Hydraulic fracturing, or fracking, has become an increasingly widespread method of natural resource extraction—but it has been criticized as damaging to the environment. A team of researchers have developed a solution that could make the process greener—a solution that could also capture atmospheric CO2 in the process.
Fracking extracts resources from shale rock by injecting fluids—usually water mixed with sand and other materials—into the rock, fracturing it to release the resources trapped inside. But roughly 30 to 50 percent of the millions of liters of fluid injected is left behind in the rock after extraction, making it an environmentally-damaging form of energy resource harvesting.
The high water consumption, contamination concerns and frequent production problems have led to criticism from the extraction industry and environmentalists. But researchers from the Shanghai Advanced Research Institute at the Chinese Academy of Sciences suggest using carbon dioxide instead of water to reduce or eliminate those concerns.
Using CO2 eliminates the need for a massive water supply—reducing the pressure on water resources such as reservoirs and opening arid locations for fracking. It also creates underground storage capacity for captured CO2.
The team studied the differences between using water and CO2 on a microscopic level by fracking samples of shale from outcrops in Chongqing, China. The result: CO2 outperformed water, creating complex networks of fractures that led to higher volumes of extracted shale gas.
However, once CO2 has been injected in the fracture, it has low viscosity that limits its ability to carry sand to the fractures: the sand is needed to wedge open the fractures to extract the shale gas. The team recognized the need to improve the viscosity of the CO2 while keeping costs in check and minimizing the effect on the environment.
“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,” said researcher Nannan Sun. “This changes the mechanism by which the fractures are created, generating more complex fracture networks that result in more efficient shale gas production.”
The researchers believe that this technology could be scalable. But that possibility is hampered by the scarcity of captured CO2 on the market—which can be too expensive to make the technique economically viable today.
The team is currently studying the limits of CO2 fracking technology in the hopes of better understanding how it can be deployed. They also intend to collaborate with the industry to develop a way to make the technology more practical and more affordable.
If they are successful, CO2-based fracking could have a profound effect on the resource extraction industries—and on the environment.
Read more about fracking at Fracking explained: opportunity or danger.