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The effect of microstructural heterogeneity on pore size distribution and permeability in Opalinus Clay (Mont Terri, Switzerland): insights from an integrated study of laboratory fluid flow and pore morphology from BIB-SEM images

By
T. Philipp
T. Philipp
Structural Geology, Tectonics and Geomechanics, Energy and Mineral Resources Group (EMR), RWTH Aachen University, Lochnerstrasse 4-20, 52056 Aachen, GermanyInstitute of Geology and Geochemistry of Petroleum and Coal, Energy and Mineral Resources Group (EMR), RWTH Aachen University, Lochnerstrasse 4-20, 52056 Aachen, GermanyPresent address: Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Surface Processes Division, Bautzener Landstrasse 400, 01328 Dresden, Germany
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A. Amann-Hildenbrand
A. Amann-Hildenbrand
Institute of Geology and Geochemistry of Petroleum and Coal, Energy and Mineral Resources Group (EMR), RWTH Aachen University, Lochnerstrasse 4-20, 52056 Aachen, Germany
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B. Laurich
B. Laurich
Structural Geology, Tectonics and Geomechanics, Energy and Mineral Resources Group (EMR), RWTH Aachen University, Lochnerstrasse 4-20, 52056 Aachen, GermanyPresent address: Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, D-30655 Hannover, Germany
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G. Desbois
G. Desbois
Structural Geology, Tectonics and Geomechanics, Energy and Mineral Resources Group (EMR), RWTH Aachen University, Lochnerstrasse 4-20, 52056 Aachen, Germany
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R. Littke
R. Littke
Institute of Geology and Geochemistry of Petroleum and Coal, Energy and Mineral Resources Group (EMR), RWTH Aachen University, Lochnerstrasse 4-20, 52056 Aachen, Germany
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J. L. Urai
J. L. Urai
Structural Geology, Tectonics and Geomechanics, Energy and Mineral Resources Group (EMR), RWTH Aachen University, Lochnerstrasse 4-20, 52056 Aachen, Germany
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Published:
January 01, 2017

Abstract

Opalinus Clay (OPA) is considered as a potential host rock for the deep geological disposal of radioactive waste. One key parameter in long-term storage prediction is permeability. In this study we investigated microstructural controls on permeability for the different facies of OPA. Permeability and porosity were determined under controlled pressure conditions. In addition, the pore space was investigated by SEM, using high-quality surfaces prepared by broad ion beam (BIB) milling. Water permeability coefficients range from 1.6 × 10−21 to 5.6 × 10−20 m2; He-pycnometer porosities range between approximately 21 and 12%. The sample with the highest He porosity (shaly facies) is characterized by the lowest permeability, and vice versa (carbonate-rich sandy facies). This inverse behaviour deviates from the generally reported trend of increasing permeability with increasing porosity, indicating that parameters other than porosity affect permeability. Visible porosities from SEM images revealed that 67–95% of the total porosity resides within pores smaller than the SEM detection limit. Pore sizes follow a power-law distribution, with characteristic power-law exponents (D) differing greatly between the facies. The carbonate-rich sandy facies contains a network of much larger pores (D(shaly)≈2.4; D(carbonate-rich)c. 2.0), because of the presence of load-supporting sand grains that locally prevent clay compaction, and are responsible for a higher permeability.

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Contents

Geological Society, London, Special Publications

Geomechanical and Petrophysical Properties of Mudrocks

E. H. Rutter
E. H. Rutter
University of Manchester, UK
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J. Mecklenburgh
J. Mecklenburgh
University of Manchester, UK
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K. Taylor
K. Taylor
University of Manchester, UK
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The Geological Society of London
Volume
454
ISBN electronic:
978-1-78620-335-9
Publication date:
January 01, 2017

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