Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Displacement-length data from dilatant fractures (joints, veins, igneous dikes) and several varieties of deformation bands were analyzed statistically to investigate the applicability of mechanical models proposed for their formation. All 17 datasets are generally consistent with equilibrium or long-term power-law slopes on the displacement-length diagram of either 1.0 or 0.5. Similar to many faults, disaggregation deformation bands are consistent with a power-law scaling relation having a slope of approximately c = 1, implying a linear dependence of maximum displacement and discontinuity length (Dmax = γL). In contrast, dilatant fractures, cataclastic deformation bands, and shear-enhanced compaction bands are consistent with a power-law scaling relation with a slope of approximately c = 0.5, implying a dependence of maximum displacement on the square root of length (Dmax = αL1/2). The scaling relations represent an average, or long-term equilibrium outcome of deformation for conditions such as length-scale, time-scale, temperature, chemistry, and an effectively homogeneous far-field stress field, allowing for variations such as rapid and/or localized behaviors. The displacement-length scaling of these geologic structures follows systematic relationships that provide information on host-rock properties and the physics of fracture and deformation-band propagation.
ISSN: 0191-8141

hal-00818130
https://hal.archives-ouvertes.fr/hal-00818130
DOI : 10.1016/j.jsg.2012.12.005

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
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.
ISSN: 0191-8141

hal-00807309
https://hal.archives-ouvertes.fr/hal-00807309
DOI : 10.1016/j.jsg.2012.11.008

Éditeur(s) : HAL CCSD Geological Society of America
Résumé : International audience
Porous sandstones tend to deform by the formation of low-permeability deformation bands that influence fluid flow in reservoir settings. The bands may be distributed or localized into clusters, and limited recent data suggest that tectonic regime may exert control on their distribution and clustering. In order to explore this suggestion, we performed a synthetic analysis based of 73 sets of bands, including 22 new sets measured for a reverse Andersonian regime that fill the important gap in data for this context. We find a surprisingly strong correlation between clustering and tectonic regime, where bands clearly are more distributed in the reverse regime compared to the normal regime. Together with the observed band distributions, capillary pressure data show evidence that efficient membrane seals are expected for extension, whereas pervasive permeability anisotropy is expected for contraction. Such a basic new rule concerning tectonic regime is very useful for assessment of reservoir properties where deformation bands are common but below seismic resolution.
ISSN: 0091-7613

hal-01355925
https://hal.archives-ouvertes.fr/hal-01355925
DOI : 10.1130/G37585.1

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Improving the prediction of sub-seismic structures and their petrophysical properties is essential for realistic characterization of deformed sandstone reservoirs. In the present paper, we describe permeability contrasts induced by cataclastic deformation bands and faults in porous sandstones (766 data synthesized from field examples and the literature). We also discuss the influence of several factors, including tectonic regime, presence of a fault, burial depth, host sandstone porosity, and grain size and sorting for their initiation and permeability. This analysis confirms that permeability decrease is as a function of grain-crushing intensity in bands. Permeability reduction ranges from very limited in crush-microbreccia of compaction bands to high permeability reduction in cataclasites and ultracataclasites of shear-dominated bands, band clusters and faults. Tectonic regime, and especially normal-fault regime, with its tendency to localize strain and generate faults, is identified as the most important factor, leading to the formation of cataclastic bands with high permeability contrasts. Moreover, moderate burial depth (1–3 km) favors cataclastic bands with high permeability contrasts with respect to the host sandstone. High porosity, coarse-grain size and good grain sorting can slightly amplify the permeability reductions recorded in bands.
ISSN: 0191-8141

hal-01218408
https://hal.archives-ouvertes.fr/hal-01218408
DOI : 10.1016/j.jsg.2015.03.013