Salt Creek: A Prototypical Basement-Involved Thrust-Generated Fold

Stone, Donald S. ¹ (1) Independent Geologist, Littleton, CO

Salt Creek oil field, on the eastern Casper arch, is the largest field in Wyoming measured by its cumulative reserves of oil and oil-equivalent gas of ~800 MM bbls to 2005. The most important, second Wall Creek producing zone, fills the 1500-ft anticlinal closure to the spill point. Discovered in the early 1900s, the field was developed with ~3000 wells and 10 distinct producing zones by 1930. Yet only one east-west structural cross section has appeared in the literature showing the deep structure below the Wall Creek sandstones. In this cross section, the Salt Creek field is interpreted as an unfaulted, asymmetric, concentric anticline, imply ductile folding of basement. As this interpretation is considered improbable, a new interpretation, based on the basement-involved thrust-generated fold model, is presented here. This new interpretation reflects the basic structural geometry seen in many similar anticlines within the foreland province.

Several unusual geologic conditions are found at Salt Creek. These include: 1) multiple, vertically stacked oil pools containing the same Cretaceous-sourced “sweet” oil, 2) overpressuring of most producing zones, 3) a strong heat anomaly over the field, 4) geochemically identical “sour” oils found in the Tensleep pool and Madison Limestone (600 ft stratigraphically below the Tensleep).

Anadarko, new owner of the field, has completed a 3-D survey over the field and initiated a CO₂ enhanced recovery project with an expected yield of ~150 MM bbls over a period of 30 years.

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana