CHARACTERIZATION OF SHALLOW EXTENSIONAL FAULTING IN A COMPRESSIONAL LARAMIDE STRUCTURE: TEAPOT DOME, WYOMING

Teapot Dome is a doubly plunging anticline, formed during the Laramide orogeny. It is one of several structures aligned along a northwest to southeast trend in the southern end of the Powder River Basin. The structure consists of an asymmetric fold with a steep flank on the west, bounded by a deep seated blind reverse fault. Over 1300 wells have been drilled into the structure providing an extensive database to work from. Previous work at Teapot Dome identified a series of normal faults in the shallow units that cross the structure almost perpendicular to the axis of the anticline. Recent work, including seismic interpretation, well log correlation, and surficial mapping, has provided new understanding the faulting geometry. This work has shown that there is a very complicated network of normal faulting and fracturing that significantly influences oil production. In many cases, the faults do not line up in a sub-parallel array as interpreted previously. Instead, many of the larger normal faults cross the field in a curvilinear manner. The shallow faults also appear to die out off of the flanks of the anticline, suggesting that faulting was a result of transpressional stresses associated with anticlinal folding. The deeper faults existed prior to Laramide deformation and may have been active during deposition of the lower Cretaceous units. These deeper faults may have contributed to a distinct change in the trend of the anticlinal axis that formed during Laramide deformation and most likely are related to pre-existing structural weaknesses in the basement.