Microstructure and petrophysical properties of deformation bands in high porosity carbonates

Abstract

Deformation bands are one of the most common strain localization structures found in deformed porous rocks. Numerous documented studies on deformation bands in siliciclastics have found that they often experience a reduction in porosity due to pore collapse and cataclasis, as well as post-deformation diagenetic alteration. However, the deformation mechanisms and post-deformation diagenetic processes that affect deformation bands in carbonates are not so well understood. To fill this knowledge gap, deformation bands were studied in porous carbonates from various locations in Europe. The study focused on assessing the deformation mechanisms occurring within deformed carbonates as well as other processes that impact the porosity and permeability of the resulting deformation bands. Varying mechanisms were identified depending on the texture and composition of a host rock, and the stress conditions during deformation. For instance, host rocks dominated by coccoliths, i.e. chalk, appear to be deformed by the collapse of macro-pores within foraminifera, reducing the overall porosity, but having negligible impact on permeability. Conversely, high porosity grainstones deform by multiple mechanisms including: mechanical disintegration of peloids and subsequent aggrading neomorphism, as well as cataclasis. Post-kinematic grain dissolution and cementation are also common in various types of deformation bands.