Can we store carbon dioxide underground?

Capturing carbon dioxide and storing it could reduce greenhouse gas emissions, but how safe is it?
11 July 2013


power plantBetter sites could now be identified for carbon dioxide storage.

The last few decades have seen more research into renewable and greener energy solutions.

One such solution is Carbon Capture and Storage (CCS).

Rather than tackling how much C02 we are producing, CCS is based on the idea that if we can stop the C02 from reaching the atmosphere, it can't contribute to the climate change.

One approach is to sequester carbon dioxide inside porous rocks, like chalk or sandstone. But some sites hold that gas better than other. This new study has been trying to understand what makes a good CCS site.

To find out, a group at Bristol University has looked at three sites in Norway, Canada, and Algeria.  Although similar amounts of C02 was stored (around one mega tonne of gas per year), they have all reacted differently.

Using satellite measurements accurate up to one millimeter to monitor movement and geophones to detect seismic waves, the researcher built up a picture of what was happening deep underground and how each site was reacting to gas injection.

By using an array of geophones around the site, some placed in bore holes; the source of any waves could be pinpointed.

Lots of seismic activity indicates a lot of movement and energy. This energy could cause a crack, and depending on where that crack is, the sequestered CO2 could be released.

Originally a site of natural gas, the Sleipner site, in Norway has shown little sign of faults within the rock, though this may be because it is a very large site so even with a megatonne of CO2 being added every year, it is only 0.003% full. Because it used to house natural gas the site has had little problem coping with the pressure of the gas.

Things haven't gone so well at the other sites with the Canadian site showing large amounts of seismic activity, and rock deformities, where areas of rock are raised or distorted from their original shape at the Algerian site.

To make a marked impact on C02 emissions, 30 billion tonnes a year must be stored in CCS around the world. If we can better understand what makes a good site we can begin to reach this target.

For CCS to really work, the gas needs to remain trapped in the rocks for thousands of years. This requires very stable rocks that will not fracture under the pressure of gas addition.

All the sites showed some seismic activity, ranging from low rumbles that couldn't be felt, to tremors in the local area. While no major incident was recorded, it is of course not idea for the surrounding environment to experience these regular tremors. And with every tremor you run the risk of causing a major fault line, possible releasing the stored gas.

The research will improve how sites for gas injection are chosen and will lead to more reliable containment of the gas.

It should be noted that this is not a final solution to C02 emissions. It's a stop gap measure that has its limits. Once the best sites for CCS are filled up what should we do then?

Claudia Efstathiou spoke to the author of the study, Dr James Verdon from the University of Bristol. James Verdon - Carbon Capture Interview


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