Study sees North Sea storage facility for CO2 overrated

06.05.2025

Source: E & M powernews

A new study by Greenpeace warns of safety risks and unrealistic expectations regarding CO2 injection under the North Sea and casts doubt on its climate policy benefits.

Greenpeace has fundamental doubts about the geological suitability and climate impact of planned CO2 repositories in the North Sea. The environmental organization bases its opinion on a recently published study. The paper was written by geochemist Ralf Krupp. In particular, the expert takes a close look at the Henni salt pillow investigated by the Geostor research association. This is a geological structure in the German Exclusive Economic Zone that is considered a potential storage site for carbon dioxide.

According to the author of the study, the assumed barrier rocks there are partially eroded or are not deep enough to guarantee a safe containment function. In addition, known fault systems would indicate that CO2 could escape from the reservoir. Krupp also considers the calculated storage capacity of 368 million tons of CO2 to be exaggerated. The calculation is based on optimistic model assumptions and an efficiency value of up to 20 percent - in practice, however, values of between two and eight percent are common.

Criticism of storage strategy and climate impact

In addition to geological and technical concerns, the author also expresses climatic concerns. The planned injection rate of ten million tons of CO2 per year is more than ten times higher than the level of implemented projects such as Sleipner in Norway. Background: Sleipner is the first commercial project for the capture and geological storage of CO2 (Carbon Capture and Storage, CCS) worldwide. It has been operated by Equinor (formerly Statoil) since 1996 and is located in the North Sea, around 250 kilometers west of Norway.

According to the study, the required injection pressure of 125 bar is also significantly higher than usual in practice. In addition, supercritical CO2 can dehydrate clay minerals, which could make originally dense layers permeable. "Supercritical CO2" is a physical state of carbon dioxide that is neither clearly liquid nor gaseous, but combines properties of both phases.

The study argues that CO2 reservoirs are not closed systems. In order to accommodate the injected CO2, the existing pore water would have to escape - with potential environmental risks. According to the study, there is a risk that methane, hydrocarbons and radioactive substances will be released in addition to CO2. Above a certain ratio, the damage to the climate could exceed the savings effect of CCS, the author warns.

The overall assessment of the study is clear: CO2 injection is ineffective, technically unsafe and counterproductive in terms of climate policy. Krupp calls CCS an "end-of-pipe" technology that is associated with high energy and material costs. It would also tie up large amounts of renewable energy, which would not be available for the actual conversion of the energy system. Complete CO2 capture is also technically unachievable - between 5 and 20 percent of carbon dioxide continues to escape into the atmosphere despite CCS.

Greenpeace sees the debate on the use of the North Sea as a CO2 sink as a sham. Karsten Smid, climate expert at Greenpeace, explains: "CCS technology is an offshoot of the oil and gas industry that primarily serves to perpetuate fossil fuel business models. Instead of relying on CO2 injection, the organization calls for a consistent phase-out of the use of fossil fuels and an intensification of natural climate protection through renaturation and the expansion of natural carbon sinks on land and in the sea.

The 103-page study "Geological risks of CO2 injection in the North Sea" can be downloaded from the Greenpeace website.

Author: Davina Spohn