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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 63 (1979)

Issue: 3. (March)

First Page: 433

Last Page: 433

Title: Petroleum Generation and Migration in Denver Basin: ABSTRACT

Author(s): J. L. Clayton, P. J. Swetland

Article Type: Meeting abstract

Abstract:

Crude oils and shales from the northern Denver basin were analyzed using organic geochemical techniques to determine relations between oil and source beds. Hydrocarbon analyses (gasoline-range, C15+ saturates, and C15 to C20 isoprenoids) and stable sulfur isotope ratios show that, in general, Cretaceous oils are compositionally similar throughout the basin and are dissimilar to oil produced from the Permian Lyons Sandstone.

Shales were evaluated for source-rock potential based on organic richness, thermal maturity, and geochemical correlation with crude oils. These analyses showed that most of the Cretaceous oils have been derived from Carlile Shale, Greenhorn Limestone, Graneros Shale, and Mowry Shale. These units have a maximum collective thickness of about 600 ft (180 m) and can be grouped together on the basis of similar geochemistry. The source bed for the Lyons oil has not been identified.

Analyses of samples from the Carlile-Greenhorn-Graneros-Mowry interval from throughout the basin show that the effective source beds are limited to the basin-axis area. Although shale samples from eastern Colorado and southwestern Nebraska are organic-rich, they are generally thermally immature (Ro values 0.32 to 0.49%) and contain hydrocarbon distributions unlike the Cretaceous oils. Samples from the basin-axis area of Colorado have Ro values of 0.60 to 0.85% and petroleumlike distributions of hydrocarbons. Rocks in southeastern Wyoming generally have intermediate reflectance values (0.48 to 0.62%) but large quantities of extractable, heavy (C15+) hydrocarbons (~700 to 1,600 ppm), and have good source potential. However, geochemical correlations revea ed that the Wyoming samples are compositionally somewhat different from the oils and are not considered a major petroleum source in the Denver basin.

The occurrence of petroleum on the east flank of the basin and the limited geographic distribution of effective source beds indicate that extensive (perhaps 100 mi; 160 km) lateral migration has occurred. This suggests that an understanding of lateral-migration pathways is important for petroleum exploration in the Denver basin.

Cretaceous oils in the Terry and Hygiene reservoirs have probably undergone extensive vertical migration (2,500 ft or 762 m in the Central Front Range area).

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Copyright 1997 American Association of Petroleum Geologists