Saft and FMC Technologies, the leading manufacturer and supplier of subsea production systems, are working on a joint development project to demonstrate the operational and environmental advantages of electric subsea technology powered by rechargeable lithium-ion (Li-ion) battery modules. In the first prototype stage, six Saft Li-ion battery modules will power electrically operated control valves for Statoil’s Norne oil and gas system, operating at a depth of 350 m below the North Sea. Electric subsea technology utilises existing low-power umbilical and connector technology, which provides a safer operating environment and prevents corrosion from stray high voltage currents. Basing the system on local energy storage with rechargeable batteries reduces costs for topside power generation, transformer equipment and umbilicals, no high power/high voltage cable from the surface is needed and the components are adaptable to upgrade existing systems. ”Electrical subsea technology based on rechargeable battery systems is already field-proven, following a successful installation on Statoil’s Statfjord,” said Vidar Sten Halvorsen of FMC Technologies. “The recent development work with Saft has shown that Li-ion battery technology will offer significant benefits in operational performance by enabling us to store much more energy within a compact, lightweight package with high-cycling capability than with traditional cells.” Trond Beyer of Saft said “There is also another key factor in favour of Li-ion technology, which is that it is easy to make diagnostic measurements of a cell’s state of charge (SOC) and state of health (SOH). This provides an excellent basis for remote monitoring and control of the battery system, which will be essential as oil and gas exploration moves to ever greater exploration depths. Saft Li-ion cells are completely hermetically sealed and maintenance free, ensuring that no gas can escape into the local environment.“ Saft Li-ion modules: The Li-ion battery modules developed by Saft in conjunction with FMC Technologies comprise seven VL41M cells connected in series, providing a nominal 24 V and 800 Wh capacity in this application. The cells are housed in a robust, nitrogen-filled enclosure designed to withstand extreme water pressures.
The Li-ion modules will be maintained on float charge from the subsea tree’s local 24 V DC supply, and will deliver a current of up to 120 A for the high torque motors that operate the control valves. At the Norne system, 21 electrically operated actuators are being retrofitted to operate manual (ROV operated) and electro-hydraulic valves. Saft VL cells: Saft VL series cylindrical Li-ion cells are manufactured on established production lines in Bordeaux, France. For maximum performance, life and safety, this advanced design Li-ion cell uses a nickel-based positive active material, doped with aluminium and cobalt. Saft VL cells offer an ideal combination of light weight, small size, high-energy and operational reliability, with an extended lifetime even at high ambient temperatures.