The Search for Subtle Stratigraphic Traps with High Resolution Seismic Data: Examples from the Powder River Basin, NE Wyoming, U.S.A.

Optimizing the temporal resolution of seismic data in both the acquisition and processing stages increases the detection rate of subtle, multiple stratigraphic traps in complex lithologic sequences. Field sizes ranging from 1 MMBO to 40 MMBO are found in the coastal facies of eolian sandstone reservoirs of the Permian Minnelusa Formation in northeast Wyoming, U.S.A. Generally, three main trap styles exist: (1) an erosional unconformity providing the top and lateral seals with a shoreline marine carbonate acting as the bottom seal; (2) marine carbonates providing both the top and bottom seals; and (3) topographic relief at the top of dune complexes that lack a bottom seal but are overlain by marine carbonates. Usable frequencies in excess of 100 Hz from depths greater than 3300 m allow resolution of 10 m sandstone reservoirs with 15-20% porosity. With this frequency it is possible to distinguish not only porous sandstone reservoir signatures, but also the trapping mechanisms involved. High resolution seismic data acquired prior to a recent oil discovery is shown here to demonstrate a successful methodology used to discover and develop Minnelusa oil in subtle stratigraphic traps.

Successful exploration in coastal deposits such as the Minnelusa Formation requires an integrated approach to exploration. This includes broad band, high frequency seismic data acquisition and processing with a combined geological and geophysical interpretation. Using these techniques, discoveries are possible even in mature basins at exploratory drilling success rates well above the U.S. onshore industry average of 8-12%.