Pore space relevant for gas permeability in Opalinus clay : statistical analysis of homogeneity, percolation, and representative volume element

Keller, Lukas M.; Holzer, Lorenz; Schuetz, Philipp; Gasser, Philippe

doi:10.1002/jgrb.50228

Publication type:	Article in scientific journal
Type of review:	Peer review (publication)
Title:	Pore space relevant for gas permeability in Opalinus clay : statistical analysis of homogeneity, percolation, and representative volume element
Authors:	Keller, Lukas M. Holzer, Lorenz Schuetz, Philipp Gasser, Philippe
DOI:	10.1002/jgrb.50228
Published in:	Journal of Geophysical Research: Solid Earth
Volume(Issue):	118
Issue:	6
Page(s):	2799
Pages to:	2812
Issue Date:	Jun-2013
Publisher / Ed. Institution:	Wiley
ISSN:	2169-9313
Language:	English
Subjects:	Map
Subject (DDC):	620.11: Engineering materials
Abstract:	Local porosity theory in combination with percolation theory was applied to shale microstructures that were reconstructed on the basis of focused ion beam nanotomography and scanning transmission electron microscopy. This allowed characterizing pore microstructures in Opalinus clay with length scales on the order of tens of microns. In a sample from the sandy facies (with low clay content), the fraction of “larger” pores ϕ(radii~ > 15 nm) = 0.076 is substantially higher than that in the shaley facies (with a higher clay content), where ϕ(radii~ > 15 nm) = 0.015. The resolved porosity possesses a certain degree of homogeneity, and the representative volume element (RVE) of porosity can be determined in terms of a given relative error on porosity. For example, if we accept a relative error of 10%, the RVE is on the scale of a few hundreds of microns. Both pore microstructures from sandy and shaley facies show anisotropic characteristics with respect to connectivity and percolation threshold. Using finite scaling, we found percolation thresholds with critical porosities ϕc,b = 0.04-0.12 parallel to bedding and ϕc,perp = 0.11-0.19 perpendicular to bedding. The resolved porosity of the sandy facies (low clay content) is close to the percolation threshold, whereas the porosity of the shaley facies (high clay content) is below the percolation threshold. The porosity in carbonate layers is around ϕ = 0.027, and the pore size is substantially larger when compared to the pores in the clay matrix. In the analyzed sample, pores in carbonate layers are poorly connected.
URI:	https://digitalcollection.zhaw.ch/handle/11475/2202
Fulltext version:	Published version
License (according to publishing contract):	Licence according to publishing contract
Departement:	School of Engineering
Organisational Unit:	Institute of Computational Physics (ICP)
Appears in collections:	Publikationen School of Engineering

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Keller, L. M., Holzer, L., Schuetz, P., & Gasser, P. (2013). Pore space relevant for gas permeability in Opalinus clay : statistical analysis of homogeneity, percolation, and representative volume element. Journal of Geophysical Research: Solid Earth, 118(6), 2799–2812. https://doi.org/10.1002/jgrb.50228

Keller, L.M. et al. (2013) ‘Pore space relevant for gas permeability in Opalinus clay : statistical analysis of homogeneity, percolation, and representative volume element’, Journal of Geophysical Research: Solid Earth, 118(6), pp. 2799–2812. Available at: https://doi.org/10.1002/jgrb.50228.

L. M. Keller, L. Holzer, P. Schuetz, and P. Gasser, “Pore space relevant for gas permeability in Opalinus clay : statistical analysis of homogeneity, percolation, and representative volume element,” Journal of Geophysical Research: Solid Earth, vol. 118, no. 6, pp. 2799–2812, Jun. 2013, doi: 10.1002/jgrb.50228.

KELLER, Lukas M., Lorenz HOLZER, Philipp SCHUETZ und Philippe GASSER, 2013. Pore space relevant for gas permeability in Opalinus clay : statistical analysis of homogeneity, percolation, and representative volume element. Journal of Geophysical Research: Solid Earth. Juni 2013. Bd. 118, Nr. 6, S. 2799–2812. DOI 10.1002/jgrb.50228

Keller, Lukas M., Lorenz Holzer, Philipp Schuetz, and Philippe Gasser. 2013. “Pore Space Relevant for Gas Permeability in Opalinus Clay : Statistical Analysis of Homogeneity, Percolation, and Representative Volume Element.” Journal of Geophysical Research: Solid Earth 118 (6): 2799–2812. https://doi.org/10.1002/jgrb.50228.

Keller, Lukas M., et al. “Pore Space Relevant for Gas Permeability in Opalinus Clay : Statistical Analysis of Homogeneity, Percolation, and Representative Volume Element.” Journal of Geophysical Research: Solid Earth, vol. 118, no. 6, June 2013, pp. 2799–812, https://doi.org/10.1002/jgrb.50228.