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Multi-Resolution Modeling of Ephemeral Fluvial-Aeolian Interactions: Implications for Reservoir Characterization

Abstract

Arid continental basins commonly comprise sedimentary fill from both fluvial and aeolian environments. While the preserved facies associations within each of these environments have been studied in great depth, the sedimentary interactions between coeval environments have received comparatively little attention, despite their likely influence upon localised reservoir quality and basin-scale fluid migration. We present results from extensive fieldwork studies of sedimentary interactions between the deposits of fluvial and aeolian systems from the Kayenta Formation of the Colorado Plateau, USA, along with insights into the allocyclic controls upon them. The Kayenta Formation comprises fluvial-aeolian associations of highly varied reservoir quality. Relationships between them are spatially predictable, governed by one system’s dominance. The temporal evolution between systems preserves unique facies, but a switch in dominant system takes place quickly, severely limiting the vertical extent of interactions and potentially isolating reservoir intervals of basin fill. Complex interactions between ephemeral fluvial and aeolian environments are present throughout the whole expanse of the Kayenta Formation and occur at a variety of scales, from small-scale reworking of aeolian sediment into the fluvial system, to large-scale intertonguing of the aeolian and fluvial strata within the top third of the Kayenta. Field data coupled with three-dimensional photogrammetric models allow reconstruction of ancient channel forms and dune fields, providing quantitative data on architectural elements for reservoir models. Statistical analysis of these data provides a framework for calculating likely sizes and geometries of equivalent elements recognised in subsurface core, to provide representative input for reservoir models. Our work is applied to a case study of cores from the Lower Permian Leman Sandstone of the Rotliegend Group, a principal gas reservoir in the Southern North Sea Basin, to reconstruct geometries and dimensions of elements for reservoir characterisation, in order to further enhance recovery from this longstanding and exploited resource.