Permeability effects of deformation band arrays in sandstone

Abstract

We use established analytical methods and numerical computation techniques to model the net effect on sandstone permeability induced by realistic arrays of low-permeability deformation bands. Our two-dimensional approach, based on homogenization theory, allows the local permeability impact of any deformation band pattern to be calculated and provides a framework within which to extrapolate the effects of systematic patterns to the reservoir-simulation scale. We demonstrate the method for each of three characteristic deformation band patterns—parallel, cross-hatch, and anastomosing—exposed in the Aztec Sandstone at the Valley of Fire, Nevada, which provides an excellent exhumed analog for active sandstone reservoirs. Our analysis indicates that these systematic and extensive deformation band patterns can reduce overall permeability by as much as two orders of magnitude at scales relevant to reservoir production while inducing similar magnitudes of permeability anisotropy. We conclude that accounting for the aggregate effects of deformation bands in the subsurface would significantly improve reservoir simulation and production management in sandstone.