MESOSCALE HETEROGENEITY OF FLUVIAL-LACUSTRINE RESERVOIR ANALOGUES: EXAMPLES FROM THE EOCENE GREEN RIVER AND COLTON FORMATIONS, UINTA BASIN, UTAH, USA

摘要

The Eocene Uinta Basin of Utah is a dominantly lacustrine basin that affords the opportunity to survey analogue sandstone reservoirs developed within and adjacent to the lacustrine system. From its SW to NE margin, Eocene strata in the Uinta Basin record fluvial, deltaic, profundal lacustrine, and wave-dominated shallow-lacustrine environments. Of these depositional systems, analogue sandstone reservoirs are well-exposed in outcrop in the fluvial-deltaic and wave-dominated intervals. Field and petrographic examination of selected fluvial-lacustrine reservoir analogues are used to document the mesoscale fades architecture and heterogeneity. Complex depositional geometries and heterogeneity exist at a variety of scales, both within single subenvironments and between opposite sides of the basin. Three outcrops in the Uinta Basin were studied. Outcrops One and Two are located in the SW portion of the basin in Nine Mile Canyon, and represent the interface between fluvial rocks of the Cotton Formation and dominantly lacustrine strata of the Green River Formation. Outcrop Three is located at Raven Ridge in the NE of the basin, a shallow wave-dominated lacustrine margin. Photomosaics and multiple vertical measured sections were described for each outcrop, and were utilized to document lithofacies assemblages, bounding surfaces, and sandbody architecture and heterogeneity. Sandstone samples from each outcrop were analyzed petrographically to capture the small-scale heterogeneity characteristic of the three outcrops.