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ABB subsea substation

Factory on the sea floor

Image credit: ABB

Inspiring technology for the most challenging environment on Earth – building a factory on the deep ocean floor.

The abyssal plains are not the ideal working environment – even an unmanned industrial one. There is not a scrap of sunlight, the temperature hovers just above freezing, and most importantly the pressure of around 300 atmospheres (at 3,000m) is enough to crush a typical military submarine.

There are, however, good reasons for the oil and gas industry – and potentially other industries in the future – to make this hostile and barren environment its home. And a project has just been completed that is a foundational step in making such a goal a reality. Subsea Power is a Joint Industry Partnership (JIP) to provide power distribution on the seabed, rather than having such an operation on the surface.

Why go to the seabed? Jeremy Cutler, director of R&D of Total’s R&D Centre in Stavanger, explains: “This is disruptive technology, it is transformative technology. It allows us to put power subsea where we need it, without the topside VSDs [variable speed drives] and different power cables. It’s going to enable us to open up some of the unexplored areas of deep water down to 3,000m, bringing in new reserves.”

Total joined forces with Chevron, Equinox and ABB in this JIP, which has signed off the testing phase – a 3,000-hour shallow-water test. This completes a project that has cost $100m since its inception in 2013. The technology is now in place to allow energy companies to access a reliable supply of up to 100MW of power, over distances up to 600km and down to 3,000m depth.

As a result, oil production can be taken far offshore and to far greater depths than currently possible. And beyond opening up new areas for exploitation, it also has significant economic benefits. Production platforms, the topsides, are expensive in themselves, but all services on the sea floor require separate connections – every compressor or pump or any device requiring power and control (each compressor or pump has a VSD to control motor speed and torque) needs its own cable from surface to sea floor. At depths down to 3km that is a lot of heavy and expensive cables, especially as projects mature and spread. By putting power distribution and control equipment on the seabed there only needs to be a single cable from shore (or other infrastructure) that serves all equipment in the locality.

‘This is clearly the biggest enabler. Once you can get 100MW of power on the sea floor that opens up the possibility for sub-sea compressing as well as processing.’

Kevin Kosisko, ABB

Energy efficiency is also tackled by placing equipment on the sea floor. “On the Norwegian shelf we probably run some of the best gas turbines in the world, but still they are relatively low in efficiency,” explains Dr Per Gerhard Grini, manager of subsea and topside technology at Equinor. “If we could switch that to power from the shore, which for the Norwegian Shelf would be 100 per cent hydro power, that reduces our CO2 footprint tremendously. And we are under enormous pressure on the Norwegian Shelf because our industry represents 25 per cent of CO2 emissions in Norway so politicians are looking to us to get a reduction for the nation.”

Prior to the JIP, only the transmission cable and subsea step-down transformer were existing and proven to operate under­water. Following the success of the JIP, ABB’s subsea power distribution and conversion system now comprises: step-down transformer, MV variable speed drives, medium voltage switchgear, control and low-voltage (LV) power distribution, and power electronics and control systems supported with 230/400V.

Is this a building block towards a subsea factory? “Most of the components are there now but some are still being worked on,” says Kevin Kosisko, ABB’s global managing director, energy industries. “This is clearly the biggest enabler. Once you can get 100MW of power on the sea floor that opens up the possibility for sub-sea compressing as well as processing and the type of things that typically take place in a platform; we start to look at how much of that we can move sub-sea. And I think that is clearly the vision, to get there.”

Economic benefits may mean that this greenfield application is just a starting point. “The other one is existing fields, where you may need additional compression or other things,” adds Kosisko. “You can use this technology without having to restructure the platform. Instead employ this subsea and connect to the platform. These might be the first applications we do because it’s a clean solution for the mature wells as they go through their life cycles.”

ABB subsea infographic inline

Image credit: ABB

ABB is not new to sub-sea technology – it has been putting transformers on the seabed for over 20 years – but managing pressure for the control equipment has been a major challenge. The vessels themselves have an inner module for the electronics which is filled with nitrogen, encased in an outer vessel containing the switchgear. Filling this outer vessel with oil naturally pressure-compensates as the depth increases. “You have sort of bellows, which is a double barrier. When you install this they will compensate for the expansion of the oil and the pressure, so it is the same inside as outside. There is another benefit of that because if the connectors see the same pressure either side they are more reliable,” explains Asmund Maland, ABB’s group vice president, oil & gas energy industries.

Reliability is absolutely key to the viability of putting equipment of this nature 3km under water. Quite simply it has to last for approximately 30 years without failure, replacement or maintenance. It was for this reason that the 3,000 hours of underwater testing was imperative to conclude this stage of creating the subsea factory.

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