Powering the deep

Longer step-outs, harsher environments, deeper waters all point to an increasing need for power on the seafloor. Statoil and its partners are working on solutions. Elaine Maslin reports.

ABB’s power from shore vision.

Electrifying the seabed has been a long-term aim for the oil and gas industry. A bid to achieve that goal is getting closer, however, as subsea processing becomes not just a necessary technology, but also a more mature one, which requires ever greater power supply on the seafloor at greater step-outs.

In Norway, Global Center of Expertise (GCS) Subsea partner Statoil is helping to lead efforts to create a subsea power distribution system. In 2013, the oil major inked a US$100 million, five-year joint industry project (JIP) with power and automation giant ABB to qualify a system able to transfer 100MW over up to 300km in up to 3000m water depth. Siemens and GE Oil & Gas are separately working on similar systems.

It’s quite a goal, but it’s one Statoil thinks the industry needs. “We see this as a key building block for subsea processing in the future, both subsea distribution and long distance power transmission,” says Steinar Midttveit, leading advisor, subsea electrical power, Statoil. “The fact that this technology enables the introduction of subsea processing without major topside modification is important. The Åsgard subsea compression development included a 900-tonne topside module on the existing asset, which is a major job to integrate. With this technology [subsea power distribution] we can place the majority of the equipment on the seabed, supplied by one power cable. We can also take power from shore easily, using renewable sources, reducing CO2 emissions and making subsea power processing more independent from where you take the power from.”

An ABB subsea power station visualization. Images from ABB.

The past year has seen a lot of progress on the JIP, ABB says. It has passed technology readiness level 2, which means the concept has been selected and key components tested. Concepts for power switching under pressure have been verified and switchgear components have been pressure tested and verified. The next steps are building sub-assemblies and prototypes.

“The next milestone is testing a power cell assembly,” says Jan Ø Bugge, vice president and project manager, ABB. “This test is testing the drive-cell under full operation conditions at pressure test facilities in Trondheim.”

“Before making final technology decisions, we want to see how it operates in the final environment,” says Stian Ingebrigtsen, principal engineer, subsea, ABB. “We will simulate the operation and the power cycling in normal operation. The target is to identify what works well and what needs to be improved for next round of design improvements.”

“Showing it is able to handle switching under pressure [in oil filled containers] will be a key milestone,” Bugge adds. “The next step after this is to qualify these components to make sure they handle the pressures to 3000 m water depth before building the full prototypes.”

At the same time, ABB is also working on the medium-voltage switch gear, transformer and control systems. All in all, an extraordinary array of components and materials all require testing and verification, to select the optimum arrangement, alongside third party components, especially around connectors and penetrators.

A key challenge will be making sure the equipment will be reliable over the design life of a subsea field, with as little as possible or no maintenance. “Most of this is well known in ABB product development, the new aspect is pressure,” Bugge says. “Also, we will have new types of material interfacing with live parts that will see varying temperatures depending on load conditions. A large part of the project is working with material technologies,” Ingebrigtsen says.

Then, the next step will be going into a live environment: ABB is looking to start shallow water testing of a complete system towards the end of 2018.

ABB has something of a heritage when it comes to subsea power distribution. In the late 1990s, the firm drove the Subsea Electrical Power Distribution System (SEPDIS) subsea electric power distribution project, resulting in a subsea frequency converter being designed and tested by 2000. At the time, the industry wasn’t quite ready for it.

It is hoped the industry will be ready once again, after the JIP completes in 2018 and progresses towards technology readiness levels 5-7 in 2019 onwards.

While Statoil has been postponing projects in response to the reduced oil prices over the past year-18 months, there are a few projects at select phase for such technologies, Midttveit says. “We are working on some projects, but they are in the early phase,” he cautions. 2019 might be better timing.