At Safe Depths

The team working with Dr. Johannes Miocic of the Institute of Earth and Environmental Sciences of the University of Freiburg and Dr. Stuart Gilfillan of the University of Edinburgh in Scotland has demonstrated that the greenhouse gas carbon dioxide (CO₂) can safely be stored in the earth's lower layers of rock even in the presence of geological faults. The researchers have published their findings in the specialist journal "Scientific Reports."

The article addresses reducing emissions of CO₂ – a byproduct of industrial processes – using an approach that involves the capture and storing of the greenhouse gas. The researchers say the strategy could help to achieve the targets set in the UN Paris agreement to reduce global warming to much lower than two degrees Celsius from pre-industrial levels. But some experts nevertheless say storing large amounts of CO₂ underground is risky because some of the gas could escape back into the atmostphere through geological faults. These faults are places in the earth's lower strata where there are fractures that move and dislocate layers of underground rock.

The researchers chose and observed a naturally-occurring CO₂ reservoir in the US state of Arizona for their study. There the gas migrates along faults from the underground store to the surface. When the CO₂ is released, certain types of carbonate rocks known as travertines are formed. The researchers dated these rocks so they could determine the amount of CO₂ that had come out of the store during the last 420 thousand years. Their measurements showed levels were very low, accounting for less than 0.01 percent of the store's volume per year. Based on those findings, sites with geological faults would therefore also be suitable for storing carbon dioxide. "The safety of CO₂ storage is crucial for a successful, wide-spread implementation of much needed carbon storage (CSS) technology. Our research shows that even imperfect sites can be secure stores for hundreds of thousands of years," said Miocic.

Original publication:
Miocic, J.M., Gilfillan, S.M.V, Frank, N., Schroeder-Ritzrau, A., Burnside, N.M., Haszeldine, R.S. (2019): 420,000 year assessment of fault leakage rates shows geological carbon storage is secure. In: Scientific Reports, DOI:10.1038/s41598-018-36974-0 www.nature.com/articles/s41598-018-36974-0