--> Clastic/Evaporitic Interactions in Arid Continental Settings: Implications for Reservoir Characterization and Modelling

AAPG ACE 2018

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Clastic/Evaporitic Interactions in Arid Continental Settings: Implications for Reservoir Characterization and Modelling

Abstract

In arid continental settings, the interactions between competing aeolian, fluvial, lacustrine and evaporitic environments exert strong controls on the sediments deposited, their preservation, and lithofacies connectivity in the subsurface. They strongly influence basin-wide fluid migration, along with reservoir-scale character, petrophysical properties and production behaviour. 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 received comparatively little attention despite their potential to affect both basin-scale fluid migration and reservoir quality.

We present results of sedimentary interactions between evaporitic deposits and those of other arid environments from the Paradox Basin, USA, along with the influence of physical versus chemical processes and analysis of the allocyclic-controls upon them. Studies are based upon extensive regional fieldwork examining the sedimentology, geometries, and interactions, complimented with petrographical analyses and outcrop gamma ray logging.

The margin of the Cedar Mesa erg of the Paradox Basin preserves complex interactions of clastic and evaporitic sediments. The highly variable sedimentary fill shows large variations spatially and temporally which grade through aeolian, sabkha and lacustrine settings with complex interactions occurring where these environments transition. Where present, the sabkha facies dominate, reworking aeolian dune sediment into poor reservoir quality evaporite rich sands and blocking fluid pathways.

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.

We apply our results 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.