The study identifies for the first time the physical conditions of pressure and temperature that increase the safety of underground CO2 storage. These conditions are found in shallow volcanic areas. With this methodology, each injection well could store CO2 emissions equivalent to those produced between 75,000 and 1.1 million people.
Researchers from the Institute for Environmental Assessment and Water Research (IDAEA-CSIC) and the Technical University of Freiberg, Germany, propose an innovative method to store CO2 underground in a feasible and safe way. The work, published in the journal Geophysical Research Letters, is proposed as a possible solution to mitigate the effects of climate change.
Carbon dioxide (CO2) capture and storage is one of the strategies in the battle against global warming. This technology has been in development for 25 years, but there are still many challenges to address.
"Around 20% of CO2 emissions come from industrial processes, such as cement, steel or ethanol production, which will continue to generate CO2 even if all the energy they consume came from renewable sources", explains the researcher and author of the study Víctor Vilarrasa. To achieve carbon neutrality, this technology proposes to capture CO2 and store it underground. This process, however, has a high risk of leakage. Employing current methods in porous and permeable rocks located between 1 and 3 km deep, CO2 is less dense than water and floats. This is one of the main obstacles encountered in the CO2 storage strategy.
Using analytical solutions and computer simulations, the recently published study demonstrates that CO2 could be safely stored if injected into wells where supercritical conditions exist. Supercritical conditions are found where the temperature and pressure are above 374ºC and 218 atmospheres, respectively. "In this state, the density of CO2 is higher than that of water, so it sinks", clarifies Dr. Vilarrasa.
These conditions are found around 3-5 km deep in volcanic areas, and below 13 km in other areas. Drilling at 13 km is not technically possible at present, so volcanic areas seem to be a more feasible option. "We found out that each well could store emissions equivalent to those emitted between 75,000 and 1.1 million people", says the researcher.
Countries such as Spain (in the Canary Islands), Italy or Turkey, whose territories have volcanic areas, have great potential to develop this technology. In Iceland, they found these conditions in a volcanic area about 4.5 km deep in 2016, so the proposal seems realistic.
“However, many questions remain to be resolved, such as the development of techniques to locate areas with supercritical conditions, the risk assessment in volcanic areas, the improvement of drilling techniques and the adaptation of measurement devices to such high temperature”, Víctor Vilarrasa points out.
This work is part of the GEoREST project, funded by the European Research Council, and whose objective is to develop a methodology to predict and mitigate earthquakes induced by fluid injection into the subsurface for the development of geothermal energy.
More about Georest project: https://www.youtube.com/watch?v=IABFRcoosnk
Francesco Parisio, Víctor Vilarrasa. Sinking CO2 in supercritical reservoirs. Geophysical Research Letters, 47, e2020GL090456, DOI: 10.1029/2020GL090456
Alicia Arroyo / IDAEA-CSIC Communication