Reservoir-scale Analysis of Deformation Heterogeneity at the Seal-reservoir Interface in the Entrada Sandstone, San Rafael Desert, Utah

Leslie N. Clayton and James P. Evans
Utah State University, Logan, UT

The mechanical relationship between seal and reservoir is critical to understanding how the seal may leak or be breached. Along with researchers at New Mexico Tech, we investigate the nature of deformation at the interface between seal and reservoir in the Entrada Sandstone near the San Rafael Swell, Utah. The questions we aim to address are: How does seal rupture occur, and what are the sedimentological conditions involved with seal bypass systems? What are the properties of deformation bands and fractures on either side of the interface? How might these properties change laterally? To examine these questions we study multiple field sites, focusing within 2-3 meters of the seal-reservoir interface, as well as tracing faults with several meters of separation through the Entrada Sandstone. Ideal sites have good exposure, and transition from good reservoir to a presumed effective seal. In the initial field survey, we observed iron staining associated with deformation bands at several locations, and calcite diagenetic features that indicate several episodes and chemistries of fluid movement and higher permeability. To quantify current permeability contrast, we obtained in-field TinyPerm II data which show an order of magnitude permeability difference between deformation bands and matrix rock. Future work will include additional structural analysis, in part using high-resolution outcrop and aerial photographs to map and analyze fractures and deformation bands. Fractures and the seal-reservoir contact will be mapped at a larger scale, including a survey of deformation band clusters to identify patterns of band characteristics.

AAPG Search and Discovery Article #90181©2013 AAPG/SEG Rocky Mountain Rendezvous, University of Wyoming, Laramie, Wyoming, September 27-30, 2013