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ABSTRACT: Channelised lobes in sand-rich turbidite systems: high-resolution quantification of lateral heterogeneities in exceptional outcrops from the Grès d'Annot, SE France

Lomas, Simon A1, Bryan T Cronin1, Adrian J Hartley1, Davide Duranti1, Emma Mackay1, and Sean Kelly2
(1) University of Aberdeen, Aberdeen, United Kingdom
(2) Shell UK Expro, Aberdeen, United Kingdom

The Trois Evêchés outcrop of the Grès d'Annot (Annot Sandstones) represents one the world's best-exposed examples of a confined sandy turbidite system. The Grès d'Annot is a large Eocene-Oligocene sand-prone turbidite basin-fill now exposed as a series of basin remnants fringing the French Alps. The Trois Evêchés remnant has exceptional exposures of sub-seismic to seismic-scale architectural geometries which have seen little previous work. Our studies here show the Grès d'Annot to be up to 980 m thick with an overall 'net:gross' >75%, mean sandstone bed thickness of 0.70 m and mean sand-body thickness of 26.1 m. Sand-bodies have simple tabular external geometries (lobe/sheet-like) but show complex internal organisation characterised by a combination of scouring, bypass and aggradational features (channel-like).

The best-exposed, most laterally continuous sand-bodies were targeted for very detailed studies. A key result is a panel 35 m thick, 1700 m long ('downdip') within which all zones are fully characterised in terms of key properties (grain-size, sorting, cementation, primary and secondary structures) and all key surfaces are absolutely correlated (i.e. directly physically traced). This unique database allows quantification of lateral facies relationships and deterministic definition of both architectural components and stratal hierarchy. Numerical simulations of this outcrop panel are compared with an analogous turbidite field from the Central North Sea to evaluate reservoir modelling constraints and best practice in high-N:G turbidite reservoirs, where the scale and distribution of intra-reservoir heterogeneities are believed to have critical effects on production. Particular emphasis is placed on the modelling and production impact of reservoir heterogeneity on long-reach horizontal wells.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia