Downhole packer

Abstract

A method of sealing a downhole annulus comprises: providing a fusible member 106 on an inner pipe 104; locating the fusible member and the inner pipe downhole and within an outer pipe or open hole, and reconfiguring the fusible member from a first configuration in which the fusible member describes a smaller first diameter to a second configuration in which the fusible member describes a larger second diameter. With the fusible member in the second configuration the member is heated and fluidised. The fluidised fusible member then cools and solidifies to provide a seal between the inner pipe and a surrounding wall of the outer pipe or the borehole.

Description

FIELD This disclosure relates to a downhole packer and to a method of sealing a downhole annulus. BACKGROUND In the oil and gas exploration and production industry there may be circumstances where it is necessary or desirable to create a seal between two coaxial pipes or tubulars, or between a casing and the open hole. This may be achieved by providing a packer on the exterior of the inner pipe. A typical packer will include a sealing element and grips or slips. The packer may be run into the outer pipe in a smaller first diameter configuration and then radially extended to describe a larger second diameter configuration in which the sealing element and the slips engage an inner surface of the outer pipe. The sealing element may comprise an elastomer which will radially expand or extend under axial compression. SUMMARY According to a first aspect of the disclosure there is provided a method of sealing a downhole annulus, the method comprising: providing a fusible member on an inner pipe; locating the fusible member and the inner pipe downhole and within an outer pipe or open hole; reconfiguring the fusible member from a first configuration in which the fusible member describes a smaller first diameter to a second configuration in which the fusible member describes a larger second diameter; heating and fluidising the fusible member, and permitting the fluidised fusible member to cool and solidify and provide a seal between the inner and outer pipes or the borehole wall. According to a second aspect of the disclosure there is provided a downhole packer for location in an outer pipe, the downhole packer comprising: an inner mandrel; a fusible member located on the inner mandrel, and a heater, the packer being reconfigurable from a first configuration in which the fusible member describes a smaller first diameter to a second configuration in which the fusible member describes a larger second diameter, wherein the heater is activatable to heat and fluidise the fusible member and the fusible member may then cool and solidify to provide a seal between the inner mandrel and the surrounding wall. The packer may thus provide a seal between the inner mandrel and a surrounding wall, which may be the surface of an outer pipe or the borehole wall. The inner mandrel may be mounted on or incorporated in an inner pipe. The fusible member may be formed of any suitable material that may be melted or fluidised in a downhole environment on exposure to an appropriate energy source and will then solidify or refreeze when the energy source is removed or exhausted. Suitable materials may include low melt metals or alloys such as bismuth-tin alloys. A single fusible member may be provided, or multiple members may be provided. The fusible member may incorporate or be provided in combination with a flux or other material adapted to facilitate bonding between the fusible material and the surrounding wall. The fusible member may be provided with a coating, for example with a heat-resistant polymer film, to minimise or prevent flux leaching prior to heating and fluidising of the member. The fusible member may initially be provided in a solid or structural form, such as a cast, powder compacted or sintered form. The fusible member may be machined or otherwise formed to an appropriate configuration. In some examples the fusible member may be deformable to achieve the second larger diameter. The fusible member may be porous, for example formed of sintered alloy beads. The fusible member may be mechanically manipulated to achieve the second configuration prior to being heated and fluidised. The fusible member may be in a solid or structural form as the member is reconfigured from the first configuration to the second configuration. The fusible member may displace ambient material from between an outer surface of the fusible member and an inner surface of a surrounding wall as the packer is reconfigured from the first configuration to the second configuration. Upper and lower back-up members may be mounted on the inner mandrel and the fusible member located between the back-up members. With the packer in the first configuration the back-up members may describe a smaller first diameter and with the packer in the second configuration the back-up members may describe a larger second diameter and may engage the surrounding wall. The fusible member may be constrained within a volume between the back-up members. As the fusible member is reconfigured, the displaced ambient material may be ejected from the volume. One or both of the back-up members may include slots or bypass passages to facilitate displacement of the ambient material from the volume. Bypass passages may be provided by forming the back-up members of porous material. The back-up member may be formed of any suitable material, for example elastomers or metals. Each back-up member may be formed as a single part or may comprise multiple parts, which may be interlocked. With the packer in the second configuration the fusible member may substantially fill a volume between the inner mandrel and the surrounding wall, to minimise the volume of ambient material present. The ambient material may include wellbore fluid, suspended solids, or material adhered to the inner surface of the outer pipe. The packer may include cam surfaces, and the fusible member may be reconfigurable from the first configuration to the second configuration by translation of the fusible member relative to the cam surfaces. Cam surfaces may be provided on the inner mandrel, or cam surfaces may be provided on part of the heater. In one example the fusible member may comprise tapered solid alloy forms which may be driven over a cam surface provided by a tapered packer mandrel. The fusible member may be reconfigurable from the first configuration to the second configuration in response to axial translation or compression. Stops may be provided to restrict or limit axial translation or compression, to prevent extrusion of the fluidised fusible member. The fusible member may take any appropriate form, for example one or more rings which may be cut or split to facilitate radial expansion, one or more cylinders which may be axially compressible or may include axial or helical cuts to facilitate radial expansion, or discs which are initially dished, inclined or angled and which describe a larger diameter when flattened. The packer may be reconfigured by any appropriate means, for example hydraulic pistons or springs, such as leaf springs, acting on the fusible member directly or via back-up members. The heater may take any appropriate form and may be deployed simultaneously with the packer or may be separately deployed into a packer bore. The heater may comprise an exothermic heater, such as a thermite heater, or may be an electric heater. The heater may be initiated by any appropriate means, for example by a predetermined fluid pressure or a sequence of pressure signals, or by other signals relayed from surface through bore fluid or through a pipe or other signal carrier. In one example a thermite heater has an exothermic reaction initiation means and is adjacent to the fusible material. The heater may be activated by application of well pressure which closes a pressure switch to power an initiation process. In such an example an operator may apply wellbore pressure which activates a piston to act on packer back-ups, the piston closes the pressure switch, thermite initiation is triggered, the fusible member, which may comprise a low melt alloy in intimate contact with the thermite heater, melts and, constrained by the back-ups, forms a barrier. An exothermic heater may be mounted on the mandrel adjacent to the fusible member or may otherwise be located proximate the fusible member or incorporated into the fusible member. The heater may retain its form following activation or may be at least partially fluidised on activation. The heater may be incorporated into the fusible member. The heater may form a structural part of the sealing member that is formed by the resolidified fusible member and may serve as a reinforcing member for the sealing member. The heater may be a compacted thermite hollow cylinder and may be sealed to prevent ingress of wellbore fluids. The heater may be thermally coupled to the fusible material, for example by providing a solid rod of thermally conductive material that extends from the heater into contact with or through the fusible material. The packer may comprise slips or grips for extending into contact with the outer pipe. The slips may be provided integrally with the fusible material or may be provided separately of the fusible material. The slips may be formed of any suitable material and may coated with a material, for example tin or copper, to facilitate bonding with the fusible material. Elements of the packer, or the surface of a surrounding pipe or casing, may be coated with a material, for example tin or copper, to facilitate bonding with the fusible material. According to a third aspect of the disclosure there is provided a method of sealing a downhole annulus, the method comprising: providing a packer comprising a solid alloy member on an inner mandrel between upper and lower back-up members; locating the packer downhole and within an outer pipe or open hole; radially expanding the alloy member to occupy a volume between the inner mandrel and an inner surface of the outer pipe or borehole wall; constraining the alloy member between the back-up members; heating and fluidising the alloy member, and permitting the fluidised alloy to cool and solidify and provide a seal between the inner and outer pipes or the borehole wall. This aspect of the disclosure may be provided in combination with one or more of the features described above. The skilled person will understand that the various individual features described above, in addition to being useful in combination with the various aspects of the disclosure, may have individual utility. BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a partial section of a packer in accordance with a first example of an aspect of the disclosure; Fig. 2 is a partial section of part of a packer in accordance with a second example of the present disclosure; Fig. 3 shows a petal of the packer of Fig. 2; Fig. 4 is a partial section of a packer in accordance with a third example of an aspect of the disclosure; Fig. 5 is a partial section of a packer in accordance with a fourth example of an aspect of the disclosure; and Figs. 6-15 illustrate various features of packers made in accordance with examples of aspects of the disclosure. DETAILED DESCRIPTION OF THE DRAWINGS Referring first to Fig. 1 of the drawings there is illustrated a downhole packer 100 in accordance with a first example of an aspect of the disclosure. The packer 100 is adapted for mounting on an inner pipe and is run from surface into an outer pipe 102, for example a section of downhole casing. The packer 100 comprises an inner mandrel 104 and fusible members in the form of V-section alloy split rings 106 located on the inner mandrel 104. As will be described, the packer further comprises V-section steel split rings 108 which act as back-ups for the alloy rings 106, and V-section steel rings 110 which act as camming wedges for the alloy rings 106. The packer 100 is provided in combination with a heater 112, in this example the heater 112 being run into the casing 102 separately of the packer 100 and located within the mandrel bore 114. The drawing illustrates the packer 100 in a first configuration in which the alloy rings 106 describe a smaller first outer diameter to facilitate the location of the packer 100 in the casing 102. With the packer 100 in a second configuration the alloy rings 106 describe a larger second outer diameter corresponding to the inner diameter of the casing 102, that is the rings 106 have been pushed into contact with the casing 102. As the rings 106 transition to the second diameter, ambient material (e.g., well fluid, suspended solids, and casing surface contamination) in the annulus 116 between the outer surfaces of the rings 106 and the inner surface of the casing 102 is axially displaced such that little if any ambient material remains between the opposing surfaces of the rings 106 and the casing 102. In this example the alloy and steel rings 106, 108, 110 are accommodated within an annular recess 118 in the outer surface of the mandrel 104 between a lower fixed shoulder 120 and an upper axially movable shoulder 122. The three alloy rings 106 are located in external recesses formed between four of the steel camming rings 110, and the two steel split rings 108 are located in external recesses formed between the upper and lower pairs of steel camming rings 110. To set the packer 100 the upper movable shoulder 122 is moved towards the lower fixed shoulder 120; tubing pressure may be applied to a piston coupled to the shoulder 122. Such movement axially compresses the rings 106,108,110 and pushes the split rings 106,108 radially outwards and into contact with the casing 102. The heater 112 is then activated and supplies sufficient energy to heat and fluidise the alloy rings 106. The molten alloy may then flow to create a continuous volume of alloy. Given that the alloy is likely to be relatively dense, in a vertical section of casing 102 the molten alloy will likely displace any ambient material remaining in the volume between the extended steel rings 108 towards the upper end of the volume and provide a continuous alloy barrier between the mandrel 104 and the casing 102. The heater 112 may then be retrieved to surface, or otherwise stop generating heat, such that the various elements of the packer 100 will cool and return to the ambient temperature of the well. The molten alloy will thus cool and solidify to create a sealing member providing a fluid and pressure-tight seal between the mandrel 104 and the casing 102. The skilled person will understand that the number, composition, and configuration of the rings 106, 108, 110 may be varied to provided packing elements of different length and having different expansion and sealing characteristics. For example, the angles and shapes of the rings may be selected to minimise the gaps left between the rings when expanded, and thus minimise the volume of ambient material present when the alloy is fluidised. In other examples the alloy split rings may be separated by steel split rings to provide distinct alloy sealing areas or elements to provide extra redundancy. Reference is now also made to Fig. 2 of the drawings, a partial section of part of a packer 200 in accordance with a second example of the present disclosure, and to Fig. 3 which shows a petal 230 of the packer of Fig. 2. The packer 200 is of similar form and construction to the packer 100 described above but features metal petals 230 for retaining the end V-section steel rings 210 which act as camming wedges for the alloy rings 206. The petals 230 are fixed to a ring-shaped holder 232 by respective pins 234 and are overlapped or stacked such that when the packer 200 is set and the petals 230 bend outwards there are no gaps between the petals 230. The free ends of the petals 230 are pushed into contact with the inner surface of the surrounding casing 202. When the steel ring 210 engages the holder 232 no further deformation of the petals 230 is possible, such that any remaining axial setting forces are available for expanding the alloy rings 206. Reference is now also made to Fig. 4 of the drawings, a partial section of a packer 300 in accordance with a third example of an aspect of the disclosure. In this example the fusible member is a cylinder of low melt alloy 306 formed with external and internal grooves 340, 342. When the alloy cylinder 306 is axially compressed the cylinder will shorten, crumple, buckle and radially expand to the inner diameter of the surrounding tubing or casing 302. The cylinder 306 is mounted between upper and lower expandable back-up rings 308. The radially expanded cylinder 306 may then be heated and fluidised, and then allowed to cool and refreeze, in a similar manner to the packer 100. The skilled person will appreciate that the expansion characteristic of the cylinder 306 may be adjusted by varying the number, location and configuration of the grooves 340, 342, and that the groove configuration may be varied along the length of the cylinder 306 to control the crumpling of the cylinder, for example it may be desirable to have a selected portion of the cylinder expand initially to facilitate displacement of ambient material in a particular direction. A single cylinder 306 may be provided, or multiple shorter cylinders may be stacked to provide a desired length of alloy on the packer 300. Reference is now also made to Fig. 5 of the drawings, a partial section of a packer 400 in accordance with a fourth example of an aspect of the disclosure. In this example the fusible member comprises multiple low melt alloy cone-shaped washers 406 located between cone-shaped steel end washers 408. The washers 406, 408 initially describe a smaller first diameter and on axial compression the washers 406, 408 are flattened to describe a larger second diameter. As the washers 406, 408 are flattened the ambient material between the packer 400 and the casing 402 is displaced and the washers 406, 408 contact the inner surface of the casing 402. On heating, the twelve flattened alloy washers 406 melt and flow to create a continuous body of molten alloy. The flattened steel end washers 408 do not melt and retain the molten alloy in the volume between the mandrel 404 and the casing 402. On cooling, the alloy refreezes and forms a continuous sealing element which is bonded to the mandrel 404 and the casing 402. Reference will now be made to Figs. 6 - 15 of the drawings, which illustrate various features of packers made in accordance with examples of aspects of the disclosure. Figs. 6a &6b show a fusible member in the form of a solid alloy cylinder 500 with an axial cut 502 which may be radially expanded from an initial smaller diameter Di to a larger diameter D2. Figs. 7a &7b show a fusible member in the form of a solid alloy cylinder 510 with a helical cut 512 which may also be radially expanded from an initial smaller diameter Di to a larger diameter D2. Figs. 8a &8b show the cylinder 510 mounted on a mandrel 514 between expandable back-up members 516. On axial compression of the cylinder 510 and back-up members 516 the diameters increase until the cylinder 510 and the members 516 engage the surrounding casing 518. The expanding cylinder 510 forcefully extrudes surrounding ambient material, including casing fluid 520 and solid contamination 522 on the casing surface, past the back-up members 516. Following expansion, the cylinder 510 is melted and the molten alloy is constrained in the volume 524, which has been substantially cleared of ambient material 520, 522, between the back-up members 516. Figs. 9a, 9b &10 show an alternative packer configuration in which the fusible member comprises solid tapered alloy forms 530 which may be driven up a tapered packer mandrel 532, via back-up members 534, by a hydraulic piston 536, to transition from an initial smaller diameter Di to a larger diameter D2. Fig. 10 illustrates the provision of a positive stop 538 to limit the travel of the actuating piston 536. This prevents further travel of the piston 536 and movement of the back-up members 534, once the alloy forms 530 have been fully radially extended. In the absence of such a stop 538 it is possible that the mobile fluidised alloy, under continuing pressure from the back-up members 534, would be extruded from the volume 540. The piston arrangement also includes a lock arrangement 542, to prevent release if the piston 536 on loss of actuating pressure. Figs. 11 a &11 b illustrate a packer 550 having expanded alloy forms 552 on a tapered packer mandrel 554 between back-up members 556. In other examples a taper may be provided by locating a heater with a tapered surface between a non-tapered mandrel and the alloy forms. The forms 552, the mandrel 554 and the members 556 are configured such that there are no gaps between the parts of the forms 552, no external gap between the outer surfaces of the compressed and expanded forms 552 and the surrounding casing 558, and no internal gap between the inner surfaces of the forms 552 and the mandrel 554. Thus, expansion and compression of the forms 552 results in expulsion of all the ambient well material from the volume 560 between the back-up members 556. Figs. 12a &12b illustrate a detail of the upper back-up member 556, an external groove 562 which allows ambient well material to be extruded from the volume 560 after the member 556 has engaged the casing 558. Fig 13 illustrates a wireline-mounted heater 564 positioned within the mandrel bore 566, such that activation of the heater 564 results in heating of the packer 550 and melting of the alloy forms 552. Fig. 14 illustrates an alternative heating arrangement, in which a packer 570 incorporates an exothermic heater, such as a thermite heater 572. The heater 572 comprises an annular thermite cylinder 574, incorporating a control module and an initiator. The cylinder 574 is mounted on the packer mandrel 576 directly adjacent the fusible annular alloy form 578. The alloy form 578 and the thermite cylinder 574 are both located between the back-up members 580, with the cylinder directly above the lower back-up member 580. On activation, the heater 572 maintains its form while the alloy form 578 melts and settles in the annular space between the back-up members 580. The molten alloy will occupy any gaps or spaces around the heater 572 such that on the alloy cooling and resolidifying, the heater 572 will be incorporated into the resulting sealing member, and may serve to reinforce the sealing member. Fig. 15 illustrates a packer 590 with a tapered mandrel 592 in which the expandable alloy forms 594 contain slip elements 596. The slip elements 596 feature casing-gripping teeth 598 and are initially contained within the cast forms 594. Compressed steel coil springs 600 may also be cast within the forms 594. When the expanded alloy forms 594 are melted, the springs 600 may extend and urge the slip elements 596 along the tapered mandrel 592 and radially outwards to engage the casing 602. When the alloy cools and freezes, the slip elements 596 are maintained in the extended configuration and thus mechanically anchor the packer 590 to the casing 602. The elements 596 are coated with tin or copper to facilitate bonding of the elements 596 to the alloy. The apparatus as described herein may incorporate features of or may be provided in combination with apparatus such as described in applicant’s earlier patents and patent applications, for example WO2020 / 144091, WO2020 / 216475, WO2021 / 043443, WO2021 / 043444, WO2022 / 096149 and GB2586796, the disclosures of which are incorporated herein in their entirety. REFERENCE NUMERALS: downhole packer 100 outer pipe / casing 102 inner mandrel 104 alloy split rings 106 steel split rings 108 steel rings 110 heater 112 mandrel bore 114 annulus 116 annular recess 118 lower fixed shoulder 120 upper axially movable shoulder 122 packer 200 casing 202 alloy split rings 206 5 steel end rings 210 petal 230 petal holder 232 pins 234 10 packer 300 alloy cylinder 306 back-up rings 308 external grooves 340 internal grooves 342 15 packer 400 casing 402 inner mandrel 404 alloy washers 406 20 steel end washers 408 solid alloy cylinder 500 axial cut 502 25 solid alloy cylinder 510 helical cut 512 mandrel 514 back-up members 516 casing 518 30 casing fluid 520 solid contamination 522 containment volume 524 solid tapered alloy forms 530 5 tapered packer mandrel 532 back-up members 534 hydraulic piston 536 piston stop 538 containment volume 540 10 piston lock 542 packer 550 alloy forms 552 tapered packer mandrel 554 15 back-up members 556 casing 558 volume 560 external groove 562 heater 564 20 mandrel bore 566 packer 570 thermite heater 572 thermite cylinder 574 25 mandrel 576 alloy form 578 back-up members 580 packer 590 30 tapered mandrel 592 alloy forms 594 slip elements 596 teeth 598 coil springs 600 5 casing 602

Claims

1. A method of sealing a downhole annulus, the method comprising: providing a fusible member on an inner pipe;locating the fusible member and the inner pipe downhole and within one of an outer pipe and an open hole;reconfiguring the fusible member from a first configuration in which the fusible member describes a smaller first diameter to a second configuration in which the fusible member describes a larger second diameter;heating and fluidising the fusible member, andpermitting the fluidised fusible member to cool and solidify and provide a seal between the inner pipe and a wall of the outer pipe or the borehole wall.

2. The method of claim 1, further comprising deforming the fusible member to achieve the second configuration.

3. The method of claim 1, further comprising mechanically manipulating the fusible member to achieve the second configuration prior to the fusible member being heated and fluidised.

4. The method of any preceding claim, further comprising displacing ambient material from between an outer surface of the fusible member and an inner surface of a surrounding wall as the packer is reconfigured from the first configuration to the second configuration.

5. The method of any preceding claim, further comprising:providing upper and lower back-up members on the inner pipe and locating the fusible member between the back-up members;reconfiguring the back-up members from a first configuration in which the back-up members describe a smaller first diameter to a second configuration in which the back-up members describe a larger second diameter and engage the wall.

6. The method of claim 5, further comprising:constraining the fusible member within a volume between the backup members.

7. The method of claim 6, further comprising displacing ambient material as the fusible member is reconfigured and ejecting the displaced ambient material from the volume.

8. The method of any preceding claim, further comprising reconfiguring the fusible member in response to axial translation or compression.

9. The method of any preceding claim, further comprising activating an exothermic heater to heat and fluidise the fusible member.

10. The method of claim 9, further comprising integrating the heater in the solidified fusible member.

11. The method of claim 10, further comprising reinforcing the solidified fusible member with the heater.

12. A downhole packer for location in an outer pipe, the downhole packer comprising:an inner mandrel;a fusible member located on the inner mandrel, anda heater,the packer being reconfigurable from a first configuration in which the fusible member describes a smaller first diameter to a second configuration in which the fusible member describes a larger second diameter, wherein the heater is activatable to heat and fluidise the fusible member and the fusible member may then cool and solidify to form a sealing member between the inner mandrel and the surrounding wall.

13. The downhole packer of claim 12, wherein the fusible member is provided in combination with a flux material adapted to facilitate bonding between the fusible material and the surrounding wall, and the fusible member is provided with a coating to minimise flux leaching prior to heating and fluidising of the member.

14. The downhole packer of claim 12 or 13, wherein the fusible member is provided in a solid or structural form.

15. The downhole packer of claim 12 or 13, wherein the fusible member is deformable to achieve the second larger diameter.

16. The downhole packer of any of claims 12-15, further comprising: upper and lower back-up members mounted on the inner mandrel, with the fusible member located between the back-up members.

17. The downhole packer of claim 16, wherein when the packer is in the first configuration the back-up members describe a smaller first diameter and with the packer in the second configuration the back-up members describe a larger second diameter and may engage the surrounding wall.

18. The downhole packer of claim 16 or 17, wherein at least one backup members includes bypass passages to facilitate displacement of ambient material from a volume between the members.

19. The downhole packer of any of claims 12 to 18, wherein the packer includes cam surfaces, and the fusible member is reconfigurable from the first configuration to the second configuration by translation of the fusible member relative to the cam surfaces.

20. The downhole packer of any of claims 12 to 19, wherein the fusible member is reconfigurable from the first configuration to the second configuration in response to axial translation or compression.

21. The downhole packer of claim 20, wherein the fusible member comprises a plurality of rings cut to facilitate radial expansion.

22. The downhole packer of any of claims 12 to 21, wherein the fusible member comprises powder compacted material.

23. The downhole packer of any of claims 12 to 22, wherein the heater comprises an exothermic heater.

24. The downhole heater of claim 23, wherein the heater is mounted on the inner mandrel proximate the fusible member.

25. The downhole heater of any of claims 12 to 24, comprising surfaces coated with a material to facilitate bonding with the cooled and solidified fusible member.

26. A method of sealing a downhole annulus, the method comprising:providing a packer comprising a solid alloy member on an inner mandrel between upper and lower back-up members;locating the packer downhole and within an outer pipe or open hole; radially expanding the alloy member to occupy a volume between the5 inner mandrel and an inner surface of the outer pipe or borehole wall; constraining the alloy member between the back-up members; heating and fluidising the alloy member, andpermitting the fluidised alloy to cool and solidify and provide a seal between the inner and outer pipes or the borehole wall.10

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