With the drive towards the all-electric subsea factories, the need for reliable subsea electrical power is ever more important. Power is delivered subsea either from turbines located on a platform via an umbilical or through a shore to subsea cable. Either way, ensuring the integrity of the cable and any subsea connection is paramount to ensuring that production is not halted.
Considering the cost of the umbilical itself and the cost of installation, an operator would be looking at something in the region of $2,000 per meter, making a typical two kilometers long a $4 million capital expense. That’s before you factor in the lost production.
A bad mixture
The fundamental physical fact is that electricity and water do not mix very well. Over time, through any number of reasons, water will penetrate these electrical cables and electrical connectors, which ultimately leads to an electrical failure.
“It’s an operational problem that all operators experience,” Neil Douglas, Managing Director of Viper Innovations, said. The operators are aware of the problem and there have been several joint industry studies trying to get to the root cause of the problem. They do talk to each other and they are open to the fact that it is a problem.”
As a solution to this increasing problem, engineers at Viper developed an innovative yet on the face of it, an unpretentious solution called V-Life. “Effectively, our solution is a box of electronics that sits on the platform,” Douglas explained. “It simply connects to the umbilical at one end and we apply small electrical signals to the cables or the copper conductors in the umbilical.”
This has two effects utilizing both electrokinetic, and then electrochemical technology. With the electrokinetic technique, the water molecules are driven into the umbilical where water has penetrated. Then, with the electrochemical technique, a precipitate is created.
Douglas explained that it is a temporary paste that blocks the holes where the water gets in. “We always describe it as something like a pain relief,” he added. “If you have an Illness and you’ve got a headache, you take a pain reliever. It makes the headache go away, but it doesn’t get to the root cause of why you’ve got the headache.
“Our paste or our precipitate which we use to block the holes in the cables is non-permanent. It stays there whilst our equipment is connected. As soon as you take the equipment away, this precipitate eventually dissolves and gets washed away. We keep the electronics connected, and that maintains the precipitate in place. We apply different electrical signals to hold that plug there.”
Technology in action
One client that contacted Viper Innovations had already written a procurement specification for a new umbilical and umbilical termination assembly. The original umbilical, 15km in length, was installed in 1992 and both electrical power channels were deteriorating with one of them at such a low level that it was unserviceable.
This meant that the entire subsea system of eight wells was operating on a single power channel with no prediction as to how long it would last. The lead time for a new umbilical was anticipated to be two years. Production was at risk and so Viper Innovations was asked to install V-LIFE on the failed electrical channel.
A portable unit was delivered, and an engineer was mobilized offshore to undertake the installation and the commissioning. The power was removed from the subsea system for a total of two hours and the unit was commissioned within a single offshore shift.
Within two weeks the insulation resistance (IR) had increased from less than 50kOhms to more than 20MOhms. This was in December 2013. Since then the IR has risen to, and plateaued at, 80Mohm. The client has installed a second unit on the same umbilical and is now operating with good margins on both power channels.
Repair or prevent
Douglas explained that they have some clients now who are leaving them out for the life of the field with the longest potential insulation until 2030. “Clearly, it becomes very attractive where you get close to the cessation of production, so close to the end of field life,” he said. “Let’s just say there are just three years left on the field to go.
“If you get an electrical failure which stops production, the economics are generally such that you wouldn’t go and replace the umbilical or have a big intervention. It would bring the cessation of production forward. What this technology does is effectively resurrect the production and keeps it going until the end of field life.”
If the cable deterioration is too bad, then it will be impossible to repair using V-Life which creates the valid argument for early installation. “If the failure gets too bad, too much water gets in, we get to a point where we cannot recover it,” Douglas added. “We can’t get enough energy into the system.
“We want to try and encourage operators to use it or to turn it on when they see the start of the cable or the umbilical degrading or deteriorating. The earlier they get it on, the higher the probability that our system works. We’ve got a couple of clients, again, who have perfectly good systems with no water ingress at all, but they’ve got the system installed just to keep the systems up and healthy and prevent any future problems.”