Application of spatial correlation functions in permeability estimation of deformation bands in porous rocks

Millimeter-thick strain localization structures in porous sandstones, known as deformation bands, are reported to perturb the permeability structure of petroleum reservoirs and aquifers. However, the internal permeability structure of deformation bands is difficult to assess by means of classical methods. We have used spatial correlation functions to estimate the porosity and specific surface area in deformed sandstones from high-resolution backscatter images. This work demonstrates the use of a modified version of the Kozeny-Carman relation to calculate permeability based on the information obtained from image processing. We have identified anisotropy with regard to petrophysical properties in deformed sandstones, and demonstrated variations in microstructure and properties across and along the deformation bands. Our results show that properties outside the deformation bands (in the host rock) differ significantly from those inside the band (up to three orders of magnitude). Moreover permeability varies by up to two orders of magnitude along a single band. Furthermore, our porosity and permeability estimates are lower than those obtained from plug measurements. While plug measurements measure the effective permeability across a 2.54 cm (inch) long sample, the method demonstrated here provides a means to estimate porosity and permeability on the microscale, and to map out the variations in these properties both along and across deformation bands and similar structures.