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Eolian and Dryland Reservoir Characterization, Process Sedimentology and Stratigraphic Architecture of the Permian Weber Sandstone, Rangely Field, Colorado

Ryan Grimm

Complex interstratification of Late Paleozoic eolian dune sandstone reservoirs with associated non-reservoir interdune and alluvial deposits has created significant hurdles to enhanced recovery and production within the Weber Sandstone at Rangely Field, Rio Blanco County, Colorado. Relatively minor facies variations introduce important heterogeneities, influencing fluid-flow and production. Application of contemporary techniques of dryland process sedimentology and continental stratigraphy allows for depositional environment interpretation of archived cores and a new appraisal of reservoir architecture from core-calibrated wireline logs and available seismic data. Results from the description, analysis, and interpretation of 4400 feet of cores from nine Rangely Field wells have defined recognition criteria for ten end-member depositional facies evident from vertical sequences. Reservoir facies are predominantly associated with four distinct eolian dune facies ñ Sandsheet, Dune Slipface, Slumped Dune, and Bioturbated Dune. Four interdune facies - Paleosols, Dry, Wet and Massive interdune and two alluvial facies - Ephemeral channel and Overbank splay - are vertically and laterally interstratified with eolian facies. Comparison of facies with plug petrophysical data suggests strong poro-perm relationships with depositional facies. Vertical associations of facies can be qualitatively subdivided into approximately 38 chronostratigraphic sequences, ascribed to cyclical changes in regional paleoclimate and sediment availability. Although individual sequences are typically thin (<20 ft) and subseismic, multiple sequences can be grouped into seismically perceptible packages, mappable on seismic data across the study area. The updated stratigraphic architecture of the Weber Sandstone provides an initial facies distribution model for inter-well reservoir and flow barrier prediction from vintage log suites and a pilot seismic survey.


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