Could Ice-like Cages Be Used To Trap Carbon Dioxide Underground?

Two U of C researchers are investigating the potential for permanently storing carbon dioxide in geological reservoirs, by locking the global-warming gas within solid, cage-like structures called hydrates.

“A main attraction of utilizing hydrates is CO₂ storage, including in some depleted gas reservoirs near oilsands operations in northern Alberta,” says Mehran Pooladi-Darvish, professor of chemical and petroleum engineering in the Schulich School of Engineering.

“Once you get the CO₂ into a reservoir that has the right conditions and it contacts the reservoir water and forms hydrates, it’s in a pretty stable form,” says Jocelyn Grozic, associate professor of civil engineering at Schulich.

The Alberta government has committed $2 billion to develop carbon capture and storage (CCS) projects, to reduce the industrial CO₂ emissions that contribute to global warming and climate change.

CCS technology typically involves capturing emissions at, for example, a coal-fired power plant or an oilsands facility. The CO₂ is then injected underground for storage in a depleted oil and gas reservoir or a saline aquifer, a large formation filled with salt water.

However, carbon dioxide stored this way can take centuries or eons to naturally dissolve into the aquifer water or turn into a solid mineral, Pooladi-Darvish notes.

All during this time, there is a potential risk that the CO₂ could find its way through abandoned well bores or natural fractures and be released at the surface—creating safety or environmental risks.

“But by storing CO₂ in hydrates, you’re essentially turning the gas into a solid,” thereby greatly reducing the risk of leakage, Pooladi-Darvish says.

And it should also be possible, because of the compact geometric structure of hydrates, to pack a lot more CO₂ into this form of storage compared with conventional methods, Grozic says.

Pooladi-Darvish and Grozic’s three-year study, funded by the Natural Sciences and Engineering Research Council, is focused on understanding permeability, or the ability of fluids to flow through CO₂-hydrate reservoirs. In her laboratory, Grozic is able to form hydrates within a small sand sample and then push CO₂ gas through this miniature “reservoir,” enabling her to measure the permeability and stresses. 

Pooladi-Darvish then takes the data from Grozic’s experimental physical model and creates computer simulations of large-scale reservoirs, in which he models larger flow rates and volumes, reservoir pore spaces and various injection and recovery well configurations and operating processes.