Burying CO2 underground safer than previously thought

Storing carbon dioxide (CO2) in reservoirs deep underground may be better for the climate than emitting the gas directly into the atmosphere as researchers have found that this process is much safer over long periods of time than previously thought.

The researchers found that natural accumulations of CO2 that have been trapped underground for around 100,000 years have not significantly corroded the rocks above.

These findings, published in the journal Nature Communications, demonstrate the viability of a process called carbon capture and storage (CCS) as a solution to reducing carbon emissions from coal and gas-fired power stations, the researchers said.

"With careful evaluation, burying carbon dioxide underground will prove very much safer than emitting CO2 directly to the atmosphere," said lead author Mike Bickle, Professor at University of Cambridge.

Carbon capture and storage involves capturing the carbon dioxide produced at power stations, compressing it, and pumping it into reservoirs in the rock more than a kilometre underground.

The CO2 must remain buried for at least 10,000 years to avoid the impacts on climate.

One concern in this process is that the dilute acid, formed when the stored CO2 dissolves in water present in the reservoir rocks, might corrode the rocks above and let the CO2 escape upwards.

The new research found that CO2 can be securely stored underground for far longer than the 10,000 years needed to avoid climatic impacts.

The study showed that the critical component in geological carbon storage, the relatively impermeable layer of "cap rock" that retains the CO2, can resist corrosion from CO2-saturated water for at least 100,000 years.

To understand these effects, this study examined a natural reservoir in the US state of Utah where large natural pockets of CO2 have been trapped in sedimentary rocks for hundreds of thousands of years.

The team drilled deep down below the surface into one of these natural CO2 reservoirs to recover samples of the rock layers and the fluids confined in the rock pores.

"A major obstacle to the implementation of CCS is the uncertainty over the long-term fate of the CO2 which impacts regulation, insurance, and who assumes the responsibility for maintaining CO2 storage sites. Our study demonstrates that geological carbon storage can be safe and predictable over many hundreds of thousands of years," Bickle said.

--IANS

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