July 5, 2018, by Eric Roston
A Cold War-era joke has an American economist asking a Soviet peer how the communist economy is progressing. “In a word: good” the Russian responds. “In two words: not good.”
So it goes this century with the rapidly changing energy industry. Advances are taking place in clean energy, transport and efficiency that may have rightfully been considered miraculous a decade ago.
But here’s the catch: As fast as everything is proceeding, it’s still not fast enough. The International Energy Agency (IEA) reported last year that a critical technology—capturing carbon dioxide emissions from generators and either burying or otherwise disposing of them—isn’t expanding fast enough. The IEA reported that current “carbon capture and storage” (CCS) facilities are capable of handling just 7.5 percent of the emissions that the world will need eliminated every year by 2025. That’s necessary if nations are to meet the goal of keeping any increase in global warming below 2 degrees Celsius (3.6 Fahrenheit).
In China, researchers have been looking for ways to accelerate CCS. They decided to look out to sea.
On land, CCS isn’t just promising in principle—it’s been shown to work. There will be more than 20 large-scale capture facilities available by the end of the year, according to the Global CCS Institute. But there’s still concern about making sure the CO2, once buried, stays buried. The same can be said for the idea China has about burying CO2 at sea. For companies and countries to exploit the vastness of the ocean floor, they also need some kind of confidence that it’ll stay there.
By studying the long-term interactions of major physical forces in “unconsolidated marine sediment” such as loose silt, clay and other permeable stuff below the sea floor, researchers Yihua Teng and Dongxiao Zhang report that extreme conditions at the bottom of the ocean essentially hold CO2 in place, “which makes this option a safe storage.”
Under great pressure and low temperature, CO2 and water trapped in the sediment below the sea floor crystallize into a stable ice called hydrate. (Through a similar process, energy-rich methane freezes with water beneath the ocean and terrestrial permafrost, a potential source of energy being scrutinized by China, Japan, the U.S. and others.) The new paper on CCS demonstrates through simulation that the hydrates become an impermeable “cap” that keeps the CO2 below it from migrating back up to the sea floor.
Peking University’s carbon capture and storage research receives support from the multinational metals, mining, and petroleum company BHP Billiton Ltd., according to the paper.
The research appears this week in the journal Science Advances. The study should provide some confidence, they write, that ocean CO2 storage remains a viable tool in the push to reduce emissions of the most dangerous heat-trapping gas, even as commercialization of the process remains way off. In the meantime, there are other questions to answer, including how CO2 may behave differently under different kinds of geological conditions.
The big assumption, as with most underground CO2 storage scenarios, is that there’s no telling what the Earth’s living geology will do over the centuries and millennia. Fractures in the subsea sediment, either preexisting or created by tectonics or CO2 injection itself, could open a pathway for CO2 to escape—though significant uncertainty remains.
“In our assumption,” they write, “the unconsolidated marine sediment is intact.”