Surveying the Danish Energy Island Site
Article

Surveying the Danish Energy Island Site

Denmark is building an energy island. Located in the North Sea, a power plant is planned that will distribute wind energy far and wide across Europe. The island will be situated about 80 kilometres out to sea from the Jutland Peninsula. Fugro has been awarded a marine site characterization contract for the project by Energinet – the Danish company that will construct and operate the electrical transmission system connecting the island to adjacent countries. A. Padwalkar is Fugro’s project manager responsible for overseeing coordination of the project.

Can you tell us a little more about the project and your role within it?

Denmark is establishing the world’s first energy islands in the North Sea and Baltic Sea. These islands will act as transmission centres for hundreds of surrounding wind turbines and will be able to supply 5GW of power – enough energy to meet the average electricity consumption of five million households.

Energinet has tasked Fugro with performing geophysical and unexploded ordnance (UXO) magnetometry surveys, which will be used to prepare an integrated geological and geotechnical soil model on which wind farm developers will base future tenders. Fugro is also supporting Energinet with wind-resource mapping at the energy island site using our Seawatch Wind Lidar Buoys and is set to start cable route surveys for the North Sea Energy Island Project in March 2022. These cable route surveys will also include the use of the Fugro Blue Snake™, our latest innovation for sampling and shallow cone penetration tests (CPTs).

In addition to this, Fugro is executing a geotechnical investigation to provide the geotechnical design parameters for preparation of the foundation and construction of the energy islands, the wind turbines and the cable route trenching. This part of the project started in January 2022 using our dedicated geotechnical seabed testing and drilling vessels.

I am Fugro’s project manager, responsible for overseeing the coordination of the various stakeholders during the different phases of each project’s lifecycle, ensuring that the project is delivered safely, on schedule and within budget.

Seawatch Wind Lidar Buoys record continuous wind measurements to support wind-resource mapping for the two energy islands.

Can you describe how the survey was/is being performed, which platforms and sensors were/are used, and so on?

The fieldwork can be divided into multiple phases, with each phase tailored to meet the client’s needs. When focusing on the geophysical site survey, which included a 2D ultra-high-resolution (UHR) seismic survey, we aimed to exceed the client’s expectations. Energinet required high specification data, but through the use of our dedicated survey vessels and innovative solutions we were able to deliver superior data quality.

Fugro mapped the high-resolution bathymetry, static and dynamic elements of the seabed surface and the sub-surface geological soil layers to at least 100m below the seabed. For this, we used Fugro Pioneer, a multipurpose dedicated survey vessel, as well as a range of innovative UHR specialized survey equipment including:

- Positioning: Starfix PPP GNSS, INS, USBL
- Geophysical: dual frequency SSS, Parametric echo sounder, 360 tips Sparker, Magnetometer
- Geotechnical: dual van Veen and Day grab
- Passive Acoustic Monitoring (PAM)

The geophysical site survey was completed in October 2021. Our survey and offshore wind consultancy teams then used the acquired geodata to provide reliable site interpretation.

Fugro Pioneer and Fugro Frontier are multipurpose dedicated survey vessels used to complete the energy island site surveys.

We began the UXO survey in December 2021, and we’re currently surveying 90 location areas, each location being 150 x 50m in size. We will also conduct a high-resolution acoustic survey of the seabed. For this, we are using Fugro Frontier, a multipurpose dedicated survey vessel that can be configured to tow a variety of survey equipment. The equipment used includes:

- Positioning: Starfix PPP GNSS, INS, USBL
- Geophysical: dual head MBES, tri-frequency SSS, Geowing with five magnetometers in M configuration

While we’re using the best available sensors on the market, it’s how we combine them with our dedicated survey vessels, our innovative in-house solutions and software for data acquisition, as well as the expertise of our geologists, data processors and geo-consulting team for site development, that really sets us apart.

For a project like this, what are the biggest survey challenges – and did you run into unexpected issues, such as unexpected UXO or environmental conditions?

While we have very detailed project plans that try to mitigate as many risks as possible, there are always challenges that come up on a project of this size and duration. Our three biggest challenges were related to fishing activities, pycnoclines and poor weather conditions.

For example, gill nets, which are used by fishermen, are often not picked up by sonar. The chance of our equipment getting tangled in the nets is therefore high, and results in damage to the nets and our equipment – something all parties would like to avoid. Together with Energinet, we worked to build a good relationship with the local fishing community. We had a fishing liaison officer onboard our vessels and kept the fishing community well informed of the areas we were surveying. We also had a dedicated scouting vessel to ensure we didn’t run across any nets.

Fugro’s innovative Blue Snake technology optimises data correlation, improving design and engineering for future cable installation works.

If for any reason we came across fishing activities, we increased the height of our towed survey sensors to ensure they avoided the nets. While this limited any impact on fishing activities and equipment, it resulted in scans with diluted resolution and less coverage, and we had to redo the survey to ensure data quality as per client specifications.

Another challenge was the impact of pycnoclines on site investigations. A pycnocline occurs when water density increases rapidly with depth due to changes in temperature and/or salinity. Sound travels differently depending on the density of the water, which impacts the coverage of our sonar. Pycnoclines cause artefacts in the data, obscuring a good image of the seafloor. To avoid this, we conducted a sound velocity check six hours prior to each survey. We also used a moving vessel profiler that continuously recorded sound velocity – critical for sonars on a survey.

Finally, challenging weather conditions resulted in vessels being placed on standby. Fortunately, both Fugro Pioneer and Fugro Frontier are very stable vessels for surveying, although there are limitations. While we can’t change weather conditions, we have a very accurate weather model that provides weather forecasts and our Seawatch Wind Lidar Buoys deployed on-site provide accurate measurements of wind profiles, waves and current profiles that feed into the weather model. All this information helps us foresee potential delays and better plan our survey schedule.

Denmark Energy Island Survey Update

Fugro’s dedicated survey vessels will mobilize to site in March 2022 to begin the geophysical and geotechnical surveys. These will include remotely operated vehicle (ROV) inspections and shallow geotechnical investigations using Fugro’s innovative Blue Snake geotechnical system. The Blue Snake integrates CPT and sampling technology to enable data to be captured in a single pass with testing completed consecutively at fixed distances along the cable route. The system integrates a high performance vibrocorer and ten-ton CPT into a single frame with a customized launch and recovery system – minimizing manual handling and improving workability in difficult weather conditions. This innovative technology optimizes data correlation, improving design and engineering for future cable installation works.

 

Dual fish configuration of the Geowing on the Fugro Frontier.

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