Empirical Models for the Reconstruction of Eolian Dune Architecture from One-Dimensional Core Data

Data derived from core and well-logs are essentially one-dimensional and determining eolian system type and likely dimensions and orientation of architectural elements present in subsurface eolian successions is typically not possible from direct observation. This is problematic because accurate predictions of the three-dimensional distribution of interdune elements that commonly form low-permeability baffles to flow, of net-to-gross, and of the likely porosity-permeability distribution in eolian reservoirs is crucial for reservoir characterization.

Direct measurements from both modern eolian bedforms and eolian elements preserved in the ancient record has enabled the establishment of a series of empirical relationships with which to make first-order estimates of a range of parameters that are not observable directly in core. For modern eolian dunes, relationships exist between bedform type, wavelength, height, sinuosity of crestlines, and the distribution of primary sediment type, including grainflow, wind ripple, grainfall and interdune lithofacies. In preserved eolian successions, the distribution of primary lithofacies types occurs in a predictable manner for different types of dune sets, whereby the distribution of grainflow, wind ripple and grainfall strata can be related to set architecture, which itself can be related to original bedform type.

Detailed characterization of individual eolian dune sets has been undertaken through outcrop studies of the Permian Cedar Mesa Sandstone and the Jurassic Navajo Sandstone in southern Utah. The transition between lithofacies types seen vertically in preserved sets enables predictions to be made regarding the relationship between preserved set thickness, individual grainflow thickness, original bedform size, the likely proportion of the original bedform that is preserved, angle of system, and the along-crest variability of facies distributions within sets. The repetitive stacking of grainflow and wind-ripple-dominated packages of strata in some sets can be related to annual advance cycles (or cycles of potentially longer duration) and this provides a method to determine likely bedform migration rates.

A series of graphical models demonstrate common facies arrangements within bedsets for a suite of dune types and these show inherent facies variability. Results are being applied for reservoir characterization of the Jurassic Norphlet Sandstone (Gulf of Mexico) and the Permian Auk Formation (Central North Sea).

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California