How fluids flow through shale

May 2, 2017
The pore network of the Woodford shale sample (left) and the fluid that fills the pores according to the computer model (right). Credit: Yidong Xia

Most of the world's oil and natural gas reserves may be locked up inside the tiny pores comprising shale rock. But current drilling and fracturing methods can't extract this fuel very well, recovering only an estimated 5 percent of oil and 20 percent of gas from shale. That's partly due to a poor understanding of how fluids flow through these small pores, which measure only nanometers across.

But new computer simulations, described this week in the journal Physics of Fluids, can better probe the underlying physics, potentially leading to more efficient extraction of oil and gas.

With more porous rocks like sandstone, where the pores are as big as a few millimeters, oil and gas companies can more easily extract the fuel by injecting water or steam into the ground, forcing out the oil or gas.

"Their physical characteristics are well understood," said Yidong Xia, a computational scientist at Idaho National Laboratory. "There are a lot of well-calibrated mathematical models to design the engineering tools for extracting the oil."

But that's not the case for shale.

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

Hydraulic fracturing can create cracks that connect those pores, but without a solid understanding of the pore distribution and structure of the shale, oil and gas companies are working blind.

To better understand the physics of how fluids like water, oil and gas flow through such tiny pores, researchers have increasingly turned to computer simulations. Yet those too have been limited. When pores are large, 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.

In principle, a computer can simulate the behavior of every individual molecule that makes up the fluid, Xia said. But that would take too much computing power to be practical.

Instead, Xia and his colleagues used what's called 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 how much computational muscle is needed.

What also sets these new results apart is the incorporation of high-resolution imagery of shale samples. Researchers at the University of Utah used focused ion beam scanning electron microscopy on a piece of Woodford shale a few millimeters in diameter. The in this method cuts through the sample, scanning each slice to generate a 3-D image of the rock and its detailed structure at the nanometer scale. Those 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.

Still, these kinds of simulations alone won't revolutionize and gas extraction, he said. You would need a broader understanding of the entire structure of the shale, not just small samples. But, he said, you could take multiple samples throughout the shale and run computer simulations to gain more insight into its physics.

To be clear, Xia added, they're not endorsing any particular technology or energy source. As researchers, their focus is to simply better understand the basic physics of shale.

Explore further: Team takes deeper look at unconventional oil and gas

More information: "Many-body dissipative particle dynamics modeling of fluid flow in fine-grained nanoporous shales," Physics of Fluids May 2, 2017. DOI: 10.1063/1.4981136

Related Stories

Team takes deeper look at unconventional oil and gas

February 9, 2017

Understanding how oil and gas molecules, water and rocks interact at the nanoscale will help make extraction of hydrocarbons through hydraulic fracturing more efficient, according to Rice University researchers.

New research aims to improve natural gas production

April 27, 2011

Natural gas is an abundant energy resource for the United States, but much of it remains trapped in shale or tight-sand formations. Researchers at Missouri University of Science and Technology hope to develop a way to extract ...

Can we accurately model fluid flow in shale?

January 4, 2013

(Phys.org)—Given that over 20 trillion cubic meters of natural gas, a third of the United States' total reserves, are thought to be trapped in shale, and given the rush to exploit shale oil and gas resources by Australia, ...

Recommended for you

Carefully crafted light pulses control neuron activity

November 17, 2017

Specially tailored, ultrafast pulses of light can trigger neurons to fire and could one day help patients with light-sensitive circadian or mood problems, according to a new study in mice at the University of Illinois.

Strain-free epitaxy of germanium film on mica

November 17, 2017

Germanium, an elemental semiconductor, was the material of choice in the early history of electronic devices, before it was largely replaced by silicon. But due to its high charge carrier mobility—higher than silicon by ...

New imaging technique peers inside living cells

November 16, 2017

To undergo high-resolution imaging, cells often must be sliced and diced, dehydrated, painted with toxic stains, or embedded in resin. For cells, the result is certain death.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

ski137
not rated yet May 02, 2017
Can we just let it go? The age of CH4 combustion should be over.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.