Core-based Sedimentologic, Stratigraphic, and Geochemical Analysis of the Lacustrine Upper Green River Formation, Uinta Basin, Utah: Implications for Conventional and Unconventional Petroleum Development

Michael Vanden Berg, Lauren Birgenheier, and Morgan Rosenberg

Lacustrine basin systems have always been valued for their abundant conventional oil and gas reserves, but they also contain significant unconventional petroleum development potential. This research describes the lacustrine sedimentary facies and stratigraphic stacking patterns in the upper Douglas Creek and Parachute Creek Members of the Green River Formation along a 30-mile, five-core, east-west trending cross section. The easternmost core from the recently drilled Skyline 16 well captures marginal-lake sediments on the western flank of the Douglas Creek Arch, including shallow lake microbialite sequences, while the westernmost core, EX-1, is located near the basin's paleo-depocenter. This cross section provides a unique opportunity to highlight significant lateral changes in upper Green River Formation facies architecture. The cross section demonstrates that Lake Uinta evolved in three phases: 1) a freshwater, rising-lake phase below the Parachute Creek Member's Mahogany oil shale zone characterized by 10-foot-thick shallowing/coarsing upward proximal to distal siliclastic and carbonate cycles, 2) an anoxic, deep-lake phase above the base of the Mahogany zone characterized by organic-rich calcium carbonate oil shale, and 3) a hypersaline-lake phase within the middle and upper R-8 oil shale zone characterized by abundant deposition of saline minerals. The Skyline 16 core (portions will be displayed) provides excellent examples of each lake phase. The long-term evolution of Lake Uinta was driven by tectonic basin development and the balance of sediment and water fill with neighboring basins. Abrupt early Eocene global-warming events may have had significant control on sediment production and deposition rates, such that siliclastic zones below the Mahogany zone record hyperthermal events and organic-rich zones record periods between hyperthermals. This type of climatic control on short-term and long-term lake evolution and deposition has been previously overlooked.

AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012