The last thing you want to do with a problem is sweep it under the rug, so there is a bit of irony that one potential tool for keeping carbon dioxide from getting trapped in our atmosphere involves burying it under our feet. As carbon capture and storage (CCS) technology continues to evolve, scientists and startups are increasingly looking for opportunities to inject harmful carbon emissions underground.
Carbon capture operates on the idea of a closed loop. Using a variety of technologies, it is possible to capture CO2 generated by burning fossil fuels and stash it in rock formations deep under the planet’s surface, returning the greenhouse gas to where it originally came from.
As experts increasingly view this technology as a potential key to combatting climate change and meeting the globally agreed upon goal of limiting the increase of the planet’s temperature to 1.5 degrees Celsius above pre-industrial levels, states and nations are increasingly opening up their land for potential use in carbon sequestration.
Carbon capture and storage is an innovative environmental technology designed to reduce atmospheric carbon dioxide by intercepting emissions at their source and storing them safely underground. The process begins at industrial facilities and power plants, where technologies using methods like chemical filtration or pre-combustion separation are used to capture carbon dioxide directly from emission streams.
Once captured, the carbon dioxide is compressed into a dense liquid and transported to underground storage sites. These sites are typically deep geological formations that contain porous materials like sandstone, limestone and basalt.
“The properties of the reservoir rock are of particular importance,” says Mathias Steiner, a Manager and Senior Technical Staff Member focused on sustainable materials at IBM Research. “During injection, carbon dioxide enters the connected pore space of reservoir rock, where it replaces the resident fluids, such as brine and oil. Ultimately, the carbon dioxide will chemically react within the rock’s pore space and mineralize into solid carbonate.”
Using immense pressure, the compressed CO2 is injected deep into the earth, often as far as 3,000 feet beneath the surface—deep enough that other impermeable and dense layers like shale sit above it. According to Ian Hayton, Group Lead of Materials and Chemicals at Cleantech Group, those denser layers serve as “natural barriers” that contain the carbon.
While CCS is far from a panacea, it is gaining traction as a potential solution for reducing emissions. This year, the United Kingdom announced a USD 28.5 billion investment in the technology, aimed at attracting and facilitating the development of carbon storage projects within its borders. Similarly, the United States Department of Energy has set aside USD 518 million for long-term carbon storage projects.
As carbon capture efforts continue to grow, the focus of the industry turns to where the carbon can be stored.
Earlier this summer, Texas announced that it would open more than a million acres of offshore land and water off the Gulf of Mexico available for companies to drill carbon wells—injection sites where carbon can be locked into natural rock formations for storage. California granted approval for the state’s first carbon wells back in October, and the EPA is expected to give West Virginia the go-ahead to issue permits for underground carbon storage projects by the end of the year.
According to Hayton, there are a number of places that make for good injection sites, including “depleted oil and gas fields, saline aquifers and other [suitable geological formations].” This is because these sites typically have the geological composition that is needed for carbon injection. For example, the same rocks that once held oil and gas resources could effectively be repurposed to stash CO2.
The good news for CCS efforts: “There are abundant suitable sites in most regions,” Hayton says. The US Geological Survey found that the US alone has the carbon storage potential to hold 3,000 metric gigatons of CO2 in geologic basins throughout the country. For context, it is estimated that 2,400 gigatons of CO2 were emitted by human activity between 1850 to 2019.
And, once carbon is stored, it tends to stay there. “Once underground, studies show leakage from natural pathways is low,” Hayton says. Nonetheless, he warns that faulty wells and degradation of plugs could lead to more leakage. “Better regulation around their use and maintenance can help to minimize this risk,” he explains.
“Considering that mineralized carbon dioxide can be stored for thousands of years, geological storage, if scaled, could contribute significantly to achieving mitigation goals,” Steiner says.
New technology can also help researchers uncover sites for carbon storage that are likely to have high success rates. IBM Research, for example, developed a tool that allows scientists to simulate carbon injections into different types of rocks to determine how efficiently the material would hold onto the liquified gas.
“The surface properties of the rock at pore scale are essential for determining a reservoir’s carbon dioxide storage potential,” Steiner says. “Geological estimates suggest that the amount of pore space globally available in geological formations should, in principle, be sufficient for storing all the airborne carbon dioxide once captured.”
But there are risks, too. The long-term effects of carbon storage are still unknown. And even in the short term, the solution is not without its potential pitfalls. Injecting carbon into the Earth can carry the risk of triggering earthquakes. Well blowouts are a possibility for injection sites that are not properly secured, and leakage remains a possibility.
Underground carbon storage may be an important tool in combatting climate change and meeting emissions reduction goals, but it is not a solution on its own. As CCS technology advances and carbon injection becomes a more common practice, scientists and industry experts will need to take further steps to determine safe sites and mitigate risk.