CO₂ sequestration in Switzerland: a promising avenue or a dead end?

Seven million tonnes! That is the total volume of CO₂ that the Federal Council plans to capture and store in Switzerland in order to reach the net-zero emissions target by 2050. Its strategy rests on two approaches: storage in durable products, such as construction materials, and geological burial, to the tune of three million tonnes. However, a major problem remains: uncertainty about the exact location where this carbon dioxide will be stored.

In recent days, a new study cast doubt on the feasibility of capturing and storing CO₂ in Switzerland. “In Switzerland, according to a study by the Swiss Federal Institute of Technology Zurich (ETH Zurich), storing CO₂ in the ground is not realistic”, headlined an ATS dispatch. Based on their findings, the scientists indeed estimate that the durable storage of CO₂ would not be viable, neither in the short nor in the long term.

The impossible in-situ mineralization in Switzerland

This position, however, concerns a very specific storage method: in-situ mineralization. For it to be durable, this technique, which consists of dissolving CO₂ in water before injecting it as carbonic gas into the subsurface, requires a set of preconditions. “The rock must be rich in calcium, magnesium and iron, while containing as little silica as possible. Three types of rocks stand out: basalt, peridotite and serpentinite,” explain the authors of the study.

To optimize storage capacity, in-situ mineralization requires that the rock reach a certain volume and be located at a depth of at least 350 meters, thus ensuring sufficiently high pressure to dissolve the CO₂ in the water. Added to this are several determining factors, such as the rock’s age, its degree of weathering, its porosity, its temperature and its permeability. “These are some of the essential criteria for a region to be considered a reservoir,” explains Adrian Martin. Now a sustainability project manager at Nespresso Switzerland, his master’s work at ETH Zurich served as the basis for the study.

“These results confirm the findings of a study commissioned by the Federal Office of Energy, which had judged the geological conditions in Switzerland unfavorable to in-situ mineralization,” says Robin Poëll, spokesperson for the Federal Office for the Environment.

According to Thanushika Gunatilake, another participant in the study and now an assistant professor at Vrije Universiteit Amsterdam, this mapping at the scale of Switzerland of suitable rock types is “the first of its kind.” Indeed, the researchers did not limit themselves to analyzing the many available scientific studies: they also examined Switzerland’s geological maps, region by region.

Some areas, such as Zermatt-Saas, the Tsaté nappe in Valais or the Arosa nappe in Graubünden, initially seemed suitable for CO₂ storage, before being ultimately ruled out. Take the Zermatt-Saas site as an example: in addition to showing signs of prior mineralization, its underground rocks are very dense and contain few open cavities or fissures into which CO₂ could infiltrate.

CO₂ storage in Switzerland: a dead end?

Is the storage option definitively compromised for Switzerland? Will we be forced to continue exporting captured CO₂ to other countries, as with the pilot project conducted with Iceland? No, say the specialists, who were ultimately not very surprised by the Zurich findings. “These results confirm the findings of a study commissioned by the Federal Office of Energy, which had judged the geological conditions in Switzerland unfavorable to in-situ mineralization,” says Robin Poëll, spokesperson for the Federal Office for the Environment.

To meet the targets set by the Confederation, it will actually be necessary to drill deeper in order to reach the saline aquifers. “Compressed in a supercritical or liquid phase, CO₂ is injected into porous geological formations (so-called reservoirs) filled with non-potable water. These are located at depths greater than 800 meters, where the pressure is sufficient to keep it in a dense form,” explains Eleni Stavropoulou.

An associate researcher at the Soil Mechanics Laboratory of EPFL, she is responsible for activities related to CO₂ storage. “We can inject and store 25 times more CO₂ than if it were in gaseous form in the atmosphere,” she adds. One of the main advantages of saline aquifers lies in their large extent and wide distribution worldwide, including in Switzerland.

“CapRocks are quasi-impermeable geological layers that block CO₂ in place and over the long term, thanks to their favorable multi-physical properties,” explains Eleni Stavropoulou, associate researcher at the Soil Mechanics Laboratory of EPFL.

Identifying the right zones

However, the favorable zones for this storage still need to be identified. To be truly effective and prevent CO₂ from rising to the surface, an additional geological condition is essential: a natural trapping mechanism that scientists call CapRock. “These are quasi-impermeable geological layers that block CO₂ in place and over the long term, thanks to their favorable multi-physical properties,” explains Eleni Stavropoulou.

According to the EPFL researcher, knowledge about this technology is already solid, but further studies will be necessary to analyze the properties of the different geomaterials composing the future storage areas. “With this in mind, we are currently developing a metre-scale demonstrator of the storage system (reservoir and CapRock, editor’s note), which will allow us, among other things, to evaluate the effectiveness of injection into Swiss soils and to estimate associated risks, such as potential CO₂ leaks,” she explains.

According to Robin Poëll, patience will still be required. “Geological storage sites in Switzerland will probably not be developed before 2030. According to estimates by the Federal Office of Energy, they will not be operational for another 15 to 20 years,” explains the FOEN spokesperson.

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