CARBON STORAGE: IS IT LEAK-PROOF?

Undersea carbon storage is undergoing a renaissance. It is an active industry in places, but with the UK’s net zero commitments, there is fresh energy in investigating its large-scale viability.

The most well-known underwater CO 2 storage site is the Sleipner project in the North Sea, west of Norway. It is the world’s first commercial CO 2 storage project and has been operational since 1996, storing away about one million tonnes of CO 2 each year.

There are CO 2 emissions hotspots in the UK, mostly in the Humber and Teeside, where groups of industries are collaborating to establish how to build the infrastructure and pipework to collectively capture and store their CO 2 beneath the seabed.

But can we be sure the captured CO2 won’t leak? And how would we know about a leak before it is too late?

Rachael James, Professor of Geochemistry, is answering those questions. She outlined: “CO2 that’s captured before it’s emitted, such as from power plants or the cement industry or other big emitters, can be pumped and stored in geological reservoirs beneath the seabed that previously contained oil and gas and are therefore expected to be secure, having stored oil or gas for tens of millions of years.”

Rachael’s work is focused on the surety that CO 2 leaks could be detected and quantified. She uses geochemical fingerprinting techniques to distinguish leaks from natural sources of CO 2

“We did a release experiment in the North Sea,” she said. “We injected CO2 into the sub-seabed sediments, then monitored the CO 2 as it moved through those sediments and out into the water column. We were able to detect it both in seawater and as it moved through the sub-seabed sediments before it got out into the water. That’s important, because a leak is defined as a leak when it goes out into the water column, so you want to be able to pinpoint where it’s coming out. We were also able to measure the amount of CO 2 coming out.”

Rachael and her colleagues have also worked with Tim Leighton, Professor of Ultrasonics and Underwater Acoustics, and Paul White, Professor of Statistical Signal Processing, on using acoustic techniques to detect the bubbles of a leak.

The Geochemistry team’s research has also demonstrated that pH changes caused by CO 2 dissolving into the seawater are only detectable close to the source of the leak, and they have begun to investigate the effects on sea life.

Rachael explained: “We have looked at potential impacts on the seabed biology. We did an experiment in a Scottish sea loch, and the first sign that CO2 was affecting the biology was lots of sea urchins came scuttling to the surface. We don’t know why –whether it was a reaction to bubbles or to the chemical change. But it was very clear that organisms that can move wanted to move out of the way.

“For microbial organisms that cannot move, we found that there were changes to the microbial biochemistry, but when we stopped the experiment, it returned to normal very quickly – within a few weeks.”

With research such as Rachael’s continuing to add to the picture of the viability of underwater CO 2 storage, she believes it is a strong option for the near future. “With the UK committed to net zero by 2050, I think this has to be a technology in the mix for achieving that,” she concluded.