Frequently asked questions

During ONE-Dyas’ discussions with stakeholders, a large number of questions were asked and answered. We have listed them here. Is your question not included? Please feel free to send us an e-mail. You will get an answer as soon as possible.

Usefulness and necessity of gas

The Netherlands is committed to a CO2-neutral energy supply by 2050. During this energy transition, natural gas will continue to play an important role in the foreseeable future. Dutch natural gas is preferable to importing gas from abroad. It is more sustainable than imported gas, it contributes to the Dutch economy and it means a greater security of supply for our energy.

Platform N05-A will be the first offshore gas production platform in the North Sea to run entirely on wind energy. For this purpose, a cable will be laid to the nearby German wind farm Riffgat. The electrification of platform N05-A with the help of wind energy means a considerable reduction in emissions. Emissions from the production platform will be zero and for the entire project a reduction of 85 percent. With this innovation, ONE-Dyas wants to make a serious contribution to the energy transition.

Obstruction of view

The drilling and production platform will be located about 20 kilometres north of Schiermonnikoog and Borkum. The platform will rise approximately 50 metres above the water surface and, in clear weather, will be visible from Schiermonnikoog and Borkum. The visible size is comparable to the height of passing ships.

Drilling platform (6 July 2017)) seen from Strandpaviljoen de Marlijn, Schiermonnikoog. This temporary drilling platform was at the intended platform location and had a height of 138 meters.

ONE-Dyas wants to reduce the visibility of the offshore infrastructure as much as possible by choosing the lowest possible platform. The intended location offers the best opportunities for drilling multiple gas fields from a single production platform. At the same time, the northern location ensures minimum visibility from the West and East Frisian Islands.

Impact on nature and the environment

Platform N05-A will be the first offshore gas production platform in the North Sea to run entirely on wind energy. The electrification of platform N05-A with the help of wind energy means a considerable reduction in emissions of methane, nitrogen and CO2 . Emissions from the production platform will be zero, and for the entire project we are talking about an 85% reduction.

During the drilling, drilling fluid is used. This fluid removes the drilling cuttings to the surface. The fluid also ensures that there is sufficient pressure in the well and lubricates the drill bit. The largest part of the well is drilled with water-based drilling fluid. In the North Sea, it is common practice to discharge the drilling cuttings and water-based drilling fluid into the sea. Oil-based drilling fluid is always discharged and processed on land.

A variant is to also dispose of the water-based drilling fluid with the cuttings. However, disposal also means that a considerable waste flow is created: for all the drilling operations together, a total of 16,000 tonnes. Disposing of this waste requires additional transport at sea and on land and leads to energy consumption and emissions during transport and processing. The waste also takes up space in a landfill. In view of the relatively limited consequences of discharge for nature and the environment and the minor advantages of disposal, ONE-Dyas has decided to stick to its usual method and discharge the drill cuttings and drilling mud on a water basis.

The effects are investigated in the Nature Assessment.

Construction phase

The driving of the anchoring piles to install the production platform is the main source of underwater noise. This takes approximately two days.

The driving of the anchor piles requires mitigating measures. To mitigate the effects of underwater noise on marine animals, a bubble screen is installed around the platform during the pile driving. This will lead to a considerable reduction of the underwater noise by 7 to 11 decibels. The noise pollution therefore remains within the Dutch and German standards. ONE-Dyas will keep the option open to apply other noise-reduction techniques, as long as these can reduce the noise by a sufficient number of decibels.

Drilling phase

The most significant noise emissions in the drilling phase are caused by the driving of the conductors (maximum of twelve). The driving of each conductor takes approximately twelve hours. After the drilling is completed, a VSP survey is carried out. VSP stands for Vertical Seismic Profiling. This involves a detailed mapping of the earth layers that have been drilled through. The sound waves of the VSP survey (up to five) also create underwater noise. Each survey takes approximately one day. Temporary disturbance of marine mammals by underwater noise is avoided as much as possible by starting the VSP surveys with a low source power to give them enough time to leave the area (a soft start).

The driving of the conductors and the performance of a VSP survey comply with the legal standards.

Emissions of pollutants into the sea occur as a result of the activities. These emissions ( spills ) may affect nature. Emissions to water occur mainly during the drilling and production phases.

In the drilling phase, this is water-based drilling mud and cuttings, and in the production phase, the production water that is released during gas treatment. In both phases, the sanitary water and rainwater that washes off the decks is also discharged into the sea. The Mining Regulations sets rules for discharge of pollutants into the sea, such as a maximum oil concentration in discharged water. ONE-Dyas and the operator of the drilling platform ensure that the requirements are met.

No significant effects

Turbidity and sedimentation as a result of the discharge of drilling mud and drill cuttings can have an effect on nature and have been investigated in the Nature Assessment. This study shows that there are no significant effects due to turbidity, because the effect is small and temporary and the area is naturally dynamic. Sedimentation of the drilling mud does not have significant effects either.

The coarse fraction of drilling cuttings will sediment quickly. Per drilling, a maximum layer thickness of approximately 23 cm is expected within a radius of 95 metres from the platform. In twelve drillings, taking the worst-case situation into account, the joint layer thickness of one and a half centimetres is only exceeded within a distance of approximately 105 metres from the discharge pipe. Beyond that, there is no or a negligible amount of additional sedimentation.

ONE-Dyas wants to limit the occurrence and duration of flaring as much as possible. ONE-Dyas, therefore, wants to use the treatment process as much as possible to test newly drilled gas fields after drilling. If flaring is necessary, a birdwatcher is called in to advise on the appropriate time for flaring. Flaring is, as much as possible, done during the day. This protocol is applied by ONE-Dyas by default and so far there have been no incidents with birds.

Gas extraction and nature development need not be mutually exclusive. No other activity may take place within 500 metres surrounding a drilling platform. This means, for example, that no shipping or (trawl) fishing is allowed. This allows marine life to develop undisturbed. The platform provides a hard substrate on which flora and fauna (including shellfish) can develop. Together with nature organisations, ONE-Dyas wants to draw up a monitoring proposal for new research.

At the end of the extraction process, all boreholes will be decommissioned.

There are two possibilities:

  1. suspend – the borehole is closed off with a valve.
  2. abandonment – putting mechanical and cement plugs at various heights in the borehole. Then the plugs and the conductor are cut off and removed 6 metres below the seabed.

When extraction is complete, all the boreholes are capped. The platform is removed, its anchoring posts are cut away and removed 6 metres below the seabed. This ensures that no fishing gear can get stuck behind them. ONE-Dyas first writes a work plan for this, which must be approved by the State Supervision of Mines. Everything is returned to its original state, which is generally better than before due to the nature development that has taken place.

The choice of location for the platform takes into account other uses. ONE-Dyas is aware of the effects the project may have on the environment and wants to be a reliable partner and good neighbour. This is achieved, among other things, by ensuring that the activities fit in as well as possible with the (other activities in the) surroundings. All this is done in the safest and most responsible way for both people and nature. ONE-Dyas is committed to proactively seeking dialogue and possible cooperation with stakeholders.

Cumulation test

The research in the cumulation test shows that there are no significant effects due to cumulation of effects of the intended activity N05-A with the effects of other activities that (may) take place in the future. To prevent cumulative effects with future projects of ONE-Dyas itself, ONE-Dyas will ensure that no cumulation of underwater noise occurs during the (simultaneous) implementation of the projects.

Soil subsidence

The intended soil subsidence caused by gas production is estimated to be less than 5 centimetres at the deepest point of the subsidence basin after completion of the production phase. TNO and SodM endorse this calculation and indicate that the soil subsidence basin lies entirely in the North Sea and that the soil subsidence will not affect the Wadden Islands and the mainland.

The geological composition of the GEMS area and the gas reservoir consists of good permeable sandstone. It probably will not be necessary to use fracking. The technology used in such cases, including the possible application of hydraulic stimulation, is described in the extraction plan.

The intended seismic risk from gas production is negligible for gas fields N05-A and N05-A-North, which thus fall in the lowest seismic risk category (SRA Cat. I). TNO and SSM endorse this assessment. The Tanzanite-Oost gas field has a probability of trembling of 19%, but on the basis of a more detailed analysis data is also classified in the lowest seismic risk category. Because of the low negligible seismic risk and the large distance to the Wadden (islands) and the mainland, no detrimental effects and damage as a result of soil vibration are expected from this gas production.


Shipping is prohibited within a zone of 500 metres around a platform. ONE-Dyas always conducts several safety studies for new and existing activities, including a study of the risks of collision with ships. The MARIN study, which is appended to the EIA, shows that the probability of a collision with the platform (worst-case approach) has been calculated at 1 / 273 years. All platforms are equipped with an Automatic Identification of Shipping System. (AIS system). This is a type of anti-collision system that raises the alarm well in advance of an approaching ship and thus a possible collision. The use of AIS reduces the chance of a collision, which in the worst case is calculated at once in 273 years, by another 75%.

The project area is located in a moderately trafficked part of the North Sea and is also used for shipping and fishing. A few kilometres north of the intended location of the platform is the Terschelling-German Bight shipping route. No shipping or other use is allowed in a zone of 500 metres around the platforms. This causes local restrictions for fishery, shipping and recreation (sailing). Within this safety zone, dragging fishing nets over the seabed and in the water column is not allowed either. The choice of location for the platform takes shipping and other uses into account. The platform will be equipped with the required navigation lights and collision prevention systems.