Application of Sequence Stratigraphy in Reservoir Characterization of a Lacustrine to Terrigeneous Succession: Green River Formation, Uinta Basin, Utah, U.S.A.

Kjemperud, Audun V., Edwin Schomacker, Department of Geoscience, University of Oslo, Oslo, Norway

The Eocene, Green River Formation of the Uinta Basin has been studied in the central Nine Mile Canyon, Utah. The Uinta Basin originated by compressional partitioning of the marine Sevier Foreland Basin during Late Cretaceous to Paleocene time.

The 700 meter thick interval studied directly overlies the fluvial dominated Colton Formation. Vertical and lateral facies variations have been recorded and applied to create a depositional model for the studied interval within a sequence stratigraphic framework based on variations in the A/S-ratio. The succession has been divided into nine informal stratigraphic progradational units bounded by lacustrine flooding surfaces. The strati­graphic units progressively thin upward through the studied interval.

The nine units reveal a similar regressive facies development, starting with transgres­sive open lake facies, succeeded by lacustrine shoreline and/or fluvial, coastal plain facies. The study has demonstrated that in this basinal setting it is of great importance for reser­voir modelling to discriminate between pointbar deposits and mouth bar deposits. Three fine-grained stratigraphic intervals are characterized by high frequency ooide/ostracode grainstone beds interpreted to be related to periods of coastline starvation of siliciclastic sedimentation. These stratigraphic intervals coincided with initiation of large scale progra­dations of terrigeneous deposits.

The high-frequency lacustrine to terrigenous sequence stratigraphy found is a response of variation in rate of accommodation due to lake level fluctuations and sediment supply. The effect of the fluctuations is amplified by a low gradient coastal plain.