Model-Based, 2-D Seismic Definition of Subthrust Structure in the Uranium Peak Area, Northwest Colorado

Recent exploration on the west flank of the Grand Hogback in northwest Colorado has demonstrated west-directed movement of the White River Uplift on a deep thrust fault, believed to be part of the Yellowjacket Thrust complex. The subthrust Paleozoic section displays easterly dip necessary for structural trapping along the north-south trending Grand Hogback. Porous dolomites in the Redcliff Member of the Mississippian Leadville Formation indicate regional reservoir potential for Mississippian age carbonates in the Piceance Basin and surrounding area. An integrated exploration approach employing model-based, prestack depth migration of 2-D seismic data was utilized to predict the presence of a subthrust Paleozoic section in this frontier area. Iterative velocity models were constructed to approximate the geologic structure prior to drilling, and were used to control velocity and geometric variables during prestack depth migration. Post-drilling analysis, including detailed dipmeter interpretation, proved the pre-drilling depth migration to be a non-unique solution for the geologic section and structure encountered. Post-drilling, prestack depth migrations portray the correct geometry and depth of the subthrust Paleozoic horizons in agreement with well information. Prestack depth migration techniques are outlined to demonstrate the application of this technique in complex structural terrain. Risk reduction through the application of this model-based methodology can be considerable if geologic constraints are properly identified and multiple models are tested.