Acergy France Sa

Stolt Offshore S.a.

Vincent Marcel Ghislain Alliot

Jean Louis Hoss

A method of installing a subsea structure, such as a hybrid riser tower, is disclosed. The riser tower includes a main portion and a buoyancy portion. When installed, the riser tower extends substantially from the seabed towards the surface with the buoyancy portion attached at a top end. The method includes taking the riser tower to an installation site in a substantially horizontal configuration with the main portion containing a first fluid and the buoyancy portion containing a second fluid, the second fluid being more dense than the first fluid. Then, tilting of the riser tower is performed such that it takes a substantially vertical configuration by allowing the first fluid in the elongate portion to interchange with the second fluid in the buoyancy portion. Also disclosed is a suitable apparatus for performing the method.

Hybrid riser tower and method of installation thereof

The invention provides a marine riser apparatus () for use in the production of hydrocarbons from offshore wells and an associated method of installation of the apparatus at sea. The riser tower comprises rigid pipelines arranged in a riser tower bundle () and extending from a wellhead on the seabed () to a point below the sea surface where they are connected to flexible jumpers () which extend from the tower structure to connect the tower structure to a surface vessel or platform (). The riser apparatus further comprises a buoyancy device () attached to the riser tower bundle, such that the buoyancy device is located above and exerts a buoyancy force on the riser tower, the buoyancy module also supporting an intermediate section of at least one of the jumpers.

Marine riser tower

An elongate article () such as a prefabricated pipeline of several kilometers length is towed through water. The article is provided along its length with buoyancy adjusting material () fitted closely to the article. The buoyancy adjusting material is sufficient to give the article overall a positive buoyancy so that it will not sink to the seabed, and is distributed unevenly along the length of the article so as to create regions of negative buoyancy. This causes the article to adopt a wave profile with peaks (+) and troughs (&#x2212;) along its length. The article is connected at its extremities to lead and trail tugs () for controlling movement of the article through the water. Intermediate peaks are optionally coupled to intermediate tugs () or buoys () via self-adjusting ballast chains (). The wave profile allows the towed structure to extend without undue tension on the article itself. The article can be laid to the seabed progressively removing buoyancy elements () using an ROV ().

Towing and subsea installation of long articles

There are disclosed methods of and apparatus for interconnecting lined metal pipes (), applying in particular to the offshore oil and gas industry. Corrosion is a common problem in the industry. Lining pipes overcomes the problem, but welding sections of pipe together can be a complicated and time-consuming task, requiring dedicated and sophisticated tooling. More desirable is the ability to use conventional pipe-laying equipment () with little additional tooling. As such, there are disclosed methods and apparatus compatible with known offshore connection methods, particularly where the spacing of joints on the pipe is less than 100 m. The chosen technique will not significantly impact the laying rate of the lined pipe, compared with unlined pipe. The method includes connecting lined pipes () using a corrosion-resistant bridging member () internally overlapping both linings, leaving a void space () behind the weld region () while at least the initial stages of welding () are performed, and expanding () the bridging member to provide a seal against the liners, in a controlled sequence. There is also disclosed a bridging member (), tooling () and pipelay apparatus suitable for use with this method.

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Paris, France

Vincent Marcel Ghislain Alliot