Structure for dismantling and transporting a fixed offshore oil platform with a U-shaped floating hull mounted on at least three lifting legs carrying a shuttle to move the hull along the legs

摘要

The shuttle is made of at least three elements (31), each connected to a lifting leg and each containing mechanical means of independently driving the hull of the structure along the corresponding lifting leg. Each element also has means of connecting the structural element of the platform to be moved. The platform comprises skeletal elements formed in particular by a bridge and at least one supporting column. The structure comprises a U-shaped floating hull (11) with at least three legs (12) for lifting the hull by pressing on the seabed. Each lifting leg has mechanical means of displacement (20) placed in a structure (16) carrying the hull. A shuttle (30) which can be moved along the legs is designed to move one of the structural elements of the platform. Each element of the shuttle has a vertical guiding branch on the bearing structure and a horizontal branch supporting the driving mechanism on the corresponding leg. The driving mechanism for each element comprises two opposing plates (21) carried by each rib of the corresponding lifting leg, each with a series of teeth (22), and at least two opposed assemblies (42, 43) on the horizontal branch made of a pinion driven round and acting with one set of teeth. The means of connecting to the bridge of the platform are at least one horizontal plate supporting the bridge and placed at the lower part of the vertical branch of each element of the shuttle. Alternatively, the means of connecting to the bridge of the platform include a vertical linear traction system at the level of each shuttle element, formed by a chain or cable and two assemblies for locking this traction system. One of the assemblies is on the element and the other is on the hull for a step by step vertical displacement of the support column by successive locking of the assemblies. Each locking assembly is made of two opposed screws which can be vertically basculed relative to each other between a free and a blocking position. An independent branch of the structure can close the opening of the hull and locks onto the hull. An independent claim is made for a method of dismantling and transporting a structural element of a fixed oil platform comprising a bridge, between the oilfield and a dismounting quay, where a structure as described above is placed under the bridge; its legs are pushed against the seabed to lift the hull and the shuttle to bring the shuttle into contact with the bridge. The shuttle is locked onto the lifting legs and the hull is lowered to allow it to float. The bridge is separated from its support column and lifted by the shuttle as the lifting legs are raised. The structure supporting the bridge is dismantled to disengage the bridge from the support column. The shuttle is lowered to put the bridge on the hull and the structure is floated to a dismantling quay or a site for offloading onto a barge. The lifting legs are applied to the seabed to stabilise the hull and the bridge is freed from the structure and discharged onto the quay or barge.