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Source of Shallow Simpson Group Oils in Murray County, Oklahoma

I. Zemmels, D. M. Tappmeyer, C. C. Walters

Oils produced from the Simpson Group (Middle Ordovician) in three shallow fields located north of the Arbuckle Mountains in Murray County, Oklahoma, have widely differing compositions: SW Sandy Creek, 28.9° API, 0.57°% sulfur; Davis NE, 25.9° API, 0.72% sulfur; Sulfur NW, 16.4° API, 1.44% sulfur. From gas chromatography and biomarker analysis, we determined that the oils were derived from the same source and that the differences in composition are due to biodegradation of the oils in the shallow reservoirs. A comparison of the biomarker assemblage of the Simpson Group oils to several other oils produced in the Arbuckle Mountain area showed that the Simpson Group assemblage highly resembled the assemblage of a Woodford Formation oil (Devonian) but had n similarity to a Viola Formation oil (upper Middle Ordovician). The Simpson Group oils also differed markedly from an oil produced from the Arbuckle Group (Lower Ordovician) in the nearby, shallow Southeast Hoover field.

Our data suggest that the source of the shallow Simpson Group oils is the Woodford Formation located in the downthrown Mill Creek syncline south and west of these oil fields. A large vertical migration along faults or within the fault block is implied by this geometry. However, the Arbuckle Group oil from the Southeast Hoover field, south of the syncline, has a different source.

AAPG Search and Discovery Article #91037©1987 AAPG Southwest Section, Dallas, Texas, March 22-24, 1987.