Abstract: Source Beds of Petroleum in Denver Basin
Crude oil and shale samples from the Denver basin were analyzed by organic geochemical techniques to determine oil-source-bed relations. Infrared spectrophotometry, gas chromatography of the C15+ saturates, mass spectrometry, and carbon- and sulfur-isotopic ratios were used to characterize both the crude oils and the extractable organic matter in shales. The oils were characterized further by gas chromatography of the C4-C7 fraction and optical rotation measurements.
In general, oils in Cretaceous rocks are compositionally similar, and they can be distinguished from oils in the Permian Lyons Sandstone. The Cretaceous oils were compared with extractable organic matter in Cretaceous shales to determine the regional and stratigraphic occurrence of petroleum source beds. The results show that most Cretaceous shales are thermally immature over a large part of the basin. In areas where the Cretaceous section has had a thermal history sufficient to cause generation of petroleum like hydrocarbons within the shales, many potential source beds exist. The geographically limited occurrence of source beds and the occurrence of oil in thermally immature areas suggest that extensive vertical and lateral migration has occurred.
AAPG Search and Discovery Article #90971©1976 AAPG-SEPM Rocky Mountain Sections 25th Annual Meeting, Billings, Montana