UW Researchers Enhance Understanding of Hydrocarbon Phase Behavior in Mowry Shale Nanopores

Research recently conducted at the University of Wyoming’s Phase Behavior of Nanoconfined Fluids Lab provides new insight into how hydrocarbons behave when confined within shale nanopores. The work aims to improve understanding and prediction of fluid phase behavior in unconventional reservoirs.

The paper, titled “Phase Transition and Pore Criticality in a Natural Nanoporous Medium: Adsorption-Desorption and Calorimetry Experimentation and Equation-of-State Representation,” investigates the phase behavior of propane confined in Mowry Shale using adsorption-desorption measurements, differential scanning calorimetry and thermodynamic equation-of-state representation. The paper was published Sept. 23 in Physical Chemistry Chemical Physics, a leading journal of the Royal Society of Chemistry.

Funded under the competitive Mowry Shale proposal opportunity through the School of Energy Resources (SER), the study was written by Ephraim Kakra Owusu-Banahene, a Ph.D. candidate in UW’s Department of Energy and Petroleum Engineering, along with Morteza Dejam, an associate professor in UW’s Department of Energy and Petroleum Engineering, School of Computing and Hydrologic Science Interdisciplinary Program, and Hertanto Adidharma, a professor emeritus in UW’s Department of Chemical and Biomedical Engineering.

“Shale formations contain extremely small pores, often only a few nanometers in size. Fluids confined within these pores behave differently from the same fluids in larger, unrestricted environments,” Owusu-Banahene says. “These confinement effects alter important properties, such as phase transition temperatures and pressures, making conventional descriptions of bulk fluid behavior potentially inadequate for fluids stored in unconventional reservoirs. While several works have looked at phase behavior and criticality in synthetic nanopores, transitioning findings to shale samples remained challenging for a variety of reasons.”

During its research, the team combined adsorption-desorption measurements, differential scanning calorimetry and thermodynamic modeling to investigate propane phase behavior in Mowry Shale. The two experimental methods showed closely agreeing capillary evaporation conditions, after which the three-line approach was used to determine the pore critical point.

Unlike results commonly reported for pure fluids in synthetic nanoporous materials, the pore critical point of propane in Mowry Shale exceeds the bulk critical conditions. The finding shows that natural shale can exhibit phase behavior that differs from idealized synthetic systems and highlights the importance of directly studying confined fluids in natural porous media.

“While the energy sector continues to diversify, oil and gas will remain an important part of Wyoming’s energy landscape for years to come, making it essential to improve our understanding of unconventional resources, such as Mowry Shale,” says Tim Fischer, oil and gas program manager in SER’s Center for Economic Geology Research, and lead of the Mowry Shale Project. “By studying how hydrocarbons behave within its nanoscale pore structure, this work can contribute to better characterization of the formation and, ultimately, to more informed approaches to evaluating and developing shale resources in Wyoming and beyond.”

The findings provide a foundation for further investigation of confined fluid behavior in shale and other natural nanoporous materials, where complex pore structures, mineralogy and surface properties may influence phase behavior.

To read the full paper, go to https://doi.org/10.1039/d6cp02502a.