EC-OG’s subsea turbine system was launched at Offshore Europe, ahead of new deployment trials backed by OGTC
Subsea power and electrification continues to be one of the sector’s biggest areas of research and investment. It is therefore encouraging to see promising technologies make it through the difficult developmental stages, and garner some interest along the way.
One such successful technology is East Coast Oil & Gas (EG-OG’s) Subsea Power Hub – a seafloor turbine for powering subsea equipment – which saw its commercial launch at SPE Offshore Europe 2017 in September. InnovOil profiled the Hub (abbreviated to SPH) just over a year ago in September 2016. Devised to meet the challenge of powering subsea equipment economically, and for long periods, it consists of a recognisable template structure, with space for up to three turbines mounted in the centre of the frame.
Typical seafloor current strength is around 0.4 m/s, meaning each turbine will deliver an average base-case output of 300 kW per annum, with the largest models producing around 150 kWh per year. Hubs can also be clustered and configured by a distribution network for larger project footprints.
An intelligent energy management system (IEMS) optimises battery life by considering the energy available in ocean currents and the repeat performance of the unit in powering the battery system, helping to increase design life far beyond battery-only systems.
While typical subsea battery systems may last a year or so, the SPH can extend operating life up to 5 years, the company says. EC-OG managing director Richard Knox told InnovOil that while an exact cost comparison could not be made between the SPH and battery-only systems – in part because the unit includes the cost of battery storage – the economics were still favourable overall. “The comparison comes into play when we consider specific situations where the batteries may last only 6 weeks to 2 months for an application. This incurs associated costs, including the significant cost of changing these batteries on a regular basis, including the vessel hire and the associated fuel costs,” Knox said.
Out of the lab In April, the first SPH was trialled at a European Marine Energy Centre (EMEC) test site in Shapinsay Sound. This prototype used a hybrid drive system, linked directly to a lithium-based energy storage system. The unit ran autonomously as part of its test programme over the summer months, with monitoring data sent back to the centre wirelessly for analysis.
Knox said that the system performed as planned. He added: “We were happy with how closely the system was performing with what we had predicted. It was really useful to have the system mounted on [the] seabed in an uncontrolled real-life environment. We were able to take the system out of the lab to being fully operational on the seabed.” The data from the EMEC test will now be used for further optimisation.
It also provided valuable information on how the different units might perform, he said. “At present, following these tests, we have a better understanding of how we can use the different configurations (either the single or the triple unit). This information and data has helped us to refine the sizing of the units for different applications.”
That data also helps the company predict the energy requirements of its potential clients: “Our web application, which was used as a market research tool at Offshore Europe, has allowed us to refine our offering specifically to client needs by using real live results. The use of this data means that we can confidently provide the energy needed for a variety of applications.”
Interest in those applications is growing. As the industry begins to embrace the potential of subsea electrical power, EC-OG is well positioned to take advantage. Knox commented: “Subsea electrification is no longer being perceived as a radical or novel method. It is now seen as something that can be adopted in the near term and for EC-OG this is an immediate reality.”
“We’ve seen companies that have been testing fully electric trees for a long period of time. The economics of this are now becoming more attractive, especially within the context of the low oil price environment. The risks associated with adopting the technology are reducing as well. It feels like we are on the cusp of a more general adoption of a fully electrical system for use in wells,” he continued.
Knox identifies two distinct sets sub-sets of subsea electrification: the fully electrified “subsea factory” concept, and applications in marginal fields where electricity is used for very distinct applications. Although one requires large amounts of power and the other small, the two should act as complementary disciplines. He added: “The more that we can implement electrification in the small pools scenario then that helps the further use of the building blocks for the subsea factory. An intermediate step is created where learnings from low power networks can be transferred to high power, long distributed networks. This helps build a reliability database. I think that this will be the way that people will exploit fields moving forward.”
Deployment decisions EC-OG is now undertaking FEED work for a North Sea field trial, backed by the Oil and Gas Technology Centre (OGTC) in Aberdeen. The work will focus on the in-place SPH design, optimised deployment procedure and de-risking the installation and operational phases.
Knox explained: “Installation of the SPH is a very important part in the successful functionality of the system. We are interested in finding out the best way this is achieved technically as well as the associated costs of doing so.” The study will focus on key installation factors such as necessary vessel requirements, overall costs, installation analysis, diver safety and recovery of the system at the end of the life cycle. “This will allow us to have an accurate holistic view of the overall life-cycle cost,” he added.
The priority being placed on subsea electrification marginal field development suggests that the SPH could easily find a secure home in the wider subsea power toolbox – and as oil and gas operators look for greener, cheaper and more reliable systems, this innovation ticks all the right boxes.