Stanley field provides a new model for exploration in the Mission Canyon Formation of the Williston basin. Moreover, it establishes for the first time the economic significance of early mechanical compaction of limestone with implications for both trapping and preservation of primary porosity.

Stanley field is a stratigraphically trapped oil accumulation producing from the Bluell interval of the Mission Canyon Formation. The field, discovered in 1977, lies midway between older established production along the Nesson anticline in the center of the basin and anhydrite stratigraphic traps paralleling the northeast side. There are currently 18 producing wells with the pay interval (maximum thickness, 37 m) cored in 16 wells in and near the field.

At Stanley field, during late Mission Canyon time, low, intertidal-supratidal barrier islands developed along depositional strike, separated laterally by marine channels and shoreward by shallow lagoons. Island sequences were syndepositionally cemented by both freshwater and beach rock-like marine cements whereas marine sequences remained uncemented, and both were overlain by massive anhydrite. Subsequent deposition of the overlying Charles Formation caused progressive mechanical compaction of upper Mission Canyon marine sediments, while cemented island sediments resisted compaction. The distribution of the different depositional facies and their control over subsequent diagenesis resulted in a reservoir formed of porous (primary interparticle porosity) marine grainstone-packstone and fractured, cemented island sediments locally retaining primary fenestral porosity. Trapping is accomplished by combination of overlying massive anhydrite and updip compacted marine (lagoonal) lime mudstone and wackestone.

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