Safe carbon storage

Global emissions from fossil fuel-based energy and industries were estimated to be 37.5 billion tonnes in 2022. According to the United Nation’s Intergovernmental Panel on Climate Change (IPCC), global carbon emissions must be reduced by 50-85 percent before 2050 in order to achieve the tough goals of the Paris Agreement.

Norway has set a goal to cut emissions by 55 percent by 2030, but many emissions are difficult to cut out. This is because for some sectors, we have no alternative production methods that have lower emissions. Carbon capture and storage, or CCS, is the only strategy available that can remove carbon emissions from critical industrial sectors such as metal and cement production and waste incineration.

The only way of achieving climate goals in Norway, and the rest of the world, is to use CCS to cut emissions in these sectors alongside other climate initiatives. The International Energy Agency (IEA) has calculated that around 14 percent of total emissions reductions must come from CCS by 2060 if we are to achieve our goals.

One of the biggest concerns around CCS is the storage aspect. The question of whether the carbon has been stored safely and whether it could leak out again from the storage site has been a vital one to answer.

Permanent carbon storage

Natural underground storage sites have proven that hydrocarbons (oil and gas) are found in, for example, sandstone formations and then pumped out. These hydrocarbons have been held there for thousands of years by dense caprocks.

On the Norwegian Continental Shelf, carbon can either be stored in saline aquifers or in depleted hydrocarbon formations. A saline aquifer is an underground geological formation that has salt water in porous spaces, while a depleted hydrocarbon formation has rocks that previously contained hydrocarbons (oil and/or gas). In addition, basalt (solidified lava) has shown itself to be a potentially good candidate for permanent carbon storage. Offshore saline aquifers are currently the preferred storage location.

To permanently store carbon, it must be injected into a porous and permeable formation (it must have enough porous space to retain large amounts of carbon, and there must be contact between the porous spaces so that the carbon can move across the formation). Such formations can typically be hundreds of metres thick. It is also important that the formation is covered by a sealing caprock that prevents the carbon from seeping out. Carbon dioxide is lighter than water and will move up across the formation.

It is preferable that the storage formation is covered by multiple layers of low-permeable rocks, which then form an impenetrable barrier between the stored carbon and the seabed. The IPCC has estimated that a proactively managed carbon storage site will be able to retain about 99 percent of the stored carbon over a 1,000 year period.

There are a number of mechanisms that ensure that the carbon is stored permanently (see figure). Firstly, there is structural capture. This means that the dense caprocks ensure that the carbon does not escape to the water column or atmosphere. Then there is residual capture, where carbon molecules are captured in the formation water on its journey up across the formation, and then there is solubility capture, where the carbon dissolves into the formation water. This makes the formation water heavier, making it sink towards the bottom of the formation. Finally, mineralisation of carbon will take over and increasingly bind the carbon dioxide to carbonate minerals.

Great experience in carbon storage

Norway has a long history of carbon storage using wells and underneath the North Sea. As of today, there are two operational full-scale CCS facilities in Norway. The facilities are called Sleipner and Snøhvit.

Sleipner is the world’s first industrial-scale CCS project, where the aim is to reduce carbon emissions. Injecting carbon dioxide into a saline aquifer under the seabed began in 1996. Since then, the project has shared knowledge with innumerable research projects worldwide with the aim of increasing expertise and knowledge around CCS as measure for reducing carbon emissions.

Monitoring carbon storage sites

Strict monitoring requirements are in place for carbon storage sites to ensure that the storage is safe and permanent. The carbon storage sites are carefully monitored for signs of the carbon dioxide seeping out. There are a number of different monitoring strategies adapted to the geological conditions at the individual storage sites. There are many methods to monitor conditions down the well from the surface and via satellite. The figure below shows a selection of methods that are in use at carbon storage sites around the world.

The strict procedures for the choice of storage area and monitoring the storage site mean that the safety margins for carbon storage are extremely high on the Norwegian Continental Shelf.

Experience from the Sleipner Field and Snøhvit show that it is safe to permanently store carbon on the Norwegian Continental Shelf and that the chances of a leakage are small. Since 1996, Sleipnir has stored around 1 million tonnes of carbon dioxide each year and has shown no signs of leakages from the storage site.

Huge potential on the Continental Shelf

The Norwegian Petroleum Directorate has mapped the storage potential of the Norwegian Continental Shelf. The Norwegian Petroleum Directorate has calculated that it will be possible to store 80 billion tonnes of carbon dioxide on the Norwegian Continental Shelf using aquifers and depleted oil fields. As an example, SINTEF estimates that if 10 percent of the storage capacity is used, it would be possible to store about 40 years’ worth of carbon emissions from the European cement industry.

By way of comparison, the Norwegian CCS project Longship has planned to store a total of 800,000 tonnes of carbon per year once it is operational. Northern Lights is the transport and storage operator for the project and has a storage capacity of 1.5 million tonnes of carbon per year during the first phase. This is all to say that there is good capacity for carbon storage under the seabed on the Norwegian Continental Shelf from both Norwegian and European sources for many years to come.  

Please visit our CCS dictionary if there are professional expressions or abbreviations in this text you are not familiar with.