Petroleum Systems in Central and Southwestern Wyoming Rocky Mountain Laramide Basins

Illich, Harold, John Zumberge, Stephen Brown
GeoMark Research, Houston, TX

The use of geochemistry of large numbers of oils and gases is a novel exploration strategy supplementing the search for new opportunities in “mature” basins. In this study, organic geochemical data for more than five hundred gases and four hundred newly analyzed oils were acquired for samples from the Utah-Wyoming Thrust Belt, Wind River, Bighorn, and Greater Green River basins. The study sought to determine the number, stratigraphic and map distribution, and probable source identity of petroleum systems in the basins. “Vagrant” oils, possibly representing under-explored opportunities, were especially important to identify.

Oils and gases associated with sources in the Permian Phosphoria and Cretaceous Mowry are present in all of the basins. Often more than one source facies can be attributed to each of these regionally important intervals. In addition, each basin contains oils and gases derived from a number of sources previously undefined or poorly defined. These oils and gases usually represent a variety of proximally and distally deposited shale-rich source intervals. Oils from sources deposited in lacustrine environments also occur in most of the basins.

The probable identities of the sources for each of the systems are assigned based on provenance and age diagnostic biomarker data, and on the stratigraphic dispersion of oils belonging to the compositionally distinct families. Each basin contains vagrant oils or gases that may represent under-explored petroleum systems.