The installation, in the North Sea, of the world’s longest static electricity cable and the first dynamic cable to floating structures in extreme environments allows for underwater AC power supplies beyond all previously known limits. With these two world firsts, Total’s teams are pushing back the boundaries of offshore electricity supplies.

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Erwan Delaunay

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Édouard Thibaut

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Lars Anders Myklebust

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Tore Andre Orvik

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Wilfried Vandersippe

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A long-distance static cable for cheaper and greener operations

Until recently, the longest underwater cables for supplying offshore oil rigs with an alternating current supply were 90 km. But now a new record has been set: since 2015, an underwater electrical power cable measuring over 160 km long has connected the offshore rig in the Martin Linge deepwater field with the onshore Kollsnes plant in Norway. The energy needed to power rig operations now comes directly from the Norwegian national hydro-electricity network.

This technological advance was made possible thanks to design modifications and adaptations of the underwater static electrical cables we had been using up until now.

Extremely reliable and easy to reproduce, this technique effectively removes the constraints for long-distance AC power supplies. Unlike offshore generators, the cable has no maintenance costs, while still reducing the level of HSE risk. The electrical power supply is responsible for direct annual savings of $12 million in fuel. With almost zero greenhouse gas emissions (and emissions reduced by 2 million tons of CO2), Martin Linge has also set the bar for 100% “green” offshore operations. The cable also provides a connection via 108 optical fibers, which will enable the offshore facilities to be controlled remotely and in real time from the Total operations center in Stavanger.

When the Martin Linge cable was connected to the Norwegian power grid, we were able to successfully test its electrical parameters against all the design criteria for onshore equipment.

The dynamic cable: a new asset for floating structures

At the beginning of the project, supplying the Martin Linge field with electricity from land concerned only the offshore rig. Its storage and crude refining vessel (FSO[1]) was intended to be powered using diesel generators. Indeed, there was no technology at the time that could ensure electrical power between the rig and the FSO through a dynamic cable capable of withstanding the extreme fatigue brought about by the difficult weather conditions in the North Sea.

However, thanks to operational excellence and the perseverance of the project teams, we were finally able to make a breakthrough. After three and a half years of design, production, and prototype testing, in 2016 we successfully made and installed the FSO power cable, measuring 3.5 km long, that could withstand extreme dynamic stresses, in particular those caused by the boat moving 35 m from its anchor point.

A world first, this innovation has opened up new possibilities for cabled power supplies to floating structures (FPSO[2], FLNG[3] or loading buoys) over long distances, even in the most challenging of environments. The development of this dynamic cable will help make projects safer, cheaper, greener, and better connected!

 

[1]  Floating Storage and Offloading

[2]  Floating Production and Storage Offloading

[3]  Floating Liquefied Natural Gas

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