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High-resolution stratigraphic architecture and lithological heterogeneity within marginal aeolian reservoir analogues

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Abstract

Marginal aeolian successions contain different lithological units with variable geometries, dimensions and spatial distributions. Such variations may result in considerable heterogeneity within hydrocarbon reservoirs developed in successions of this type, which poses a high risk to their efficient development. Here, such heterogeneity is described and characterized at inter-well (<1 km) scales using two well-exposed outcrop analogues of ‘end member’ marginal aeolian deposits from the Permian Cedar Mesa Sandstone and Jurassic Page Sandstone of south-central Utah, USA. The sedimentology and stratigraphic architecture of the Cedar Mesa Sandstone was studied in a 1·2 km2 area in the Indian Creek region of southern Utah, where the interval consists of interbedded fluvial and aeolian deposits representative of a fluvial-dominated erg margin. The Page Sandstone was studied in a 4·3 km2 area near Escalante, close to the Utah-Arizona border, where it consists of interbedded sabkha and aeolian deposits representative of a transitional-marine erg margin. The three-dimensional stratigraphic architectures of both reservoir analogues have been characterized, in order to establish the dimensions, geometries and connectivity of high-permeability aeolian sandstones. Facies architecture of the aeolian-sabkha deposits is characterized by laterally continuous aeolian sandstone layers of relatively uniform thickness that alternate with layers of heterolithic sabkha deposits. Aeolian sandstones are thus likely to form vertically unconnected but laterally widespread flow units in analogous reservoirs. Facies architecture in the aeolian-fluvial deposits is more complex, because it contains alternating intervals of aeolian sandstone and fluvial heterolithic strata, both of which may be laterally discontinuous at the studied length-scales. Aeolian sandstones encased by fluvial heterolithic strata may form small, isolated flow units in analogous reservoirs, although the limited continuity of fluvial heterolithic strata results in vertical connectivity between successive aeolian sandstones in other locations. These architectural templates may be used to condition zonation schemes in models of marginal aeolian reservoirs.

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