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Sixsmith, Peter J.1, Gary J Hampson1, Sanjeev Gupta1, Howard D. Johnson1 
(1) Imperial College, London, United Kingdom

ABSTRACT: Sedimentology and Facies Architecture of a Transgressive Sandstone: The Cretaceous Hosta Sandstone, New Mexico, USA

Transgressive sandstones form a significant component of many shallow-marine reservoirs. However, the high net:gross of these systems often masks complex facies architecture and stratigraphy associated with significant permeability variations that impact reservoir drainage patterns and ultimate recovery. An improved understanding of the controls on sandbody type, sandbody distribution and stratigraphic architecture in these sandstones can improve predictions of reservoir behaviour. 
This study addresses the processes responsible for the formation, preservation and facies character of transgressive sandstones through detailed outcrop analysis of an exceptionally exposed reservoir analogue, the Cretaceous Hosta Sandstone in New Mexico. Mapping of facies architecture within a series of adjacent, depositional-dip-oriented canyons has enabled quantitative three-dimensional reconstruction of key stratigraphic surfaces and sandbody distributions from up-dip to down-dip pinch-out of the transgressive sandstone complex. 
The Hosta Sandstone contains a complex arrangement of wave- and tide-dominated facies arranged in a net transgressive pattern. Tidal channel-fills, tidal sand bars and muddy tidal creek facies comprise the stratigraphy in the up-dip part of the system and these pass abruptly down-dip into wave-dominated shoreface sands, via a succession of ebb- and flood-tidal deltas. Facies are partitioned both vertically and laterally by transgressive ravinement surfaces which can be physically traced for several kilometers. Reconstructing the geomorphology of these surfaces is critical to understanding sandbody distribution and facies partitioning at high-resolution (intra-reservoir zone) scale. Key challenges in applying this work to the subsurface include the cryptic character of sand-on-sand contacts, complex facies interdigitation at inter-well scale, and complex geometry of key stratigraphic surfaces.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.