Removal of platforms at sea

This application claims the benefit of U.S. Provisional Application No. 61/102,570, filed Dec. 10, 2007, the contents of which are incorporated herein by reference.

The present invention relates to a method and system for removing a part of a platform at sea, the platform resting on a seabed.

Methods for removing such platforms are known in the field of the art.

It is widely known that platforms at sea, for instance in the oil and gas industry, have a certain life span, after which they are to be decommissioned and removed. This removal process often is a costly, complicated and sometimes dangerous operation. There is a general need in the field of the art for cost-effective, simple, and safe methods for removing such platforms.

US2003/0108392 discloses a system for removing decks from offshore structures. A drawback of this system is that it requires two barges, which is expensive and cumbersome during transport.

GB2165188 discloses a method for installing and removing an upper part of a platform (called deck module) at sea from a leg assembly of the platform.

A disadvantage of the system of GB2165188 is that it comprises a support frame 20 (comprising of girders 51) which is integral with the deck module itself, see FIG. 2 and page 1, lines 78-80 of GB2165188. The support frame 20 is essential to the system, and hence the system of GB2165188 can only by used for removing deck modules having such a support frame 20. Since most existing platforms do not have such a support frame 20, the value of the system of GB2165188 is limited in practice.

A disadvantage of the system of GB2165188 is further that it requires barges which extend to a substantial height above the water surface, in order to remove the deck module from the leg assembly. This is due to the fact that for safety reasons, the deck module is located at a substantial height above the water line, and consequently the support structure 20 is also located at a substantial height above the water line.

WO98/24980 discloses a system for lifting a sea-going structure. One drawback of this system is that it requires two vessels, which is expensive and cumbersome during transport. Another drawback of this system is that it is difficult to unload the sea-going structure from the vessels once it is lifted with the vessels.

It is an object of the invention to provide an alternative method and device for removing an upper part of a platform which rests on a seabed.

It is an object of the present invention to provide a method and device suffering less from at least one of the drawbacks mentioned above.

It is an object of the invention to provide a simple, cost-effective and reliable method and device for removing an upper part of a platform which rests on a seabed.

At least one of the objects is achieved in a method of removing an upper part of a platform which rests on a seabed and which extends above the waterline, the platform comprising legs which extend upwards from the seabed, the method comprising the subsequent steps of:

providing a vessel comprising a single hull, the hull defining a contour of the vessel when viewed from above;

providing a support structure which is configured to rest on the vessel, the support structure comprising one or more beams, the one or more beams having connection ends that are connection ends configured to be connected to the legs of the platform;

positioning the vessel between the legs of the platform;

connecting the connection ends to the legs of the platform;