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Reservoir Characteristics of Deepwater Massive Sandstones: Case Studies from the Numidian Flysch and Mediterranean Region

Stow, Dorrik 1
1 Indtitute of Petroleum Engineering, Heriot-Watt University, Edinburgh, United Kingdom.

The deep-water turbidite play is currently one of the most prolific and important in hydrocarbon exploration and production. Within this play, the best reservoirs are those that occur in thick sequences of deep-water massive sandstones (DWMS). These are very thick (1- >50m) sand beds or units that are devoid of primary sedimentary structures, deposited by high-density turbidity currents and/or sandy debris flows. They are commonly associated with thin-bedded turbidites, hemipelagites and other deep-water sediments, and display excellent and uniform reservoir properties and geometries. Typically, they also give rise to sand injection structures within the superjacent and laterally adjacent sediments, and display a variety of feather-edge relationships with the associated facies. The Oligo-Miocene Numidian Flysch system from both northern Tunisia and Sicily provide excellent analogues of DWMS reservoirs. Within an overall mud-dominated system, the DWMS complexes in northern Sicily represent channel-fill deposits (channel width 150-3000m, channel fill 25-300m thick, sand:shale ratios from 9.5:1 to 7.5:1). The channels were sinuous to meandering across a muddy slope-apron represented by the normal range of deepwater facies. The north Tunisian succession is closely comparable with the Sicilian examples, although channel dimensions are less readily determined. Thin conglomerates and thicker debrites co-occur within the DWMS facies association, whereas slide-slump units and injectionite sands occur within the more mud-rich associations. The likely depositional setting is a mud-rich slope system traversed by isolated slope channels and associated sand-rich lobes. Trace fossil assemblages suggest middle to upper slope depths, whereas other evidence points towards considerable shallowing. This contribution aims to present an overview of what we know about DWMS, with particular focus on their reservoir characteristics, and to place the Numidian system within the context of DWMS globally.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009