Although CO2 can stay in the atmosphere, trapping heat, for thousands of years scientists think they have turned it into rock in just a few months. Juerg Matter from the University of Southampton, UK, and his colleagues in the CarbFix project have injected 170 tons of pure CO2 into the reactive basalt underneath Iceland. Their findings suggest around 85% of it reacted with the rock over the short distance between injection and monitoring boreholes in less than one year.
“We think that was because all that CO2 precipitated out as carbonate minerals in the reservoir,” Juerg, who’s also an adjunct scientist at Lamont-Doherty Earth Observatory in New York, told me. “To really prove it this summer we will drill a borehole into the injection reservoir to retrieve rock core samples.” But the CarbFix team has also emphasised this week that it will take higher carbon prices for this and other carbon capture and storage technology to fulfil their potential.
The latest UN Intergovernmental Panel on Climate Change (IPCC) says the cheapest way to avoid dangerous climate change is to stop using fossil fuels and switch to renewable energy. However time’s running out on that option, and the IPCC report therefore highlights the probable need to suck CO2 from the air. But before we capture CO2 straight out of the air, or even from the chimneys of power stations, we need somewhere to put it. Currently captured CO2 is simply pumped and stored underground as a gas, meaning care is needed to choose reservoirs that won’t leak. “Storage options right now are mainly in depleted gas and oil fields, in sedimentary rocks,” Juerg said.
In the air, CO2 eventually reacts with basalt naturally, but that process is far too slow to balance out what humans are emitting. Since 2007 the CarbFix team has been working to see if they can speed that process up by forcing CO2 underground. Not only would this quickly turn the gas into minerals and prevent leak worries, it would also greatly expand the number of places it could be stored. “The storage potential is just huge, there’s billions of tons of reservoir, because basically all the ocean floor is basalt,” Juerg highlighted.
Rock of ages
Iceland’s volcanoes provide it both with plenty of basalt, and also lots of geothermal energy that can generate clean electricity to help it towards its ‘carbon neutral’ target. However volcanic steam naturally contains CO2, and trapping and burying this would help balance out other emissions, like those from cars. Reykjavik Energy was therefore keen to help set up the CarbFix project in 2007 and keep it going through the economic turmoil the country has faced since.
While Juerg first revealed the surprising reaction speed in December at the American Geosciences Union meeting in San Francisco, California, the team is still publishing many of its findings. In an upcoming paper they estimate around 100 kWh of electricity is needed to pump and inject a ton of CO2 and the water they dissolve it in into basalt. In geothermally-powered Iceland, that’s not a problem, but in the mostly fossil-fuelled UK it would lead to emission of almost another half-ton of CO2.
In a few weeks the CarbFix team will start preparing to inject around 10,000 tons of CO2 into a deeper reservoir. Though last time they injected pure CO2, this time they will use exhaust gases from the geothermal power plant that also include smelly hydrogen sulphide. Injecting these gases together could help make a stronger case for carbon capture, Juerg explained. “Hydrogen sulphide is a big problem for the gas industry,” he noted. “Gas with hydrogen sulphide is called sour gas, which makes up over 40% of natural gas globally. The hydrogen sulphide has to be separated and something has to be done with it.” Co-injection and storage of hydrogen sulphide and CO2 would avoid the separation cost, he added.
Gem of an idea
Juerg is now also looking away from Iceland, to warmer climes in Saudi Arabia’s neighbour, Oman, where CO2 could be mineralised even quicker. He’s on the trail of rock richer still in olivine, the mineral in basalt that reacts fastest with the greenhouse gas. That rock is called peridotite, whose name relates to a gemstone often found in it called peridot. “There is enough mantle peridotite on continents to sequester basically all human-caused CO2 emissions, if you find a way to engineer it,” Juerg stressed.
That work is at a much earlier stage than the basalt research. “Our knowledge for peridotite is less than for basalt,” Juerg said. “What we first did in Oman was characterise this rock, look at how peridotite naturally is carbonated by atmospheric CO2. Now we’re looking at how can we engineer it, how can we speed it up. We are planning an international basic science project to drill boreholes into the peridotite to better characterise the potential of peridotite as a CO2 storage reservoir.”
Yet these ideas face more than just technical challenges before they can be used to fight climate change. In a perspective piece in the journal Science this week, two of Juerg’s CarbFix teammates point out the financial barriers to use. Sigurdur Gislason from the University of Iceland in Reykjavik and Eric Oelkers from Université Paul-Sabatier in Toulouse, France highlight that the CarbFix way of storing CO2 in basalt could cost as little as $17/ton.
Challenges in store
Given that people emitted almost
10 36* billion tons of CO2 in 2012 $17/ton may not seem cheap. But Sigurdur and Eric also point out that ‘the cost of carbon capture and storage is dominated by capture and gas separation, which costs $55-$112/ton CO2’. By contrast the carbon price in the EU emission trading scheme is just $7/ton. “Until either market forces or taxes result in a higher price on carbon emission, there is no financial incentive for carbon capture and storage using any of these technologies,” they write.
“We have capture technology that’s ready to be used at stationary sources on a large scale,” Juerg added. “We already have sedimentary storage options available on a large scale. In 5-10 years the in-situ mineralisation that we’re looking at could be ready. The problem is not technology or engineering. The problem is more that we do not have a policy and economic framework to do it. Right now you pay to dispose of CO2, but you don’t gain anything if you do. That’s why the US Department of Energy a couple of years ago decided the economic model right now is enhanced recovery, injecting CO2 into depleted oil and gas reservoirs to get more out. For pure disposal we don’t have that, because we have no price on CO2 emissions. We don’t pay for those CO2 emissions. I agree with my colleagues – to really do it on a large scale we really need a policy framework and we need an economic model.”
Such problems go beyond the ability of scientists like Juerg, Eric and Sigurdur to solve. They need our governments to adopt carbon prices big enough to make carbon capture and storage a reality.
* Amended April 26 to correct from figure for carbon emissions (almost 10 billion tons) to CO2 emissions (almost 36 billion tons).
Matter, J.; Stute, M.; Hall, J. L.; Mesfin, K. G.; Gislason, S. R.; Oelkers, E. H.; Sigfússon, B.; Gunnarsson, I.; Aradottir, E. S.; Alfredsson, H. A.; Gunnlaugsson, E.; Broecker, W. S. (2013). Quantification of CO2-Fluid-Rock Reactions Using Reactive and Non-Reactive Tracers American Geophysical Union, Fall Meeting 2013, abstract #V41A-2753
Gadikota, G., Matter, J., Kelemen, P., & Park, A. (2014). Chemical and morphological changes during olivine carbonation for CO2 storage in the presence of NaCl and NaHCO3 Physical Chemistry Chemical Physics, 16 (10) DOI: 10.1039/c3cp54903h
Gislason, S., & Oelkers, E. (2014). Carbon Storage in Basalt Science, 344 (6182), 373-374 DOI: 10.1126/science.1250828
The CarbFix project’s full energy use analysis is in the process of publication in the International Journal of Greenhouse Gas Control