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More out of subsea wells

March 16, 2006, 09:30 CET

Vessels are to be used even more extensively for workovers on subsea wells. In 2006, light well interventions will be carried out in around 20 wells, almost twice as many as last year.

"Light well intervention is an important tool for improving the recovery factor in subsea wells," says Lars Christian Bacher, senior vice president for the Tampen business cluster. "Today's recovery factor is 43 per cent, while the ambition is 55 per cent. This will provide increased earnings and reduced costs compared to the use of traditional rigs, and thereby benefit both companies and society."

Organising across licences and areas will ensure that this successful commitment continues. Whereas light intervention was carried out on 12 subsea wells last year, this year's campaign involves about 20 wells. The operations will be performed from April to the end of November.

Light well intervention involves wireline-based workovers of subsea wells. The wireline is run directly through the sea to the well through a gate and a safety valve, enabling work in a pressurised well. This eliminates the need for the risers required when such work is carried out from a drilling rig, and jobs can be carried out more quickly from vessels. Each intervention takes between six days and two weeks.

"It's far cheaper to carry out workovers on subsea wells from vessels rather than drilling rigs," indicates Mr Bacher. "The savings are currently around 50 per cent, but the goal is to reduce costs further, to around 30 per cent."

He also points out that the use of vessels gives the companies greater flexibility with regard to moving from well to well.

With nearly 300 subsea wells, Statoil is the world's second largest operator of this type of well. It is the only company carrying out light well intervention from vessels on the Norwegian continental shelf.

"Experiences have been good across the licences," says the senior vice president. "No licence could have done this alone, but we have 15 licences behind us."

In 2004 and 2005 light well interventions were carried out from the Seawell vessel. This year another vessel, Island Frontier, will be used. Statoil has also procured a new vessel, Island Wellserver, on behalf of the licences.

"Construction starts this spring, and from the spring of 2008 this newbuilding will make light well interventions on our subsea wells even more efficient," says Mr Bacher.