Computer simulations offer insight on the physics of fracking

By Patrick C. Miller | May 02, 2017

Researchers at the Idaho National Laboratory (INL) have developed computer simulations that further the understanding of the physics of oil and gas trapped within shale formations and could lead to more efficient extraction techniques.

The simulations are unique in that they require far less computing power than other methods and incorporate high-resolution shale sample imagery. The research is described in an article published Tuesday in the Physics of Fluids journal from AIP Publishing.

Yidong Xia, an INL computational scientist, said that although the physics of extracting oil from more porous rock is well understood, the pore structure of shale creates a more complex problem.

"The difficulty is that the pore size is very small, and most of them are scattered—they’re isolated," he explained. "So if you can fill part of the pores with water, there's no way it can move into other pores."

While hydraulic fracturing can create cracks that connect the pores, Xia said oil and gas companies are essentially working in the blind without a solid understanding of the pore distribution and structure of the shale.

To better understand the physics involved in fracking, researchers have used computer simulations with limited success. When pores are large, fluid moves as a smooth continuum and models can treat it as such. But with nanoscale pores in shale, the fluid acts more like a collection of particles.

Xia and his colleagues used what's known as a coarse-grain approach. They modeled the fluid as a collection of particles in which each particle represents a cluster of a few molecules. This dramatically cuts down on the amount of computational power needed to run the simulation.

The incorporation of high-resolution imagery of shale samples has also contributed to better understanding the physics of fracking in oil shale formation. Researchers at the University of Utah used focused ion beam scanning electron microscopy on a piece of Woodford shale a few millimeters in diameter.

This method cuts through the sample, scanning each slice to generate a 3-D image of the rock and its detailed pore structure at the nanometer scale. The images are then fed into the computer model to simulate fluid flow through the scanned nanostructures.

"The combination (of microscopy and simulations) is what really produces meaningful results," Xia said.

He added that these types of simulations alone won't revolutionize shale oil and gas extraction because a broader understanding of the entire structure of the shale fomation is needed. However, Xia noted that having multiple samples throughout the shale on which to run the computer simulations would result in greater insight into the physics involved in oil and gas extraction.