Pore-scale displacement mechanisms as a source of hysteresis for two-phase flow in porous media Public Deposited

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  • The macroscopic description of the hysteretic behavior of two-phase flow in porous media remains a challenge. It is not obvious how to represent the underlying pore-scale processes at the Darcy-scale in a consistent way. Darcy-scale thermodynamic models do not completely eliminate hysteresis and our findings indicate that the shape of displacement fronts is an additional source of hysteresis that has not been considered before. This is a shortcoming because effective process behavior such as trapping efficiency of CO₂ or oil production during water flooding are directly linked to pore-scale displacement mechanisms with very different front shape such as capillary fingering, flat frontal displacement, or cluster growth. Here we introduce fluid topology, expressed by the Euler characteristic of the nonwetting phase (χ[subscript]n), as a shape measure of displacement fronts. Using two high-quality data sets obtained by fast X-ray tomography, we show that χ[subscript]n is hysteretic between drainage and imbibition and characteristic for the underlying displacement pattern. In a more physical sense, the Euler characteristic can be interpreted as a parameter describing local fluid connectedness. It may provide the closing link between a topological characterization and macroscopic formulations of two-phase immiscible displacement in porous rock. Since fast X-ray tomography is currently becoming a mature technique, we expect a significant growth in high-quality data sets of real time fluid displacement processes in the future. The novel measures of fluid topology presented here have the potential to become standard metrics needed to fully explore them.
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  • Schlüter, S., Berg, S., Rücker, M., Armstrong, R. T., Vogel, H. J., Hilfer, R., & Wildenschild, D. (2016). Pore‐scale displacement mechanisms as a source of hysteresis for two‐phase flow in porous media. Water Resources Research, 52(3), 2194-2205. doi:10.1002/2015WR018254
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  • 52
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  • 3
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  • This research used resources of the Advanced Photon Source which is a DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. We acknowledge the support of GeoSoilEnviroCARS (Sector 13), which is supported by the National Science Foundation Earth Sciences (EAR-1128799), and the Department of Energy, Geosciences (DE-FG02-94ER14466). This research was supported by the US National Science Foundation, award # EAR-1344877. We thank Mark Rivers at the Advanced Photon Source for assistance at the GSECARS beam line, Holger Ott and Apostolos Georgiadis (Shell) for assistance during the fractional flow experiment, as well as Anna Herring and Tianyi Li (OSU) for proving data. The first author is grateful to the Alexander-von-Humboldt Foundation for granting a Feodor-von-Lynen scholarship. Rudolf Hilfer thanks the Deutsche Forschungsgemeinschaft for financial support.
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