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Outcrop to Subsurface Reservoir Characterization of the Lower Mesaverde Group, Red Wash Field, Uinta Basin and Douglas Creek Arch, Utah and Colorado

Abstract

The Mesaverde Group within the Uinta Basin produces oil and natural gas from unconventional fluvial sandstone reservoirs. This study addresses the stratigraphic architecture and connectivity of fluvial reservoirs through a combination of outcrop analysis and static and dynamic modeling of equivalent reservoirs. The Cretaceous Mesaverde Group in outcrop and at Red Wash field, Uinta Basin, Utah serves as an excellent outcrop analog and consists of a succession of fluvial channel sandstones, crevasse splays, floodplain mudstones, and paludal coals that were deposited by meandering- and braided-river systems within coastal- and alluvial-plain settings. Fluvial reservoir bodies are inherently heterogeneous at a range of scales. To analyze the range of spatial variability and to aid in constraining subsurface reservoir models, field descriptions including hand-held spectral-gamma-ray measurements were acquired for four stratigraphic sections (total footage= 650 ft; 198 m) from lower Mesaverde outcrops (near Dinosaur, Colorado). Detailed core descriptions yield facies, facies associations, and architectural elements present within the subsurface at Red Wash Field for comparison to outcrop. The outcrop/core observations and statistics, combined with fluvial sandstone-body statistics from three additional localities (Douglas Creek Arch), and subsurface well data are used to reconstruct local depositional styles, to aid in subsurface correlation, and to condition multiple-point geostatistical models (i.e. multipoint statistics – MPS) of fluvial reservoirs at Red Wash Field. Geologically constrained, well-log-based electrofacies are estimated in non-cored wells using a k-nearest neighbor approach combined with outcrop-based thickness criteria. Three-dimensional models of architectural elements, porosity, and permeability show the spatial variability of reservoir properties and are used to evaluate static and dynamic connectivity across the field and stratigrapically. Static modeling and dynamic simulation results explore the significance of crevasse splays and channel-sandstone bodies (fluvial bars) on reservoir connectivity and effective well spacing.