The Role of Cataclasis in Shear and Compaction Bands on Water Flow in Porous Sandstone, Provence, France

Determination of membrane seal capacity of deformation bands is a critical problem for the managing of the geologic reservoirs in porous sandstones. In this study, we describe the geometry, the microstructure and the petrophysical properties of two sets of deformation bands: (1) a set of shear enhanced compaction bands and (2) a set of shear bands. At the microscopic scale, the image analysis porosities and the grain size distributions allow us to define three different types of microstructural deformation: crush microbreccia, protocataclastic, and cataclastic. Cataclastic strands are characterized by a porosity reduction of 10% to 25% and permeability reduction of 3 to 5 orders of magnitude compared to the host rock. Field observations of iron hydroxide precipitations around the bands suggest that only cataclastic shear bands were membrane seals to water flow under vadose condition. This study therefore highlights the importance of the degree of cataclasis in deformation bands as membrane seals to subsurface fluid flows in sandstone reservoirs.