four questions about the “CO2 cemetery” inaugurated in the North Sea, which will store carbon dioxide injected underground

A world first. On Wednesday March 8, Denmark inaugurates in the North Sea a first storage site for carbon dioxide (CO2) imported from abroad. The “Greensand” project, in the pilot phase, was inaugurated in Esbjerg, in the south-west of the country. The carbon dioxide will be stored under the North Sea, through a former oil deposit.

This inauguration is part of a movement to develop carbon capture and storage (CCS) projects, a technique presented by some as a solution – not without limits – in the fight against global warming. What is CO2 capture and storage, and how will this new project work? What do we know about the effectiveness of such measures in curbing climate change? Response elements.

1 What is carbon capture and storage?

This technique aims to capture CO2, the main cause of global warming, and then bury it “in a geological formation to prevent it from being present in the atmosphere”, summarizes the Ecological Transition Agency (Ademe) in a technical opinion (PDF document) on the subject. The process is carried out in three stages: capture, transport of CO2 and then its geological storage.

In order to capture carbon dioxide, there are “a large portfolio of technologies at different stages of maturity”, specifies Ademe. The technique “marketed and implemented on an industrial scale” is that of “post-combustion by solvent absorption”. Concretely, it is a question of using solvents to extract the greenhouse gas from fumes after combustion, explains The new factory. Then comes the transport of this CO2 to its storage site, which can be done by train, boat or pipeline.

Finally, several places are possible for the geological storage of this carbon dioxide. Ademe cites in particular old hydrocarbon reservoirs, as is the case for the “Greensand” project, coal seams, but also saline aquifers, which are made up of porous or cracked rocks and which contain salt water.

According to a recent report by the Global CCS Institute* think tank, the number of CO2 capture and storage projects has increased by 44% in one year worldwide. There are now nearly 200 CCS initiatives, including 30 in use and 164 at a more or less advanced stage of development. The institute ensures that once completed, these projects will enable the capture and storage of 244 million tonnes of CO2 per year. A result still far from the objective of around 1.2 billion tonnes of CO2 captured and stored per year by 2030, recalls the International Energy Agency*.

2 How will this “Greensand” project work?

The peculiarity of the “Greensand” project is that it brings in carbon dioxide from abroad, more precisely from a factory of the German chemical giant Ineos in Belgium, where carbon capture already takes place, according to the site. of the project*. The CO2 is then liquefied and transported by sea to the Nini West platform, located in the North Sea. Then he is “sent underground via an existing offshore platform and a well dedicated for this purpose”. The carbon dioxide is then permanently stored 1,800 meters deep under the North Sea, in a sandstone reservoir.

According to the actors of the project, “Greensand” will allow, by 2025 and 2026, to store 1.5 million tons of CO2 per year. The goal is to achieve a storage of 8 million tonnes of CO2 per year in 2030, or around 13% of Denmark’s annual CO2 emissions. “As our subsoil contains a much greater storage potential than our own emissions, we are able to also store carbon from other countries”welcomed the Danish Minister for Climate and Energy, Lars Aagaard, to AFP.

3 Why choose the North Sea for this type of project?

The selected area is home to numerous gas pipelines and geological reservoirs, which have become empty after several decades of oil and gas exploitation. “Depleted oil and gas deposits have many advantages because they are well documented and there is already infrastructure that can most likely be reused”Morten Jeppesen, director of the Center for Offshore Technology at the Technological University of Denmark, told AFP.

Norway has thus launched the “Northern Light” project, a terminal which is to receive and store CO2 from European industrial activities. The objective is to be able to eventually store around seven million tonnes of carbon dioxide per year in this reservoir. At the beginning of February, the oil group TotalEnergies announced that it had obtained two permits in Denmark for a potential CO2 storage project, more than two kilometers under the North Sea. The objective is to store five million tonnes of this greenhouse gas there per year, by 2030.

4 How effective is this technique in the fight against global warming?

Can the capture and storage of CO2 be an effective instrument to curb global warming caused by human activities? Nearby FinancialTimes* (article reserved for subscribers)Julian Allwood, co-author of the IPCC’s fifth report, explains that “ITechnology won’t solve climate change, because it can’t be deployed at sufficient scale in time.” The problem is as follows for the CSC: “if we wanted to take all of our CO2 emissions back into the air, we would have to devote all the world’s electricity production to it and make it carbon-free”explained at the end of 2021 to franceinfo Jean-Marc Jancovici, founder of the consulting firm Carbone 4 and member of the High Council for the Climate.

In the last part of the sixth IPCC report, made public last spring and devoted to solutions to curb global warming, scientists explain that “the deployment of carbon dioxide capture devices, to offset residual emissions, is inevitable”, but specify that this must be done in addition to an essential solution: the drastic reduction of our greenhouse gas emissions. “However, this is not to say that we can continue to emit greenhouse gases. The lower the residual emissions, the less negative emissions we need to offset them”then pointed out to franceinfo Céline Guivarch, research director at the International Center for Research on Environment and Development and co-author of Group 3 of the IPCC.

In a review on the subject (PDF file)Ademe evokes the “limited potential” of these CCS techniques to “reducing industrial emissions” In France. “Even by optimizing the capture technologies (which consume a lot of energy), CCS will remain an expensive solution, because it is only suitable for very high-emitting sites, in limited numbers, and requires adaptations on a case-by-case basis” , explains the Agency. “Another challenge concerns the societal acceptance of this technology, in view of the potential technological and health risks.