Q&A: Following The Water Flow In Shale

By North American Shale magazine staff | May 15, 2018

Scientists at the U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL) in Tennessee are studying how water moves through shale, as well as other geologic factors they believe can lead to the more efficient extraction of oil and gas.

Victoria DiStefano, ORNL graduate research assistant and an energy science and engineering fellow, recently coauthored a paper published in the Journal of Earth Science on how water uptake occurs in Eagle Ford shale. She and Larry Anovitz, senior research scientist, are also researching shale characteristics—such as fracture characteristics, rock roughness and mineralogy—to determine how they affect interactions within shale formations.

By studying how water flows through the microstructure of fractured rock, the researchers can uncover new information that could improve models for drilling, hydraulic fracturing and underground storage of carbon dioxide. They used neutrons bounced off the hydrogen in water molecules to “see” inside a rock sample without destroying it and to quantify water uptake in real time.

“One of the biggest challenges with shale is that it’s such a complex system,” DiStefano said. “Neutrons help us grasp the complex rock and fracture properties, which determine how quickly water uptake occurs in the rock.”
DiStefano and Anovitz discussed their research with North American Shale magazine and how it can assist the oil and gas industry.

How did the neutron imaging capabilities at ORNL assist your research water movement through shale?
DiStefano: Primarily what got us started is that Oak Ridge has this wonderful capability to use neutrons with the High Flux Isotope Reactor. Neutron imaging is very similar to X-ray imaging. X-rays allow you to easily see metals. Neutrons allow you to easily see water. With this capability, we can see water movement, which allowed us to image or video how water moves through fractures in shale. We were able to quantify the amount over a period of time to show how water is moving into a fracture.

Can you study both naturally occurring fractures and those from fracking?
DiStefano: Yes. The phenomena that we look at is spontaneous imbibition. We don’t apply any pressure; we just allow water to contact an open fracture. That water then imbibes into the fracture.
Anovitz: In other parts of our project, we’ve been looking at things like how acids react with carbonated rich materials. Downhole, producers will often acid-treat the rocks. We’re trying to get some understanding of how that works as well.

Were the results of your research what you expected or were there surprises?
DiStefano: It deviated a bit from what we expected. There are models already out there that try to predict how fluid is going to move through or spontaneously imbibe into shale. What we observed in our experiments is that the models didn’t fit the data precisely. This could be due to dynamic changes in the wetting properties of the rock. As a fluid moves through the rock, it’s affected by changes over time in the roughness of the rock, the fractures, the wetting properties and the different minerals in the rock. The model we were using was for an idealized fracture. It doesn’t take into account rock surfaces or a porous media where water diffuses into the rock. Some of the models need to be better developed to take into account this diffusion.  

Can ONRL’s research in this area help the oil and gas industry extract shale oil and gas resources more efficiently?
Anovitz: Victoria’s work tells industry something about how the properties of the rock around that fracture are going to affect the rate of fluid flow through it. Of course, it’s going to affect the extraction efficiencies. For future work, we’ll be looking at how we can adjust those fractures—if it’s possible—to improve extraction. Producers could actually change the pressures they use for fracturing, how they do the initial perfing and change where and how they do various chemical treatments. One of the things Victoria has done quite a bit of is looking at changes in fluid chemistry and how that affects uptake and how much you change your fracking fluid.

How can someone get access to the results of your research?
Anovitz: Our work is public domain. It’s out there in public for anybody to use who wants to. It’s not proprietary in any way. We have worked with various industry groups and are happy to work with them at any time to try to answer questions that are pertinent in the field. We have other projects being considered and discussed.