Governments across Europe are setting increasingly tight targets for reducing emissions over the next 30 years. This is putting pressure on the region’s offshore operators to ease up on oil and gas investments and diversify into renewable energy. But some also see the development as an opportunity that could extend the lives of platforms on depleting fields, converting them for new uses. Others are investigating alternate energy sources to power platforms and subsea installations.
Interest is growing rapidly worldwide in the use of hydrogen as an alternative to natural gas in industrial processes, which emit carbon dioxide (CO2), and potentially as a fuel for transport by road, sea and air. According to TNO, the scientific research organization in the Netherlands that works closely with the oil and gas industry, some of the electricity generated by wind turbines in the Dutch North Sea could be converted on platforms, through electrolysis of desalinated seawater, to hydrogen for export to the shore via existing gas trunklines. Last month, Oil & Gas UK announced that it is also examining this option for UK offshore installations as the industry seeks to step up renewable energy investments.
Transporting hydrogen molecules via established offshore infrastructure could be more economic than taking electricity from future wind farms constructed in deeper water, up to around 100 km (62 mi) offshore, with the added costs of longer power cables and transformer stations to connect the wind turbines to the onshore grid. Beyond 100 km there is also a need for costlier HDVC substations and cabling instead of relatively low-cost AC infrastructure.
The Dutch government is targeting a 95% reduction in the Netherlands’ CO2 emissions by 2050. This suggests more widespread investments will be needed in wind and solar energy but as TNO points out, both are weather-dependent energy sources which can cause fluctuations in the energy grid if the wind fails to blow or during periods of sustained cloud cover. Large-scale production of ‘green’ hydrogen, powered by renewable energy, via shallow-water platforms could provide greater reliability of supply and options for large-scale energy storage. And the maintenance costs could be shared with the owners of the offshore gas infrastructure, in turn stimulating further developments of North Sea gas, thereby avoiding the need for heavy capital investments in electric infrastructure.
In July 2019, TNO and Nexstep, the association for decommissioning and re-use in the Netherlands, selected the Q13a oil and gas production platform in the Dutch North to host the two-year pilot PosHYdon scheme involving integration of three offshore energy systems: wind, gas, and hydrogen. Since the initial announcement, five more industrial partners have joined the project: NOGAT and Noordgastransport, the owners of two of the main gas trunkline systems in the Dutch North Sea; Gasunie, which manages and maintains infrastructure for gas transportation and storage in the Netherlands and northern Germany; Eneco, a power utility specializing in sustainable energy; and most recently, DEME Offshore.
Neptune Energy operates Q13a in partnership with EBN and TAQA Offshore. The platform, 13 km (9 mi) from the coastal resort of Scheveningen in a water depth of 19 m (62 ft), was the first fully electrified production facility in the Dutch North Sea when it came onstream in 2013, with power supplied by Eneco directly from the mainland via a subsea cable: to further restrict emissions, the onshore section of the cable was placed through a disused sewage pipe on a factory site. The normally unmanned platform can accommodate up to 14 people: its produced oil is exported to TAQA’s P15 platform while the gas heads from P15 to the shore at Rotterdam.
The consortium will construct, transport, and install the pilot 1-MW PosHYdon hydrogen plant on Q13a. Power will be provided via the existing subsea power link to shore and will follow the production profile of the Eneco Luchterduinen offshore wind park nearby. It will be designed to convert seawater to demineralized water by means of a reverse osmosis desalination unit which on entering an electrolyzer will be split into hydrogen and oxygen: the oxygen will be safely disposed of, while the resultant green hydrogen will be blended into the gas export line. DEME Offshore is involved in the conceptual design for a more ambitious 100-MW hydrogen project in the Middle East. The company’s role in PosHYdon should also help build a business case for large-scale offshore hydrogen production far out to sea (100 MW+ and 100 km+).
Eneco owns and operates the Luchterduinen wind farm, 25 km (15.5 mi) north of Q13a. Although there will be no direct connection between the wind turbines and the platform for the pilot, Eneco will supply wind data from Luchterduinen which will be used to model how electricity generated from the wind farm could power the electrolysis process, and how operations might be impacted by fluctuations in wind strength. Gasunie brings experience of participation in trials of a 1-MW prototype hydrogen production plant onshore in the northern Netherlands, called Hystock, and will absorb the hydrogen produced by PosHYdon in its onshore gas grid to Rotterdam. On joining the PosHYdon consortium, the company said there had been strong interest in the development from nearby ports and industrial clusters.
The containerized green hydrogen production plant is being designed to fit on most existing southern North Sea platforms, due to its small size. Aside from answering questions on the feasibility of green hydrogen offshore, the trial should also determine whether the technology could be scaled up to 10-MW versions or higher for permanent installation on other North Sea platforms.
According to TNO’s René Peters, a specialist in integration of energy systems, the PosHYdon project is connected to a long-term program with Dutch North Sea operators concerning re-use options for platforms, pipelines, and other facilities, integrated with renewable energy. The first concept for producing hydrogen from an offshore platform emerged in 2017, and last year, Q13a was selected for the pilot following consultations with four operators. Various issues remain to be resolved before the pilot can start running, notably the fact that while a prototype electrolyser has been proven in an onshore setting, a marinized version has yet to be produced, let alone tested offshore. “But this is all part of the project,” Peters said. “Everything will be developed for operating and enduring in an offshore environment.
“The pilot will produce hydrogen from seawater, which is different from the onshore process which basically uses tap water, so we will need to add a desalination unit. That’s not challenging, but we still need to see how the system performs. And there are a lot of uncertainties concerning the economics of electrolysis offshore as opposed to onshore: we need to analyze the costs so that we can assess the future potential for scaling up to bigger plants offshore.”
“We also need to see how the electrolysis process performs in harsh environmental conditions,” said Neptune Energy’s Project Lead PosHYdon, René Van der Meer, “which is why we plan to put the equipment out in the open on the main deck. And it’s important to use this experience to select the right type of materials that will last in this environment over the long term, in compliance with NotifiedBodies (NOBO) DNV GL, and Lloyds.
“At the same time, we need to see how hydrogen fits our system on a live platform: the ATEX rules related to explosion efficiency are at least as important as the environmental conditions. And there are some regulatory issues - you cannot simply spike hydrogen into the gas network. There are stringent entry specifications before gas may be injected into the national grid. This is one reason why we are very happy to have Gasunie onboard, as operator of the Dutch gas grid.” Peters added: “We intend to run a comparable testing program comparing performance, efficiencies, and costs for the offshore and onshore units.
“Although we could theoretically use electricity generated from Luchterduinen for the PosHYdon trials, it’s more important for the pilot to mimic the wind profile on the wind farm. Using this data, we will see how the electrolyser performs under dynamic loads on the hydrogen plant, to determine the difference in efficiency compared with operations under static loads. Eneco also supplies gas to a lot of Dutch households and is interested in adding hydrogen to it via the onshore grid, to see how the system works with green hydrogen. A trajectory of certificates of origin will be explored to investigate how the value of green hydrogen can be maintained while admixing into the natural gas grid.”
For Nexstep, a successful trial would demonstrate that re-use is an option for various late-life Dutch platforms that would otherwise have to be removed, Peters said. “In terms of reconfiguration for more widespread hydrogen production offshore, all you would basically need to add is power conversion for the system to handle seawater, and maybe some compression downstream of the electrolyser.
“But it would also depend on the condition of the platform. It would have to be suited to electrification, with sufficient space and structural integrity to handle hydrogen for the next decades to come. And in the future, hydrogen production will need to scale up to be economic - initially from 1 MW (as in this trial) to 10 MW, and ultimately to 100 MW or even higher. This technology can only work with a big platform, which means around 10% of existing facilities on the Dutch shelf. Most of those will still end up being decommissioned, but it’s nevertheless important to identify as soon as possible the ones that would be suitable.”
Commercial factors would include the proximity of the platform to established offshore wind farms (connections could be provided via substations), and access to subsea pipelines to the shore which will have increasingly available capacity over the next decades as Dutch offshore oil and gas depletes. There are also some producing fields in the northern Dutch North Sea and in adjoining German waters where there is currently no offshore wind infrastructure, but which are connected to the NOGAT pipeline system. As Van der Meer pointed out, these could theoretically be powered by hydrogen supplied from platforms closer to the shore. “This way these stranded assets could be developed much quicker, independent of the limitations in the electricity network.
“The capacities of the Dutch trunklines are huge, and they reach not just the shore, but also extend onshore. The partners in NOGAT and NGT saw the market early, they are supporting this study, and they want to address the capabilities of their pipelines for hydrogen transportation. As an example, 36-in. pipeline can handle around 12-14 GW of pure hydrogen, which is about 10 times the capacity of the most powerful DC cable.
“Hydrogen and natural gas are both gases, and hydrogen has a fatigue element - its molecules are so small, they could affect the integrity of steel pipelines, and this is something that will be studied and addressed. At the same time, extensive studies have shown that both pipelines are suited to handling either 100% pure hydrogen, or hydrogen mixed with gas. Pure hydrogen has a much higher value, so the possibility of using steam methane reforming at the receiving terminal onshore convert the natural gas/hydrogen mixture to a pure hydrogen stream is also under consideration.”
After this summer, the consortium expects to resolve some of the main design uncertainties, arrange funding for the full project, and provide greater clarity over the project’s timeline.
PowerBuoy-controlled monitoring for Huntington
Earlier this year, Ocean Power Technologies (OPT) completed a seven-month trial of its PB3 PowerBuoy at Premier Oil’s Huntington oilfield in the UK central North Sea. The PB3 was installed in August 2019 to convert wave energy into electricity to power a site surveillance system. OPT has been running a longer-term trial of another PB3 for Eni in more benign conditions alongside a platform in the Adriatic Sea, in this case with an umbilical supplying wave energy-converted power from the buoy to a dummy seabed docking station for AUVs.
The PB3 is a floating autonomous power-generating platform that can be used to enable numerous technologies for multiple applications. Power is generated through the relative motion of the spar and float components: the wave energy is converted to electrical energy via a direct-drive generator that continuously charges an onboard battery pack, which can be used to help power surface or subsea payloads. Stored energy - up to a nominal 150 kWh - is said to ensure a reliable power supply during extended calm periods at sea. At the same time the PB3 provides real-time data transfer and communication to remote sites onshore, with up to 2 TB of onboard, solid-state storage. For subsea applications, power and data can be transmitted to the seabed through an umbilical. OPT has designed the system for deployment and recovery by a variety of offshore vessels. Its control and management system includes self-monitoring data collection, processing and transmission. The PB3 is moored via a three-leg compliant system that controls the response of the buoy, restricting the PB3’s movements and allowing it to remain on-station during stormy conditions.
For the recent North Sea trial, an anchor-handling tug supply (AHTS) vessel installed the 13-m (42.6-ft) high PB3, weighing around 10 metric tons (11 tons), 2 km (1.2 mi) south of Huntington’s circular FPSO. The three-point mooring system was fitted with motion and strain sensors to monitor its condition. The primary mission for this deployment was to monitor the local environment and alert ships of the field’s safety zone, as a potential solution that could aid future decommissioning-related operations. Surveillance equipment on the PowerBuoy comprised radar, an HD/IR camera, mooring sensors, 4G wireless communications, AIS (Automatic Identification System), GPS, wind speed sensors, and WiFi.
The payload was designed to provide real-time communications to remote operators onshore; a 24/7 warning to marine vessels in the vicinity; radar tracking of marine activity in the area; an early real-time warning of incursions, relayed to remote operators; evidence gathering of incursions; and monitoring of mooring line tension and of the buoy’s motions, using a Pulse INTEGRIpod. Exclusion Zone monitoring involved use of the AIS device to transmit the PB3’s location to nearby AIS receivers, heading sensor, radar, camera, and the onboard server running TIMEZERO software. The 4G wireless communications via Tampnet enabled round-the-clock, real-time data feed, with a dedicated workstation at Premier’s offices in Aberdeen replicating the offshore TIMEZERO interface.
All data generated by the system were relayed via the cloud: TIMEZERO monitoring data to Premier’s offices in Aberdeen; mooring data to Pulse (which was responsible for monitoring the moorings); and system performance data to OPT’s global operations center in Monroe, New Jersey. A second, independent GPS system transmitted location data to the OPT center via satellite. The trial ended in March this year when the PowerBuoy and mooring system were recovered, and the PB3 has since been shipped back to OPT’s headquarters for inspections ahead of a next potential deployment.
According to Paul Watson, UK & Europe Business Development Director for OPT, development of the PB3 PowerBuoy began early in the 2000s. Various test deployments of the technology followed. “OPT was keen to get the technology into the oil and gas sector,” he explained, “and the Huntington project fitted perfectly for all operational and risk profiles.”
The Oil & Gas Technology Centre (OGTC) in Aberdeen helped set up the trial. During 2017, staff at the newly opened facility were identifying emerging technologies relevant to the future of the UK North Sea. According to the OGTC’s Project Manager Graeme Rogerson, one topic highlighted by the Marginal Developments Solutions Centre was installing and operating subsea tiebacks differently: areas under investigation included how to reduce the risk of fishing trawlers damaging subsea infrastructure, and powering, monitoring and controlling subsea tiebacks without the need for an umbilical to a host facility. “This transformational approach to offshore power generation offers huge potential for decarbonizing our industry and supporting the transition to a low-carbon economy,” Rogerson said.
According to Premier’s Decommissioning Lead Pieter voor de Poorte, the company’s first introduction to OPT came in 2012, when Premier was part of a consortium in the running for a carbon capture and storage project under a competition organized by the UK government. “Our scheme had two main facets: offshore disposal of CO2 in remote sites, and enhanced recovery. For the disposal option, rather than running a long umbilical to the Christmas tree connection, we wanted something different. We were aware at the time that Total had deployed an all-electric subsea tree Christmas tree for a field development in the Dutch North Sea: we thought of using renewable power generation to control the tree. We then engaged with OPT via the Industrial Technology Facilitator (later absorbed into the OGTC), and maintained regular contact with OPT after that.”
For the 4G wireless communications, Premier selected Tampnet, which already had strong connectivity to many North Sea assets, voor de Poorte said. “We engaged with them to see what level of coverage they could provide, including a connectivity trial on a standby vessel prior to bringing the buoy out to the field.
“The buoy was installed in August when the weather was calmer, which allowed us to extensively test the monitoring capability. Later in the winter, when storms became more regular, the mooring system was really put through its paces. Because the North Sea is so lively, the PB3 generated more power than we expected, or was needed, so the PB3’s control logic was updated to avoid unnecessary wear and tear and dumping of large amounts of unused power. There were various issues with the mooring system during the trial, but the PB3 was nevertheless kept securely on station, and the sensors allowed us to see if something was wrong and take action accordingly.”
“The PB3’s monitoring software manages various aspects of the system’s health,” Watson explained. “We designed the system so that engineers can monitor its status anywhere in the world via cloud computing.” With Huntington, the data were streamed live to Premier. “I could get a view from my office, seeing vessels in the area,” voor de Poorte added.
OPT plans to use data from the trial to improve the PB3 going forward, Watson said. “Now we will look at how to improve the mooring system, simplify deployment and recovery, and maybe use different sensors and integrate the various software better for the users. OPT is also improving the communications as some areas of the world don’t have 4G coverage. The amount of power the buoy generated was surprisingly high. This allows us to look at other potential applications going forward.”
The PowerBuoy’s rechargeable lithium iron phosphate batteries range from 50-150 kWh. “For Huntington, the system required around 150 W, but during significant wave heights of 1.5-2 m [4.9-6.56 ft], it actually generated 800-1,000 W. With this trial, because the main asset was still live, we couldn’t connect the buoy to the subsea infrastructure.” However, the subsea power capability is of interest to Premier for future projects, and Huntington remains the most likely candidate in the company’s portfolio for a future, permanent deployment of a PB3, voor de Poorte said.