Tension arrangement for subsea Christmas tree

Abstract

The present disclosure describes a subsea well installation including an Xmas tree coupled to a wellhead. A guide frame is located at a lower region of the Xmas tree. A flush and cap tool (FACT) adaptor is mounted on an upper region of the Xmas tree. A tension arrangement extends between the guide frame and the FACT adaptor, to apply a compressive force through the Xmas tree.

Claims

1. A subsea well installation, comprising: an Xmas tree coupled to a wellhead; a base structure located at a lower region of the Xmas tree, wherein the base structure is supported relative to a seabed by the wellhead and is disposed above the seabed; a subsea package mounted on an upper region of the Xmas tree; and a tension arrangement extending between the base structure and the subsea package, to apply a compressive force through the Xmas tree; wherein the Xmas tree defines an axial length between the base structure and the subsea package, the tension arrangement extending across at least that axial length, to apply the compressive force through the axial length of the Xmas tree.

2. The subsea well installation of claim 1, wherein the tension arrangement comprises at least one tensioning member extending across at least the axial length.

3. The subsea well installation of claim 1, wherein at least one of: the base structure is mounted to the wellhead, and the base structure is mounted to, and supported relative to the seabed by, the wellhead itself such that a part of the tension arrangement associated with the base structure is fixed relative to the wellhead.

4. The subsea well installation of claim 1, wherein the tension arrangement comprises at least one tensioning member, and wherein the at least one tensioning member extends between the subsea package and the base structure.

5. The subsea well installation of 1, comprising a tension monitor for monitoring tension or loading in at least one of: the tension arrangement; and the Xmas tree.

6. A subsea well installation, comprising: an Xmas tree coupled to a wellhead; a base structure located at a lower region of the Xmas tree, wherein the base structure is supported relative to a seabed by the wellhead; a subsea package mounted on an upper region of the Xmas tree; and a tension arrangement extending between the base structure and the subsea package, to apply a compressive force through the Xmas tree; wherein the Xmas tree defines an axial length between the base structure and the subsea package, the tension arrangement extending across at least that axial length, to apply the compressive force through the axial length of the Xmas tree; and a first mounting arrangement for connecting the tension arrangement to the upper region of the Xmas tree and a second mounting arrangement for connecting the tension arrangement to the lower region of the Xmas tree.

7. The subsea well installation of claim 6, wherein at least one of: the first mounting arrangement is axially proximal to the subsea package and axially distal to the wellhead; and the first mounting arrangement is connectable to or provided as part of the subsea package, and wherein the second mounting arrangement is axially proximal to the wellhead and axially distal to the subsea package.

8. The subsea well installation of claim 6, wherein the first mounting arrangement is connectable to or provided as part of an adaptor sub or interface sub provided as part of or connectable to the subsea package.

9. The subsea well installation of claim 6, wherein the second mounting arrangement is connectable to or provided as part of the base structure.

10. A method for supporting a subsea well installation, the subsea well installation comprising an Xmas tree coupled to a wellhead and a base structure located at a lower region of the Xmas tree, the method comprising: providing a tension arrangement between the base structure and a subsea package mounted on an upper region of the Xmas tree, wherein the base structure is supported relative to a seabed by the wellhead and is disposed above the seabed; and applying a compressive force through an axial length of the Xmas tree extending between the base structure and the subsea package using the tension arrangement to apply tension between the base structure and the subsea package.

11. The method of claim 10, wherein the tension arrangement comprises at least one tensioning member extending between the subsea package and the base structure.

12. The method of claim 11, comprising controlling or varying tension in the tension arrangement to control compressive force applied through the Xmas tree.

13. The method of claim 10, comprising monitoring tension or loading in at least one of the tension arrangement or the Xmas tree, and determining the compressive force acting through the Xmas tree using the monitored tension or loading.

14. The method of claim 13, comprising varying tension in the tension arrangement in response to a tension value registered during monitoring of the tension or loading in the at least one of the tension arrangement or the Xmas tree.

15. The method of claim 13, comprising controlling movement of the subsea package relative to the Xmas tree in response to a tension value registered during the monitoring of the tension or loading in the at least one of the tension arrangement or the Xmas tree.

16. The method of claim 10, further comprising performing an operation on a well that is accessible via the wellhead, wherein the operation comprises at least one of: a completion; production; intervention; or plugging and abandonment operation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects or examples of the present disclosure will now be described with reference to the accompanying drawings, in which:

(2) FIG. 1 illustrates a side view of a subsea well installation including a tension arrangement according to an example of the present disclosure;

(3) FIG. 2 is a side view of a component for supporting the tension arrangement according to an example of the present disclosure; and

(4) FIG. 3 is a side view of a component for supporting the tension arrangement according to a further example of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring initially to FIG. 1, there is illustrated a subsea well installation 10 including a production or Christmas (Xmas) tree 12 connected to a wellhead 14 for a well (not shown) which extends below a seabed 16. The subsea well installation 10 may require some form of intervention, for example to plug and abandon (P&A) the well. In this example, the subsea well installation 10 has a number of structural features, which due to their design and/or age, may cause issues during such an intervention operation.

(6) FIG. 1 is a schematic representation of a subsea well installation 10. In some circumstances, for example where the installation 10 has been deployed for a significant time period, the well installation 10 may suffer from integrity concerns, and may not be able to support the loads generated during an intervention operation, or at best, the operation may accelerate the fatigue at the subsea well installation 10 to undesirable levels.

(7) The Xmas tree 12 includes a number of components such as valve blocks 18. The connection between the valve blocks 18 may be at risk of degrading or separating if excessive loading is applied to the Xmas tree 12. In the present example, a number of tree flanges 20 are represented by several dashed lines 20 which connect adjacent valve blocks 18.

(8) If it is desired to perform an intervention operation, a subsea package 22 is lowered onto the Xmas tree 12 using a subsea-surface connector 23 deployed from a rig or other vehicle (not shown). The subsea-surface connector 23 may include a riser, running string, landing string, or the like. In this example, the subsea package 22 includes a flush and cap tool (FACT) adaptor 24, such as provided by the applicant of the present disclosure. However, a person of ordinary skill in the art will appreciate that the subsea package 22 could take any appropriate form and/or have any appropriate functionality for performing intervention or P&A operations, including, for example, well control (e.g., BOP) functionality for closing off at least one bore of the subsea package 22 so as to isolate the associated well either temporarily or permanently.

(9) The FACT adaptor 24 provides an operator with the capability to access the well (not shown) via the Xmas tree 12 and wellhead 14, while providing the functionality for at least one of: performing well intervention operations; flushing and fluid displacement (e.g. lubrication) operations; setting plugs for suspending the well; and any other intervention or P&A operations.

(10) The FACT adaptor 24 includes a number of valves (not shown) e.g. for opening or closing off a main bore 26 and/or an annulus bore 28 of the FACT adaptor 24. The FACT adaptor 24 may be used for at least one of: providing a required route for any fluids e.g. in an intervention or P&A operation; cutting wireline or coil tubing, or the like, if required; and permanently or temporarily suspending the well if required. If for any reason well integrity cannot be established during an operation, then the appropriate valves of the FACT adaptor 24 can be closed permanently or at least until the operator can establish an appropriate course of action. The FACT adaptor 24 also includes plug setting profiles (not shown) for allowing crown plugs (not shown) to be set as required.

(11) A base structure, which in this example is in the form of a guide frame 30, is located at a lower region of the Xmas tree 12, on or around the wellhead 14. The guide frame 30 includes a guide base 32 for mounting to the wellhead 14 and guide posts 33 which may be used to assist with aligning components of the subsea well installation 10 relative to the wellhead 14 (e.g. during initial installation of Xmas tree 12, during running of the FACT adaptor 24, etc.).

(12) The subsea well installation 10 further includes a tension arrangement 34 for applying a compressive force through the Xmas tree 12 between the guide frame 30 and the FACT adaptor 24. The Xmas tree 12 defines an axial length between the base structure (i.e. guide frame 30) and the subsea package 22. The tension arrangement 34 extends across at least that axial length, to apply the compressive force through the axial length of Xmas tree 12.

(13) The tension arrangement 34 includes a first mounting arrangement 36, which in this example is in the form of a number of pad eyes 38 mounted (e.g. by welding or another attachment method) on an adaptor sub 40 which connects the FACT adaptor 24 to the Xmas tree 12. The first mounting arrangement 36 is axially proximal to the subsea package 22 and axially distal to the wellhead 14. In other words, the first mounting arrangement 36 is axially closer to the subsea package 22 than the wellhead 14 with respect to a vertical axis defined by the Xmas tree 12 and subsea-surface connector 23. The adaptor sub 40 may provide functionality in ensuring appropriate connection and interfacing with the type of Xmas tree 12. The pad eyes 38 are spaced apart from each other circumferentially around the adaptor sub 40. In this example the FACT adaptor 24 is connected to the adaptor sub 40, which includes a flange 41 at each end thereof for connecting the adaptor sub 40 to the FACT adaptor 24 and Xmas tree 12 respectively. In this example, the tension arrangement 34 extends between the adaptor sub 40 and the guide frame 30 so that the tension arrangement 34 can apply a compressive force through the Xmas tree 12 between the FACT adaptor 24 and the guide frame 30. It will be appreciated that adaptor sub 40 may be provided as a separate component to the FACT adaptor 24, or may be provided as an integral part of the FACT adaptor 24, or the like.

(14) The tension arrangement 34 also includes a second mounting arrangement 42 in the form of a number of tension support members 44 mounted on the guide frame 30. The tension support members 44 are mounted (e.g. by welding or another attachment method) to the guide frame 30. The tension support members 44 are spaced apart from each other circumferentially around the guide frame 30. The second mounting arrangement 42 is axially proximal to the wellhead 14 and axially distal to the subsea package 22. In other words, the second mounting arrangement 42 is axially closer to the wellhead 14 than the subsea package 22 with respect to the vertical axis defined by the Xmas tree 12 and subsea-surface connector 23.

(15) The tension arrangement 34 includes a number of tensioning members 46 in the form of cables 48 extending between the pad eyes 38 of the first mounting arrangement 36 and the tension support members 44 of the second mounting arrangement 42. In this example, each pad eye 38 is connected to two cables 46 via a cable coupling 50 (e.g. a loop, ring, carabiner, or the like). Each of the two cables 48 are connected to two separate, spaced-apart, tension support members 44 of the second mounting arrangement 42 such that there are twice as many tension support members 44 as there are pad eyes 38.

(16) The cables 48 each include a tension adjuster 52 in the form of a turnbuckle 54 for varying the tension in the cable 48. If there is tension in the cable 48 between the first and second mounting arrangements 36, 42, a compressive force is applied through the Xmas tree 12. By appropriately positioning the first and second mounting arrangements 36, 42 around the subsea well installation 10, the cables 36 can be used to compensate for bending loads applied to the Xmas tree 12 as well as providing a compressive force through the Xmas tree 12 for helping to maintain the integrity of the Xmas tree 12 and preventing structural damage to or separation of the components of the Xmas tree 12.

(17) The tension arrangement 34 can be readily installed between the first and second mounting arrangements 36, 42. For example, the pad eyes 38 and the tension support members 44 can be attached to the subsea well installation 10 using any appropriate method. An installer, such as a diver, remotely operated vehicle, autonomously operated vehicle or the like can then install the cables 48 between the appropriate pad eyes 38 and the tension support members 44 in an initially relaxed state and subsequently increase the tension in the cables 48 by actuating each of the turnbuckles 54 in turn to gradually apply an even or balanced compressive force around the subsea well installation 10. In this example, the turnbuckles 54 each include a tension monitor in the form of a strain gauge 55 for indicating a level of tension in at least one of the cables 48 so that the installer/operator can determine whether the tension in the cables 48 is appropriate for providing the even or balanced compressive force through the Xmas tree 12. It will be appreciated that any part of the tension arrangement 34 may include at least one tension monitor. For example, at least one of: the tension support members 44; the cables 48; and any other part of the tension arrangement 34 may include at least one tension monitor in addition to or instead of the tension monitors in the turnbuckles 54 of the present example.

(18) The subsea well installation 10 may include a tension control system (not shown) for monitoring the tension in the cables 48 during installation of the FACT adaptor 24 and/or during a well operation. An installer/operator may use the tension control system to evaluate how best to carry out the installation of the tension arrangement 34 or well operation in such a manner that avoids or reduces the risk of damage occurring to the Xmas tree 12 or any other components. It will be appreciated that monitoring tension in at least one of the cables 48 may also provide an indication of the loading experienced by the Xmas tree 12. For example, a higher tension measured on one side of the Xmas tree 12 may be indicative of an adverse bending moment being experienced by the Xmas tree 12. By monitoring the tension in at least one the cables 48, it may be possible to determine information relating to the loading in the Xmas tree 12, which may be used to suspend, alter or otherwise change the way in which an operation is being carried out to control or reduce the loading in the Xmas tree 12, and/or the operate may change the tension in at least one cable 48 to control or reduce the loading in the Xmas tree 12.

(19) FIG. 2 illustrates a bracket 56 including one of the tension support members 44 of the second mounting arrangement 42. Although not illustrated, the bracket 56 can be attached to e.g. the guide frame 30 illustrated by FIG. 1. Also illustrated in FIG. 2 is part of the cable 48 which extends towards one of the pad eyes 38 (not shown in this Figure) at a first angle 58, the first angle 58 being defined between a vertical direction 60 defined by the Xmas tree 12 and cable 48. The bracket 56 is spaced apart from the Xmas tree 12 by a first distance 62. The first angle 58 is relatively small by virtue of the ratio of the first distance 62 to the distance between the first and second mounting arrangements 36, 42 being relatively small. Therefore, once the cable 48 applies a tension through the Xmas tree 12, there will be a relatively large component of tension vertically in the cable 48, i.e. parallel to the vertical direction 60 compared with a relatively small component of tension acting in a horizontal direction, i.e. perpendicular to the vertical direction 60, such that the cable 48 will be less resistant to horizontal movement of the Xmas tree 12 (e.g. via bending loads, and the like).

(20) In contrast to FIG. 2, FIG. 3 illustrates an extended bracket 64 for increasing the resistance to horizontal (e.g. bending, or the like) movement of the Xmas tree 12. Although not illustrated, the extended bracket 64 can be attached to e.g. the guide frame 30 illustrated by FIG. 1. The tension support member 44 of the extended bracket 64 is mounted at the end of a horizontally extending arm 66 of the extended bracket 64 so that a second distance 68 is defined between the tension support member 44 and the Xmas tree 12 where the second distance 68 is greater than the first distance 62 so as to define a second angle 70, the second angle 70 being defined between the vertical direction 60 defined by the Xmas tree 12 and cable 48. The distance (e.g. the height) between the first and second mounting arrangements 36, 42 is the same for FIGS. 2 and 3. Therefore, in contrast to the example of FIG. 2, the extended bracket 64 of FIG. 3 provides a relatively smaller component of tension vertically in the cable 48 (e.g. due to having a relative larger (second) angle 70 than the first angle 58) compared with a relatively larger component of tension acting in the horizontal direction such that the cable 48 will be more resistant to horizontal movement of the Xmas tree 12 (e.g. via bending loads, and the like). However, due to the decreased component of tension acting in the vertical direction (e.g. due to having a relative larger (second) angle 70 than the first angle 58), the compressive force acting through the Xmas tree 12 may be smaller than in the example of FIG. 2 such that the tension arrangement 34 of FIG. 3 may be less resistant to vertical separation forces, e.g. jarring movements, and the like. In either case (e.g. FIG. 1, 2 or 3), the tension arrangement 34 provides support for the subsea well installation 10 and may assist in maintaining structural integrity of the installation 10 during an intervention or P&A operation, or the like.

(21) Although the present disclosure describes aspects or examples of subsea well installations and associated methods for supporting older Xmas trees and/or wellhead systems, the person of ordinary skill in the art will appreciate that at least one feature of or any of the principles of the present disclosure may be equally applicable to or for use in connection with any wellhead and/or Xmas tree system, including newer wellhead and/or Xmas tree systems.

(22) Although at least one example of the base structure is in the form of the guide frame 30, it will be appreciated that the base structure could take any appropriate form and be locatable or mountable in any appropriate way relative to the wellhead 14 and/or Xmas tree 12. The base structure may be mountable on at least one of: the Xmas tree 12; the guide frame 30; and the wellhead 14. The base structure may be mountable on any other infrastructure associated with the subsea well installation 10, or indeed, on the seabed 16.

(23) It will also be appreciated that the compressive force may be applied through the Xmas tree 12 via any appropriate configuration of the tension arrangement 34, which may extend between a subsea package such as the FACT adaptor 24 and/or an adaptor sub 40 for connecting the subsea package to the Xmas tree 12, and the base structure such as the guide frame 30.

(24) Although at least one example refers to the use of a FACT adaptor 24 as an example of a subsea package, it will be appreciated that any other subsea package may be used, for example, a subsea package comprising an auxiliary tree block, or the like.

(25) The tension support members 44 in this example are provided as separate components mounted to the guide frame 30 during installation of the tension arrangement 34. However, it will be appreciated that the tension support members 44 could form an integral part of the guide frame 30, or indeed be integral with any other component for mounting the second mounting arrangement 42.