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Abstract

AAPG Bulletin, V. 96, No. 11 (November 2012), P. 21672186.

Copyright copy2012. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/04051211097

The importance of the degree of cataclasis in shear bands for fluid flow in porous sandstone, Provence, France

Gregory Ballas,1 Roger Soliva,2 Jean-Pierre Sizun,3 Antonio Benedicto,4 Thibault Cavailhes,5 Suzanne Raynaud6

1Unite Mixte de Recherche Centre National de la Recherche Scientifique 5243 Geosciences Montpellier, Universite de Montpellier 2, Unite de Formation et de Recherche Sciences et Techniques, Place Eugene Bataillon, Montpellier Cedex 5, France; [email protected]
2Unite Mixte de Recherche Centre National de la Recherche Scientifique 5243 Geosciences Montpellier, Universite de Montpellier 2, Unite de Formation et de Recherche Sciences et Techniques, Place Eugene Bataillon, Montpellier Cedex 5, France; [email protected]
3Unite Mixte de Recherche Centre National de la Recherche Scientifique 6249 Chrono-Environnement, Departement Geosciences, Unite de Formation et de Recherche Sciences et Techniques, Universite de Franche-Comte, 16 Route de Gray, Besancon Cedex, France; [email protected]
4Areva Nuclear Cycle, Business Unit Mines Direction Geosciences, La Defense, Paris, France; [email protected]
5Unite Mixte de Recherche Centre National de la Recherche Scientifique 5243 Geosciences Montpellier, Universite de Montpellier 2, Unite de Formation et de Recherche Sciences et Techniques, Place Eugene Bataillon, Montpellier Cedex 5, France; [email protected]
6Unite Mixte de Recherche Centre National de la Recherche Scientifique 5243 Geosciences Montpellier, Universite de Montpellier 2, Unite de Formation et de Recherche Sciences et Techniques, Place Eugene Bataillon, Montpellier Cedex 5, France; [email protected]_montp2.fr

ABSTRACT

Determination of the membrane seal capacity of deformation bands is critical for managing geologic reservoirs in porous sandstones. In this study, we have analyzed a cataclastic shear-band network developed in uncemented porous sandstone in Provence, France. Geometrical analyses of the bands show significant differences between three types of bands (single strand, multistrand, and band cluster), sorted by their number of strands, their amount of shear displacement, and their thicknesses. At the microscopic scale, the image-analysis porosities and the grain-size distributions allow definition of three different types of microstructural deformation: damage zone, protocataclastic, and cataclastic. Whereas damage zone and protocataclastic deformations are observed in each type of band, cataclastic strands are observed in clusters and, sometimes, in multistrands. Cataclastic strands are characterized by a porosity reduction of 10 to 25% and a permeability reduction of three to five orders of magnitude compared to the host rock. Field observations of iron hydroxide precipitations around the bands suggest that cataclastic strands were membrane seals to water flow under vadose condition. This study therefore highlights the importance of the degree of cataclasis in shear bands as membrane seals to subsurface fluid flows in sandstone reservoirs.

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