Stratigraphy and hydrocarbon potential of the Fort Union and Lance Formations in the Great Divide and Washakie basins, south-central Wyoming

The Lance and Fort Union Formations of the Greater Green River Basin record the retreat of the Cretaceous Western Interior Seaway and the transition from marine deposition to continental, synorogenic sedimentation. Structural development of the eastern Greater Green River Basin began during the latest Cretaceous, with its main depocenter in the northeast, near the modern-day Granite Mountains. Later in the Paleocene, Laramide uplifts partitioned the basin into the Great Divide and Washakie Basins. Subsidence was episodic; times of high subsidence resulted in sediment-starved regions and the formation of thick and persistent coal zones. With the addition of up to 13,000 ft of Eocene and Miocene overburden, those coal zones that reached thermal maturity became the most likely source of thermogenic methane. The purpose of this study is to establish the stratigraphy and basin development of the Great Divide and Washakie Basins, with the ultimate goal of constraining the timing and hydrocarbon-generation potential of the Lance and Fort Union petroleum systems. Stratigraphic correlations, interpreted from 883 oil and gas wells, were extended from outcrops along the Atlantic Rim into the subsurface of the Washakie and Great Divide Basins. These correlations were used to create a series of cross sections, isopach maps, and subsurface structure maps, which, when integrated with age control data, yield a more complete picture of basin development.