By Mark Lowey
Ice-like “cages” of gas trapped underground may offer a safe and efficient way to reduce global warming.
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.