Abstract

Located on the eastern Casper Arch, the Salt Creek Anticline provides the trap for the giant Salt Creek Field, the largest oil field in Wyoming. The Upper Cretaceous 2nd Wall Creek Sandstone (at ~1400 to ~2800-ft drill depths) is the most important Salt Creek producing zone, accounting for two-thirds of the ~800 million barrels of total cumulative oil and oil-equivalent gas produced through 2005. Fifteen hundred feet of vertical closure on this producing zone is filled to the spill point with sweet crude oil. Discovered in the early 1900s, the field was developed with ~3000 wells producing from 10 distinct zones by 1930. Yet only one west-east structural cross section has appeared in the literature showing the deep structure below the Wall Creek producing zones. In this cross section, the Salt Creek Field is interpreted as an unfaulted, asymmetric, concentric anticline showing crystalline basement and the Phanerozoic cover folded conformably without associated faulting. Because this interpretation is considered unlikely, a new interpretation, based on the basement-involved thrust-generated fold model, is presented here. This new interpretation displays the basic structural geometry observed in many similar anticlines throughout the foreland province.

The following unusual geologic conditions are found at the Salt Creek Oil Field: 1) multiple, vertically stacked oil pools through the Mesozoic section; 2) overpressuring in most producing zones; 3) a strong heat-flow anomaly over the field; and 4) essentially identical sweet oil is found in all Mesozoic pools, while an essentially identical sour oil is found in the Pennsylvanian Tensleep (Minnelusa) pool and in the Mississippian Madison about 600 ft stratigraphically below the Tensleep.