DEPLOYABLE CASING CENTRALISER WITH LATCH FOR BOW SPRINGS

Abstract

A centraliser for use in a wellbore includes: first and second collars, at least one resilient device extending between the first and second collars, and a locking ring for receiving a tubular in a position radially inside the resilient device and axially between the first and second collars; the resilient device being resiliently biased in a radial direction away from the locking ring; the locking ring having at least one catch device adapted to engage with the at least one resilient device in a radially restricted configuration and the catch device is adapted to resist radial movement of the resilient device away from the locking ring when the catch device is engaged with the resilient device; and at least one fixing between the at least one catch device and the locking ring and made from a sacrificial material adapted to degrade in wellbore conditions.

Claims

1. A centraliser assembly for use in an oil, gas or water well, the centraliser assembly comprising: a centraliser having a body comprising first and second collars, and having a bore with an axis adapted to receive a tubular to be centralised, and at least one resilient device extending between the first and second collars, and a locking ring for receiving the tubular in a position radially inside the resilient device and axially between the first and second collars; the resilient device being resiliently biased in a radial direction away from the locking ring towards a radially extended configuration, and being movable radially relative to the locking ring from the radially extended configuration into a radially restricted configuration in which the resilient device is closer to the locking ring than in the radially extended configuration; the locking ring having at least one catch device adapted to engage with the at least one resilient device in the radially restricted configuration of the resilient device and wherein the catch device is adapted to resist radial movement of the resilient device away from the locking ring when the catch device is engaged with the resilient device; and at least one fixing between the at least one catch device and the locking ring; the at least one fixing comprising a sacrificial material adapted to degrade in wellbore conditions faster than the material of the locking ring or the at least one catch device.

2 The centraliser assembly as claimed in claim 1, wherein the at least one resilient device comprises at least one wing protruding circumferentially from an edge of the resilient device.

3 The centraliser assembly as claimed in claim 2, wherein the at least one wing extends radially inward from an outer surface of the at least one resilient device.

4 The centraliser assembly as claimed in claim 1, wherein the at least one catch device comprises a plate which defines a recess radially inside the plate.

5 The centraliser assembly as claimed in claim 4, wherein the recess is adapted to receive a portion of the resilient device.

6 The centraliser assembly as claimed in claim 1, wherein a portion of the catch device is adapted to deform when the sacrificial material degrades in borehole conditions.

7 The centraliser assembly as claimed in claim 1, wherein the catch device engages a recessed portion of the at least one resilient device in the radially restricted configuration.

8 The centraliser assembly as claimed in claim 1, wherein the at least one fixing comprises a pin with a long axis disposed along a radius of the locking ring, perpendicular to the bore of the centraliser body.

9 The centraliser assembly as claimed in claim 8, wherein at least a part of the pin passes through at least one aperture in the locking ring and/or the catch device.

10 The centraliser assembly as claimed in claim 1, wherein the at least one fixing connects the resilient device and the locking ring.

11 The centraliser assembly as claimed in claim 1, wherein the at least one fixing is held in tension, perpendicular to the axis of the bore of the centraliser body.

12 The centraliser assembly as claimed in claim 1, wherein the sacrificial material comprises one or more of magnesium, zinc, aluminium manganese and alloys of these.

13 The centraliser assembly as claimed in claim 1, incorporating at least one permanent fixing between the at least one catch device and the locking ring.

14 The centraliser assembly as claimed in claim 1, wherein at least a portion of the at least one catch device is adapted to remain attached to the at least one resilient device when the sacrificial material degrades and the resilient device moves to the radially extended configuration.

15 The centraliser assembly as claimed in claim 1, wherein at least a portion of the at least one catch device is adapted to remain attached to the locking ring when the sacrificial material degrades and the resilient device moves to the radially extended configuration.

16 The centraliser assembly as claimed in claim 1, wherein the at least one fixing further comprises a collet and the sacrificial material is a plug inserted into a bore of the collet.

17 A method of centralising a tubular in an oil, gas or water well, the method comprising: passing the tubular into an axial bore of a centraliser comprising first and second collars, the centraliser having at least one resilient device extending between the first and second collars, and passing the tubular through a locking ring in a position radially inside the resilient device and axially between the first and second collars; the resilient device being resiliently biased in a radial direction away from the locking ring towards a radially extended configuration, and being movable radially relative to the locking ring from the radially extended configuration into a radially restricted configuration in which the resilient device is closer to the locking ring than in the radially extended configuration; the locking ring having at least one catch device adapted to engage with the at least one resilient device in the radially restricted configuration of the resilient device and wherein the catch device is adapted to resist radial movement of the resilient device away from the locking ring when the catch device is engaged with the resilient device; wherein at least one fixing extends between the at least one catch device and the locking ring, the at least one fixing comprising a sacrificial material adapted to lose integrity in wellbore conditions faster than the material of the locking ring or the at least one catch device, wherein the method includes: deploying the centraliser into the well with the catch engaged with the resilient device and the resilient device in a radially restricted configuration, running the centraliser into the well in the radially restricted configuration, and releasing the catch by at least partially degrading the fixing through contact with fluids in the well before the degradation of the locking ring and the catch device.

18 The method as claimed in claim 17, including engaging the at least one catch device and the at least one resilient device by sliding one of the at least one catch device and the at least one resilient device relative to the other in an axial direction with respect to the bore of the collars.

19 The method as claimed in claim 17, including securing the catch device to the locking ring by the at least one fixing in the radially restricted configuration and releasing at least a portion of the catch device from the locking ring in the radially extended configuration.

20 The method as claimed in claim 17, including tensioning the at least one fixing along an axis perpendicular to the axis of the bore of the body.

21 The method as claimed in claim 17, including releasing the at least one catch device from the locking ring when the sacrificial material in the at least one fixing degrades.

22 The method as claimed in claim 17, wherein the fixing comprises a sacrificial component formed from a sacrificial material and a non-sacrificial component which is less reactive to wellbore conditions than the sacrificial material, and wherein the method includes degrading the sacrificial material in the fixing, and separating the sacrificial material from the non-sacrificial material in the fixing.

23 The method as claimed in claim 17, wherein the at least one fixing further comprises a collet and the sacrificial material is a plug inserted into a bore of the collet.

24 A centraliser assembly for use in an oil, gas or water well, the centraliser assembly comprising: a centraliser having a body comprising first and second collars, and having a bore with an axis adapted to receive a tubular to be centralised, and at least one resilient device extending between the first and second collars, and a locking ring for receiving the tubular in a position radially inside the resilient device and axially between the first and second collars; the resilient device being resiliently biased in a radial direction away from the locking ring towards a radially extended configuration, and being movable radially relative to the locking ring from the radially extended configuration into a radially restricted configuration in which the resilient device is closer to the locking ring than in the radially extended configuration; the locking ring having at least one catch device adapted to engage with the at least one resilient device in the radially restricted configuration of the resilient device and wherein the catch device is adapted to resist radial movement of the resilient device away from the locking ring when the catch device is engaged with the resilient device; at least one fixing between the at least one catch device and the locking ring; the at least one fixing comprising a pin adapted to be held in tension perpendicular to the axis of the bore of the body and formed from a soluble sacrificial material adapted to dissolve in wellbore conditions faster than the material of the locking ring or the at least one catch device, and wherein the at least one catch device is adapted to release from the locking ring when the at least one fixing at least partially dissolves, and wherein at least a portion of the at least one catch device is adapted to remain attached to the at least one resilient device when the at least one catch device releases from the locking ring.

25 A centraliser assembly for use in an oil, gas or water well, the centraliser assembly comprising: a centraliser having a body comprising first and second collars, and having a bore with an axis adapted to receive a tubular to be centralised, and at least one resilient device extending between the first and second collars, and a locking ring for receiving the tubular in a position radially inside the resilient device and axially between the first and second collars; the resilient device being resiliently biased in a radial direction away from the locking ring towards a radially extended configuration, and being movable radially relative to the locking ring from the radially extended configuration into a radially restricted configuration in which the resilient device is closer to the locking ring than in the radially extended configuration; the locking ring having at least one catch device adapted to engage with the at least one resilient device in the radially restricted configuration of the resilient device, wherein the at least one catch device has at least one plate spaced radially from the locking ring which defines a recess radially inside the at least one plate, wherein the recess receives and retains a portion of the at least one resilient device, and wherein the catch device is adapted to resist radial movement of the resilient device away from the locking ring when the catch device is engaged with the resilient device; at least one fixing between the at least one catch device and the locking ring; the at least one fixing comprising a pin adapted to be held in tension perpendicular to the axis of the bore of the body, and formed from a soluble sacrificial material adapted to dissolve in wellbore conditions faster than the material of the locking ring or the at least one catch device; the at least one catch device also incorporating at least one permanent fixing between the at least one catch device and the locking ring; wherein the at least one catch device is adapted to remain attached to the locking ring when the at least one fixing at least partially dissolves, and wherein the at least one catch device is adapted to deform when the at least one fixing at least partially dissolves.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

[0051] FIG. 1 is a perspective view of a first example of a centraliser assembly comprising a centraliser body and a locking ring, with resilient devices in a radially extended configuration;

[0052] FIG. 2 is a detailed view of one of the catch devices on the locking ring shown in FIG. 1;

[0053] FIG. 3a is a perspective view of the centraliser assembly shown in FIG. 1 with the resilient devices in a radially restricted configuration and the catch devices on the locking ring not yet engaged with the resilient devices;

[0054] FIG. 3b is a perspective view of the centraliser assembly shown in FIG. 3a with the catch devices on the locking ring engaged with the resilient devices;

[0055] FIG. 3c is a detailed view of the catch devices engaged with the wings protruding from the resilient devices shown in FIG. 3b;

[0056] FIG. 4a is a perspective view of the centraliser assembly shown in FIG. 3b with a first example of a tubular to be centralised received into the bore of the body of the centraliser and the centraliser assembly ready to be run into the wellbore;

[0057] FIG. 4b is a perspective view of the centraliser assembly shown in FIG. 4a with the catch devices released and the resilient devices in a radially extended configuration;

[0058] FIG. 5 is a perspective view of a second example of a centraliser assembly comprising a centraliser body and a locking ring, with resilient devices in a radially extended configuration;

[0059] FIG. 6 is a detailed view of one of the catch devices on the locking ring shown in FIG. 5;

[0060] FIG. 7a is a perspective view of the centraliser assembly shown in FIG. 5 with the resilient devices in a radially restricted configuration and the catch devices on the locking ring not yet engaged with the resilient devices;

[0061] FIG. 7b is a perspective view of the centraliser assembly shown in FIG. 7a with the catch devices on the locking ring engaged with the resilient devices and a second example of a tubular to be centralised received into the bore of the centraliser body;

[0062] FIG. 7c is a detailed view of the catch device engaged with the wings protruding from the resilient devices shown in FIG. 7b;

[0063] FIG. 8a is a perspective view of the centraliser assembly shown in FIG. 7b with the catch devices deformed on the locking ring;

[0064] FIG. 8b is a perspective view of the centraliser assembly shown in FIG. 8a with the resilient devices in a radially extended configuration and the catch devices still attached to the locking ring.

[0065] FIG. 9a is a perspective view of the centraliser assembly shown in FIG. 7b showing a third example of the fixings incorporated in the catch device shown in FIG. 5 and the catch devices separated from the locking ring;

[0066] FIG. 10 shows one optional design of tab on a resilient device;

[0067] FIG. 11 shows an optional design of locking ring;

[0068] FIG. 12 shows a further optional design of locking ring;

[0069] FIG. 13a illustrates an alternative fixing; and

[0070] FIG. 13b illustrates a collet of the alternative fixing.

DETAILED DESCRIPTION

[0071] Referring now to the drawings, a first example of a centraliser assembly 10 is shown in FIG. 1. The centraliser assembly 10 comprises a centraliser with a body 15 and a locking ring 30. The centraliser body 15 has a bore with an axis X and first and second collars 16, 17 at opposing ends of the centraliser body 15. The first and second collars 16, 17 are coaxial with the axis X of the centraliser body 15 and have a constant inner diameter CD. In this example the first and second collars 16, 17 are cylindrically shaped with a circular cross-section and constant and equal inner diameters CD, but in other examples the inner diameters of the first and second collars need not be constant or equal. The inner diameters CD of the first and second collars 16, 17 are sufficient to receive an outer diameter of a tubular T within the bore of the centraliser 15 as is shown in FIG. 4a.

[0072] The centraliser body 15 has at least one resilient device, and in this example six resilient devices in the form of bow springs 20 extend between the first and second collars 16, 17, but in other examples there may be fewer, or more, resilient devices. The opposing ends of each bow spring 20 connect the opposing circumferential edges of respective first and second collars 16, 17. In this example, the bow springs are spaced equidistantly around the opposing circumferential edges of the first and second collars 16, 17. Put another way, the six bow springs are spaced at regular 60 degree intervals around the circumferential edge of the first and second collars 16, 17.

[0073] In this example the resting configuration of the bow springs is the radially extended configuration shown in FIG. 1. In this configuration the bow springs 20 curve radially outward from the first and second collars 16, 17 to form arcs between the collars 16, 17. In this example the bow springs 20 are long and narrow in the direction of axis X, and have axially extending apertures or slots between each adjacent pair of bow springs 20.

[0074] The locking ring 30 is shown in FIG. 1 within the centraliser body 15 and coaxial with the axis X of the centraliser body 15 after insertion through one of the apertures between adjacent springs 20. The locking ring 30 is generally cylindrical with a circular cross-section. The inner diameter LD1 of the locking ring 30 is equal to or slightly greater than the outer diameter of the tubular T to be received within the bore of the centraliser 15 so that the locking ring 30 fits tightly over the tubular T, and can move axially along the tubular, but can be locked to the tubular T against axial movement along the tubular T by a grub screw or the like extending through the locking ring 30 and driving into or pressing against the outer surface of the tubular T. The outer diameter LD2 of the locking ring 30 is greater than the inner diameter CD of the first and second collars 16, 17, so when the locking ring and centraliser are assembled on the tubular T, the locking ring 30 is locked in place between the collars 16, 17, and cannot pass the collars 15, 16. In this example the locking ring is annular and surrounds the tubular T, but in other examples the locking ring 30 may be discontinuous and might only extend only part-way around the tubular T.

[0075] Typically, the locking ring 30 can be moved into position in the body 15 of the centraliser by orientating the locking ring 30 such that the axis X of the centraliser body is coplanar with the plane of the locking ring. In this orientation the locking ring 30 can be passed edge on through an aperture between an adjacent pair of bow strings 20 into the bore of the centraliser body when the centraliser is in the FIG. 1 radially extended configuration. The plane of the locking ring 30 can then be rotated again so that the axis of the locking ring 30 is coaxial with the axis X of the centraliser body 15 as shown in FIG. 1, ready for a tubular T to pass through the aligned bores of the collars 16, 17 and the locking ring 30 as shown in FIG. 4a.

[0076] A first example of a catch device 40 is shown in FIG. 2 fixed onto the outer circumference of locking ring 30; others are similar. The catch device 40 comprises a central portion 40c in the form of a central plate 41 optionally following the radius of the locking ring 30 which has at least one fixing 46 between the catch device 40 and the locking ring 30 and securing the catch device 40 to the locking ring 30; in this example, three fixings 46 are shown but other examples may have more than three or less, depending on how firmly the catch device 40 is to be secured to the locking ring 30. As is shown in FIG. 2, a central fixing 46c is larger than peripheral fixings 46p disposed on either side of the central fixing 46c. In different examples, multiple fixings can have the same or different characteristics. As also shown in FIG. 2, the central fixing 46c and peripheral fixings 46p are pins which pass through apertures in both the catch device 40 and locking ring 30 (as best seen in FIG. 4b). In this example the central fixing 46c and peripheral fixings 46p are cylindrically shaped solid bodies having a circular profile, but in other examples the central fixing 46c and/or peripheral fixings 46p can have a non-circular profile. The axes of the central fixing 46c and peripheral fixings 46p are coaxial with the radius of the locking ring 30 and the radii of the bore of the collars 16, 17, and hence perpendicular to the axis X of the bore of the centraliser body 15. In this example the central fixing 46c and peripheral fixings 46p are exposed to the surrounding environment on the radially outer surface of the catch device 40. Optionally in some examples (not shown) the assembly can incorporate channels between the catch device and the fixing to allow fluid in the well to access the fixing more predictably, for example, taking the form of hollow channels through the fixing, or channels around the fixing (which can be as simple as making the ID of the hole larger than the OD of the pin, thereby allowing fluid access to the pin and allowing increased accuracy in terms of the time taken to degrade the pin to the required extent.

[0077] In various examples the central fixing 46c and peripheral fixings 46p can be exposed to the surrounding environment on the radially inner surface of the locking ring 30 (as the locking ring 30 is generally not sealed against the tubular) and/or between the catch device 40 and the locking ring 30. In this example the length of the central fixing 46c and peripheral fixings 46p along their axes is approximately equal to the combined radial thicknesses of the locking ring 30 and the catch device 40 so that the ends of the fixings optionally terminate on exposed surfaces of the locking ring 30 and catch device 40 respectively, but in other examples the length of central fixing 46c and/or peripheral fixings 46p can be longer or shorter than this.

[0078] In this example the inner plate 41 is formed as a single piece but in other examples the opposing ends of the catch device 40 could be formed separately. The catch 40 has end portions 40e at each circumferentially opposing end, optionally spaced circumferentially apart on either side of a single bow spring 20 in this example. Each end portion 40e comprises an outer plate 43 connected to the inner plate 41 by an arcuate re-curved transition portion 42, so that the outer plate 43 is radially spaced from the inner plate 41 by the transition portion 42. Radially inside each outer plate 43 there is a recess 40r (or void). In this example, each outer plate 43 and recess 40r is formed by re-curving the circumferentially opposing ends of the inner plate 41 so each opposing end 40e of the catch device 40 is re-curved in a general C-shape when viewed along the axis X, and the recess 40r is formed between the opposing and radially spaced faces of the inner and outer plates 41, 43, but in other examples the recess can be formed in other ways. The opposing faces of the inner and outer plates 41, 43 are typically parallel so the recess 40r has parallel faces, which may optionally be curved with the radius of the locking ring 30 or may be straight. The recess 40r has open sides or ends facing the axis X in both directions, and a closed (optionally arcuate) back face comprising the transition portion 42 connecting the inner and outer plates 41, 43. The back faces in this example are disposed on circumferentially opposite sides of the catch device 40, e.g. with the recesses 40r on the opposed ends facing one another.

[0079] As shown on FIG. 3c, at least one wing 21 extends from at least one circumferentially facing edge of each bow spring 20, and in this case, each spring 20 typically has a wing 21 extending in a circumferential direction with respect to the axis X from each circumferentially facing edge, i.e. one wing on each side. Typically the wing 21 is disposed approximately midway along the axial length of the bow spring 20, but could be anywhere along the length of the spring 20. In this example, as best seen in FIG. 3c, the at least one wing 21 also extends radially inward below the radially outer surface of the bow spring 20, and in this example, the at least one wing 21 is stepped radially inwards from the radially outermost surface of the spring 20, which is optionally parallel to and radially spaced by the step from an outer face of the wing 21. The inward radial displacement of the radially outer surface of the wing 21 from the radially outer surface of the bow spring 20 is optionally equal to or greater than the radial thickness of the outer plate 43 of the catch device 40, for reasons that will be explained later.

[0080] The assembly 10 is intended to be fitted to a tubular T by inserting the locking ring 30 through a slot between adjacent springs 20 as described above optionally before insertion of the tubular T through the aligned bores of the locking ring 30 and body 15. This assembly of the tubular T with the centraliser 10 and locking ring 30 is optionally performed after the springs 20 have been compressed radially inwards into the radially restricted configuration shown in FIG. 3a, but could also be performed when the springs 20 are in the radially extended configuration as shown in FIG. 1.

[0081] In the present example, before being deployed in a wellbore and before the centraliser assembly is assembled together with the tubular T, the springs 20 are compressed radially inwards towards the axis into a radially restricted configuration, which facilitates insertion into the wellbore with reduced friction when the string is assembled. The springs 20 are compressed into a radially restricted configuration as shown in FIG. 3a by means of an external radially inward compression of the bow springs 20, for example an external constraining band (not shown) tightened radially around the body of the centraliser, a ring of hydraulic pistons, by the use of tongs, by pushing the centraliser through a funnel device etc. (not shown but the specific compression method can vary in different examples). As also seen in FIG. 3a, the locking ring 30 is positioned aligned with the axis X of the bore of the centraliser body 15 but spaced eccentrically along the axis, in this example, being axially closer to the first collar 16 and spaced from the axial position of the wings 21 on the bow springs 20. The locking ring 30 is also rotationally positioned around the axis X of the bore of the centraliser so that the recesses 40r of the catch devices 40 are circumferentially aligned with the wings 21 of the bow springs 20.

[0082] One of the centraliser body 15 and the locking ring 30 is then moved axially relative to the other, for example by moving the locking ring 30 along the axis X of the bore of the centraliser body 15 toward the second collar 17 until the wings 21 slide axially into the open ends of the catch devices 40, between the inner and outer plates 41, 43 of the C-shaped ends of the catch devices 40, so that the wings 21 are engaged in the recesses 40r, radially under the outer plates 43, and optionally radially between the inner and outer plates 41, 43. This engages the catch devices 40 with the wings 21 as shown in FIG. 3b, since the resilience of the bow springs 20 urges the wings radially outward against the outer plates 43, which resist the radial expansion of the bow springs 20, and keep the centraliser 10 in the radially restricted configuration. FIG. 3c shows a detailed view of two catch devices 40 and the wings 21 of two adjacent bow springs 20 engaged with each other. To engage the catch devices 40 with the wings 21, the locking ring 30 is displaced axially with the axial end surfaces of the wings 21 aligned with the open ends of the recesses 40r on the catch devices 40. Sliding the wings 21 between the inner plates 41 and the outer plates 43 of the catch devices 40 completes the engagement. Optionally, the axial end surfaces of the wings 21 slide into the open ends of the recesses 40r on the catch devices 40 simultaneously, allowing the catch devices 40 to engage the wings on each resilient device 20 simultaneously. In this example, the axial movement of the locking ring 30 is continued until the outer plates 43 of the catch devices are disposed approximately midway along the wings 21 in an axial direction. Optionally the C-shaped ends of the catch devices 40 can be squeezed circumferentially together circumferentially to deform and tighten the catch devices 40 circumferentially around the springs 20. After the engagement of the wings 21 and the catch devices 40 is complete, as shown in FIG. 3b, the central fixing 46c and peripheral fixings 46p are held in tension applied by the resilient force of the bow springs 20 trying to expand, along the axes of the central fixing 46c and peripheral fixings 46p, between the locking ring 30 and the catch device 40. The tension in the central fixing 46c and peripheral fixings 46p resists relative axial movement between the locking ring 30, which is fixed to the tubular T, and the outer plates 43 of the catch devices 40, which are urged radially outward by the stored elastic potential energy of the bow springs 20 in the radially restricted configuration. Optionally the wings 21 can incorporate a pocket or circumferential waist in which the outer plates 43 can lock against axial movement when, for example, in a central axial position on the wings 21 (or for example between a radially extending protrusion on either side of the outer plate 43) and this can be arranged to resist axial movement of the resilient devices 20 relative to the locking device 40.

[0083] As described previously, in this example the inward radial displacement of the radially outer surface of the wing 21 from the radially outer surface of the bow spring 20 is greater than the radial thickness of the outer plate 43. Therefore when the catch devices 40 are engaged with the wings 21, the radially outermost surface of the plate 43 remains within the outer diameter of the body of the centraliser. This provides the advantage that when the tubular T is inserted into the wellbore, the catch devices 40 are held away from the walls of the wellbore by the radially outermost surfaces of the bow springs 20, which have a greater diameter than the circumference formed by the radially outer surfaces of the outer plates 43 and hence engage the inner surface of the wellbore before any part of the catch device 40, and this reduces the chance of unintended contact between the wellbore wall and the catch devices leading to unintended release of the catch devices 40.

[0084] Once the catch devices 40 are engaged with the wings 21 as shown in FIG. 3b, the tubular T is inserted through the aligned bores of the locking ring 30 and body 15 into the centraliser assembly 10 as shown in FIG. 4a. When the centraliser assembly is in the desired position relative to the tubular T (optionally approximately midway along the length of the tubular T in this example) the locking ring 30 is fixed to the tubular T by means of at least one locking device (such as a grub screw or locking bolt etc. which is driven radially through the locking ring 30 into the outer surface of the tubular T or other locking method). Optionally, the centraliser assembly can be assembled in the factory and shipped to the well location in the radially restricted configuration, which saves on space during shipping and on assembly time when running into the hole.

[0085] Once the locking ring 30 has been fixed to the tubular T, the tubular T with the centraliser assembly is run into the wellbore still in the radially restricted configuration. Typically the outer diameter of the centraliser assembly with the bow springs in the radially restricted configuration is less than the inner diameter of the wellbore. This is advantageous for the running in procedure as friction between the centraliser assembly and the wall of the wellbore is greatly reduced due to the bow springs 20 clearing the inner wall of the wellbore. Therefore the insertion force required to run in the tubular is also reduced, which can minimise the risk of damage to the tubular or to the wellbore or casing during running in, and/or allow longer tubular strings to be run in to the wellbore, and/or can also allow a smaller annulus between the tubular and the internal wall of the wellbore, and/or a stronger force applied by the springs 20.

[0086] When the tubular has been run in to the correct position in the wellbore, in this example, the fixings 46 between the locking ring 30 and the catch devices 40 are exposed to downhole fluids. Typically these fluids can be acidic or otherwise corrosive, or comprise a chemical salt solution such as brine or seawater. In this example the fixings 46 are exposed to the downhole environment on the radially outer surface of the catch devices 40, as best seen in FIG. 2. The sacrificial material in the fixings 46 is, in this example, electrochemically reactive and at least partially dissolves when exposed to such downhole fluids. As the sacrificial material in the fixings 46 dissolve, their structural integrity is reduced until the fixings 46 fail under the outward radial load exerted by the bow springs 20 in the radially restricted configuration. Note that this can occur when the fixings 46 completely dissolve in some cases, but often it is sufficient for the material of the fixings 46 to dissolve only partially, so that they lose a certain amount of their structural integrity (e.g. 30%-80%, and optionally at least 50%, e.g. 50%-80%) and can no longer resist the radial tension applied by the springs 20. When the fixings 46 fail due to the sacrificial material dissolving, the catch devices no longer secure the springs 20 to the locking ring 30 and the bow springs 20 resiliently return to the radially extended configuration. In this example, the catch devices 40 separate from the locking ring 30 but remain attached to the wings 21. This is particularly advantageous as this reduces the risk of any parts of the centraliser assembly 10 separating from the centraliser assembly into the downhole environment after the bow springs 20 move into the radially extended configuration, where dropped objects could cause damage to other parts or components of the well.

[0087] FIG. 4b shows the centraliser assembly of FIG. 4a after the bow springs 20 have released into the radially extended configuration, which in this example is the resting configuration of the bow springs. In the radially extended configuration, the bow springs 20 are compressed against the wall or casing of the wellbore. The centraliser body 15 will adopt a radial position within the wellbore that balances the radial forces exerted on the centraliser body 15 by the compression of each bow spring 20, which will centralise the radial position of the tubular T within the wellbore. The catch devices 40 are radially clear of the inner surface of the well because of the step in the wings 21, and hence do not resist rotation or sliding of the centraliser in the wellbore.

[0088] A second example of a centraliser assembly 110 is shown in FIG. 5. The second example is generally similar to the first example, and equivalent parts (which will not be described again in detail) are numbered similarly, but the reference numbers are increased by 100. In the second example, the centraliser body 115, first and second collars 116, 117, bow springs 120, wings 121 and locking ring 130 are equivalent in form and in function to the corresponding parts described previously in the first example.

[0089] A catch device 140 is shown in FIG. 6 on the outer circumference of locking ring 130. In this example, the catch device 140 is different from the catch device 40 in the first example described above; other catch devices in this second example are similar. In this example the catch device 140 has a central portion 140c with a central plate 141 which optionally follows the radius of the locking ring 130 and end portions 140e which incorporate outer plates 143 which are stepped radially outwards from the central plate 141 at each opposing end of the central plate 141. The outer plates 143 are connected to the central plate 141 by generally S-shaped arcuate re-curved transition portions 142, which are formed by reversing the curvature of the central portion to extend radially outwards, and then again reversing the outward curvature in the transition into the outer plate 143, which is optionally parallel to the locking ring 130. Each end 140e therefore has a general S-shape when viewed along the axis and the outer plate 143 of each wing is radially stepped from the central plate 141.

[0090] The central plate 141 has at least one central fixing 145 extending between the catch device 140 and the locking ring 130. In this example one central fixing 145 is shown, but other examples may have more than one depending on how firmly the catch device 140 is to be secured to the locking ring 130. The catch device 140 also has at least one peripheral fixing 146, optionally at least two peripheral fixings 146, between the transition portions 142 and the locking ring 130. As shown in FIG. 7c, the peripheral fixings 146 are disposed on either side of the at least one central fixing 145, and the peripheral fixings 146 are smaller than the at least one central fixing 145. In other examples, the at least one central fixing 145 and peripheral fixings 146 may have the same or different structure. In this example the central plate 141, transition portions 142 and outer plates 143 are formed as a single piece but in other examples could be formed separately. In this example each outer plate 143 and each recess 140r is formed by introducing a concave-convex re-curve to the opposing ends 140e of the central portion 140c, so that each outer plate 143 also optionally follows the radius of the locking ring 130, but is displaced outward radially from the outer surface of the locking ring 130 so that the recess 140r is formed between the radially outer surface of the locking ring 130 and radially inner surface of the outer plate 143. In other examples the recess 140r can be formed in other ways. The opposing faces of the radially outer surface of the locking ring 130 and radially inner surface of the outer plate 143 are typically parallel so the recess 140r has parallel faces, which may optionally be curved with the radius of the locking ring 130 or may be straight. The recess 140r has open sides or ends facing the axis X of the centraliser body 115 in both directions, and a closed back face where the transition portion 142 re-curves to connect the outer plate 143 to the central plate 141.

[0091] In this example, the peripheral fixings 146 between the transition portions 142 and the locking ring 130 are formed from a sacrificial material which degrades (e.g. dissolves) more readily than the material of any of the locking ring 130, the inner plate 141, the transition portions 142 and the outer plates 143. Also, in this example, the central fixing 145 between the inner plate 141 and the locking ring 130 is a permanent fixing such as a spot weld, rivet or screw which is adapted to be substantially unreactive to conditions that sacrificially dissolve, degrade or disrupt the peripheral fixings 146.

[0092] At least one wing 121 extends in a circumferential direction with respect to the axis X of the centraliser body 115 from at least one circumferentially facing edge of each bow spring 120, and in this example, each bow spring 120 typically has a wing 121 extending from each circumferentially facing edge, as described previously in the first example.

[0093] The centraliser assembly 110 is intended to be fitted to a second example of a tubular T by inserting the locking ring 130 through the aperture between adjacent bow springs 120 and then inserting the tubular T through the aligned bores of the centraliser body 115 and locking ring 130, as described previously in the first example. The steps of fixing the locking ring 130 to the tubular T, compressing the bow springs 120 into the radially restricted configuration as seen in FIG. 7a, and engaging the catch devices 140 with the wings 121 by moving the locking ring 130 (and the tubular T) along the axis X of the centraliser body 115 as seen in FIG. 7b, are also essentially as described previously in the first example. In this example, the ordering of these steps is typically as just described, since the fixings to fix the locking ring 130 to the tubular T are typically disposed between the catch devices 140 on the outer surface of the locking ring 130. in this example, the locking ring 130 is optionally fixed to the tubular T before compressing the bow springs 120 into the radially restricted configuration, since after the bow springs 120 are compressed into the radially restricted configuration, the fixings to fix the locking ring 130 to the tubular T may be less accessible from the outer surface of the centraliser.

[0094] As best illustrated in FIG. 7c, as the locking ring 130 (and tubular T) are moved relative to the centraliser body 115, the catch devices 140 are engaged by the wings 121 sliding through the recess 140r between the outer surface of the locking ring 130 and the inner surface of the outer plates 143 of the catch devices 140. As in the first example described previously, in this case the axial movement of the locking ring 130 is continued until the outer plates 143 of the catch devices 140 are disposed approximately midway along the wings 121 in the direction of the axis X of the centraliser body 115. Optionally the catch devices 140 can be secured to the wings 121 by a waist or pockets or protrusions on the wings 121 as previously described.

[0095] Once the locking ring 130 has been fixed to the tubular T and the catch devices 140 have engaged the wings 121, the tubular T with the centraliser assembly is run into the wellbore in the radially restricted configuration as described previously in the first example.

[0096] When the tubular T is deployed in the wellbore, the central fixing 145 and peripheral fixings 146 are exposed to the downhole fluids described previously in the first example. In this example, the peripheral fixings 146 are formed at least partially from a sacrificially dissolvable material, but in contrast the central fixing 145 is a permanent fixing such as a weld or steel bolt which is not adapted to degrade in the well at the same rate as the fixings 146. When the bow springs 120 are in the radially restricted configuration they exert a radially outward load on the outer plates 143 of the catch device 140. As the sacrificial material of the peripheral fixings 146 dissolves, their structural integrity is reduced until the peripheral fixings 146 eventually fail under the outward radial load exerted by the bow springs 120 in the first radially restricted configuration. When the peripheral fixings 146 fail, the transition portions 142 of the catch device 140 are no longer secured to the locking ring 130, but the inner plate 141 remains secured to the locking ring 130 by means of the unreactive central fixing 145. The outward radial load exerted by the bow springs 120 on the outer plates 143 is sufficient to deform the unsecured transition portions 142 between the inner plate 141 and outer plates 143 so that the outer plates 143 move from a parallel orientation with respect to the outer surface of the locking ring 130 toward a perpendicular orientation with respect to the outer surface of the locking ring 130 as shown in FIG. 8a.

[0097] As shown in FIG. 8b, after the transition portions 142 between the inner plate 141 and outer plates 143 have deformed, the outer plates 143 eventually clear the wings 121 and no longer restrain the bow springs 120, allowing the bow springs 120 to resiliently return to the radially extended configuration, which in this example is the resting configuration of the bow springs 120, as also shown in FIG. 4b in the first example described previously.

[0098] A third example of a centraliser assembly 210 is shown in FIG. 9a. The third example is very similar to the second example 110 except for differences in the composition of the central fixings 245 and the manner in which the catch devices 240 release from the locking ring 230. Like parts again have the same references increased by 100.

[0099] In this example, the catch device 240 also has a central fixing 245 and optionally at least one peripheral fixing 246, optionally at least two peripheral fixings 246, between the transition portions between the inner plate 241 and outer plates 243 and the locking ring 230, which are substantially as previously described.

[0100] In this example, both the central fixing 245 and the peripheral fixings 246 incorporate a sacrificial material which degrades (e.g. dissolves) more readily than the material of any of the locking ring 230, the inner plate 241, the transition portions 242 and the outer plates 243.

[0101] The locking ring 230 is fixed to a third example of a tubular T and the catch devices 240 are engaged with the wings 221 in the same manner as described previously in the second example and as shown in FIGS. 7a and 7b. The tubular T with the centraliser assembly 210 is then run into the wellbore in the radially restricted configuration as described previously in the second example.

[0102] When the central fixing 245 and peripheral fixings 246 are exposed to the downhole fluids as described previously in the first and second examples, the sacrificial material degrades as previously described, and the fixings 245, 246 lose structural integrity until they fail under the outward radial load exerted by the bow springs 220 in the first radially restricted configuration. When the fixings 245, 246 fail, the inner plate 241 and outer plates 243 of the catch device 240 are no longer secured to the locking ring 230. Therefore the outward radial load exerted by the bow springs 220 acts to urge the catch devices 240 radially outward and away from the centraliser body 215 as shown in FIG. 9a.

[0103] After the catch devices 240 have separated from the locking ring 230, the bow springs 220 are no longer restrained and resiliently return to the second extended configuration, which in this example is the resting configuration of the bow springs 120, as also shown in FIGS. 4b and 8b in the respective first and second examples described previously.

[0104] FIG. 10 shows a possible alternative configuration of resilient device 220 having a similar wing 221 as previously described in relation to the wing 21 of the first example, but which incorporates a waist 221w in the wing 221 on each side of the resilient device 220, but it is sufficient for a waist to be formed on only one of the sides. The waist 221w is formed in the radially inwardly displaced peripheral edge of the wing 221, and provides a circumferentially extending notch in which a catch device can engage, for example the generally C-shaped transition portion 42 of the first example. The waist 221w can resist axial movement of the catch device engaged in the waist 221w along the resilient device 220 when fixed in place.

[0105] FIG. 11 shows a further optional modification of a locking ring 330, similar to the locking ring 30 shown in the first example, but in which the fixing 346 comprises a generally C-shaped band comprising a sacrificial material, which is wrapped around a portion of the catch device 340 and the locking ring 330. Both the catch device 340 and the locking ring 330 have notches 340n, 330n in which the fixing 346 can engage, and in which it can optionally be tensioned, for example by crimping etc as previously described. The FIG. 11 locking ring functions essentially as described for the first example, and the sacrificial material in the fixing 346 degrades to release the fixing 346 from the assembly which releases the catch device 340 from the locking ring 330.

[0106] FIG. 12 shows an analogous example to the example shown in FIG. 5, having a locking ring 430, and a catch device 440 similar to the catch device 140 shown in the FIG. 5 example, but which is secured to the locking ring 430 by fixings 446 similar to the fixing 346 described in the FIG. 11 example, and which engages in notches 440n, 430n as previously described with respect to FIG. 11.

[0107] Any of the optional modifications set out in FIGS. 10-12 can be used with any of the examples described previously.

[0108] FIG. 13a illustrates an alternative fixing 500. FIG. 13b illustrates a collet 501 of the alternative fixing 500. The alternative fixing 500 may include the collet 501 and a plug 510. The collet 501 may be made from a non-sacrificial material, such as a ferrous or non-ferrous metal or alloy, such as steel, and the plug 510 may be made from any of the sacrificial materials, discussed above. The alternative fixing 500 may be used instead of any of the sacrificial fixings 46c,p, 146, 245, 246, discussed above. The collet 501 may have first and second end rings 502, 503, first and second shoulders 504, 505 extending from the respective end rings, and a plurality of fingers 506 connecting the shoulders. Each end ring 502, 503 may be split by a plurality of slots extending through a wall thereof, along the respective shoulder 504, 505, between adjacent fingers 506, and to the other shoulder. The slots may alternate between the end rings 502, 503. Each end ring 502, 503 may have an enlarged outer diameter relative to a reduced outer diameter of the fingers 506 and each shoulder 504, 505 may be tapered to gradually transition between the enlarged and reduced outer diameters. The reduced diameter may correspond to the outer diameter of the sacrificial fixing 46c,p, 146, 245, 246 that the alternative fixing 500 is replacing.

[0109] The collet 501 may have a longitudinal bore formed therethrough and one 503 of the end rings 502, 503 may have may have a seat extending into the bore for receiving an end of the plug 510. Assuming the alternative fixing 500 is replacing the central fixing 46c and is to be inserted into aligned apertures in the catch device 40 and the locking ring 30, the collet 501 (or at least one of the end rings 502, 503 and one of the respective shoulders 504, 505 thereof) may be compressed to a reduced outer diameter less than or equal to the diameter of the apertures and held in the compressed position. The collet 501, in the compressed position, may then be inserted into the aligned apertures and released, thereby allowing the collet to expand to its natural position. A length of the fingers 506 may correspond to a length of the apertures such that the end rings 502, 503 and shoulders 504, 505 protrude therefrom. In the natural position, the enlarged outer diameter of the end rings 502, 503 may be greater than the diameter of the apertures, thereby trapping the collet 501 within the apertures. The plug 510 may then be inserted into the trapped collet 501, thereby locking the collet into the natural position. The plug 510 may have an outer diameter slightly greater than the diameter of the collet bore, thereby forming an interference fit therewith, to secure the plug into the collet bore.

[0110] The plug 510 may have a longitudinal bore formed therethrough (shown) or may be solid (not shown). After the centraliser assembly 10 has been assembled, the bow spring 20 will exert a tensile force onto the collet 501. The shoulders 504, 505 will then engage the walls of the locking ring 30 and the catch device 40 surrounding the apertures, thereby exerting a compressive force onto the plug 510. Once the plug 510 has been sufficiently dissolved by exposure to wellbore fluid, the collet 501 will be unlocked and free to compress and release the catch device 40 from the locking ring 30. The collet 501 may remain trapped in one of the apertures after release. The plug bore may be sized to adjust the release time of the alternative fixing 500 after exposure to the wellbore fluid.

[0111] Advantageously, having the plug 510 in compression allows less and/or smaller fixings to be used to withstand the load exerted by the compressed bow springs 20. The plug 510 in compression may also allow more accurate estimation of release time of the bow springs 20.

[0112] Alternatively, for any of the embodiments discussed above, the sacrificial material may be a composite material including a sacrificial material and a non-sacrificial material. The composite material may be a cermet including a ceramic, such as tungsten carbide, and a sacrificial metal or alloy, such as magnesium, zinc, or aluminium manganese alloy. The sacrificial composite may be made by sintering the ceramic and the sacrificial metal or alloy together.

[0113] Alternatively, for any of the embodiments discussed above, the locking ring may not be fixed to the tubular and the centralizer assembly may further include a pair of external locking collars for surrounding and being fixed to the tubular about the centralizer body for trapping the centralizer body therebetween.

[0114] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope of the invention is determined by the claims that follow.