Modeling Discrete Fracture Networks in the Tensleep Sandstone: Teapot Dome, Wyoming
The Tensleep Sandstone at Teapot Dome, WY is a tight, naturally fractured oil producing reservoir. In this case study, we develop a model of the discrete fracture network in this unconventional reservoir. The observational foundations used to develop the reservoir fracture network include FMI log interpretations, fracture characterization at the surface above the reservoir and examination of Tensleep field analogs. Analysis incorporates 3D seismic interpretation and post-stack processing of a 3D depth-converted seismic volume. 3D seismic enhancement workflows include Ant Tracking on a dip-deviation volume integrated with 3D volume curvature. Ant Track discontinuities are interpreted to represent possible reservoir scale faults and fracture zones. Volume curvature is used to identify areas of increased flexure that are likely to be more intensely fractured. Ant Track discontinuity and volume curvature are combined to produce a single fracture intensity driver that is upscaled into the gridded reservoir model. Areas bounding faults and areas of relatively high bed curvature often correspond to areas of increased fracture intensity. Fracture sets included in the reservoir model are based primarily on FMI log observations. FMI log observations are consistent with fracture data collected from Tensleep exposures along the culmination of the Alcova anticline and also on the NE flank of Granite Mountain anticline. The FMI logs from Teapot Dome reveal three prominent open fracture sets: hinge-oblique, hinge-parallel and hinge-perpendicular sets that are present in the approximate ratio of 4 to 2 to 1, respectively. Teapot Dome is a Laramide structure that developed partly as a forced fold in response to basement uplift and partly through compression resulting in a west-southwest verging fold developed over a steeply dipping east-northeast dipping thrust fault. Open fractures penetrated by the wellbore are about twice as numerous as healed fracture penetrations. The discrete fracture network developed in this process is used to define fracture porosity and permeability distributions throughout the field scale model. The results define pore volume (potential capacity) variations throughout the reservoir and yield insights into potential EOR and CO2 sequestration strategies. The variability of porosity and permeability distribution predicted from the model compare favorably with the variations of oil production localized in the Teapot Dome structural culmination.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California