Foam could offer greener option for petroleum drillers

John Sullivan ・ Engineering Communications

Hydraulic fracturing, or fracking, uses large amounts of fresh water while producing corresponding amounts of wastewater. Water-based foams, which use about 90 percent less water than fracking fluids, could provide an alternative, but the mechanism for foam-driven fracture is not well understood.

Now, Princeton researchers led by PEI associated faculty Howard Stone, the Donald R. Dixon ’69 and Elizabeth W. Dixon Professor of Mechanical and Aerospace Engineering, have experimentally tested a detailed description of foam’s fracturing behavior. The research, which was supported by the Princeton Environmental Institute’s Mary and Randall Hack ’69 Graduate Fund and Carbon Mitigation Initiative, was published July 26 in the journal Proceedings of the National Academy of Sciences.

Foam, or gas bubbles suspended in a liquid, are compressible, while liquids are not. In typical hydraulic fracturing, incompressible fluid is injected at high pressure to fracture the shale reservoir. When compressible foams are injected, their behavior is more complex. Pressure applied to foam causes bubbles to squeeze and expand, creating changes throughout the foam.

Using a tabletop setup, the researchers simulated fracking using a common foam (shaving cream) injected into a gelatin-filled chamber. The experiment, which mimics fracking conditions, allowed them to study parameters such as injection rate and fluid viscosity. The researchers used the data to produce a detailed description of compressible foam’s impact on fracturing.

“The foam we use here consists [of] only about 10 percent of the water by volume,” said first author Ching-Yao Lai, who received a 2016 Hack Graduate to support the research. “The majority of the space in foams is taken up by gas bubbles. The use of foams significantly changes the dynamics of fracture propagation compared to the standard cases with water injection.

“Foam fracturing has been developed in Canada to minimize the use of water and other environmental issues caused by the water injection. This motivates us to develop a system to study the physics behind fracturing with foams,” said Lai, who received her doctorate in mechanical and aerospace engineering from Princeton this spring.

The researchers said the analysis can be extended to other flow systems that use compressible foams such as firefighting and energy storage.

“This project allowed us to study a little-studied aspect of fluid-driven fracture,” Stone said. “It also allowed us to develop new insights relevant to other poorly understood foam flows, which we hope to study in the future.”

In addition to Stone and Lai, the paper’s authors include: Bhargav Rallabandi and Antonio Perazzo, postdoctoral researchers at Princeton; Zhong Zheng, who received his doctorate at Princeton and is now a researcher at Cambridge University; and Samuel Smiddy, who graduated with a degree in chemical and biological engineering from Princeton this year. Support for the work also was provided the National Science Foundation and the Maeder Graduate Fellowship of the Andlinger Center for Energy and the Environment.