TURRET MOORING BUOY SYSTEM

Abstract

A mooring buoy system releasably connects risers and anchor lines to a turret of a floating structure, and includes: a buoyant body carrying the risers, which extend to a subsea hydrocarbon well; anchor line connectors, for connecting anchor lines to the buoyant body, each anchor line having one end connected to a connector and the opposing end to the seabed; and a reconnection wire running through a channel coinciding with a center line of the buoyant body, connectable to each anchor line below the buoyant body at some distance from the anchor line connectors through anchor line connection sections on one end and includes a stopper and winch wire connection arrangement on the other end. Also disclosed is a method for pulling up risers and anchor lines, for releasably attaching the risers and anchor lines, as well as a method for constructing a mooring buoy.

Claims

1-11. (canceled)

12. A mooring buoy system for releasably connecting one or more risers and anchor lines to a turret of a floating structure, wherein the buoy comprises: a buoyant body for carrying the one or more risers, which extend to a subsea hydrocarbon well; a number of anchor line connectors, for connecting a number of anchor lines to the buoyant body such that each anchor line has one end connected to one of the connectors and the opposing end is connected to the seabed; and a reconnection wire, wherein in an equilibrium state the buoyancy of the buoyant body is equal to a mass of the buoyant body plus a suspended weight of the one or more risers and a pulling force of the anchor lines, wherein a main section of the reconnection wire runs through a channel coinciding with a center line of the buoyant body, and is connectable to each of the anchor lines below the buoyant body at some distance from the anchor line connectors through anchor line connection sections of the reconnection wire on one end and comprises a stopper and winch wire connection arrangement on the other end, situated on the opposite side of the buoyant body from where the anchor line connectors are located.

13. The mooring buoy system according to claim 12, wherein the anchor line connectors are at a non-zero radial distance from the center line of the buoyant body.

14. The mooring buoy system according to claim 12, wherein a length of the reconnection wire is such that the anchor line connector sections form a slack when the stopper and winch wire connection arrangement is in contact with a side opposite of the side of the buoyant body where the anchor line connectors are connected to anchor lines and the reconnection wire anchor line connection sections are attached to the respective anchor lines at a connection point.

15. The mooring buoy system according to claim 12, wherein the reconnection wire is connectable to the anchor lines at a distance from the anchor line connection to the buoyant body, such that a short anchor line section, being the anchor line section between the connection point and the buoyant body, is tension released when the reconnection wire is pulled up, thereby creating distance between the stopper and winch wire connection arrangement and the buoyant body.

16. The mooring buoy system according to claim 15, wherein the release of tension on the anchor lines comprises the removal of the anchor line weight from the force counteracting the buoyancy so as to exert a reduced force onto the buoyant body.

17. A method for pulling up one or more risers and a number of anchor lines, for releasably attaching the risers and anchor lines in a turret of a hull of a vessel, by means of a mooring buoy system, and wherein the buoy comprises a buoyant body, carrying the one or more risers, which extend to a subsea hydrocarbon well, and a number of anchor lines, having an anchor line connector connected to the buoyant body on one end and a seabed connection on their other end; and a reconnection wire which runs through a channel coinciding with a center line of the buoyant body, and is connected to each of the anchor lines, at a connection point at some distance from the anchor line connectors, through anchor line connection sections, and which comprises a stopper and winch wire connection arrangement on the other end, situated on the opposite side of the buoyant body from where the anchor line connectors are located, comprising the steps of: attaching a winch wire from a turret mooring system of the vessel to the reconnection wire of the mooring buoy system, when the buoy is in an equilibrium state in which the buoyancy of the buoyant body being equal to a mass of the buoyant body plus a suspended weight of the one or more risers and a pulling force of the anchor lines; pulling in the winch wire, resulting in the reconnection wire pulling directly onto the anchor lines, through the center of the buoyant body, such that a section of the anchor lines between the reconnection wire connection and the anchor line connector becomes slack, reducing the suspended weight on the buoyant body; reeling in of the winch wire such that the anchor line section between the connection point and the anchor line connector remains slack, allowing the buoyant body carrying the one or more risers to float upwards using the buoyancy force of the buoyant body only.

18. The method according to claim 17, whereby the velocity of the reeling in of the winch wire directly controls the buoy rise-up.

19. The method for attaching one or more risers in a cavity of a turret of a vessel's hull, through use of a method according to claim 17, comprising the steps of: pulling up the one or more risers, whereby the reeling in of the winch wire continues until the buoyant body is received in the turret structure; locking in of the buoyant body inside a cavity of the turret structure; releasing the reconnection wire, such that it forms a slack below the buoyant body where it is connected to the anchor lines and the slack is removed from the section of the anchor lines between the reconnection wire connection and the anchor line connector.

20. A vessel for offshore operations and comprising a turret mooring system, wherein the turret mooring system is connected to the anchor lines and one or more risers through the mooring buoy system according to claim 12.

21. A vessel for offshore operations and comprising a turret mooring system, wherein the turret mooring system is configured for use of the method in accordance with claim 17.

22. A method for manufacturing a mooring buoy comprising the steps of: providing a buoyant body, comprising a through channel in the buoyant body coinciding with a center line of the buoyant body; installing a number of anchor line connectors on a transverse side to the through channel; installing one or more riser connectors on the side comprising the anchor line connectors; installing a reconnection wire through the through channel of the buoyant body, whereby the reconnection wire contains an equal number of wires to the number of anchor line connectors on the reconnection wire extremity exiting the buoyant body on the side having the anchor line connectors attached, and a stopper and winch wire connector arrangement is installed on the opposite extremity of the reconnection wire.

23. The method for manufacturing a mooring buoy according to claim 22, further comprising the step of manufacturing the buoyant body and providing a through channel in the buoyant body coinciding with a center line of the buoyant body.

24. The mooring buoy system according to claim 13, wherein a length of the reconnection wire is such that the anchor line connector sections form a slack when the stopper and winch wire connection arrangement is in contact with a side opposite of the side of the buoyant body where the anchor line connectors are connected to anchor lines and the reconnection wire anchor line connection sections are attached to the respective anchor lines at a connection point.

25. The method for attaching one or more risers in a cavity of a turret of a vessel's hull, through use of a method according to claim 18, comprising the steps of: pulling up the one or more risers, whereby the reeling in of the winch wire continues until the buoyant body is received in the turret structure; locking in of the buoyant body inside a cavity of the turret structure; releasing the reconnection wire, such that it forms a slack below the buoyant body where it is connected to the anchor lines and the slack is removed from the section of the anchor lines between the reconnection wire connection and the anchor line connector.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0030] The invention will be explained in more detail below with reference to drawings in which illustrative embodiments thereof are shown. The drawings are intended exclusively for illustrative purposes and not as a restriction of the inventive concept. The scope of the invention is only limited by the definitions presented in the appended claims.

[0031] FIG. 1 shows a cross-section of the mooring buoy system in a submerged equilibrium state;

[0032] FIG. 2 shows a cross-section of the mooring buoy system in a buoy lifting state;

[0033] FIG. 3 shows a cross-section of the mooring buoy system in a buoy final lifting before connection state;

[0034] FIG. 4 shows a cross-section of the mooring buoy system in a connected state;

[0035] FIG. 5 shows a cross-section of a vessel for offshore operations and comprising a turret mooring system, moored using the mooring buoy system.

DETAILED DESCRIPTION OF EMBODIMENTS

[0036] FIG. 1 shows a cross-section of the mooring buoy system in an equilibrium state, whereby the mooring buoy 100 comprises a buoyant body 1, anchor line connectors 5, and a reconnection wire. The reconnection wire comprises a main reconnection wire section 2 with reconnection wire anchor line connection sections 10 located on one end and a stopper and winch wire connection arrangement 7 located at the other end. The buoyant body 1 comprises a channel 8 running along a centerline C, providing a through-cavity from a top side to a bottom side through the buoyant body 1. The reconnection wire runs through this channel 8, such that the stopper and winch wire connection arrangement 7 is located on a top side of the buoyant body 1 and the anchor line connection section 10 is located at some distance from a bottom side of the buoyant body 1.

[0037] Furthermore the mooring buoy 100 is connected to one or more risers 3 and at the anchor line connectors 5 to anchor lines. The anchor lines each comprise a main anchor line section 4 with a shorter anchor line section 9 connected to it on one end. The anchor lines could be wires, lines or chains or a combination thereof made from metals and/or polymers.

[0038] The one or more risers 3 are connected to the buoyant body 1 at the bottom side.

[0039] The anchor line connections 5 are placed at a non-zero radial distance from the center line C of the buoyant body 1 on the same side as the one or more risers, i.e. the bottom side. This ensures the reconnection wire anchor connection sections 10 of the reconnection wire do not become entangled with the main reconnection wire 2, the anchor lines or the one or more risers 3. The anchor line connectors 5 and the riser connectors are spaced sufficiently apart and at a sufficient distance from the center line C where the main reconnection wire 2 is located.

[0040] The anchor lines are connected to the buoyant body 1 at the anchor line connectors through the free ends of the shorter anchor line sections 9.

[0041] The free ends of the anchor line connection sections 10 of the reconnection wire are attached to the anchor lines at connection point 6, at some distance below the buoyant body 1, where the main anchor line sections 4 connect to the shorter anchor line sections 9. The non-zero radial placement of the anchor line connectors from center line C, ensures the anchor line connection sections 10 of the reconnection wire and the shorter anchor line sections 9 to work in a manner that either one of the lines carries a substantial part, or preferably all, of the tension from the anchor lines.

[0042] In this equilibrium state, the stopper and winch wire connection arrangement 7 of the reconnection wire is resting on top of the buoyant body 1, such that the main reconnection wire section 2 extends some distance below the buoyant body 1. The reconnection wire anchor line connection sections 10 are slack, thus all mooring line loads pass through the anchor lines main and shorter line sections 4,9. The equilibrium exists due to the buoyancy of the buoyant body 1 being equal to the buoyant body mass plus the suspended weight of the one or more risers 3 and the pulling force of the anchor lines.

[0043] FIG. 2 shows a cross-section of the mooring buoy system in a buoy lifting state. In this state, a winch wire 11 is connected to the stopper and winch wire connection arrangement 7 of the mooring buoy 100 from FIG. 1. Engaging the winch wire 11 causes the stopper and winch wire connection arrangement 7 to be released from the top of the buoyant body 1 and the main reconnection wire section 2 to displace itself along the center line C with respect to the channel 8 of the buoyant body 1 such that the reconnection wire anchor line connection sections 10 on the opposite side of the buoyant body 1 are tensioned and the shorter anchor line sections 9 above the connection to the pull-up line are freed. As a result, the anchor line weight is removed from the force counteracting the buoyancy of the buoyant body 1, allowing the mooring buoy 100 to lift naturally to the surface.

[0044] Reeling in of the winch wire at a speed equal to the lifting speed of the buoy ensures the shorter anchor line sections 9 to remain slack, such that any heave motions of the mooring buoy 100 caused by the vessel motions are free from the winch wire 11 during lifting state. As a result the motions of the mooring buoy 100 and a vessel from which the winch is operated are decoupled and therefore the winch is not subject to inertia and dynamic loading anymore, allowing a safe connection in high sea-state.

[0045] FIG. 3 shows a cross-section of the mooring buoy system in a buoy final lifting before connection state. Before reaching the water line WL, the mooring buoy 100 arrives in a cavity 110 of a turret 150 containing a winch 12 reeling in the winch wire 11. As long as the winch wire 11 remains engaged, the mooring buoy 100 remains in a lifting state, exerting a pull-up force onto the one or more risers 3 and the lifting motion of the mooring buoy only stopped by the turret 150.

[0046] The buoyant body 1 is then locked into the cavity 110 of the turret 150 and pull of the winch wire 11 is released from the stopper and winch wire connection arrangement 7.

[0047] The resulting state is shown in FIG. 4, which shows a cross-section of the mooring buoy system with the mooring buoy 100 in a connected state to the vessel 200. The stopper and winch wire connection arrangement 7 is resting on top of the buoyant body 1, which again causes the main reconnection wire section 2 to extend some distance below the buoyant body 1 and the reconnection wire anchor line connection sections 10 to become slack. As a result all mooring line loads pass through the anchor lines main and shorter line sections 4,9. The buoyancy of the buoyant body 1 is less than the downward pulling force resulting from the anchor lines and suspended weight of the risers 3, causing a combined anchoring load to be transferred onto the turret 150.

[0048] FIG. 5 shows a cross-section of part of a vessel 200 for offshore operations and comprising a turret mooring system, wherein the turret mooring system is connected to the anchor lines and one or more risers through the mooring buoy system.

[0049] The invention has been described with reference to the preferred embodiment. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims.