Surface Mapping Validates 3D Seismic Faulting Interpretations at Teapot Dome Field, Natrona Co., Wyoming

Mark D. Milliken, Rocky Mountain Oilfield Testing Center, 1319 Hornchurch Ave, Casper, WY 82609, phone: 307 261-5161 Ext 5162, fax: 307 261-5817, [email protected] and Timothy J. McCutcheon, Western Interior Natural Resources, 642 North Glenn Road, Casper, WY 82601.

The importance of fault control on production at Teapot Dome Field has been known by workers at NPR-3 since the 1920s. Traditional production-based fault maps provided usable reservoir compartment models during the period of “low hanging fruit.” In the 21st century, Teapot Dome's low hanging fruit is gone, and decisions regarding further development, must be based on subtle information provided by modern technology. The interpretation of a 3D seismic survey acquired in 2000 has yielded a picture of structural complexity far beyond that imagined in the past. Accurate reservoir compartmentalization models are crucial to future EOR and CO2 sequestration projects at NPR-3. Basement-cored faults have been extrapolated to the surface, where mapping and trenching have yielded new ideas on the geometry and sealing nature of fault planes. Seismic data suggest basement-cored faults cross the anticlinal structure obliquely, and exhibit changes in apparent throw directions with decreasing depth. This character suggests a degree of wrenching overprint. The faults splay upward into complex horsetail patterns. On the surface, this geometry is manifested by clusters of sub-parallel normal faults with small, outcrop-scale vertical displacements. Faults projected to the surface are difficult to map in the Steele Shale Formation unless distinctive markers are present. The most useful markers include the Sussex Bentonite and Sandstone Members. Faults are invisible on the surface where marine shale is juxtaposed against marine shale. Diagenetic effects in faults include carbonate fracture fillings, subsequently offset by later fault movement. Subsequent fault movement led to fracturing within the vein-filling material, creating a pathway for oil to seep to the surface from the Shannon Sandstone Member. Trench logging has shown that larger, more laterally extensive fault planes exhibit clay smears dragged up from deeper bentonite layers.