Recognition of the Stratigraphic Heterogeneity of Late Paleozoic Eolian Erg Margin Deposits for Improved Oil Recovery: Weber Sandstone, Rangely Field, Colorado
Ryan Grimm, Leigh Owens, Carlos Collantes, Laura Murray, Marina Borovykh, Tashika Charles, Ed Bucher, and Roy Cramer
Chevron Energy Technology Company
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 modern 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 15,000 feet of core as well as new borehole image data define the recognition criteria for ten end-member depositional facies evident from vertical sequences. Reservoir facies are predominantly associated with four distinct eolian dune facies – Sandsheet, Dune Slipface, Slumped Dune, and Bioturbated Dune. Non-reservoir facies include 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 greater than 25 chronostratigraphic sequences, ascribed to repetitive arid-pluvial shifts in regional paleoclimate and sediment availability. Although individual sequences are typically thin and subseismic, multiple sequences can be grouped into seismically perceptible packages, mappable on both seismic and vintage wireline log 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, highlighting new opportunities from vintage log suites and a pilot seismic survey.
AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013