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    FLNGs on the horizon?

    News // April 5, 2001
    Floating Production, Storage & Offloading (FPSO) platforms have become well known in the oil industry and are often the preferred solution for the development of deepwater oil reserves.

    However, floating platforms for the production and processing of Liquefied Natural Gas (LNG) are less well known, and, until recently, their design was in its infancy.

    This situation is changing rapidly, though, and studies carried out over the last 12 months on behalf of a number of companies engaged in LNG production have demonstrated that Floating LNG (FLNG) platforms are feasible, and economically viable.

    In March, Bouygues Offshore in France announced that it had successfully completed a research and development project dubbed 'Azure' in which a consortium of companies it was leading examined a number of concepts for FLNGs.

    The consortium of companies led by Bouygues Offshore also included nine other European concerns, including French shipyard Chantiers de l'Atlantique, Italian yard Fincantieri. Also participating were FMC Europe, M W Kellogg Ltd (MWKL), Gaz Transport & Technigaz (GTT, which is 30 per cent owned by Bouygues Offshore), plus classification societies BV and RINA, and the Institut de Recherché de la Construction Naval (IRCN).

    Five international oil and gas companies - Shell, TotalFinaElf, Chevron, Texaco and Conoco - lent technical and financial support to the project, which was carried out under the European Union's Thermie, programme. The main aim was to address all of thetechnical and safety issues involved in floating LNG production, from the gas well to gas distribution.

    Under the terms of the 18-month programme of work, the partners were required to design floating liquefaction plants, floating LNG terminals, and offshore LNG transfer systems. All of the main components in the chain were subjected to thorough testing, including the cryogenic storage system, which is based on a membrane containment system developed by Technigaz and GTT.

    Fincantieri was made responsible for developing the floating receiving terminal, which would be located in Southern Europe; the regasification process, developed by Technigaz, being based on the use of submerged combustion vaporisers. The LNG storage capacity at the terminal would be in the order of 200,000m3.

    FMC determined that transfer of LNG at sea could be safely undertaken in a tandem loading configuration using a 'Boom-to-Tanker' system, a large scale model of which was successfully tested using motion data from tests in a model basin.

    Both steel hulled and concrete hull LNG FPSO designs were examined during the project, Chantiers de l'Atlantique being responsible for the design of the steel hulled ship with Bouygues Offshore responsible for designing the concrete hull alternative.

    Computer tools developed by IRCN were used to address issues such as liquid motion in slack LNG storage tanks - tests carried out by GTT determined that sloshing would not be an issues - and BV and RINA carried out a full safety assessment of the entirechain.

    Jaap de Wilde, a researcher scientist at Maritime Research Institute Netherlands (MARIN), which has carried out a number of studies for Shell independently of the collaborative effort, says FLNGs could be especially useful in the remoter oil fields of the world, and in 'green field' gas developments.

    "In remote developments, the FLNG could turn a problem into a revenue generating opportunity", explained de Wilde. "Gas has associated with oil production has to be disposed of somehow, and the FLNG is an economic means of doing so, and also represents an economically sound way to develop green field gas".

    In the FLNG system that MARIN studied for Shell, a floating barge with a mooring turret, gas conditioning, liquefaction plant, storage tanks, offloading facilities and accommodation, would sit over the reservoir. When sufficient LNG had accumulated in the storage tanks on the barge, it would be offloaded to a LNG carrier with reception facilities for the liquefied gas, and transported to the customer.

    Unlike an FPSO, which normally offloads oil to a shuttle tanker via a pipeline, in the FLNG, which would usually operate in relatively calm waters - such as the Timor Sea, North West Australia - the LNG carrier would berth and load alongside the barge. As de Wilde explained, side-by-side loading will also allow conventional loading arms to be used.

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