Atmospheric concentrations of carbon dioxide are expected to double by later this century. Keeping warming below the 1.5°C threshold predicted to have severe global consequences requires a multi-pronged approach including avoiding and reducing emissions through a minimum annual 3% decline in fossil fuel production, leaving the majority of oil and gas reserves in the ground. However, another contributor poised to partially reduce atmospheric greenhouse gases is carbon capture and storage. One technique showing promise is highlighted in new research by Benjamin Tutolo, Adedapo Awolayo and Calista Brown at the University of Calgary. Modelling the potential for carbon dioxide storage in undersea basalt formations, the team estimate that this technology, if scaled up, could remove carbon dioxide on a gigaton-per-year scale.
Tutolo, who headed the project, began studying carbon capture and storage terrestrially, in sedimentary basins like those in Alberta. Later, Iceland’s CarbFix experiment caught his attention. CarbFix uses a process that converts carbon dioxide gas to solid stone. Since 2014, the pilot project has injected over 73,000 metric tonnes of carbon dioxide. But “society emits about 51 billion tons of CO2 to the atmosphere — or CO2 equivalents to the atmosphere — each year,” says Tutolo. So, to attain a reduction of even 1% of that, we need to get to the Gigaton per year scale. That sparked Tutolo’s interest in whether storage could be achieved at a larger scale, in other environments.
CarbFix has successfully converted gaseous carbon dioxide to calcium carbonate, but the process requires an enormous volume of water, explains Tutolo, making it not practical in areas where water is in short supply. So his team has crunched the numbers on the chemical dynamics for a different process; injecting CO2 directly, without needing to first dissolve it in water.
After direct air capture, CO2 is pressurized to produce supercritical CO2 – which is essentially dense CO2. This is then injected into an undersea basaltic aquifer. Once it enters the aquifer, the CO2 dissolves in the water, “like a classic soda stream or Perrier water,” he says. Then, mineralizing the carbon requires dissolving the basalt. “Injecting the CO2 makes carbonic acid, lowers the pH, and then increases the reactivity with respect to the basaltic minerals,” things like olivine, feldspar and pyroxene, says Tutolo. These minerals donate their calcium, magnesium and iron into the solution, which combined with the dissolved CO2, produces carbonate minerals like calcium carbonate, calcium iron carbonate, calcite or anchorite. Once solidified, this form of carbon is “ridiculously stable,” he says. “There’s no feasible scenario that would destabilize that carbon for millions of years.”
The biggest challenge with implementing this technology, says Tutolo, is scale. But he uses the analogy of solar panels, which started out expensive and impractical, and over time have become practical and cheaper. “That gives me hope,” he says. Another challenge is monitoring the injection site. Monitoring how much CO2 gets injected is straightforward. What’s challenging is quantifying how much CO2 has turned into stone, he explains, so developing monitoring technologies is another avenue of research.
Geoscientist Adedapo Awolayo, postdoctoral researcher with Tutolo and co-author on the research, notes that in comparing carbon storage on land versus undersea, oceanic basalt has an advantage. “The minerals in sedimentary rock are not as reactive,” he says, so converting carbon to a stable, solid form in sedimentary rock takes much longer than it would in undersea basalt.
Geologist Hélène Pilorge, Research Associate at the Kleinman Center for Energy Policy and Clean Energy Conversions Laboratory at the University of Pennsylvania, who did not participate in the study, says this research is important because it bridges the gap between lab and field experiments. Both, she notes, are essential. Lab experiments are valuable in helping us understand the dissolution of silicates and precipitation of the carbonates. “But these simulations help us to understand how it would work in different environments than the ones that are more easily set up in the lab,” Pilorge says.
A formidable challenge to seeing oceanic basaltic carbon storage go from theory to practice – at scale – is the cost. “We are still doing the economics,” Awolayo says, but the team is looking at using alternative energies like wind power, plentiful at sea, to drive costs down. The team is working on a demonstration project targeting the Cascadia Basin, off the coast of Vancouver Island, as a future injection site. There, by repurposing scientific wells already in place, Tutolo’s University of Calgary team is working with researchers at University of Victoria and Columbia University to put the first pilot scale project into action in by 2025.