Abstract: Source Rock/Oil Characterization and Hydrocarbon Migration in the Tertiary Petroleum System of the Uinta Basin, Utah

MUELLER, ERIC, University of Oklahoma, School of Geology and Geophysics, Norman, OK

Several types of source rocks varying in bulk and biomarker composition have been deposited in the Tertiary lacustrine Green River Formation of the Uinta Basin. In addition to the oil shale type source rocks a number of other organic rich rocks are present, which are, based on analysis of 52 oil samples, the main sources of the oils produced in the basin.

The variation of source rock geochemistry and lithofacies reflect temporal changes in the depositional environment and source input. Episodic recurrence of source rock types similar in composition to oil shales indicate a more complex basin evolution than the commonly assumed general trend to higher salinity and hydrologically closed lacustrine conditions. Lithofacies interpreted as marginal lacustrine exhibits excellent hydrocarbon generation potential, suggesting that marginal lacustrine settings are conducive to the development of source rocks as well. Multivariate statistics of oil analysis resolved several distinct oil types, which provides evidence that hydrocarbons have been generated from different source rock facies, resulting in considerable geochemical variability of oils on a field and basinwide scale.

Extended hopanes provide the most consistent biomarker maturity parameter, while others appear to be influenced by source input. Oil maturity and composition suggest that hydrocarbons are generated from sources at low maturity. If biomarker maturity indicators are correct, the area of oil generation in the basin is larger and extends to shallower depths than previously assumed, such that marginal fields receive their charges also from local sources and not necessarily from the deep north-central part of the basin.

AAPG Search and Discovery Article #90931©1998 AAPG Foundation Grants-in-Aid