Characterization of deformation bands associated with normal and reverse stress states in the Navajo Sandstone, Utah: Discussion

Abstract

In a recent article about deformation-band networks in Utah, Solum et al. (2010) present the thesis that deformation bands forming in the contractional regime are more areally extensive and not associated with discrete faults, whereas those forming in the extensional regime are generally limited to damage zones around faults. This is an attractive thesis and, insofar as it holds true, of great value for predicting deformation-band distributions in high-porosity sandstone reservoirs. We believe that Solum et al. (2010) touch on an important relationship between tectonic regime and strain distribution and, as geologists, we are constantly looking for simple relationships like this one. However, the authors base their suggestion on very limited data (two scanlines of 16 and 60 m [52 and 197 ft]), comparing localities that differ not only in tectonic regime, but also in tectonic style or boundary conditions as well as petrophysical properties. To add to the reflections of Solum et al. (2010) on how tectonic regime may control deformation-band distribution, we find it appropriate to discuss factors other than tectonic regime that may be at least as important for the characteristics and distribution of deformation bands in deformed porous sandstone reservoirs. Furthermore, their permeability considerations could be improved considering the anisotropic and architectural characteristics of deformation bands and deformation-band clusters. The development of millimeter-thick deformation bands in highly porous sandstone is a fine-scale strain localization phenomenon that closely relates to the local state of stress and material properties at the time of deformation (e.g., Wong et al., 1997; Aydin et al., 2006; Schultz et al., 2010). This is a useful approach, particularly when dealing with deformation bands at the scale of laboratory samples and outcrops. However, the distribution of deformation bands on the hectometer to kilometer scale within a sandstone unit may, in many cases, …