Chinese scientists say CO2 may make a better hydraulic fracturing fluid than water.

The finding could help pave the way for a more eco-friendly form of fracking that would double as a mechanism for storing captured atmospheric CO2.

In normal fracking operations, fluid (usually water mixed with sand, foaming agents, biocides, and other chemicals) is injected into rock, fracturing it to release the resources within.

Of the approximately 7-15 million litres of fluid injected, 30 to 50 per cent remains in the rock formation after extraction ends.

Its high water consumption, environmental risks, and frequent production issues have led to concerns about fracking among both industry experts and environmental advocates.

“Non-aqueous fracturing could be a potential solution to circumvent these issues,” says Professor Nannan Sun, a researcher in the Shanghai Advanced Research Institute at the Chinese Academy of Sciences.

“We chose CO2 fracturing from a range of options because the process includes multiple benefits. However, we were still lacking a fundamental understanding of the technology, which is greatly important for its further development and deployment.”

Benefits of CO2 fracturing include eliminating the need for a hefty water supply (which would make fracking viable in arid locations), reducing the risk of damage to reservoirs (as often happens when aqueous solutions create blockages in the rock formation), and providing an underground repository for captured CO2.

“We demonstrated that CO2 has higher mobility than water, and, therefore, the injection pressure can be better delivered into the natural porosity of the formation,” Prof Sun says.

“This changes the mechanism by which the fractures are created, generating more complex fracture networks that result in more efficient shale gas production.”

While the researchers believe this hydraulic fracturing technology will be scalable, its large-scale development is currently limited by CO2 availability.

The cost of CO2 captured from emission sources is still prohibitively expensive to make CO2 an industry-wide fracking fluid replacement.

The team also notes that once CO2 has been injected into the fracture, it acquires a low viscosity that inhibits it from effectively transporting sand to the fractures. Since the sand is intended to prop open the fractures while shale gas is harvested, it is critical that scientists learn to improve the fluid's viscosity.

The team is not yet sure how to do so while keeping costs low and minimizing the environmental footprint.

Their latest study is accessible here.