed between the link member and the cam surface includes a threaded bush 20 to translate rotation of the linlc member to the crank to facilitate rotation of the cam surface.

The device advantageously includes securing elements to retain a guide member in the desired position. Securing elements prevent the radial projection of a guide member from being altered due to pressure from the second string.

25 The or each guide member is advantageously secured between retaining plates. A guide member can therefore be easily replaced when desired, without having to

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replace the entire centralising device.

Preferably, the body portion is provided in two sections, the two sections being located around the first string and secured together. The two part clamp enables rapid attachment and detachment of the centralizer device.

5 The or each retaining plate optionally includes one or more guide apertures engaging lugs on the guide member to ensure that the guide member moves in a radial direction.

Brief Desiplionnf he" Drawings The centralising device will now be described more particularly with reference to 10 the accompanying drawings which show, by way of example only, two embodiments of centralising device. In the drawings: Figure 1 is a plan view of a centralizing device in accordance with the first embodiment; Figure 2 is a sectional view of the first embodiment of the device taken along the 15 lines B-B of Figure 1; Figures 3 and 4 are detailed cross-sectional side elevations of a guide member in non-extended and extended positions, respectively; Figure 5 is a sectional side elevation of a retaining bracket for an adjustable guide member taken along the lines C-C of Figure 4; 20 Figure 6 is a detailed side elevation of an adjustable guide member of Be second embodiment; Figure 7 is a detailed side elevation similar to that of Figure 6 illustrating the means for adjustment of cam surfaces to effect radial adjustment of the guide members;

À e Figure 8 is a sectional side elevation of a retaining bracket for an adjustable guide member of a centralising device of the second embodiment, Figures 9a and 9b are respectively, a side, and end view of a centraliser; and Figure 10 is an enlarged sectional view of the region encircled in Figure 9a.

5 Detailed Description of the Inyenti

Referring to the drawings and initially to Figure 1, the centralizing device 10 comprises a body portion which is split into two halves 12A, 12B which in use are bolted or otherwise fixed together to engage a string or other tubular element (not shown). In the illustrated embodiment, the body halves 12A, 12B are releasably 10 secured to a string by securing bolts 13.

At the interface of the two halves 12A, 12B of the body portion, plates 14A, 14B having fixing holes to accommodate the securing bolts 13 combine to form non adjustable guide members or fins 15A, which define the minimum diameter of the centralising device 10. Four adjustable guide members or fins 15B are also 15 provided about the body portion of the device 10, two on each half 12A, 12B.

The guides 15A, 15B are spaced equidistant about the device 10, the guides 15A being opposite each other, so as to facilitate centralizing the string within a bore or outer string. In its non-extended configuration, where the adjustable guides or fins 15A, 15B have not been extended radially, the overall diameter of the 20 centralizing device is less than the inner diameter of the bore or outer string which is illustrated in Figure 1 as a dashed line D. The body portion is defined by upper and lower collars 16 each of which are split as described above to define the two body halves 12A, 12B. A pair of strengthening ribs 17 are provided around the outer surface of each collar 16 and 25 comprise plate sections between each of the guide members or fins 15A, 15B.

The plate sections of the ribs 17 provide structural integrity and rigidity to the device 10.

ÀÀ Àe Àe À-eÀ Figure 2 is a false sectional view taken along the lines BB of Figure 1 to illustrate the overall construction of the device with particular reference to the body portion and guide members or fins 15A, 15B. It will be readily appreciated by the skilled reader that the body portion may comprise a cylindrical or tubular body split S along its length to define the two halves 12A, 12B.

As shown and described more particularly with reference to Figures 3 and 4, each adjustable guide member or fin 15B is mounted on the device by disposing the fin 15B between a pair of mounting plates 18A, 18B which are welded or otherwise fixed to the device body, in this case, to the upper and lower collars 16. The fin 10 15B is movably retained between the plates 18A, 18B as will be described in more detail hereinbelow with respect to each of the two exemplifying embodiments The first embodiment of centralising device is characterized by means to move a fin 15B radially as illustrated in Figures 3 to 5. The reference nwnbering for 15 elements used in Figures 1 and 2 will be repeated without further description of

those elements.

A mounting plate 14 is secured to a support ring 17 by means of a welded joint.

The mounting plate 14 has projections 30 equidistantly spaced along its length to engage corresponding holes 31 in the fin 15B. The holes 31 are elongate to 20 permit lateral movement of the fin 15B in relation to the supporting section 12.

In order to provide the force required to move the fins 15B two wedges 32 are provided. Each wedge has a trapezium cross-section to engage a cut out on the inward facing portion of the fin 15B. The surface of the inward facing portion is inclined. Movement of the wedges 32 from the position shown in Figure 3 to that 25 shown in Figure 4 engages the inclined surface and forces the fin 15B in an outward radial direction. As the fin 15B moves in We radial direction, the projections 30 slide along the holes 31, the fin 15B being prevented from sideways movement around the circumference of the device, by the plates 14 to either side.

-9- À. a: In the particular embodiment shown, the wedges 32 are threadably mounted to an adjusting screw 33. The adjusting screw 33 has two separate counter-helical threads which engage a corresponding thread on each wedge 32. Clockwise rotation of the adjusting screw 33 therefore causes the separation between the 5 wedges 32 to increase as each wedge 32 is pulled along the thread. As the separation increases, each wedge 32 engages the inclined slope of the fin 15 causing it to move outwards. Conversely, when the adjusting screw 33 is moved in an antilockwise fashion the wedges 32 move together, allowing the fin 15 to move inwards radially.

10 The second embodiment of centralising device is characterized by an alternative means to move a fin 15B radially as illustrated in Figures 6 and 7. As before the reference numbering for common elements which are similar to those indicated in Figures 1 and 2 will be utilised with respect to the description of the second

embodiment. 15 In this embodiment the shape of the internal profile of the fin 15B is modified to accommodate a cam 60 and to provide a cam follower surface. A bearing plate or strip may also be provided between the fin mounting plates 18A, 18B to support the cams where the body portion of the device 10 is not continuous or where the cams are not aligned with the collars 16. Each cam 60 is fixed to a crank lever 61 20 which in turn is connected to a link rod 62 which couples a pair of cams 60 associated with each fin 15B. At one end of the link 62 an internally threaded section 63 receives a correspondingly threaded adjustment bolt 64. The bolt 64 is held in threaded engagement with a limiter post 65 which primarily transfers the rotation of the adjustment bolt 64 to a linear motion of the link 62 which in turn is 25 translated to rotational motion at the cams 60. The post 65 also acts to limit the adjustment range of the bolt.

The cam, link and bolt mechanism is shown in section in Figure 8. The sectional elevation has been modified to illustrate how the collar 16, tubular body portion or bearing plate or strip can be modified to receive the cam 60 in a channel 66 to 30 enhance stability and therefore durability of the cam, link and bolt mechanism.

1........DTD: In an alternative embodiment, not illustrated, the adjustment bolt threadably engages the crank lever 61, such that rotation of the adjustment bolt causes a corresponding pivoting of the crank lever 61.

A further embodiment 15 of a centraliser is shown in Figures 9a,9b and 10. Such 5 a centralizer is particularly convenient for use when space is limited as the adjustment bolt is not located beneath the fins giving a narrower overall cross section. In this embodiment, the wall of the body 90 is thinner than of those disclosed in the previous embodiments. The body 90 is split into two sections 91A,9lB of semicircular cross-section held together by bolts 92.

10 Four cut-outs running parallel to the axis of the body 90 are cut into the outer wall of the body 90, and bars 94 attached along the outside of the cut-outs to form a guide. In use, the body 90 is then clamped to the outside of a tubular riser or casing by fixing the two semicircular sections 91A,9lB around the riser or casing and fixing these together using the bolts 92. The blades 95 are then fitted. The 15 blades 95 have a series of ramps 96 along their inner surface, a groove 97 along their length, and rest on a steel bar 98 fitted with a series of wedge-shaped ramps 99. The steel bar 98 has a threaded upper section which passes through a lug on the cylindrical section of the body 90. Initially, the blades 95 rest on the outer surface 20 of the body 90 to allow the centraliser to be installed. When the centraliser is installed, the nuts 100, fitted to the Breaded edge of the wedges 99, are tightened, drawing the wedges 99, in the same direction, along the centraliser and forcing the blades 95 radially outwards. The effective diameter of the riser or casing is thereby increased, reducing its lateral movement.

25 The use of an adjusting screw or bolt 33, 64 enables an incremental and exact adjustment of the radial projection of a fin 15B. The device 10 can therefore be caused to engage the outer string either loosely or tightly as desired. As the motion of the fin when the present invention is purely in a radial direction, the stress imparted to the inner string as the fin engages the outer string is primarily in

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a radial direction. As the axial components of the stress are small, there is no tendency for the inner string to distort in any way which could reduce the effectiveness of the string, especially where tolerance limits have been set precisely. 5 It is envisaged that a number of devices can be employed along the length of an inner string to better control the motion of the string. The devices can also be conveniently located to dampen down any harmonic vibrations which may be set up along the string due to outside vibrational forces. Such harmonic vibrations can be potentially very damaging as the vibrational force is concentrated in a 10 particular area as the vibrations reinforce each other.

The materials from which the device is formed will be selected depending on strength required, but also on the surrounding environment. Where corrosive chemicals are present, the device can be formed from, or coated With an inert material. 15 It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention.

Claims

À; r 1. A centralising device suitable for centralising a string within a

bore or a second string, the device comprising: a body portion including clamp means for attaching the body portion to a 5 string to be centralized; and a plurality of guide members mounted on said body portion and projecting radially therefrom, two or more of said guide members being adjustably mounted on said body portion, each of said adjustable guide members being extensible in a 10 purely radial direction.
2. A centralising device according to Claim 1, wherein the body portion

comprises a pair of annular rings one adjacent each end of the centralising device onto which the guide members are secured.
3. A centralising device according to Claim 1 or Claim 2, wherein the body 15 portion comprises a tubular body defined by a cylindrical tube.
4. A centralising device according to Claim 3, wherein the body portion is split into two equal semi-circular halves which are bolted or otherwise fixed together so as to be secured to the string.
5. A centralising device according to any preceding claim, wherein the 20 device includes one or more wedges engaging an inclined inner surface of a guide, movement of the or each wedge changing the radial projection of the corresponding guide member.
6. A centralising device according to Claim 5, wherein the or each wedge is slidably moveable in a direction parallel to Me main axis of the first string.

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7 A centralizing device according to any preceding claim, wherein the radial projection of a guide member is controlled by two sliding wedges, both wedges being threadably engaged on separate threads on a control screw, the threads on the control screw having opposite orientations.

5
8. A centralizing device according to Claims 1 to 7, wherein two or more wedges are mounted on one or more screw threads mounted on one or more screw threads on a control screw, the screw threads having the same a orientation.
9. A centralizing device comprising: 10 a body portion including clamp means for attaching the body portion to a string to be centralized, and a plurality of guide members mounted on said body portion and projecting radially therefrom, two or more of said guides being adjustably mounted on said body portion, 15 each of said adjustable guide members being extensible in a purely radial direction by cam surfaces rotating between said adjustable guide members and the body portion.
10. A centralizing device according to Claim 9, wherein the cam surfaces are of involute form so as to ensure that radial loads on the centralizer cannot 20 force the cam surfaces to rotate and drive the guide members radially inwardly.
11. A centralizing device according to Claim 9 or Claim 10, wherein the rotation of the cam surfaces is achieved by extension of a link member which is coupled to the cam surfaces via crank shafts.

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12. A centralizing device according to Claim 11, wherein the extension of the link member is effected by a threaded adjustment bolt.

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13. A centralising device according to Claims 9 to 12, wherein rotation of the cam surfaces is achieved by rotation of a link member, the extension member being threadably engaged to the device.
14. A centralising device according to Claims 11 to 13, wherein a crank shaft 5 disposed between the link member and the cam surface includes a threaded bush to translate rotation of the link member to the crank to facilitate rotation of the cam surface.
15. A centralizing device according to Claims 9 to 14, wherein the device includes securing elements to retain a guide member in the desired 10 position.
16. A centralising device according to Claims 9 to 15, wherein the or each guide member is secured between retaining plates.
17. A centralizing device according to Claims 9 to 16, wherein the body portion is provided in two sections, the two sections being located around 15 the first string and secured together. I
18. A centralizing device according to Claims 16 or 17, wherein the or each retaining plate includes one or more guide apertures engaging lugs on the guide member to ensure that the guide member moves in a radial direction.
19. A centralizing device substantially as herein described with respect to and 20 as illustrated in the accompanying drawings.