The release of greenhouse gases, especially CO2 from the burning of fossil fuels, is already having climatic consequences that threaten to be more persistent and damaging in the immediate future. Putting a stop to that release would be the ideal solution, which is far from happening, but even if that were to be achieved, the amount of carbon dioxide released so far is such that its harmful effects would continue for a long time. There are no magical solutions, of course, but strategies are being developed that, together, could mitigate the problem. An interesting solution is the one presented to us today by our guest in Talking to Scientists, Víctor Vilarrasa, senior scientist at the Higher Council for Scientific Research (CSIC) at the The Mediterranean Institute for Advanced Studies (IMEDEA).
Víctor Vilarrasa investigates the geological storage of carbon. The basic idea is simple, it consists of collecting the CO2 emitted in industrial processes and, instead of releasing it into the atmosphere, burying it deep underground. Doing it, of course, is no longer so simple. To carry out this idea it is necessary to execute a series of processes. The first of these consists of separating the carbon dioxide present in the gases emitted by certain industries, such as coal or gas power plants, cement plants, refineries or the steel industry. Since the ideal deep layers for geological storage are usually not underground at emission sites, the collected CO2 must be transported by gas pipelines to the chosen site and treated, either by subjecting it to high pressure to liquefy it or to convert it into a supercritical fluid, that is, an intermediate state between liquid and gas. In this state, CO2 has a higher density and less volume and can be injected into geological formations suitable for confinement.
The geological characteristics of the injection site must be suitable for the injected carbon dioxide to be confined for long periods of time without causing leaks that return CO2 to the atmosphere and without causing movements that could contaminate groundwater over time. . In this sense, Víctor Vilarrasa comments during the interview, layers located below 800 meters deep are sought, much deeper than freshwater aquifers. Ideally, very old rocks, which formed from the sediments of ancient seas and were buried at great depths. These sedimentary rocks contain large amounts of salt water, a water that has been occupying the pores since the remote times when the sediment was formed, which gives an idea of its stability over millions of years.
To prevent the return of injected CO2 to the surface, formations are sought in which the porous layers are located under impermeable layers, which act as a “cover” and prevent carbon dioxide from rising to the surface. The set thus formed is similar to the one that stores the hydrocarbon pockets that are usually drilled to obtain fossil fuels. Just as oil or gas are the remnants of carbon dioxide captured by plants and other organisms from past times, deep storage is intended to return to the depths the carbon dioxide that we currently generate with the burning of fossil fuels and help thus to fight against global warming due to the greenhouse effect.
The injection of CO2 in deep layers is not without its dangers, for this reason, it is necessary to study very carefully the place where it is intended to be done and understand what the drawbacks may be. When carbon dioxide is injected into a deep layer, an increase in pressure occurs that can have negative effects, such as seismic events due to a build-up of pressure, especially when the injection site is in the vicinity of a loaded fault, or leaks that can contaminate aquifers.
In an article recently published in Geophysical Research Letters, signed by the postdoctoral researcher of Iranian origin Iman rahimzadeh Kivi and Víctor Vilarrasa, among others, the researchers calculate, using models, how the stored gas behaves both in its ability to penetrate between the different rock layers, such as the temporal evolution of these movements. Researchers have developed a numerical transport model to understand the long-term fate of CO2 in gigatonne-scale geological carbon storage. Calculations reveal that CO2 leakage is dominated by molecular diffusion at inherently slow rates, barely approaching a meter every several thousand years.
I invite you to listen to Víctor Vilarrasa, head scientist of the Higher Council for Scientific Research (CSIC) at the The Mediterranean Institute for Advanced Studies (IMEDEA)
References:
Kivi, I. R., Makhnenko, R. Y., Oldenburg, C. M., Rutqvist, J., & Vilarrasa, V. (2022). Multi-layered systems for permanent geologic storage of CO2 at the gigatonne scale. Geophysical Research Letters, 49, e2022GL100443. https://doi.org/10.1029/2022GL100443