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Book Chapter

Microstructural controls on the pressure-dependent permeability of Whitby mudstone

By
Rosanne McKernan
Rosanne McKernan
Present address: Shell International Ltd. 40 Bank Street, London E14 5NR, UK
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Julian Mecklenburgh
Julian Mecklenburgh
School of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
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Ernie Rutter
Ernie Rutter
School of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
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Kevin Taylor
Kevin Taylor
School of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
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Published:
January 01, 2017

Abstract

A combination of permeability and ultrasonic velocity measurements allied with image analysis is used to distinguish the primary microstructural controls on effective-pressure-dependent permeability. Permeabilities of cylindrical samples of Whitby mudstone were measured using the oscillating pore-pressure method at confining pressures ranging between 30 and 95 MPa, and at pore pressures ranging between 1 and 80 MPa. The permeability–effective pressure relationship is empirically described using a modified effective pressure law in terms of confining pressure, pore pressure and a Klinkenberg effect. Measured permeability ranges between 3 × 10−21 and 2 × 10−19 m2 (3 and 200 nd), and decreases by approximately one order of magnitude across the applied effective pressure range. Permeability is shown to be less sensitive to changes in pore pressure than changes in confining pressure, yielding permeability effective pressure coefficients (χ) between 0.42 and 0.97. Based on a pore-conductivity model, which considers the measured changes in acoustic wave velocity and pore volume with pressure, the observed loss of permeability with increasing effective pressure is attributed dominantly to the progressive closure of bedding-parallel, crack-like pores associated with grain boundaries. Despite only constituting a fraction of the total porosity, these pores form an interconnected network that significantly enhances permeability at low effective pressures.

Supplementary material: A CSV file containing all experimental conditions and a tabulation of results is available at https://doi.org/10.6084/m9.figshare.c.3785741

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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

GeoRef

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