Petrophysical Properties of Deformation Band Fault Zones in the Entrada Sandstone, Utah
Deformation band networks can inhibit fluid flow in permeable reservoir sandstones. Understanding the petrophysical qualities and developing geophysical methods to detect deformation bands is important to the petroleum industry, especially regarding reservoir characterization and modeling. This study analyzed the directionally dependent ultrasonic compressional and shear wave velocity of deformation bands and host rock at the core sample and meter scales. The meter scale was used as a proxy for sonic logging data collection, which is typically at a similar scale of investigation, and addresses how well we can upscale velocity data from cores to the sonic logging scale. In situ high frequency velocity studies of variable facies within the Slickrock Member of the Entrada Sandstone and cores with deformation bands provides insight into whether and how well variably dense deformation band networks can be detected in the subsurface in log and seismic data. Combining the measured velocities of different facies within the outcrop, a connection between deformation band character and width of damage zone was made between facies and velocity signature. The tested fluvial units contained deformation bands that appeared at 10% of the frequency and only extended 50% of the distance away from the fault compared to the Aeolian facies. Fluvial units had measured unconfined outcrop velocities of 1000-1100 m/s, whereas the Aeolian units' velocities were clustered around 800 m/s. A link between facies velocity and damage zone width and character can help determine the sealing or leaking nature of a damage zone surrounding a fault through a volume assessment of individual facies and their combined impact on fluid flow.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013