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Carbon Capture Works, But Not Everywhere

Pumping carbon back into the Earth can cause "microseismic events" that could eventually release it into the atmosphere.
Weyburn-Midale's carbon capture center. Photo via Petroleum Technology Research Centre

Capturing carbon dioxide at its source and piping it back into the Earth is one of the better methods we've got for cutting back on net emissions—as long as the gas we sequester underground doesn't find its way back into the atmosphere.

A new good news/bad news study published Monday finds that, though some of the world's largest carbon capture projects have successfully kept the CO2 from joining its free buddies in the atmosphere, Earth's geology is tricky to predict. The geological structures found in Norwegian, Canadian, and Algerian carbon capture fields all behave quite differently after having more than a million tons of gas shot into them.

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The University of Bristol's James Verdon and his colleagues studied In Salah carbon injection center in Algeria, which is eventually expected to hold 17 million tons of carbon; Sleipner, widely regarded as the world's most successful carbon capture center in Norway, which can store up to 600 billion tons of carbon; and Weyburn-Midale, located in Saskatchewan's depleted oil fields. Weyburn takes in emissions from a coal power plant located in North Dakota.

"We didn't find major problems, none of the sites is leaking CO2, but we've seen different responses in terms of the geomechanics of each site," Verdon, whose study is published in Proceedings of the National Academy of Sciences, said.

Some of those responses, at least in the case of In Salah, are "thousands of microseismic events."

When carbon is injected into Earth's reservoirs, the main fear is that building pressure will eventually cause the ground to fracture, allowing CO2 to leak back into the atmosphere and ruining the entire project. Verdon said that's most likely to happen at the beginning of a project.

In some cases, fracturing isn't too big of a deal: At In Salah, for instance, CO2 injection has caused roughly 200 meters of fractures in the reservoir's cap. Fortunately, the cap is about a kilometer thick, meaning those tiny seismic events haven't resulted in a project failure.

"You want a thick seal so that even if you fracture a portion of it, it's OK," Verdon said. "At In Salah, they've fractured some of the seal but it's a kilometer thick. If you have another site with similar properties but a thinner seal, that'd be a problem."

Sleipner's ridiculously huge capacity and porous aquifer has allowed carbon capture to go on there with minimal pressure increases for more than 15 years. It's an ideal reservoir, Verdon said. The problem is, there might not be enough places like Sleipner in the world for it to make a huge difference. Humans are releasing close to 40 billion tons of carbon into the air each year; a minuscule fraction of that is captured.

"The issue is the scale. We know now that it's technically feasible to put a million tons of CO2 in the ground and not have a problem," he said. "That works in some places but it won't work at every place. We've seen problems at some sites where they could eventually leak. In order to make a real difference, we need to store billions of tons of CO2 a year. We need thousands of sites."

That's not to say those sites don't potentially exist somewhere, it's just that with scale comes inevitable failures—which cost time, money, and harm the environment.

"We can't say carbon capture will work or it won't work. Sometimes it'll work and sometimes it won't," said Verdon. "We have to be prepared to accept that."