Identification of reactivation and increased permeability associated with a fault damage zone using a multidisciplinary approach

Abstract

We evaluate the fault damage zone associated with a reactivated long-strike length, small-offset normal fault in the Permian Cedar Mesa Sandstone, southeastern Utah. This fault is characterized by a single slip surface and a 9-m wide damage zone containing deformation bands and veins. Field observations include cross-cutting relationships, permeability increase, rock strength decrease, and ultraviolet-light-induced mineral fluorescence within the damage zone. These field observations, combined with the interpreted structural diagenetic sequence from petrographic analysis, suggest a deformation history of reactivation and several generations of mineralization. All deformation bands and calcite veins fluoresce under ultraviolet light, indicating fluid pathway connectivity and a shared mineralization history. Pre-existing structures act as loci for younger deformation and mineralization events, so this fault and its damage zone illustrate the importance of the fault damage zone to subsurface fluid flow.We model a simplified stress history to understand the importance rock properties and variations in differential and effective mean stress have on the structures within the damage zone. The moderate confining pressures, possible variations in pore pressure, and porous, fine-grained nature of the Cedar Mesa Sandstone produces a fault damage zone characterized by enhanced permeability and mineralization.