Jessica J. Moore¹, David A. Wavrek²

(1) University of Utah, Salt Lake City, UT
(2) Petroleum Systems International, Inc, Salt Lake City, UT

ABSTRACT: Hydrocarbon Volumetric Yields from Fresh vs. Hypersaline Organic Facies: Green River Formation, Uinta Basin, Utah

The Green River formation is one of the most extensively studied lacustrine source rock sequences in the world, yet fundamental questions remain with regard to the hydrocarbon generation potential of fresh vs. hypersaline organic facies. Answering this question has academic, as well as economic interest. Kerogen from the Green River formation is highly ranked in terms of total hydrocarbon yields, but different organic facies may display different temperature thresholds for peak oil generation. This is important to resolve since this kerogen serves as a global benchmark for Type-I organic matter.

This study examines geological and geochemical parameters used to determine prevalent water column salinity during source rock formation in lacustrine paleoenvironments. Results indicate hydrocarbons derived from fresh vs. hypersaline organic facies may be differentiated using geochemical parameters. As the water column salinity increases, the pristane/phytane ratio decreases, beta-carotane index increases, and odd-carbon preference index in high molecular weight branched alkanes increases. The gammacerane index is better correlated with water column stratification, rather than degree of hypersalinity. To determine relative volumes of hydrocarbons generated from different organic facies of the Green River formation, representative samples are analyzed from producing fields correlating to the Green River (!) petroleum system. The results are corrected from sample frequency to barrels of oil equivalent with use of available total hydrocarbon reserve volumes. The methodologies developed in this study not only apply to the Green River formation, but are applicable to other petroleum systems charged from lacustrine source rocks.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado