Researchers’ new model provides insights into improved fracking

By Patrick C. Miller | March 22, 2017

Chinese researchers believe they might have a better method for accurately modeling the effects of hydraulic fracturing in rock formations.

Two scientists at China’s Northeast Petroleum University this week released their findings in the Applied Physics Letters journal from AIP Publishing. Yikun Liu, a professor at the university, and Angi Shen, a doctoral student, co-authored an article on modelling capillary rise in nano-channels with inherent surface roughness. Although their research has other applications, it focused primarily on the oil and gas industry.

Shen said scientists often rely on the century-old Lucas-Washburn equation to calculate the expected level of capillary rise in tiny cracks created during the fracking process. However, she explained that that the equation has not been completely accurate in predicting the actual rise observed in nano-capillary laboratory experiments.

“The height of the capillary rise that was observed in these experiments was lower than what the Lucas-Washburn model would have predicted,” Shen noted.

As a result, researchers focused on understanding what caused the deviation.

“We looked at many factors and found that the surface roughness of the capillaries was the main reason for the lower-than-expected result,” Shen said. “Specifically, we realized that the model could better determine the actual level of capillary rise if we adjusted the parameters to account for the frictional drag that is caused by the inherent roughness of the surface of the capillary walls. When we saw how this made the model more accurate, we knew that we could not ignore it.”

The miniscule size of the capillaries means that even small increases in surface roughness can have a significant impact on calculations.

“Factors that might be ignored in normal conditions can have significant effects on a micro or nano level,” according to Shen.

The researchers—whose work is partially funded by the Major Projects Program for the National Science and Technology of China—studied a variety of explanations for the lower-than-expected capillary rise.

“One area of discussion has focused on the viscosity of the fluid,” Shen said. “Another has been the sticky layers of oil that form on the walls of the capillaries and narrow their diameter, which is an issue that we have also explored.”

Because just a few labs are conducting nano-capillary rise experiments, Shen and her colleagues could work only with the results from one laboratory in the Netherlands. They intend to verify their mathematical formula by examining its effectiveness at simulating the results of other experiments.

“Capillary rise is a basic, physical phenomenon that occurs in soil, paper and other biologically relevant realms,” Shen said. “Understanding how it is potentially affected at the nano-capillary level by frictional drag could shed light in a variety of scientific disciplines.”