Moving platforms from shore to their offshore locations

Paul Boughton
How to move a 15-storey oil and gas platform deck from its construction site to final location offshore.

With high seas and winds offshore, it is easier to construct oil and gas platforms on land. But then the challenge is moving the massive structures out to sea. French company Technip has solved that problem with the floatover method, a technique for moving a platform deck to its permanent offshore location.

"Installing a large deck onto its jacket, or legs, using the floatover method is gaining popularity," says David Emery, a Project Manager in the Offshore Platforms Product Business Unit of Technip. "This is because the operational cost is much lower than other methods of installation, such as modular lifts or a single piece installation by a heavy lift barge. Also, a high proportion of the pre-commissioning work can be completed onshore prior to loadout, significantly reducing the duration and cost of the offshore commissioning phase."

Trelleborg's Orkot material is used for low-friction pads that facilitate the 'skidding' of oil and gas decks onto transportation vessels and from them to the support structures at sea. The decision to use Orkot bearings was based on the material's properties such as a high load capacity and compression strength, a low friction coefficient and strong chemical resistance. Demands are high in a floatover operation. The material must remain stable during the skidding operation, while continuously withstanding high loads during the time the decks are under construction, about two years.


Loadout (Fig. 1 left) - The platform deck's journey begins at the construction site. The entire deck rests on Orkot pads laid on a runway to 'skid' the deck onto its transport barge. Due to the pads' low friction properties, hydraulic cylinders (stand jacks) can push the platform deck from the quay and onto the barge (Fig.1 second left). The deck is then towed to the offshore installation site (Fig. 1 third left).

Docking, load transfer, separation

Docking: Vessel Entry (Fig.1 right) - At the installation site, the vessel is docked to the support structure, called the jacket. Vessel positioning - At the final destination, the vessel is moored inside the jacket by eight mooring lines to ensure accurate positioning of the deck's legs over the jacket legs. Load transfer: The vessel is ballasted to make contact with the support structure and then prepared to transfer the deck. Separation: After completion of the deck load transfer, a separation occurs between the deck and the vessel and the vessel is retrieved from the jacket using tugboats.

The platform deck structures that are moved from land to their jackets offshore are massive. They can be as high as a 15-storey apartment building and each of the working levels is the size of a soccer field. The platform is a complete factory made of steel, fitted with all the equipment to extract and store oil and gas before transferring it to transport ships.

For the personnel living on the offshore rigs for months on end, they are also a home away from home. There is an average of about 100 individual bedrooms and bathrooms on a platform.

Much like a giant hotel in the middle of the sea, they also feature restaurants, fitness centers and occasionally even running tracks. The decks are fully fitted with everything from beds to plumbing before they are transported out to sea.

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