Monster Cables: Connecting the Subsea Factory

By Mario Vittone On May 13, 2015

Artist Rendering – Subsea Installation    Image: XVISION

If the oil and gas industry’s dream of a subsea factory is to become reality, then R&D that advances current technology is imperative. Companies like ABB are working to advance subsea power conversion, Aker Solutions is developing capping technologies, and OneSubsea has already built the first multiphase compressor that in and of itself is a quantum leap forward in subsea technology.

But look at any drawing of a subsea oil and gas installation and you’ll notice the miles of interconnecting cables and piping. At the distances and depths where these oil and gas wells will be, the problems of powering and connecting and controlling these complex machines seem to the layperson to be all but insurmountable. High voltage power has to get out there, low voltage control power will need to be routed, fiber optic lines would have to be run, and hydraulic control lines would have to be installed.

Now, we’ve been laying cables underwater over great distances and at depth since the last half of the 19th century, so you can imagine that the technology for subsea signal and power has dramatically advanced. But until I sat down at a table at Nexans Norway with a cross-sectional display of a modern subsea umbilical in front of me, I had no idea how far we had come.

27,000 individual elements make up each length of this subsea umbilical. Photo: M. Vittone/gCaptain

(Alright, admit it. Unless you have been directly involved with subsea umbilicals before, you saw the above picture and said, “Wow,” or something similar.)

“For every kilometer of that umbilical in front of you, how many individual component strands would you guess there are?” asked Ragnvald Graff, Sales and Marketing Director for Nexans Hybrid Underwater Cables Business Line. My guess – 12,000 – wasn’t even close; not by half. The answer? Ragnvald says 27,000, but I wasn’t going to count.

The Laggan Tormore umbilical ( 126 + 17 km) installed in the West of Shetland. Image courtesy of Nexans. (Click image for full size. Really – you should look at this.)

Nexans is combining high voltage, low voltage, fiber optic, and hydraulic control lines into a single umbilical and building them to withstand the crushing pressures of deep sea installations. A lot of what you see in the first  image above is there as “armor” to keep internal components from crushing under the ocean’s weight. As complex as they are, these umbilicals are built for reliability as well.

At the Chevron-operated Jack and St. Malo oil and gas field, Nexans designed and built the power umbilical (42 kilometers long in two sections) and installed it at 2,100 meters. The design life of the umbilical is 30 years.

One of the greatest challenges Nexans faces in the design of these modern cables is weight. Much of what goes into an umbilical is there to keep the cable from breaking under its own weight during installation. A single meter umbilical designed for Statoil’s Snøhvit (Snow White) project weighed 297 lbs (135 kg). The total main umbilical for Snøhvit – still the world’s longest subsea umbilical installed in a single length – weighs over 43 million pounds.

Cross section of the Jack/St. Malo umbilical for Chevron; 2 umbilicals, totaling 42 km, 450 km south of New Orleans, Louisiana, at 2100 m water depth. Image courtesy of Nexans

The company – now in its 100th year of operations – is involved with all phases of subsea cabling and control technology from design through to installation. In 1976, the company built the C/S Nexans Skagerrak specifically to transport and install large subsea cables. The Skagerrak can carry 7,000 tons of cable on its spool.

Workers guide the loading of miles of subsea power cables onto the spool of Skagerrak. Image courtesy of Nexans

So it would seem that for the interconnection of the subsea factory there isn’t much left to invent, but that hasn’t stopped Nexans from making advances in cabling and umbilical technology. Last week, at OTC in Houston, Nexans announced the launch of its next generation SUTA-FLEX Subsea Umbilical Termination Assembly.

The SUTA-FLEX is an electro-hydraulic system that enables multiple wells to be controlled by a single umbilical, connecting a number of subsea control modules to the same communications, electrical and hydraulic lines. Having power, signal, fiber, and hydraulics in one umbilical wasn’t enough – they designed a way to control multiple wells using that same cable.

There is no doubt boundaries will be pushed and new technologies developed in making the subsea factory a reality, but it seems that interconnection and control lines are ready and waiting for everyone else to catch up.