Subsea foundation

Abstract

A subsea foundation system and a method of connecting a lower pipe portion to a subsea foundation are provided. The method includes: providing the subsea foundation, an upper pipe portion being connected to the subsea foundation, deploying the subsea foundation subsea; and connecting the lower pipe portion to the upper pipe portion. The subsea foundation system includes: the subsea foundation; the upper pipe portion connected to the subsea foundation, and the lower pipe portion. The lower pipe portion can be connected to the upper pipe portion subsea. The lower pipe portion may be connected to the subsea foundation in a stowed position before deployment subsea. The lower pipe portion may be connected to a pull-in arrangement before deployment subsea.

Claims

1. A method of connecting a lower pipe portion to a subsea foundation, the method comprising: providing the subsea foundation, an upper pipe portion being connected to the subsea foundation; connecting the lower pipe portion to a pull-in arrangement and the subsea foundation in a stowed position in which the lower pipe portion is attached to an outside of the subsea foundation and the lower pipe portion does not protrude beyond a bottom of the subsea foundation; deploying the subsea foundation subsea with the lower pipe portion connected to the pull-in arrangement and in the stowed position; releasing the lower pipe portion from the stowed position subsea; and connecting the lower pipe portion to the upper pipe portion using the pull-in arrangement.

2. The method according to claim 1, wherein: the upper pipe portion does not protrude beyond the bottom of the subsea foundation; and when the lower pipe portion is connected to the upper pipe portion, at least part of the lower pipe portion protrudes beyond the bottom of the subsea foundation.

3. The method according to claim 1, further comprising: providing a pipe overlap section, wherein connecting the lower pipe portion to the upper pipe portion comprises overlapping the pipe overlap section on a part of the upper pipe portion or a part of the lower pipe portion.

4. The method according to claim 3, wherein the pipe overlap section is fixed to the lower pipe portion and overlaps the part of the upper pipe portion when the lower pipe portion is connected to the upper pipe portion.

5. The method according to claim 1, wherein the subsea foundation comprises a suction anchor.

6. The method according to claim 1, wherein: the pull-in arrangement comprises two pull-in lines; a first end of each of the two pull-in lines is connected to the subsea foundation; and a second end of each of the two pull-in lines is connected to the lower pipe portion.

7. A subsea foundation system for deployment subsea, the subsea foundation system comprising: a subsea foundation; a pull-in arrangement; an upper pipe portion connected to the subsea foundation; and a lower pipe portion configured to be connected to the pull-in arrangement and the subsea foundation in a stowed position in which the lower pipe portion is attached to an outside of the subsea foundation and the lower pipe portion does not protrude beyond a bottom of the subsea foundation, wherein: the subsea foundation system is configured such that, subsea, the lower pipe portion can be released from the stowed position and connected to the upper pipe portion using the pull-in arrangement.

8. The subsea foundation system according to claim 7, wherein: the upper pipe portion does not protrude beyond the bottom of the subsea foundation; and when the lower pipe portion is connected to the upper pipe portion, at least part of the lower pipe portion protrudes beyond the bottom of the subsea foundation.

9. The subsea foundation system according to claim 7, further comprising a pipe overlap section which overlaps a part of the upper pipe portion or a part of the lower pipe portion when the lower pipe portion is connected to the upper pipe portion.

10. The subsea foundation system according to claim 9, wherein the pipe overlap section is fixed to the lower pipe portion and overlaps the part of the upper pipe portion when the lower pipe portion is connected to the upper pipe portion.

11. The subsea foundation system according to claim 7, further comprising a pipe connection guide for guiding a connection between the upper pipe portion and lower pipe portion.

12. The subsea foundation system according to claim 7, wherein the subsea foundation comprises a suction anchor.

13. The subsea foundation system according to claim 7, wherein: the pull-in arrangement comprises two pull-in lines; a first end of each of the two pull-in lines is connected to the subsea foundation; and a second end of each of the two pull-in lines is connected to the lower pipe portion.

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 shows a subsea foundation comprising a suction anchor;

(3) FIG. 2 is an enlargement of Detail 1 of FIG. 1;

(4) FIG. 3 is a cross section of a pipe extension;

(5) FIG. 4 shows a subsea foundation for deployment;

(6) FIG. 5 shows a subsea foundation during deployment; and

(7) FIG. 6 shows a subsea foundation for installing on a seabed.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows a subsea foundation 1 comprising a suction anchor 2. The suction anchor 2 comprises an outer suction skirt 4, a top plate 6 and a center pipe 8 that together bound an internal suction volume. The center pipe 8 is connected indirectly in an airtight manner to the top plate 6.

(9) Whilst the present invention is described herein in relation to a subsea foundation comprising a suction anchor, it should be appreciated that the invention may be applicable to other types of subsea foundations that may not comprise a suction anchor.

(10) The center pipe 8 comprises an upper pipe portion 10 and a lower pipe portion 12. The lower pipe portion 12 is connectable and disconnectable from the upper pipe portion 10. The upper pipe portion 10 does not protrude beyond the bottom of the suction skirt 4 of the suction anchor 2. The lower pipe portion 12 however does protrude beyond the bottom of the suction anchor 2. Thus, when the subsea foundation 1 is sunk into the seabed the lower pipe portion 12 will reach and penetrate the seabed first. This may facilitate installation as a part (the lower pipe portion 12) can be penetrated into the seabed so as to hold the foundation 1 in an approximate location relative to the seabed whilst the orientation of the suction anchor 2 can be assessed and adjusted, if required.

(11) The center pipe 8 is fixed to the suction anchor 2 at an upper end to the top plate 6 and supported and centralized at the bottom end by stiffening plates 14.

(12) The suction anchor 2 comprises I-beams 16 (four can be seen in FIG. 1) on the top plate 6. These I-beams 16 act to strengthen the top plate 6 and support the wellhead (shown in phantom).

(13) The connection between the upper pipe portion 10 and the lower pipe portion 12 is overlapped by a pipe overlap section 18.

(14) The pipe overlap section 18 may be fixed, such as welded, to the lower pipe portion 12 which together may form a pipe extension 20 as shown in FIG. 3.

(15) The pipe overlap section 18 partially overlaps the lower pipe portion 12 so that a reliable connection can be made between the lower pipe portion 12 and the pipe overlap section 18.

(16) The pipe overlap section 18 and hence the lower pipe portion 12 are connected to a pull-in arrangement 22. The pull-in arrangement 22 is used to connect the lower pipe portion 12 to the upper pipe portion 10.

(17) The pull-in arrangement 22 comprises two pull-in lines 24 that extend through the suction anchor 2 through pull-in conduits 26. The pull-in conduits 26 at their upper end are connected to (and pass through) the suction anchor top plate 6 in a sealing manner. These conduits 26 allow the pull-in lines 24 to pass through the suction anchor internal volume without compromising the sealed nature of the internal volume. The pull-in lines 24 and pull-in line conduits 26 pass through the top plate 6 between two of the I-beams 16.

(18) The pipe overlap section 18 is connected to pull-in line connection wings 28. The pull-in lines 24 each extend between a pull-in line connection wing 28 at one end to a pull-in line grip 30 at the other end. The pull-in line grips 30 are shown most clearly in FIG. 2. These pull-in line grips 30 each grip a pull-in line 24 and allow it to be pulled through and out of the suction anchor only. To achieve this the grips 30 each comprise a one-way mechanism such as a ratchet and a lock to hold the pull-in line 24 once it has been pulled through the grip 30.

(19) The pull-in line connection wings 28 allow the pull-in lines 24 to be radially spaced from the center pipe 8.

(20) The pull-in line conduits 26 are held in a fixed position relative to the center pipe 8 by pull-in line conduit connectors 32. These connectors 32 connect the pull-in line conduits 26 to the center pipe 8 and the internal stiffeners 14.

(21) At the top end of the pipe overlap section 18 is a pipe connection guide 34. This guide 34 is made up of a number of obliquely angled guide pieces that forms a circumferentially discontinuous guide funnel. When the lower pipe portion 12 is connected to the upper pipe portion 10 and the pipe overlap section 18 is overlapped over the upper pipe portion 10 the pipe connection guide 34 is used to guide the upper pipe portion 10 into the pipe overlap section 18.

(22) The pipe connection guide 34 is circumferentially discontinuous so that it can be located between the internal stiffeners 14 as shown in FIG. 1.

(23) FIGS. 4, 5 and 6 illustrate the method of connecting the lower pipe portion 12 to the upper pipe portion 10.

(24) Initially, prior to deployment subsea, the pipe extension (which comprises the pipe overlap section 18 and lower pipe portion 12) is connected to the pull-in arrangement 22. This is achieved by (in any order) connecting each of the pull-in lines 24 at one end to a grip 30, passing the lines 24 each through a respective pull-in line conduit 26 and attaching the other end to the lower pipe portion 12 via the connection wings 28 connected to the pipe overlap section 18 that is connected to the top of the lower pipe portion 12.

(25) Also, prior to deployment subsea, (before, during or after the connection of the pull-in arrangement) the lower pipe portion 12 and overlap pipe section 18 are connected to the outside of the suction anchor 2 in a stowed position as shown in FIG. 4. The lower pipe portion 12 and overlap pipe section 18 when in the stowed position are supported by lugs 36 that are connected to the outside of the skirt 4 of the suction anchor 2. The lower pipe portion 12 and overlap pipe section 18 may be secured to the suction anchor 2 in the stowed position by straps (not shown).

(26) Once the lower pipe portion 12 has been connected to the pull-in arrangement 22 (in this case via the pipe overlap section 18) and connected to the outside of the suction anchor 2 in the stowed position, the subsea foundation 1 may be deployed subsea. For example, the subsea foundation may be held via lifting wires (not shown) connected to pad eyes 38.

(27) Once subsea the lower pipe portion 12 and overlap pipe section 18 may be released from the stowed position such as by cutting the straps (if present). The lower pipe portion 12 and overlap pipe section 18 are allowed to fall into a suspended position below the suction anchor 2 as shown in FIG. 5. The connection between the pull-in arrangement and the lower pipe portion 12 and overlap pipe section 18 holds the lower pipe portion 12 and overlap pipe section 18 in the suspended position.

(28) The lower pipe portion 12 may then be connected to the upper pipe portion 12 by pulling in the pull-in lines through the conduits 26 and grips 30. This pull in may be performed by a winch for example. Once pulled through the suction anchor 2 by a desired amount, excess pull-in line above the grips 30 may be cut off.

(29) As the lower pipe portion 12 is pulled towards the upper pipe portion 10 the pipe connection guide 34 may guide the bottom of the upper pipe portion 10 into the pipe overlap section 18. The upper pipe portion 10 is received in the pipe overlap section 18 until the end of the upper pipe section 10 abuts the end of the lower pipe section 12. In this position the lower pipe portion 12 and pipe overlap section 18 protrude from the bottom of the suction skirt 4 as shown in FIG. 6. The subsea foundation 1 may then be landed onto and sunk into the seabed.

(30) If it is desired to retrieve the suction anchor 2 from the seabed this may be performed in a manner that leaves the lower pipe portion 12 and the pipe overlap section 18 behind in the seabed. Before pumping fluid into the suction anchor 2 to force it out of the seabed, the pull-in lines may be released, either by cutting the lines or releasing the grips 30. As a result (and because there is no other fixing device between the upper pipe portion and lower pipe portion), when the suction anchor 2 is forced out of the seabed, the lower pipe portion 12 and the pipe overlap section 18 are left behind in the seabed.