Suction anchor for a subsea well

Abstract

A suction anchor for a subsea well is provided. The suction anchor includes a wellhead support structure. The wellhead support structure is at least in part external of the internal volume of the suction anchor.

Claims

1. A suction anchor for a subsea well, wherein the suction anchor comprises: a skirt; a top plate; a pipe that is for a well to extend through, wherein the skirt, top plate and pipe together define an internal volume in which pressure can be adjusted relative to the outside environment; and a wellhead support structure, wherein the wellhead support structure is at least in part external of the internal volume, wherein the wellhead support structure comprises a plurality of radially extending well support members, wherein the radially extending well support members are each fixed along their length to the top plate of the suction anchor such that the wellhead support structure has a dual function of supporting a wellhead and reinforcing the top plate, wherein the wellhead support structure supports the wellhead laterally or axially, and reinforces the top plate directly from above so that the top plate resists implosion.

2. The suction anchor according to claim 1, wherein the radially extending support members are each welded along their length to the top plate.

3. The suction anchor according to claim 1, further comprising connection points, wherein the connection points permit other components to be connected to the suction anchor and permit loads to transfer from the component connected to the connection points into the suction anchor.

4. The suction anchor according to claim 3, wherein the connection points are each attached to the wellhead support structure.

5. The suction anchor according to claim 1, wherein the wellhead support structure is for laterally supporting the wellhead.

6. The suction anchor according to claim 1, wherein the wellhead support structure is for axially supporting the wellhead.

7. The suction anchor according to claim 1, wherein the wellhead support structure is for resisting bending moments applied to the wellhead.

8. A subsea well assembly, wherein the assembly comprises: a suction anchor according to claim 1, and a wellhead that extends through the top plate of the suction anchor, wherein the wellhead protrudes from the top plate of the suction anchor and is not enclosed within the suction skirt from the top of the wellhead at least down to a point below where a high pressure wellhead housing of the wellhead seals to a low pressure wellhead housing.

9. The subsea well assembly according to claim 8, wherein the wellhead support structure is connected to the wellhead.

10. A method of providing support for a subsea well, wherein the method comprises: providing a suction anchor including a skirt, a top plate, a pipe that is for a well to extend through, wherein the skirt, top plate and pipe together define an internal volume in which the pressure can be adjusted relative to the outside environment, and a wellhead support structure, wherein the wellhead support is at least in part external of an internal volume of the suction anchor, and the wellhead support structure comprises a plurality of radially extending well support members, wherein the radially extending well support members are each fixed along their length to the top plate of the suction anchor such that the wellhead support structure has the dual function of supporting a wellhead laterally or axially and reinforcing the top plate directly from above so that the top plate resists implosion; and positioning the wellhead so as to extend through the top plate of the suction anchor, wherein the wellhead protrudes from the top plate of the suction anchor and is not enclosed within the suction skirt from the top of the wellhead at least down to a point below where a high pressure wellhead housing of the wellhead seals to a low pressure wellhead housing.

11. The method according to claim 10, wherein the method comprises laterally supporting the wellhead with the wellhead support structure.

12. The method according to claim 10, wherein the method comprises axially supporting the wellhead with the wellhead support structure.

13. The method according to claim 10, wherein the wellhead support structure is used to arrest thermal growth of the wellhead.

14. The method according to claim 10, wherein the wellhead support structure is used to resist bending moments applied to the wellhead.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Certain preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

(2) FIG. 1 is a perspective view of the top of a first subsea well assembly;

(3) FIG. 2 is a side view of a second subsea well assembly;

(4) FIG. 3 is a side view of a third subsea well assembly; and

(5) FIG. 4 is a perspective view of a fourth subsea well assembly.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 shows part of a subsea well assembly 1. The subsea well assembly 1 comprises a suction anchor 2. The suction anchor 2 comprises an outer suction skirt 4 around a central tube and a top plate 6 connecting the outer suction skirt to the central tube to form an internal volume inside the suction anchor 2 that is a sealed volume when the suction anchor 2 is on the sea floor and has penetrated the sea floor slightly. This penetration may be due to its own weight or due to putting extra downward force on the top of the suction anchor 2 when it is resting on the seafloor.

(7) The suction anchor 2 may be sucked into the sea floor by reducing the pressure inside the suction anchor 2 to thereby provide a subsea well foundation in the seabed.

(8) The central tube may be or receive a low pressure wellhead housing 8 in which is received a high pressure wellhead housing 10.

(9) The suction anchor 2 may comprise a plurality (there are four in the example of FIG. 1) of integral connection/strong points 12. These connection points 12 are stronger than the adjacent parts of the suction anchor 2 and provide a strong point for components to be connected to the suction anchor 2 such that load can be transmitted into the suction anchor 2 and thus into the sea floor. The connection points 12 are located equally spaced around the top of the suction skirt 4 of the suction anchor 2. The connection points 12 are integral (e.g. welded or integrally formed) with the suction anchor 2. Each connection point has a base portion 14 and a connection portion 16. The base portion 14 is fixed to the suction anchor 2 (e.g. on the suction skirt). The connection portion 16 protrudes from the top of the suction anchor 2 and provides a part to which other components such as a support frame can be connected. The connection portion 16 may also comprise a receptacle for receiving a guiding device such as guide post 20 as shown in FIG. 2.

(10) The receptacle may have a standard interface to allow it to be locked to the component it receives and for loads to be transferred from the component into the connection points.

(11) The assembly 1 in FIG. 1 shows a wellhead support 17 mounted on the suction anchor 2. The wellhead support 17 is external of the internal volume of the suction anchor 2. The wellhead support 17 may be connected to the suction anchor 2 via the connection points 12 and/or be directly attached to the top plate 6. The wellhead support 17 may for example be welded to the connection points 12 and/or the top plate 6. The wellhead support 17 may also support the connection points 12.

(12) The wellhead support 17 may rest on the top plate 6 of the suction anchor 2.

(13) The wellhead support 17 may have the dual function of supporting the wellhead and reinforcing the top plate 6 of the suction anchor 2.

(14) The wellhead support 17 may have a plurality of wellhead support members 22 (in this case eight). The wellhead support members 22 may provide lateral support to the wellhead 8 and allow the transfer loads from the wellhead 8 into the suction anchor 2. The wellhead support members 22 each comprise vertical plates (e.g. I-beams) that are spaced around the circumference of the wellhead 8 outside of the internal volume of the suction anchor. This allows the wellhead support members to provide lateral support to the wellhead 8 distributed around its circumference whilst leaving parts of the wellhead 8 exposed for wellhead interventions. The wellhead support members 22 may be connected via an outer frame 24. Thus the wellhead support 17 may comprise the wellhead support members 22 and the outer frame 24. The outer frame 24 may rigidly connect the wellhead support members 22 and be used to connect the wellhead support 17 to the suction anchor 2 via the connection points 12.

(15) The well support 17 may also comprise one or more receptacles 26 for receiving guide devices 20 (e.g. guide posts). These protruding members 20 may provide a means to which components can be attached, a means for transferring loads (such as lateral loads from components mounted on the assembly 1 to the suction anchor 2), a means for guiding the components into the correct position and orientation on the suction anchor 2 and/or a means to which guide wires 28 can be attached during an installation procedure (as shown for example in FIG. 2).

(16) The well support 17 may be integral with the suction anchor or a separate modular component from the suction anchor 2 and may be installed separately from the suction anchor 2.

(17) The well support 17 may provide a surface on which components mounted on the subsea assembly 1 may rest. For example, equipment support device 29 or subsea equipment adapter frame 30 may be located on the wellhead support 17. The subsea equipment adapter frame 30 may be a separate modular component from the suction anchor 2 and the well support 17 and/or the equipment support device 29 and may be installed separately from the suction anchor 2 and equipment support device 29.

(18) A suction anchor 2 with connection points 12 may be installed and used as an exploration well. If it is desired to convert the suction anchor 2 from an exploration well to a production well this may be possible by using the connection points 12 to connect equipment support device 29 and subsea equipment adapter frame 30 to the suction anchor 1.

(19) To install the equipment support device 29 and/or the subsea equipment adapter frame 30 on a preinstalled suction anchor 2, guide posts 20 may be installed on/in the connection portions 16 of the connection points 12 (see for example FIG. 2). Guide wires 28 may be connected to the guide posts 20. The guide wires 28 may be passed through apertures in the equipment support device 29 and subsea equipment adapter frame 30 and used to guide these components into roughly the correct location above the wellhead and onto the guide posts 20.

(20) As shown in FIGS. 2 and 3, one of the guide posts 20 may be longer than the other guide posts 20. This is so that this longer guide post 20 is received first in an aperture in the component being mounted and at that point provides a point about which the component can be rotated to get it in the correct location to be received by the other guide posts 20. This may make the installation easier as first the component can be translated to align an aperture with the longer guide post 20 and then rotated to align the other apertures with the other guide posts 20.

(21) Once the component (e.g. the equipment support device 29 and/or the subsea equipment adapter frame 30) being mounted has been roughly aligned relative to the wellhead 10 using the guide posts 20, the component may be precisely aligned using one or more fine alignment members 32. These fine alignment members 32 may be used in conjunction with the protruding members (e.g. guide posts 20) to help position and/or lock the components on the suction anchor foundation 2. The protruding members 20 may be used to guide the component (e.g. equipment support device 29 and/or subsea equipment adapter frame 30) into approximately the correct location and orientation on the suction anchor 2 and the fine alignment members 32 may be used to precisely locate the components and lock them to the subsea installation 1. The fine alignment members 32 may be machined to a high tolerance to ensure that the components are located and/or locked in a precise location relative to the suction anchor 2 and/or wellhead 10. In other words, the guide posts 20 may be used as a coarse guiding means and the fine alignment members 32 may be used as a fine guiding/aligning means.

(22) FIG. 3 shows a subsea well assembly 1 that comprises two suction anchors 2. The assembly comprises one equipment support device 29 that extends over both suction anchors 2 and one subsea equipment adapter frame 30 that is supported by both suction anchors 2. Other than the fact that the arrangement comprises two suction anchors 2 rather than one, the assembly is otherwise the same as the examples shown in FIGS. 1 and 2.

(23) In the assemblies of FIGS. 2 and 3, the wellhead supports are not shown.

(24) FIG. 4 shows another subsea well assembly 1. This is broadly equivalent to the assembly 1 shown in FIG. 1 except the well support members 22 are not connected by an outer frame. The wellhead support members 22 are integral with the top plate 6 of of the suction anchor 2 such that they can have the dual function of laterally supporting the wellhead and strengthening the suction anchor 2.

(25) The connection points 12 are mounted on/fixed to/part of the well support members 22. In this figure the connection points 16 are being shown as being used as lift points during installation or uninstallation of the assembly 1. The connection points 12 may be connected to other components, such as wellhead load relief connectors, during other phases of operation.

(26) The following clauses set out features of the invention which may not presently be claimed but which may form the basis for amendments or future divisional applications. 1. A suction anchor for a subsea assembly, wherein the suction anchor comprises connection points, wherein the connection points permit other components to be connected to the suction anchor and permit loads to transfer from the component connected to the connection points into the suction anchor. 2. A suction anchor according to clause 1, wherein the connection points are additional parts that protrude from the skirt of the suction anchor to provide an attachment point for components to be mounted on the suction anchor. 3. A suction anchor according to clause 1 or 2, wherein the connection points are stronger than the adjacent parts of the suction anchor. 4. A suction anchor according to clause 1, 2 or 3, wherein one or more of the connection points is provided at the outer perimeter of the suction anchor 5. A suction anchor according to any preceding clause, wherein one or more of the connection points extends beyond the top of the suction anchor. 6. A suction anchor according to any preceding clause, wherein the connection points are provided at approximately equally spaced locations around the outer perimeter of the suction anchor. 7. A suction anchor according to any preceding clause, wherein one or more of the connection points is integral with the suction anchor. 8. A suction anchor according to any preceding clause, wherein one or more of the connection points has a profile that permits load transfer and/or locking of the component that is connected to the connection point. 9. A suction anchor according to any preceding clause, wherein each connection point comprises a base portion integral with the suction anchor and a connection portion to which a component can be attached. 10. A suction anchor according to any preceding clause, wherein the suction anchor is for providing a foundation for a subsea well assembly. 11. A subsea assembly comprising the suction anchor of any preceding clause. 12. A subsea assembly according to clause 11, wherein one or more connection point is connected to a guide device 13. A subsea assembly according to clause 12, wherein one or more of the guide devices provides a means to which the components can be attached, a means for transferring loads to the suction anchor, a means for guiding the components into the correct position and orientation on the suction anchor, and/or a means to which guide wires can be attached during an installation procedure. 14. A subsea assembly according to clause 12 or 13, wherein one guide device protrudes further from the suction anchor than the other guide devices. 15. A subsea assembly according to clause 11, 12 or 13, wherein the subsea foundation comprises fine alignment devices, wherein the guide devices are used to guide a component into approximately the correct location and orientation on the suction anchor and the fine alignment devices are used to more precisely locate the component and/or lock it to the subsea assembly. 16. A subsea assembly according to any of clauses 11 to 15, wherein the subsea assembly is a subsea well assembly. 17. A method, wherein the method comprises providing the suction anchor or subsea assembly of any preceding clause. 18. A method according to clause 16, wherein the method comprises providing a plurality of suction anchors of different designs wherein the connection points on each suction anchor are located in the same position relative to the other connection points and/or the connection points are the same size between each of the suction anchors. 19. A method of converting an exploration well into a production well, the method comprising: providing a subsea well assembly, the well assembly comprising a suction anchor, wherein the suction anchor comprises one or more connection points, using the subsea well assembly as an exploration well assembly; and converting the exploration well assembly to a production well assembly, wherein converting the exploration well assembly to a production well assembly comprises connecting one or more components to the suction anchor via the one or more connection points. 20. A method according to clause 19, wherein no components are connected to the connection points when the well assembly is being used as an exploration well. 21. A method according to clause 19 or 20, wherein the one or more components comprises a support device and/or a subsea equipment adapter frame and wherein converting the exploration well assembly to a production well assembly comprises installing the support device and/or the subsea equipment adapter frame on the suction anchor. 22. A subsea assembly comprising: a suction anchor, a support device; and a subsea equipment adapter frame, wherein the suction anchor, support device and subsea equipment adapter frame are separate modular components that can be installed or uninstalled separately. 23. A subsea assembly according to clause 22, wherein the suction anchor is the suction anchor of any of clauses 1 to 10 and/or wherein the subsea assembly is the subsea assembly of any of clauses 11 to 16. 24. A subsea assembly according to clause 23, wherein the one or more components connected to the connection points is the support device and/or the subsea equipment adapter frame. 25. A method of installing a subsea assembly, the subsea assembly comprising a suction anchor and a support device, wherein the suction anchor is installed on a seabed and then the support device is mounted on the suction anchor. 26. A method of installing a subsea assembly according to clause 25, wherein the subsea assembly is the subsea assembly of any of clauses 22 to 24. 27. A method of uninstalling a subsea assembly, the subsea assembly comprising a suction anchor and a support device, wherein the support device is dismounted from the suction anchor and retrieved before the suction anchor is uninstalled from the seabed. 28. A method of uninstalling a subsea assembly according to clause 27, wherein the subsea assembly is the subsea assembly of any of clauses 22 to 24. 29. A suction anchor for a subsea well, wherein the suction anchor comprises: a skirt; a top plate; a pipe that is for a well to extend through, wherein the skirt, top plate and pipe together define an internal volume in which the pressure can be adjusted relative to the outside environment, and a wellhead support structure, wherein the wellhead support is at least in part external of the internal volume. 30. A suction anchor according to clause 29, wherein the wellhead support structure provides lateral support to the wellhead. 31. A suction anchor according to clauses 29 or 30, wherein the wellhead support structure reinforces the top plate. 32. A suction anchor according to clause 29, 30 or 31, wherein the wellhead support structure comprises a plurality of radially extending members that extend in a radial direction from the wellhead. 33. A subsea well assembly, wherein the assembly comprises: a suction anchor according to any of clauses 29 to 32, and a well head that extends through the top plate of the suction anchor, wherein the wellhead protrudes from a top plate of the suction anchor and is not enclosed within the suction skirt from the top of the wellhead at least down to a point below where a high pressure wellhead housing of the wellhead seals to a low pressure wellhead housing.