Shear-enhanced compaction bands formed at shallow burial conditions; implications for fluid flow (Provence, France)

Field observations of highly porous and permeable sandstone in the Orange area (S-E Basin, France) show that networks of shear-enhanced compaction bands can form in a contractional regime at burial depths of about 400 m +/- 100 m. These bands show equal compaction and shear displacements, are organized in conjugate and densely distributed networks, and are restricted to the coarse-grained (mean grain diameter of 0.6 +/- 0.1 mm) and less porous (porosity of 26 +/- 2%) sand layers. The bands are crush microbreccia with limited grain comminution and high grain microfracture density. They show reductions of permeability (mD) ranging from 0 to little more than 1 order of magnitude. They show no control on the alteration products related to meteoric water flow, which suggests that these shear-enhanced compaction bands have no or only negligible influence on subsurface fluid flow. Their selective occurrence and small (20%) reduction in transmissibility in densely populated layers prevented them from compartmentalizing the sandstone reservoirs. A comparison with compaction-band populations in the Navajo and Aztec sandtsones (western U.S.) emphasizes the role of burial depth and the presence of chemical compaction processes for the sealing potential of deformation bands. (C) 2012 Elsevier Ltd. All rights reserved.