As an independent research institution, GEUS’ task is to provide research-based knowledge about the Danish subsoil and make data and methods available to authorities and industry. In this context, GEUS has prepared estimates of the CO₂ storage potential in the Danish subsurface. The estimates are based on published research and internationally recognised calculation methods, and they are continuously updated as new data becomes available.
It is important to distinguish between the national screening estimate from 2020 and more recent estimates for specific structures. The 2020 screening estimate shows a theoretical static storage potential, which was prepared in order to compare countries’ storage options using uniform methods. The practical storage capacity is first determined through detailed studies of specific structures and depends on dynamic conditions such as pressure control and well placement.
The debate has raised questions about whether GEUS has overestimated Denmark’s potential for CO₂ storage and whether new data changes the overall picture.
This article reviews how the estimates are calculated and updated, and it explains the methodological differences between national estimates and local estimates as well as broader global scenario studies.
Main points
GEUS continues to assess that Denmark has considerable national geological potential for CO₂ storage, equivalent to several centuries of Danish CO₂ emissions.
The national screening estimate from 2020 was meant to be a theoretical basis for comparison and never reflected the practical operating capacity. Practical utilisation will only be determined through detailed studies of specific structures and the associated operational conditions.
The reduction in the efficiency factor (from 0.4 to 0.1), as reported in Politiken (26 October 2025), currently applies only to eight specific structures that have been investigated and therefore does not take into account Denmark’s national storage potential.
The downward revision of the storage potential for selected specific structures, which GEUS already pointed out in 2023 and 2024, reflects a methodological development in which new and more detailed data provide more accurate calculations for the specific structures that have been investigated.
GEUS will continue to collaborate with relevant authorities and companies to obtain even more accurate estimates of the CO₂ storage potential in the Danish subsurface, and GEUS will continue to provide regular updates on new knowledge.
Background for the national estimate from 2020
In 2020, GEUS prepared a national screening-based estimate based on older data. Denmark’s storage potential was estimated at 12–22 billion tonnes of CO₂. The estimate was based on a conservative approach, incorporating known and partially described structures, primarily in the Gassum Formation.
The original estimates therefore did not cover the entire Gassum Formation and only parts of the deeper Bunter Sandstone Formation, which several storage operators are currently investigating for potential use.
The estimate was based on combined calculations from surveyed onshore and near-shore areas as well as previous estimates for offshore areas.
The estimate was based on combined calculations from surveyed onshore and near-shore areas as well as previous estimates for offshore areas.
The estimate was expressed as a static storage potential, which is an international standard method that makes it possible to compare countries’ storage options on equal terms.
In a static estimate, the theoretical volume that can be stored is assessed on the basis of reservoir geology (area, thickness, porosity and reservoir stone properties) combined with an efficiency factor. The efficiency factor represents how much of the pore space in the reservoir it is realistic to utilise.
The national estimate from 2020 was based on the common European method at the time, which uses a relatively high efficiency factor. This approach was chosen to ensure comparability with other countries. It was already specified at that time that the estimate was associated with considerable uncertainty and that the practical exploitation of the subsurface requires further data maturation and detailed studies.
Updated estimates for the period 2022-2024
Since 2022, GEUS has carried out a number of supplementary studies for eight selected areas, financed through the National Research Reserve 2022-2024. The aim has been to develop the knowledge base for selected structures, which may benefit potential storage operators, among others. The new data has provided more accurate estimates for these specific structures. The storage potential has been found to be between 15 and 80 per cent lower than the original estimates from 2020 for four of the eight structures studied. The other four structures have not been estimated before, and therefore there is no basis for comparison here. All updates from 2022–2024 are available on the page CCS data 2022-2024.
The primary reason for the difference is an adjustment of the storage efficiency factor from 0.4 to 0.1, but also more and more accurate data. The adjustment is based on published research and applied methodological principles.
At the same time, new seismic data has provided a more accurate geometric understanding of the structures, which has also contributed to the changes in the estimates.
Future estimates of storage potential
CO₂ storage is a maturing field where uncertainties are gradually being reduced as new data and more studies become available. Future estimates will depend on:
- More studies of known and new structures
- The technical and methodological choices made by storage operators
- The Danish Energy Agency’s evaluation of projects and requirements for pressurisation and the use of reservoirs for other purposes.
GEUS has been commissioned by the Research Reserve 2025 to investigate how best to optimise the use of the subsurface as a resource. For more than a decade, GEUS has been investigating the relationship between pressure increase and storage potential, which is a shared international challenge.
One controlling factor is how quickly the resource can be exploited. When CO₂ is pumped into reservoirs where the pore space is initially filled with water, the water must be displaced to make room for the CO₂, which causes an increase in pressure. The pressure increase must therefore be monitored and minimised in order to make the best possible use of the storage potential in the subsurface.
Calculating the effect of pressure increase requires dynamic calculations (reservoir simulations). Reservoir simulation models require detailed knowledge of the geology, which requires the collection of additional knowledge and data about the subsurface. GEUS will be in close dialogue with the individual storage operators to establish models for the specific structures as well as an overall regional model.
Emphasis is placed on transparency in the choice of methods and model construction to ensure the best possible utilisation of the subsurface, also in interaction with geothermal energy and heat storage. GEUS assists the Danish Energy Agency in the development of regulatory standards, which are still under construction in both the EU and internationally.
International research and methodological differences
A recent study (Gidden et al., 2025) has presented more restrictive estimates for CO₂ storage globally. The study uses general assumptions and does not include national geological data at the formation and structural level.
The main difference is that GEUS’ studies are based on detailed analyses of specific, geographically defined structures, while this study assesses entire geological formations based on more coarse, nationwide data sets.
The European research network CO₂GeoNet, which represents 27 research institutes from 21 countries (including GEUS), has pointed out that such methods produce worst-case scenarios that should not be confused with national assessments based on detailed subsurface data.
CO₂GeoNet’s response has been published on LinkedIn and will be sent to Nature.
GEUS’ focus on specific structures rather than entire formations means that GEUS already takes into account several of the geological constraints used by Gidden et al. GEUS therefore considers that Gidden et al. significantly underestimate the Danish storage potential.
Communication and transparency
GEUS has regularly published new data and estimates in open reports.
All updates from 2022–2024 are available on the page CCS data 2022-2024.
GEUS will continue to provide regular updates on new knowledge both through open reports and through regular dialogue with relevant parties such as authorities, industry and the media.
Summary
The national screening estimate from 2020 assessed Denmark's storage potential at 12–22 billion tonnes of CO₂. This was a static, theoretical comparative estimate based on the then common European method with an efficiency factor of 0.4, chosen to ensure methodological comparability between countries. Even then, it was made clear that the estimate was subject to considerable uncertainty and that the practical utilisation of the subsurface would require further data maturation and detailed investigations. The estimate primarily covered parts of the Gassum Formation and individual parts of the Bunter Sandstone Formation, which are still being investigated.
In the period 2022–2024, eight specific structures have been investigated using new seismic data and updated reservoir models. These investigations have led to:
- Adjustment of the efficiency factor from 0.4 to 0.1 based on recently published research.
- A more precise geometric delineation of the structures.
- 15–80 per cent lower partial estimates for four of the eight structures examined compared with the screening estimates from 2020. This reflects an expected methodological development, where new and more detailed data provide more accurate calculations for the individual structures.
- The lower sub-estimates do not change the overall assessment but show that the storage potential is gradually becoming more well-defined as the data basis matures.
The updated results apply only to structures for which detailed data is now available. Other areas and deeper formations may expand the potential but have not yet been assessed at the same level of detail.
The main limitation is not the space available underground, but how quickly and safely the reservoirs can be pressurised and operated. This is the subject of ongoing research, regulation and cooperation between GEUS, the authorities and operators.
GEUS continues to assess that Denmark has significant geological potential for CO₂ storage. How much of this can be exploited in practice depends on detailed studies of specific structures, operating conditions and technical choices.
GEUS will continue to update and disseminate new results as the data base matures and make new knowledge and data available to the public.