Deformation bands in high-porosity sandstones: Do they help or hinder CO2 migration and storage in geological formations?

Small-scale deformation bands in Penrith Sandstone are used to assess the extent to which these features can act as effective mini-traps and contribute to secure CO2 geological storage. A comprehensive set of simulation scenarios is applied to one conjugate set of deformation bands and also to clusters of deformation bands, to evaluate the effects of i) deformation band density; ii) the contrast in host rock/deformation band permeability; and iii) deformation band geometry, orientation and distribution on fluid movement and its significance for CO2 storage capacity and security. The findings of this study show that one conjugate set of deformation bands can improve CO2 storage security, depending upon the plunge angle of the hinge. It has also been demonstrated that a high contrast in permeability (at least three orders of magnitude) is necessary for the CO2 to be effectively trapped by the deformation bands. It is shown that the highest number of bands observed and modelled for Penrith Sandstone outcrop, with three orders of magnitude permeability contrast, is a configuration that can contribute to the secure storage of CO2 without causing an injectivity issue. This study shows that storage security is not only controlled by the contrast in permeability, but also by the permeability of the host rock. Furthermore, some geometries may contribute to storage security, while others may compromise it. To improve storage capacity and security for the type of reservoir studied herein, the results demonstrate the importance of accounting for the optimum injection rate and well placement.