2019 AAPG Annual Convention and Exhibition:

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Allocyclic Controls Upon Clastic/Evaporitic Interactions in Arid Continental Settings: Implications for Reservoir Characterization and Modeling

Abstract

Arid continental settings deposit and preserve complex interactions between aeolian, alluvial, lacustrine, fluvial and sabkha sediments. While the distribution and preservation of different facies associations within any one of these environments are reasonably well constrained, the relationships between deposits of coeval environments and their temporal evolution have, until recently, received comparatively little attention despite their potential to affect both basin-scale fluid migration and reservoir quality. These interactions are strongly influenced by complex processes between autocyclic and allocyclic controls, including climate, however within arid continental settings these signatures are often difficult to detect within the sediments preserved. We present results from the margin of the Cedar Mesa erg of the Paradox Basin which preserves complex interactions of clastic and evaporitic sediments. Studies are based upon extensive regional fieldwork examining the sedimentology, geometries, and interactions, complimented with outcrop gamma ray data. The highly variable sedimentology shows large variations spatially and temporally which grade through aeolian, sabkha and lacustrine settings with complex interactions occurring where these sediments transition. Where present, the sabkha facies dominate, reworking aeolian dune sediment into poor reservoir quality evaporite rich sands and blocking fluid pathways. These sabkha sediments also preserve the signatures of the allocyclic-controls upon them. This work details the facies present in a continental sabkha allowing for identification and interpretation of these complex interbedded relationships over a regional scale. The results have been developed into idealised models and recognisable log signatures which characterise and assess their impact on reservoir quality. Wetting or drying climatic cyclic trends, on various orders of magnitude, have also been identified, which govern distinct spatial facies changes. Identification of these allows for basin wide correlation and prediction of where facies will occur in space and time. Our results are applied to evolutionary models applicable to subsurface data from the arid Permian basins of the North Sea, in order to better characterise basin-scale migration and reservoir quality in terms of the evolving basin fill.