MARINE SUCTION ANCHOR

Abstract

A suction anchor and method of installing the suction anchor. The suction anchor including a suction chamber bounded by: a circumferential outer wall; an upper wall; and an internal housing wall. The internal housing defining a passage for receiving wellhead components that may be secured to the suction anchor. The suction chamber has a minor upper portion and a major lower portion. The minor upper portion having internal reinforcing members extending along the inside of the upper wall from the outer walls to the internal housing. The major portion is adapted to be embedded in a seabed and the minor portion is adapted to project from the seabed when the anchor is installed. The reinforcing members serve to reinforce the upper wall of the chamber against collapse and to rigidly support the internal housing to resist forces arising from bending moments applied to wellhead components received and secured therein.

Claims

1. A suction anchor comprising: a. a suction chamber bounded by: (i) a circumferential outer wall, (ii) an upper wall having a central opening, and (iii) the wall of an internal housing; b. the internal housing defining a passage in communication with the central opening for receiving wellhead components that may be secured to the suction anchor; c. the suction chamber having a minor upper portion and a major lower portion; d. the minor upper portion comprising internal reinforcing members extending along the inside of the upper wall from the outer walls to the internal housing; e. the major portion being adapted to be embedded in a seabed and the minor portion being adapted to project from the seabed when the anchor is installed; wherein the reinforcing members serve both to reinforce the upper wall of the chamber against collapse and to rigidly support the internal housing such that it may resist forces applied to it arising from bending moments applied to a wellhead component received and secured therein.

2. A suction anchor as claimed in claim 1, wherein the major portion is substantially void.

3. A suction anchor as claimed in claim 1, wherein the internal housing is a conductor housing receptacle adapted to receive a conductor housing.

4. A suction anchor as claimed in claim 3, wherein the conductor housing receptacle further comprises a conductor housing located therein and rigidly secured thereto, the conductor housing being adapted to receive a wellhead component.

5. A suction anchor as claimed in claim 4, wherein the conductor housing is clamped into the conductor housing receptacle.

6. A suction anchor as claimed in claim 1, wherein the reinforcing members extend radially from the wall of the internal housing to the outer wall.

7. A suction anchor as claimed in claim 1, further comprising a central (inner) pipe depending from the internal housing and serving to bound the inner part of the major portion of the suction chamber.

8. A suction anchor as claimed in claim 7, wherein the central pipe is adapted to receive a well casing depending from a wellhead secured in the internal housing.

9. A suction anchor as claimed in claim 1, further comprising a suction port to enable air and/or water to be pumped from the suction chamber.

10. A suction anchor as claimed in claim 1, wherein a plurality of attachment points, such as pad eyes, are provided at the upper wall.

11. A suction anchor as claimed in claim 1, wherein the outer wall is cylindrical and/or the upper wall is substantially planar.

12. A suction anchor as claimed in claim 1 in combination with a wellhead housing and a wellhead casing, wherein the wellhead housing is rigidly secured within a conductor housing and the conductor housing is rigidly secured within the internal housing, whereby lateral forces applied to the upper part of the wellhead casing are transmitted to the suction anchor.

13. The combination of claim 12, further comprising a wellhead valve, such as a BOP, mounted above the wellhead housing.

14. The combination of claim 12, wherein the suction anchor is installed in a seabed with the major portion beneath the seabed and the minor portion projecting therefrom.

15. A method of installing a subsea structure comprising providing a subsea anchor as claimed in claim 1, locating the subsea anchor on the sea bed and pumping air and/or water from the suction chamber such that the subsea anchor descends into the sea bed.

16. A method as claimed in claim 15, wherein the suction anchor is installed in a seabed such that the major portion is beneath the seabed and the minor portion is projecting therefrom.

17. A method as claimed in claim 15, further comprising the step of landing wellhead component(s) in the internal housing.

18. A method as claimed in claim 17, wherein the wellhead components comprise a wellhead housing with a wellhead casing depending therefrom.

19. A method as claimed in claim 15, further comprising installing a wellhead valve, such as a BOP, mounted above the wellhead housing.

20. A suction anchor as claimed in claim 2, wherein the internal housing is a conductor housing receptacle adapted to receive a conductor housing.

Description

[0029] An embodiment of the invention will be described, by way of example only, and with reference to the following drawings in which:

[0030] FIG. 1 shows a perspective view of a suction anchor according to an embodiment of the invention in partial cross section;

[0031] FIG. 2 shows a cross section view of the suction anchor with a cross section through the centre of the suction anchor; and

[0032] FIG. 3 shows an enlargement of a portion of the cross section of FIG. 2.

[0033] With reference to FIGS. 1 and 2, a suction anchor foundation 1 comprises an annular closed volume forming a suction chamber 2. This closed volume is bounded by a cylindrical outer suction skirt 3 and an annular connection portion 4 in the form of a planar lid. Together these define the major part of the outer surface of the suction anchor 1.

[0034] Within the suction anchor 1 the chamber is further bounded at its upper end by receptacle support ring 5, a cylindrical conductor housing receptacle 6 and inner pipe support ring 7. Beneath these, central/inner pipe of the suction anchor 8 extends downwardly towards the base of the suction anchor. The inner pipe 8 of the suction anchor 1 has the diameter of a conventional conductor (e.g. 30 inches).

[0035] These components are all arranged co-axially with the outer suction skirt 3.

[0036] Extending radially from the conductor housing receptacle 6 to outer suction skirt 3 are a plurality of I-beam reinforcements 9.

[0037] As shown most clearly in FIG. 2, the I-beams 9 extend radially within the internal volume from the outer surface of the conductor housing receptacle 6 to the outer suction skirt 3. The I-beams 9 are each welded at their radially inner end to a conductor housing receptacle 6, inner pipe support ring 7 and receptacle support ring 5, and at their radially outer end to the suction skirt 3 of the suction anchor. Additionally, the I-beams 9 are welded along the length of their top surface to the underside of the annular connection portion 4. As such, these components form a strong and rigid structure.

[0038] A number of other components are provided at the upper end of the suction anchor 1.

[0039] One of these is pump port 10 for connection via a pipe to a vacuum pump for removing air and water from the suction chamber 2 as will be described below.

[0040] In addition, a number of pad eyes 14 are located around the circumference of the top annular connection portion. These pad eyes may be used to help lift and support the suction anchor 1 during installation and removal.

[0041] At the centre of the annular connection portion 4 is provided a clamp ring 11. This surrounds the central opening in the annular connection portion and co-operates with receptacle support ring, to which it is bolted, to secure a conductor housing 12 within the conductor housing receptacle 6. The clamp ring 11 acts against a protrusion towards the upper end of the conductor housing 12. The lower end of the conductor housing 12 rests on mount ring 15, which in turn is supported by an annular shoulder of support ring 7. This arrangement may most clearly be seen from FIG. 3.

[0042] Thus, the conductor housing 12 is clamped into the conductor housing receptacle 6 at the upper end thereof by clamp ring 11, compressing the conductor housing 12 against the mount ring 15 on the inner pipe support ring 7. As a result, conductor housing 12 is securely and rigidly attached to the conductor housing receptacle 6 and in turn to I-beams 9 etc.

[0043] The mount ring 15 can act as an adapter to allow the suction anchor 1 to be used with different sizes and geometry of conductor housings 12 that may be provided by different suppliers.

[0044] Note also from FIG. 3 that the conductor housing receptacle 6 is fixed at its top end to the annular connection portion 4 of the suction anchor via receptacle support ring 5. It may also be seen that, at the bottom end of the conductor housing receptacle 6, inner pipe 8 is hung from inner pipe support ring 7.

[0045] Extending though the conductor housing 12 is high pressure wellhead housing 16 that supports a wellhead casing 17 extending through the middle of the suction anchor as shown most clearly in FIG. 2. The high pressure wellhead housing 12 is the component onto which wellhead valves such as a BOP are mounted in use.

[0046] When the suction anchor 1 is to be installed, it is lowered to the sea bed 18 by means of cables attached to pad eyes 14. At this stage, it comprises the conductor housing 12, but not the wellhead 16 or wellhead casing 17.

[0047] Once placed on the sea bed 18, the suction anchor 1 will generally self-penetrate a certain depth into the sea bed (the exact depth depending on factors such as the weight of the suction anchor and the geology of the sea bed) such that the inner pipe 8 and outer suction skirt 3 penetrate into the seabed 18 to form the closed sealed volume 2 within which the pressure can be adjusted. The pressure is reduced by connecting the pump port 10 (shown in expanded form in FIGS. 1 and 2) in the top annular connection plate 4 to a pump (not shown). The pump removes air and/or water from inside the internal annular volume 2 to reduce the pressure. The suction anchor may thus be sucked into the seabed 18 until radially extending I-beams 9 within the internal annular volume contact the seabed 18 as shown in FIGS. 1 and 2. As the pressure is reduced in the internal annular volume of the suction anchor, the I-beams serve to reinforce the annular connection portion 4 against implosion or collapse.

[0048] Subsequently, the high pressure wellhead housing 16 and wellhead casing 17 are installed. The former is landed in the conductor housing to provide the configuration shown in the figures. It supports wellhead casing 17, which forms an extension thereof. Thus, these components extend downwardly through the inner pipe 8 of the suction anchor 1. It will be noted that, contrary to a typical well, the conductor housing 12 does not support a conductor casing. This is because the conductor casing is not required due to the presence of the inner pipe 8, which performs a corresponding function.

[0049] It will be appreciated that the conductor casing 12 and associated components serve to secure the wellhead casing 17 securely and rigidly relative to the conductor housing receptacle, I-beams, etc. In particular, the mount ring 15 (at the top) and the clamp ring 11 (at the bottom) each provide a load transmitting connection point between the conductor housing 12 (and hence a wellhead secured within it) and the suction anchor. As such, lateral forces or bending/rotational forces about a horizontal axis applied to the conductor housing and wellhead may be resisted because there is a load path from the wellhead to the seabed.

[0050] Prior to use, wellhead valves such as a blowout preventer (BOPnot shown) are connected to and mounted on top of the high pressure wellhead 16 in the known manner. As is well known in the art, these components are relatively massive and tend to apply significant lateral forces to the upper part of the wellheadi.e. they apply a bending moment to it.

[0051] Because the I-beams 9 are secured to the conductor housing receptacle 6 as well as to the annular connection portion 4 (the lid of the suction anchor), in addition to reinforcing the suction chamber, they serve the important function of providing a load path through which loads exerted on the wellhead can be transferred into the suction anchor before ultimately being transferred into the seabed. Accordingly, the suction anchor is able to protect the wellhead 16 from damage that might be caused by horizontal components of force caused by the BOP or other components connected above it.