Carbon storage in empty North Sea gas fields

In the Netherlands, CO₂ is stored in empty gas fields below the North Sea bed. Carbon storage is necessary in the fight against climate change. It is intended as a temporary solution until other sustainable technologies are ready to take over. This buys the industrial sector time to green their operations.

In the Netherlands, CO₂ is stored in empty gas fields below the North Sea bed. These gas fields used to contain natural gas trapped in porous rock. Now that the natural gas has been extracted from these fields, what is left is porous space in the rock layer. This is where we can store CO₂, deep below the ground.

As natural gas was extracted from the gas fields, the pressure in the porous cavities diminished. Injecting CO₂ will raise the pressure up to the field’s original pressure.

Above the layer of porous rock where CO₂ will be stored below the North Sea bed, there is a salt layer and a rock layer. These layers initially caused the natural gas to form and to be trapped in the cavities. Now these same layers will also prevent the CO₂ from escaping from what was originally a gas field. The only connection to the rock layer is the drill tower in the North Sea. In Norway, they have been storing CO₂ in this way for over 20 years.

After the CO₂ has been pumped into an old gas field, the field is hermetically sealed. This is when the permit holder becomes the owner of the CO₂ and responsible for monitoring the field in the subsequent years.

Learn more? Take a look at the animation on carbon storage.

Storage permit required for carbon storage below the North Sea bed

Storing CO₂ below the North Sea bed is subject to a storage permit issued by the Dutch Ministry of Economic Affairs and Climate Policy. This permit is checked and enforced by the independent regulatory authority the Dutch State Supervision of Mines.

In order to make sure that the CO₂ can be transported safely to the storage facility, things such as the pressure, temperature and composition of the CO₂ are monitored.

And both during and after CO₂ injection, there is extensive monitoring for leaks and seismic activity, and the spread of the CO₂ inside the gas field is analysed.

There are currently two major projects under development for CO₂ transport to and storage in empty North Sea gas fields: Porthos (planned to become operational in 2025) and Aramis (planned to become operational in 2027). Options in the Delta Region (province of Zeeland and Flanders) are also being explored. Gasunie, Vopak and Gate terminal are furthermore looking into whether it would be possible and viable to build an independent reception and supply terminal for liquid CO₂ at the Maasvlakte industrial area  (the CO₂next project). This terminal will ultimately be connected to Aramis. And there is also the collaboration on the Delta Rhine Corridor project. The idea behind this project is to lay multiple pipelines for the transport of hydrogen, natural gas, CO₂ and other substances.  

These projects will provide space to store dozens of megatons of CO₂. The storage capacity below the North Sea bed, however, is far greater. If we were to use all empty gas fields for carbon storage, we would be able to store as much as 1,600 megatons of CO₂ under the North Sea bed, a study by EBN shows. To put this into perspective, greenhouse gas emissions, which include not only CO₂ but also other greenhouse gases, in the Netherlands totalled 164.5 megatons of CO₂ equivalents in 2020.

Needless to say, we are not looking to use all that capacity. CCS is specifically intended as a bridging solution until other sustainable technologies become available.

The emitter is responsible for capturing the CO₂ they produce. When emissions are relatively pure, meaning that they are mainly made up of CO₂, carbon capture is more straightforward than when emissions have to be decontaminated first.

After capture, the CO₂ is transported to a compressor. The Porthos project will see four companies deliver their CO₂ directly to the compressor through a pipeline. Whenever the distance between a company and the compressor is too great, the CO₂ can be transported by ship.

The compressor pressurises the CO₂ to create a mixture of liquid and gaseous CO₂ that makes the gas easier to transport. Next, the CO₂ is transported by pipeline to an empty gas field for storage deep under the North Sea bed.

The Netherlands has chosen to store CO₂ in empty gas fields under the North Sea bed. In Norway, they have already gained a lot of experience with this storage option over the past 20 years without any significant technical issues.

Climate goals unachievable without carbon storage under the North Sea bed

CCS reduces the amount of CO₂ emitted into the atmosphere. CO₂ is a greenhouse gas. Lower CO₂ emissions are better for the climate. This is why CCS features prominently in climate plans. In fact, the goals from the Climate Agreement are unachievable without CCS.

Subsidy for CCS

Given the important role of carbon storage below the North Sea bed in achieving the climate goals, the Dutch government is incentivising carbon capture and storage. As of 2020, Dutch industry can get financial support for CCS projects under a subsidy scheme that seeks to promote the production of renewable energy (Stimulering Duurzame Energieproductie, or SDE++).

For a long time, emitting CO₂ cost less than CCS because the prices of emission allowances were so low. Since 2021, however, the European Commission has been eliminating the surplus of carbon allowances from the market, which has pushed up prices. This has made CCS also an economically competitive option for industry.