With the success achieved to date on high-profile projects offshore Angola, Norway, and Brazil, both in terms of technological innovation and operational performance, the challenge now is to push the boundaries further.

Seabed processing solutions – Statoil’s ambition to have a full “subsea factory” in the water by 2020 is one such high-profile example – will by their very nature require a step-change in the levels of power required. Subsea separation, boosting, and compression hardware is now a recognized piece of kit in an offshore operator’s toolbox, especially for those targeting deepwater and harsh environment developments.

It also is seen as a key enabling technology for enhancing oil and gas recovery in both greenfield and brownfield projects as operators strive to improve average offshore recovery rates around the world from the current levels of 30% to 40% to a desired range of at least 50% to 65%.

Dependable power

All of this equipment, however, needs dependable power – and lots of it.

One solution under development by Siemens is the company’s subsea power grid system, which is aimed at complementing the company’s existing subsea portfolio that includes connectors, power systems, and permanent reservoir monitoring technologies.

A recent briefing by Siemens on the company’s new power grid solution stressed the limited means currently available to transmit such power underwater over long distances to components such as pumps and compressors. Typically, single power feeders are run from land or topside facilities with cables running to the sea floor.

According to Siemens, these solutions add complexity and cost to operations while simply not being viable for long stepouts or for situations that need relatively high power output or a high number of power consumers.

The power grid is designed to distribute power along the seabed to multiple consumers, minimizing the number of cables running to surface and simplifying operations. It also will enable the placement of processing equipment closer to wells, boosting production.

Phased approach

The company has adopted a phased approach to developing the system, which is currently in the detail design and test phase. The transformer was successfully tested in shallow waters in 2012, while other components such as switchgear and variable speed drives have been and continue to be tested. The aim is to bring the subsea power grid to the market next year.

One recent innovation is the 36-kv subsea connector that ultimately will be used to connect the different grid modules together. The connector’s design incorporates new features to improve insulation performance, reduce the risk of leakage, and optimize pressure compensation.

Bjørn Rasch, Siemens’ head of subsea power, pointed out that the subsea sector is the global offshore E&P segment expected to grow the most, with a compound annual growth rate of 16.2%. Within that, getting reliable, field-proven subsea power distribution systems is seen as the “key enabler” for seabed processing, he said.
Rasch lists the key drivers as follows:

• Number of consumers – subsea power distribution can reduce the total length of cable and number of risers;
• Water depth – subsea power distribution can reduce the complexity of riser arrangements;
• Available space on existing platform installations – marginal fields can be developed with existing infrastructure;
• Long stepouts – Realization of subsea-to-beach; access of remote areas, e.g. Arctic; and
• Increased need for large-scale processing – subsea power distribution is the key enabling technology for realizing the subsea factory.

Likewise, the main benefits he sees are that:
• The complete system approach is important for success;
• The use of modular building blocks reduces cost and complexity;
• Built-in redundancy increases availability;
• These systems provide condition monitoring and intelligent operation;
• Operators can “trust in technology” by qualification and standardization; and
• Development has taken place in cooperation with leading oil companies.

System evolution

The last benefit has been a vital one in the subsea power grid’s evolution. Siemens began the process with the launch of the original R&D project in June 2010 with joint industry project (JIP) contracts signed the following month with supporting operators including Statoil, Petrobras, Chevron, and ExxonMobil.

The product development was enhanced through targeted acquisitions of companies with specific subsea and power expertise, including Bennex and Poseidon (both based in Norway) in March 2011 and Tronic and Matre of the UK a year later. By September last year the JIP had completed qualification of the subsea transformer; product qualification and testing of the complete subsea grid are now underway. A shallow-water system test is currently penciled in for early in 2015, with the scalable system to eventually be rated for operation in up to 3,000 m (9,843 ft) of water and capable of handling long step-out distances of up to 200 km (124 miles).

Jan-Erik Lystad, who heads up Siemens’ Subsea Technology Center in Trondheim, Norway, is in charge of the rigorous testing being undertaken on all of the company’s subsea components there – what he described as “a kind of torture chamber for technical components.” The tested components have to withstand pressures of up to 6,670 psi, equivalent to a water depth of 4,600 m (15,093 ft).

Current focus on AC

Lystad flagged AC transmission (36 kv to 145 kv) as the main focus of oil companies in terms of subsea power distribution technologies. “AC is the key focus area today, while DC by most is put off for the next three to five years,” he said, adding that technology risks are viewed as manageable “and oil companies do not see any real showstoppers.”

He also highlighted some subsea electronic power deliveries already made by the company, including converters for seabed logging – Siemens has developed and built a power converter to perform high-accuracy electromagnetic surveys offshore in extreme pressures. With a design requirement to be able to operate in water depths of up to 3,500 m (11,483 ft), endure pressure cycling, and cope with a high current of 1,500 Amps, Siemens has so far delivered 16 units and clocked up approximately 65,000 survey hours.

If the company hits its future milestones mapped out for its subsea power grid, the first system is planned to be operational circa 2016.

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