Visualizing the effect of CO2 on caprock microstructures

In October 2018, the Intergovernmental Panel on Climate Change (IPCC) published an alarming report on the effects of a 1.5°C rise in global temperatures and called for the world to achieve carbon neutrality by 2050. One of the headline measures proposed in the report was to capture and store CO₂ emitted by human activities.

This approach, used in Norway for almost 30 years and adopted more recently by other countries including Canada, involves capturing CO₂ near production plants and other places where it’s emitted in dense concentrations, and then piping it directly into underground rock formations. Common locations include depleted rock reservoirs that once contained oil and gas, sub-ocean saltwater aquifers and coal seams – all of which offer long-lasting storage capability.

In the team of Prof. Lyesse Laloui (LMS), Eleni Stavropoulou is studying shales – a material whose distinctive properties make it part-rock, part-soil – to determine whether it makes a good candidate for caprock, a type of rock formation that sits above an underground reservoir and acts as a barrier, stopping CO₂ from migrating to the surface. Her research focuses in particular on how argillite behaves mechanically in the presence of CO₂. This behavior is key to reliable, long-term storage without the risk of leaks.

Scaling down to micro

Eleni Stavropoulou is turning to less destructive analysis methods as a way to avoid damaging samples in the lab and still produce conclusive findings. She plans to use X-ray tomography (a technique used in CT scanners) and 3D imaging to generate the first-ever in-situ images of changes in the structure of argillite in the presence of supercritical CO₂, the fluid state in which the compound exists underground.

Whereas research of this kind is normally conducted on samples measured in centimeters, Eleni Stavropoulou intends to analyze samples measuring no more than 5 millimeters across, subjecting them to the same thermal, hydrological, chemical and mechanical conditions found in underground reservoirs. “By scaling down to the micro level, we can produce higher-resolution images and observe slow-acting phenomena at work” explains Eleni Stavropoulou. “More important still, using non-destructive methods means we won’t alter samples from their initial state.”

The project has received a CHF 100,000 grant from the Swiss National Science Foundation’s (SNSF) Spark program, which supports the development of new scientific ideas and methods that “show unconventional thinking and introduce a unique approach”. Eleni Stavropoulou has 12 months to demonstrate the feasibility of her method.

If Eleni Stavropoulou’s experiments go to plan, her findings could support the research that’s being conducted on CO₂ storage and rock reservoirs at the Mont-Terri Rock Laboratory, based in the Jura Mountains.