Heterogeneity within deformation bands in sandstone reservoirs

摘要

We have investigated the variation in physical and mechanical properties along cataclastic deformation bands exposed in the damage zone of Moab Fault in Waterfall Canyon, Utah. In our research, we have combined field observations including measurements of thickness, permeability (using a Tiny-Perm II) and rock hardness (using a Schmidt hammer) with laboratory measurements of the elastic modulus of the natural samples and microscopic analysis of the rock. In the study area, total local band thickness can vary from 0.5 mm (a single band) to 60 mm (a cluster of bands) in a short distance (cm). Permeability varies up to two orders of magnitude along the bands and shows an inverse relation with the band thickness. Our ultrasonic laboratory measurements reveal higher elastic moduli within bands than the adjacent undeformed host rock, indicating the dense microstructure of the band attributed to cataclasis and porosity reduction. We have employed different approaches to calculate the propagation energy release rate of the bands and found out that the thickness variation along bands can be attributed to variable tress and propagation energy release along the bands. Based on our calculation, the total propagation energy of a single cataclastic band would be very low (~2. 5 kl/m~2).