Why we need to shoot carbon dioxide thousands of feet underground

Carbon capture and storage (CCS) tech has two main steps (as you might guess from the name). First, carbon dioxide is filtered out of emissions at facilities like fossil-fuel power plants. Then it gets locked away, or stored.  

Wrangling pollution might seem like the important bit, and there’s often a lot of focus on what fraction of emissions a CCS system can filter out. But without storage, the whole project would be pretty useless. It’s really the combination of capture and long-term storage that helps to reduce climate impact. 

Storage is getting more attention lately, though, and there’s something of a carbon storage boom coming, as my colleague James Temple covered in his latest story. He wrote about what a rush of federal subsidies will mean for the CCS business in the US, and how supporting new projects could help us hit climate goals or push them further out of reach, depending on how we do it. 

The story got me thinking about the oft-forgotten second bit of CCS. Here’s where we might store captured carbon pollution, and why it matters. 

When it comes to storage, the main requirement is making sure the carbon dioxide can’t accidentally leak out and start warming up the atmosphere.

One surprising place that might fit the bill is oil fields. Instead of building wells to extract fossil fuels, companies are looking to build a new type of well where carbon dioxide that’s been pressurized until it reaches a supercritical state—in which liquid and gas phases don’t really exist—is pumped deep underground. With the right conditions (including porous rock deep down and a leak-preventing solid rock layer on top), the carbon dioxide will mostly stay put. 

Shooting carbon dioxide into the earth isn’t actually a new idea, though in the past it’s largely been used by the oil and gas industry for a very different purpose: pulling more oil out of the ground. In a process called enhanced oil recovery, carbon dioxide is injected into wells, where it frees up oil that’s otherwise tricky to extract. In the process, most of the injected carbon dioxide stays underground. 

But there’s a growing interest in sending the gas down there as an end in itself, sparked in part in the US by new tax credits in the Inflation Reduction Act. Companies can rake in $85 per ton of carbon dioxide that’s captured and permanently stored in geological formations, depending on the source of the gas and how it’s locked away.