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Fall 2019

A New View of Important Shale Rocks

New X-ray technology images shale rocks down to the nanoscale

Michael P. Hoepfner

The United States is expected to become a net energy exporter in 2020 according to the U.S. Energy Information Agency. This is due in large part to advancements in drilling technologies that allow for extraction of the crude oil contained in a type of rock called shale. However, the details of how oil is stored and flows through shale rock are still unclear.

Scientists at the University of Utah are working hard to provide new insight regarding this important rock through an Energy Frontier Research Center, Multi-Scale Fluid-Solid Interactions in Architected and Natural Materials (MUSE). Chen-Luh Lin and Jan D. Miller are pushing the limits of 3-D imaging of shale rock samples, as reported in a new research article published in the journal, Colloids and Surfaces A.

Conventional petroleum production is often depicted in classic cinema by oil shooting out of the ground. This production approach relies on wells where crude oil is stored in rocks that are porous, which allows for the oil to flow readily to the surface. The oil wasn’t formed in the porous rock, but it slowly migrated over the years from a nearby shale rock source. Source rocks contain a complex mixture of oil, gas, minerals, and kerogen. Kerogen is an organic solid that consists of the remnants of ancient plants, animals, and microorganisms that are the sources of fossil fuels.

The complication with shale rock is that the crude oil and gas are trapped in extremely small pores. These pores are so small—only nanometers across—that a red blood cell, which measures only about seven micrometers, couldn’t even dream of squeezing inside. Pores this small drastically slow flow rates and alter the behavior of the oil molecules themselves.

Horizontal drilling and hydraulic fracturing are now used to create artificial fissures in shale rock that allow for a fraction of the oil to be extracted, but much still remains in the ground. To better understand where the oil is located and how it can flow out of shale rock, researchers need a roadmap. The route for oil to navigate its way out of the source rock and into a pipeline involves a tortuous path where bends and turns occur every few nanometers.

Applying their own advances in data processing and analysis, Lin and Miller were able to provide 3-D maps of where the mineral, kerogen, and voids (oil & gas storage) are located and connected at a never-before accomplished resolution, only 20 nanometers.

The shape and surface composition of a pore located in shale rock determined using advances in X-ray computed tomography.

These challenging measurements were collected with X-ray computed tomography (CT)—experimental results that account for partial volume effects to differentiate boundaries between different materials.

These CT scans are theoretically similar to medical CAT scans used in patient diagnosis and treatment. However, Lin and Miller are able to provide insight into the structure of shale rock at a spatial resolution that is approximately 25,000 times improved over medical CAT scans. This valuable new structural insight into the multi-component structure and pore connectivity of shale will allow MUSE researchers to explore how fluids are stored and flow through this important nanoporous material.

With these advancements in instrumentation and 3-D image processing software, the MUSE EFRC is pursuing transformative research into improving the extraction of oil from shale rock and understanding the fundamental behavior of molecules in nano-sized pores. Future studies will use these 3-D structures to model multiphase fluid flow through shale rock with particular attention to the changing regions of different surface composition. While there is still much to be learned about flow through shale rocks, the 3-D structures produced by Lin and Miller open new opportunities to study this important material for the world’s energy future.

More Information

Lin C-L and Miller JD. 2019. “Spatial characterization of heterogeneous nanopore surfaces from XCT scans of Niobrara shale.” Colloids and Surfaces A: Physicochemical and Engineering Aspects DOI: https://doi.org/10.1016/j.colsurfa.2019.03.081

Yen T. 2019. “The United States is expected to export more energy than it imports by 2020.” Today in Energy.

Acknowledgments

The research discussed in this article was supported by the Multi-Scale Fluid-Solid Interactions in Architected and Natural Materials (MUSE) Project, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award #DE- SC0019285.

About the author(s):

  • Michael P. Hoepfner is an Associate Professor of Chemical Engineering at the University of Utah and a Senior Investigator in the MUSE EFRC. He completed his BS degree at the University of Utah and PhD at the University of Michigan, both in chemical engineering. Prof. Hoepfner’s research focuses on the interaction, assembly, and phase behavior of complex molecules in the liquid phase. He and his research team frequently visit national and international facilities labs to perform neutron and X-ray scattering experiments.

     

More Information

Lin C-L and Miller JD. 2019. “Spatial characterization of heterogeneous nanopore surfaces from XCT scans of Niobrara shale.” Colloids and Surfaces A: Physicochemical and Engineering Aspects DOI: https://doi.org/10.1016/j.colsurfa.2019.03.081

Yen T. 2019. “The United States is expected to export more energy than it imports by 2020.” Today in Energy.

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.