A new study led by scientists at the Chinese Academy of Sciences suggests that CO2 is a better hydraulic fracturing fluid than water. The findings may ultimately lead to a more environmentally friendly form of fracking that could also serve as a way to store atmospheric CO2.
Fracking is a method of injecting water mixed with sand and chemicals into solid rock to extract the resources from within. After the extraction is complete, 30 to 50 percent of the fracking fluid remains in the rock formation. Hydraulic fracturing has been very controversial due to its high water consumption and environmental risks.
“Non-aqueous fracturing could be a potential solution to circumvent these issues,” said study co-author Nannan Sun. “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.”
To investigate whether CO2 may be a more effective alternative to water as a fracking fluid, the researchers collected shale outcrops from China and fractured them with both fluids. The study revealed that CO2 outperformed water, creating complex networks of fractures with significantly higher stimulated volumes.
“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 Sun. “This changes the mechanism by which the fractures are created, generating more complex fracture networks that result in more efficient shale gas production.”
Using CO2 for fracturing would eliminate an excessive amount of water waste, reduce the risk of damage to reservoirs, and would provide an underground repository for captured CO2. However, CO2 from emissions sources is currently too expensive to use as an industry-wide replacement for water.
Next, the researchers plan to test the limits of CO2 fracturing technology to gain a better understanding of how it can be used.
“Further investigations are needed to identify the effects of type of reservoirs, geomechanical properties and conditions, CO2 sensitivity of the formation, and so forth,” said Sun. “Additionally, cooperation with industries will be carried out to push forward the practical deployment of the technology.”
The study is published in the journal Joule.
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