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    CSO completes well servicing with monohull

    News // July 14, 2000
    Coflexip Stena Offshore (CSO) has announced that its Norwegian subsidiary Coflexip Stena Offshore Norge has successfully completed a contract for Statoil for the first part of the abandonment of its Tommeliten subsea field, offshore Norway.

    The specialist light well intervention vessel CSO Seawell was used to kill and plug the six gas production wells on the subsea template, and recover the production Christmas tree from each well.

    This was the first time that the Norwegian authorities have given consent to an application to use a light well intervention vessel on a live well.

    Kevin Wood, Executive Vice President, Operations and Projects, for North America, the North Sea and Asia Pacific, said: "The CSO Group is particularly proud to be associated with the introduction of light subsea well intervention technology on the Norwegian continental shelf".

    "The Tommeliten project has proved that our specialist well intervention vessel can operate in Norway with much greater time and cost efficiencies than a conventional drilling rig".

    "In addition", said Wood, "the project has clearly demonstrated the added value of the versatility and mobility of the CSO Seawell. This enabled Statoil to quickly respond to an unexpected complication with the subsea equipment identified during the intervention."

    A technical complication with the equipment, installed in 1988, would not allow any of the six Christmas trees on the subsea template to unlatch from their base, after the wells were killed and plugged.

    The project team including CSO, Statoil and the tree manufacturer, quickly established that the problem could not be solved without first completing a manned underwater intervention.

    Fortunately, in addition to its well intervention role, CSO Seawell is one of the few vessels in the world capable of supporting diving operations in Norway.

    The vessel departed from the Tommeliten template immediately after completing a thorough assessment of the technical problem with the subsea production equipment.

    A saturation diving team was mobilised to Aberdeen to meet the vessel upon arrival. The team of 32 men, consisting of 12 saturation divers and attendant support personnel underwent refresher training and familiarisation on the diving regulations, procedures, equipment and scope of work.

    Less than 27 hours later, the CSO Seawell was on its way back to the field with the diving crew and equipment onboard.

    The Norwegian authorities (NPD) approved the Application for Consent to Dive prepared by CSO and Statoil, and the divers successfully disconnected all six trees from their bases within six short bell runs. The trees were safely recovered to surface usingthe vessel's derrick.

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