ILLINOIS ORDOVICIAN-CAMBRIAN OIL SOURCE FOUND

Scientists at the Illinois State Geological Survey, Champaign, have documented the first example of an oil derived from Lower Ordovician or Cambrian source rocks in the Illinois basin. Geochemical analyses were performed on oil recovered from dolomites in the Ordovician Knox group at 7,876 ft in the Unocal Corp. 1 Cisne Community well in 3-1s-7e, Wayne County, drilled in 1967 This oil, the deepest occurrence from the Illinois basin analyzed to date, is the first to document that a deep source

Feb. 17, 1992

2 min read

Scientists at the Illinois State Geological Survey, Champaign, have documented the first example of an oil derived from Lower Ordovician or Cambrian source rocks in the Illinois basin.

Geochemical analyses were performed on oil recovered from dolomites in the Ordovician Knox group at 7,876 ft in the Unocal Corp. 1 Cisne Community well in 3-1s-7e, Wayne County, drilled in 1967

This oil, the deepest occurrence from the Illinois basin analyzed to date, is the first to document that a deep source exists in the basin. Due to a lack of core, the source itself has not been identified.

Two oil samples from Middle Devonian carbonate rocks at 4,950 ft and 3,065 ft in the same well show significantly different geochemical signatures from the Knox oil. The dissimilarity of saturate and aromatic fractions between the shallower two oils and the Knox oil are indicative of differences in source and maturity.

Further, said Gary L. Salmon, an ISGS geochemist, the marked variation in quantity and complexity of substituted hetero-atomic compounds suggests organic source and depositional disparity between the two oils from the Devonian strata and the oil from the Knox.

Salmon, James B. Risatti, and Stephen I. Whitaker of ISGS plan to present a detailed discussion of the analyses of the three oils Sept. 20-23, 1992, in Champaign at the American Association of Petroleum Geologists Eastern Section meeting.