Quantitative Spatial Variability of Dune and Interdune Facies in the Aeolian Navajo Sandstone, USA: Implications for Reservoir Characterization

Abstract

The advancement of predictive aeolian facies models is important for hydrocarbon exploration, particularly in mature basins, where subtle stratigraphic traps require the use of sophisticated simulations. The presence and lithological character of interdune elements can produce sedimentological heterogeneities that can potentially partition reservoirs. Previous studies have documented spatial variation in dune bedform type and associated spatial changes in aeolian lithofacies distributions. However, relatively few studies have attempted to quantitatively record the form and spatial variability of dune and interdune facies.

Here we present a regional-scale study of the aeolian Jurassic Navajo Sandstone of south-western USA. Detailed sedimentary logs, palaeocurrent measurements, architectural panels combined with 3D photogrammetry have been integrated to quantitatively describe lithofacies distributions and sedimentary architectures from large-scale outcrops in southern Utah, western Colorado and northern Arizona. The outcrops were selected in order to quantify the relationships between dune and interdune assemblages in both the central and marginal parts of the erg.

Interdune sedimentary processes within the Navajo were determined by variations in the water table relative to the depositional surface, and we identify and quantify a range of wet, damp and dry interdune elements at various scales and throughout the formation. We consider how a series of external factors that collectively define the sediment state of the system may act to dictate spatial changes in dune and interdune morphology, geometry and importantly, their preservation. From analyses of the interactions we predict spatial and temporal variations in aeolian facies across the entire erg and we construct a suite of high-resolution, 3D, quantitative depositional models that account for the complex interactions between wet and dry aeolian environments.

Based on the analyses of the Navajo Sandstone from dune-field-centre to dune-field-margin, a suite of empirical relationships have been identified. These relationships demonstrate clear patterns in dune-interdune sedimentology, both spatially and through time, that can be related to sediment characteristics observable in core and well-log data. Consequently we use our models to predict likely architectural complexity within the reservoir and produce more realistic reservoir models than could be constructed from limited subsurface data alone.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018