Shelf-to-Basin Floor Seismic Expression of the Rosetta System (Western Nile Delta, Egypt): A Modern Analogue of Deep-Water Reservoirs

Abstract

Abstract The need of modern analogues is critical for petroleum exploration, mainly for deep-water reservoirs because of their wide variability in term of size, thickness and lithological lateral changes that make them still difficult predict. Analyse of geometry and stacking pattern of "recent" (Plio-Quaternary) sedimentary bodies can greatly improve our ability to understand buried reservoirs. Because the Nile submarine delta is the largest area of gas exploration and production of the Mediterranean and because its recent history, architecture, source and factors controlling the sediment dispersion are now well constrained, the Rosetta turbidite system (western province off Nile Delta) is probably the best site to study of a silty/mud delta-fed turbidite system. The main goal of our approach is to propose a conceptual model of a delta-fed turbidite system construction and evolution through time. A wide 2D and 3D-seismic data set from the shelf to the basin, respectively provided by GEOAZUR laboratory and GDF SUEZ was made available over the whole Rosetta system (western province of the Nile fan, off Egypt). Numerous sedimentary bodies have been characterized and discriminated along a dip synthetic profile and replaced within a relative chronological framework to build a depositional model of the system and to provide new insights on the architecture and stacking patterns of deep-water reservoirs. The Rosetta system appears to be a rapid point-source migrating system driven by large-scale slope failures and sea-level fluctuations. During sea level falling stages, sediment transfer is constrained and channelized by scars at the shelf break resulting in the construction of small channels indenting the top of mass-transport deposits and depositing ponded lobes in topographic lows. As sea level drops, a short and narrow submarine canyon is progressively formed and the turbidite system progrades toward the basin floor. Sea-level lowstands favour the development of wide shelf-margin deltas, which are feeding and prograding over the canyon head that rapidly evolves in an unconfined meandering leveed channels system. Avulsion processes affect these leveed channels systems as the slope gradient changes due to regional salt-tectonics, crevasse splays, and they deposit wide distal-lobe complexes at their mouths. This model might be used as a predictive model for gas reservoirs for the Kafr El Sheikh and El Wastani formations in the western part of the Nile Delta and, more generally, for any other unconfined delta-fed turbidite systems.