Correlation of Oils and Tar Sands in the Green River Petroleum System, Uinta Basin, Utah
The Eocene Green River Formation in the Uinta Basin, Utah, is comprised of thick packages of organic-rich calcareous shales and marlstones interbedded with coarse clastic rocks deposited in a freshwater to hypersaline lake. Petroleum source rocks in the formation have generated several different forms of petroleum (oil, gas, tar sands, and native bitumen), some of which are significantly biodegraded. Numerous studies have recognized two oil subtypes in the basin. The most common oil type, Green River A, is derived from the lower black shale facies of the Douglas Creek Member. Less common is Green River B derived from the Mahogany zone of the Parachute Creek Member. Oils produced from the Eocene Wasatch Formation are herein considered a third oil subtype. Bulk properties (high pour point) and geochemical composition (elevated pristane/phytane and land-plant biomarker ratios) suggest that Wasatch oils are sourced from the freshwater fluvial-lacustrine interval in the lower Green River Formation. Biomarker geochemistry provides insight into the biodegradation process as well as the pitfalls of genetic characterization of biodegraded oils and tar sands. Although it is widely regarded that the Uinta Basin tar sand oils are derived from the Green River Formation, correlation to a specific organic facies is difficult due to significant biodegradation. Preliminary correlations based on degradation-resistant biomarkers suggest that the Sunnyside tar sand deposit contains Green River A oil type, whereas the Raven Ridge tar sand deposit contains Green River B oil, consistent with a geologic model of oil migration updip from their respective source facies.
AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014