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Book Chapter

Effects of stress on the anisotropic development of permeability during mechanical compaction of porous sandstones

By
Wenlu Zhu
Wenlu Zhu
Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
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Laurent G. J. Montési
Laurent G. J. Montési
Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
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Teng-Fong Wong
Teng-Fong Wong
Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
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Published:
January 01, 2002

Abstract

To investigate the influence of stress on permeability anisotropy during mechanical compaction, a series of triaxial compression experiments with a new loading configuration called hybrid compression were conducted on three porous sandstones. The effective mean and differential stresses in hybrid compression tests were identical to those in conventional triaxial extension tests. Permeability was measured along the axial direction in both hybrid compression and conventional extension tests, which corresponds to flow along the maximum principal stress direction in the former case and the minimum principal stress direction in the latter case. Since their loading paths coincide, the comparison of permeability values from the two types of tests provides quantitative estimates of the development of permeability anisotropy as a function of effective mean and differential stresses. Our data show that the permeability evolution is primarily controlled by stress. Before the onset of shear-enhanced compaction C*, permeability and porosity reduction are solely controlled by the effective mean stress, with negligible stress-induced anisotropy. With the onset of shear-enhanced compaction and initiation of cataclastic flow, the deviatoric stress induces enhanced permeability and porosity reduction. The permeability tensor may show significant anisotropy. Our data indicate that the maximum principal component of permeability tensor k1 is parallel to the maximum principal stress σ1, and the minimum principal component k3 is parallel to the minimum principal stress σ3. During the initiation and development of shear-enhanced compaction, k1 can exceed k3 by as much as two orders of magnitude. With the progressive development of cataclastic flow, changes of permeability and porosity become gradual again, and the stress-induced permeability anisotropy diminishes as k1 and k3 gradually converge. Our data imply that permeability can be highly anisotropic in tectonic settings undergoing cataclastic flow, inducing the fluid to flow preferentially along conduits subparallel to the maximum compression direction. However, this development of permeability anisotropy is transient in nature, becoming negligible with an accumulation of strain of about 10%. The anisotropic development of permeability in a lithified rock is dominantly controlled by microcracking and pore collapse. This is fundamentally different from the mechanisms active in unconsolidated materials such as sediments and fault gouges, in which the permeability evolution is primarily controlled by the development of fabric and shear localization via the accumulation of shear strain.

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Contents

Geological Society, London, Special Publications

Deformation Mechanisms, Rheology and Tectonics: Current Status and Future Perspectives

S. de Meer
S. de Meer
Utrecht University, The Netherlands
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M. R. Drury
M. R. Drury
Utrecht University, The Netherlands
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J. H. P. de Bresser
J. H. P. de Bresser
Utrecht University, The Netherlands
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G. M. Pennock
G. M. Pennock
Utrecht University, The Netherlands
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Geological Society of London
Volume
200
ISBN electronic:
9781862396081
Publication date:
January 01, 2002

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