Energy release rate of propagating deformation bands and their hosted cracks

• Elastic moduli of cataclastic bands.
• Propagation energy release rate for cataclastic bands.
• Propagation energy release rate for different modes of crack within cataclastic bands.
• Maximum crack length within a cataclastic band prior to the propagation of the band.

Cataclastic bands and their mechanical properties within two mineralogically different sandstones have been studied. In order to investigate the propagation energy of these bands, we have used dynamic elastic moduli calculated from laboratory measurements of ultrasonic velocities using a portable ultrasonic measuring system. As a product of cataclasis and compaction, elastic moduli (uniaxial compressive and shear moduli) of the bands are different from their corresponding host rocks leading to heterogeneity and anisotropy within sandstone reservoirs. Poisson's ratio decreases in the cataclastic bands of sandstone with high quartz content as a result of compaction, while it increases within cataclastic bands of sandstone with high clay and phyllosilicate content (more than 30%). Using the calculated propagation energy rates, we investigate which mode of deformation can be more dominant in the setting of our samples, propagation of deformation band as a result of strain hardening within the cataclastic band or crack propagation inside the deformation band due to strain softening prior to the propagation of band. We further estimate the maximum length of cracks inside a deformation band which can precede further growth of the deformation band.