Sami Riahi

The Numidian Flysch Complex of Onshore Tunisia (Southern Kroumirie Range) - Facies Analysis and Stratigraphic Review

Sedimentological analysis and biostratigraphic review of the Oligo-Miocene deposits of northern Tunisia provide new data allowing new stratigraphic and paleogeographic reconstruction. The Kroumirie and Zouza member have the same age and correspond to sand/mud and mud/sand rich systems of a deep sea fan system with a detrital influx supplied from the North. Structural analysis demonstrate that the Numidian flysch has been displaced by a major thrust fault.

The Onshore Tunisia Numidian Flysch

The study concerns the Oligo-Miocene aged Numidian Flysch which forms the highest structural unit in northern Tunisia and consists of an interbedded unit of highly quartzose sand and shale, which are of turbiditic affinities. An integrated petrographic and geochemical study of this formation was carried out to infer the sandstones provenance, and reservoir characteristics. On the basis of the framework composition (point counting) and whole-rock geochemistry (major elements), the sandstones are classified as quartzarenite, and sublitharenite types. The modal analyses imply a recycled orogen provenance. Moreover, petrographic point count data indicate quartz-rich sedimentary (recycled), middle to high-grade metamorphic and plutonic parent rocks for Numidian sandstones. According to the plate and tectonic reconstructions of the western Mediterranean Sea it appears that the kabylean basement terrain cropping out along the Algerian coast and forming part of Calabro-Peloritani-Kabylian zone to be the parental source of the Numidian of both Sicily and Tunisia. Additionally, petrographical study indicates that the reservoir properties of the Numidian Flysch are a direct function of grain size and textural maturity.

Reservoir Characterisation of Deepwater Massive Sandstones – Case Studies from the Numidian Flysch and Mediterranean

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 includes excellent examples of DWMS, which are the subject of ongoing investigations. This contribution aims to present an overview of what we know about DWMS, with particular focus on their reservoir characteristics, to introduce some new data on examples from the Mediterranean region, and to place the Numidian system within the context of DWMS globally.