MULTI VESSEL METHOD AND SYSTEM FOR PLACING AN OBJECT ON A SEABED

Abstract

A method is for placing an object on a seabed. The method includes connecting the object to at least two vessels by use of a work wire; attaching one or more buoyancy devices to the work wire, to achieve a distributed buoyancy of the work wire that forms a double curvature which disassociates at least some vessel movement from the object, to allow for controlled movement of the object; and co-operating the vessels to move the object into a position in a sea distant from the vessels, to lower the object to the seabed and to place the object on the seabed. Also described is a system for transporting an object to a position in a sea where the water comprises gas bubbles significantly lowering the load-carrying capacity of the water and for lowering the object to an area having a wellbore from which the gas bubbles enter the sea.

Claims

1. A method for placing an object on a seabed, the method comprising the steps of: connecting the object to at least two vessels by use of a work wire; attaching one or more buoyancy devices to the work wire, to achieve a distributed buoyancy of the work wire that forms a double curvature which disassociates at least some vessel movement from the object, to allow for controlled movement of the object; and co-operating the vessels to move the object into a position in a sea distant from the vessels, to lower the object to the seabed and to place the object on the seabed.

2. The method according to claim 1, wherein the method comprises the step of: adjusting a length of the work wire released from a vessel to adjust the position of the object in the sea and to lower the object to the seabed.

3. The method according to claim 1, wherein the object is a capping stack and wherein the method further comprises the step of: containing an uncontrolled release of hydrocarbons from a wellbore by connecting the capping stack to the wellbore.

4. The method according to claim 1, wherein the method comprises the step of: connecting the object to one or more other heave-compensation devices.

5. The method according to claim 4, wherein at least one buoyancy device is a buoyancy device having adjustable buoyancy, wherein the method further comprises the step of: adjusting the buoyancy of a buoyancy device having adjustable buoyancy.

6. The method according to claim 1, wherein the method comprises the step of: shutting down a wellbore to end an uncontrolled release of gas and/or oil from the well by placing the object on the seabed to cover the top of the well-bore.

7. The method according to claim 1, wherein the method comprises the step of: connecting a relief wire to the object from at least one of the vessels to carry at least a portion of a gravitational load from the object.

8. The method according to claim 7, wherein the relief wire is used to carry a gravitational load from the object while performing the step of: deploying one or more buoyancy devices from a vessel.

9. The method according to claim 1, wherein the method further comprises the steps of: deploying an ROV; and using the ROV to monitor the position of the object to improve accuracy of the step of co-operating the vessels to lower the object to the sea-bed.

10. The method according to claim 1, wherein the method further comprises the step of: using a transponder placed at or near the object to monitor the position of the object to improve accuracy of the step of co-operating the vessels to lower the object to the seabed.

11. A system for transporting an object to a position in a sea where the water comprises gas bubbles significantly lowering the load-carrying capacity of the water and for lowering the object to an area on a seabed having a well-bore from which the gas bubbles enter the sea, the system comprising: at least two vessels; a work wire for connecting the object to the vessels; and one or more buoyancy devices attached to the work wire, wherein the object is connected to the two vessels by use of the work wire, wherein the one or more buoyancy devices are arranged for the work wire to have a distributed buoyancy that forms a double curvature which dissociates at least some vessel movement from the object for allowing for controlled movement of the object, and wherein the system is arranged for holding and lowering the object in a position in the sea distant from the vessels and for placing the object on the seabed.

12. The system according to claim 11, wherein the vessels comprises communication means for communicating between the vessels to co-operate in transporting the object and in lowering the object to the seabed.

13. The system according to claim 11, wherein the system further comprises a transponder located on or close to the object and an ROV for providing data on the position of the object in the sea.

14. The system according to claim 11, wherein the system further comprises at least one other heave-compensating device connected to the means for connection and/or to the object for providing buoyancy.

15. The system according to claim 14, wherein the system comprises a plurality of buoyancy devices for providing buoyancy, wherein the buoyancy devices are connected to the means for connection and to the object for providing buoyancy.

16. The system according to claim 14, where at least one buoyancy device has adjustable buoyancy.

17. The system according to claim 11, wherein the system comprises a relief wire for carrying at least a portion of a gravitational load from the object, wherein said relief wire is connected to the object and to at least one of the vessels.

18. The system according to claim 11, wherein the system mitigates heave, or motions in general, from the vessels.

Description

[0033] The system may comprise communication means for communicating between the vessels to co-operate in transporting the object and/or in lowering the object to the seabed. Communication means may be highly advantageous to ensure safe and accurate transport and placing of the object. The communication means may comprise means for radio communication, video communication, communication of digital data, and more. In the following is described an example of a preferred embodiment of the system and an example of the method illustrated in the accompanying drawings, wherein:

[0034] FIG. 1 shows an embodiment of the invention, where two vessels are connected to a capping stack and have moved it to a position in a sea over a wellbore;

[0035] FIG. 2 shows a capping stack being deployed from a vessel;

[0036] FIG. 3 shows two vessels as the work wire is being fed from a first vessel to a second vessel;

[0037] FIG. 4 shows the first vessel as a wire for connecting the object to the second vessel and a wire for connecting the object to the first vessel are being connected to each other and to the object via a triplate;

[0038] FIG. 5 shows a relief wire being used to carry a load from the object as buoys are being deployed from the vessel; and

[0039] FIG. 6 shows the object being suspended from two vessels following deployment of buoyancy devices.

[0040] Note that the drawings are schematic and not necessarily drawn to scale.

[0041] FIG. 1 shows a system 1 for transporting an object 200 to a position in a sea 3 where the water in the sea 3 comprises gas bubbles 23 significantly lowering the load-carrying capacity of the water and for lowering the object 200 to an area on a seabed 31 having a wellbore 2 from which wellbore the gas bubbles 23 enter the sea 3.

[0042] The system 1 comprises two vessels 110, 120, two work wires 131, 132, an object-supporting wire 233, a connector 235 for connecting the work wires to each other and to the object-supporting wire 233, and the object 200.

[0043] The object 200, in the embodiment shown in the figures, is a capping stack 200 for establishing control of the wellbore 2 which is having a blowout comprising gas, causing the gas bubbles 23 to enter the sea.

[0044] The system 1 enables deploying a capping stack 200 or other well-containment equipment from a vessel 110, 120 during a blowout comprising gas, as it allows the vessels 110, 120 involved to keep a safe distance to the blowout site and thus to avoid an area of water having its load-carrying ability reduced.

[0045] By using two vessels 110, 120 and two work wires 131, 132 connected to the capping stack 200, the capping stack 200 can safely be moved to the correct position in the sea 3 and lowered to the seabed 31 and/or the wellbore 2. The work wires 131, 132 extending from the vessels 110, 120 to the connector 135 can be 100 metres long but can of course be either longer or shorter. One or more of the vessels 110, 120 can have a winch (not shown) or other means (not shown) for changing the length of released work wire 131, 132 from the vessel or vessels 110, 120. The position of the capping stack 200 in the sea 3 can be changed by moving one or more of the vessels 110, 120 and/or by using the means for changing the length of released work wire or wires 131, 132.

[0046] Buoyancy devices 136 are fastened to the work wires 131, 132, to form a double curvature in the lowering line to disassociate the vessel 110, 120 motions from increase the buoyancy near the capping stack 200. The reduction in increased buoyancy provided by the buoyancy can e.g. improve the motions and accuracy when lowering the capping stack 200 to the seabed 31.

[0047] The system 1 may also be used to raise equipment from the seabed 31 in a sea where gas bubbles decreases the load-carrying capacity of the water.

[0048] FIG. 2 shows how a capping stack 200 to be used as part of the system 1 can be deployed. This can typically be done by use of a crane (not shown) from a dock or a barge (not shown) or a crane or an A-frame (not shown) aboard the vessel 110. The capping stack 200 is hoisted to a vessel 110 and connected to the vessel 110 by use of a work wire 131 and a tugging wire 170 and suspended by use of said wires 131, 170 from the stern of the vessel 110. The end portion of the tugging wire 170 has a tugger 171 for tugging the capping stack 200 to avoid or decrease movement of the capping stack 200 while its suspended from the stern of the vessel 110.

[0049] As a next step of the method, the vessel 110 and a second vessel 120 can typically travel to an area near a blowout-site. When reaching the area, the capping stack 200 may be connected to both vessels 110, 120 and subsequently deployed into the sea 3.

[0050] In FIG. 3 it is shown how a work wire 131 of one vessel 110 can be connected to a work wire 132 of another vessel 120. The two vessels 110, 120 align stern-to-stern, and the work wire 131 of the second vessel 120 is passed to the first vessel 110. In the embodiment shown in FIG. 3, the work wire 132 of the second vessel 120 has a buoy sling 134 comprising a plurality of buoyancy devices 136 in the form of buoys 136. When the work wire 132 of the second vessel has been passed to the first vessel 110 it can be connected to the work wire 131 of the first vessel 110.

[0051] Furthermore, FIG. 3 shows the capping stack 200 suspended from the stern of the first vessel 110.

[0052] FIG. 4 shows the first vessel 110 having the work wire 132 of the second vessel 120 (not shown) on its deck and connected by use of a connector 235 in the form of a triplate 235 to the work wire 131 of the first vessel 110. The connector 235 can of course be another type of connector 235 suitable for the purpose. Furthermore, the capping stack 200 is shown suspended from the stern of the first vessel 110 and connected to an object-supporting wire 233. The object-supporting wire 233 is about to be connected by use of the connector 235 to the work wires 131, 132.

[0053] FIG. 5 shows the capping stack 200 being suspended from the first vessel 110 by use of a relief wire 139 and from the second vessel (not shown) by use of the work wire 132 of the second vessel 120 as buoyancy devices 136 in the form of buoys are being deployed from the first vessel 110. This is done to reduce the gravitational load from the capping stack 200 affecting the buoys 136 as they are moved off the stern of the first vessel 110, to avoid damaging the buoys 136.

[0054] In FIG. 6, the capping stack 200 is shown suspended from the work wires 131, 132 from the two vessels 110, 120 via the object-supporting wire 233, following deployment of all buoyancy devices 136. The relief wire 139 no longer carries load from the capping stack 200.

[0055] When the capping stack 200 and the buoyancy devices 136 have been deployed, the vessels 110, 120 travel into a position in the sea where the water safely carries their weight while simultaneously moving the capping stack 200 into a position where gas bubbles 23 reduce the load-carrying capacity of the water, as seen in FIG. 1. While travelling into position, the necessary length of work wire 131, 132 is released from the vessels 110, 120.

[0056] When the two vessels 110, 120 and the capping stack 200 are in position, the object can be lowered to the seabed 31 and mounted onto a wellhead or otherwise connected to the well.

[0057] During lowering of the capping stack 200 to the seabed 31, an ROV and/or a transponder can be used, or any other means for providing information on the location of the capping stack 200 in the sea 3 and/or the position of the capping stack 200 relative to the seabed 31 and/or well. The capping stack 200 can be lowered to the seabed through movement of one or more of the vessels 110, 120 and/or by use of a means of paying out or pulling in work wire 131, 132.

[0058] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.

[0059] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.