Submarine Slope Systems
Initial mapping of the geometry, architecture and evolution of submarine slope channels, offshore Nile Delta, Egypt
(This page focuses on the Nile part of this initial slope systems study. The Tunisian section can be found from the Slope research home page.)
Postdoctoral research by Dr Gianluca Badalini
Objective:
A study covering the offshore basins of North Africa was undertaken. The objective of this project was to review the regional geologic evolution of offshore north Africa and to study in detail some selected study areas characterised by different feeder systems, variations in shelf width, differences in slope morphology and tectonics, in order to determine the evolution and variability of the shelf margin and slope systems, reservoir and source potential and trapping mechanisms.
Data Availability:
Data availability has so far controlled the scope of the study. Three key areas have been identified for this study:
- The Pelagian Basin , Offshore eastern Tunisia , whose structural and stratigraphic evolution can be linked to the offshore Sirte Basin of Libya;
- Offshore northern Tunisia , characterised by the presence of the Maghrebian Thrust Belt, a largely unexplored area whose petroleum potential has recently received new interest;
- The offshore Nile Delta, currently one of the most important deepwater provinces of the world.
BG provided 3D seismic data offshore Nile delta from the WDDM Concession on a confidential basis to NARG .
The project focused on the geometry, architecture and evolution of submarine slope channels. The main objectives were to:
- Map and characterise the large-scale sedimentological architectural elements.
- Identify evolutionary trends in internal/external geometry, vertical stacking patterns, and key intra-channel architectural elements.
- Define channel styles based on these bodies.
- Build a sequence stratigraphic framework, define the cyclicity of the sequences and identify allo/autocyclic processes.
- Reconstruct the 3D depositional geometries of the channels for key stages of their development.
The WDDM Concession lies 50-100 km offshore of the present day Nile Delta. The major structures within the study area are the southwest-northeast –trending Rosetta fault and the east-northeast–west-northwest –trending Nile Delta offshore anticline. Both have been active at various periods during the Pliocene and Pleistocene but have not had a major impact on the depositional geometries of the upper Pliocene channels, which can be traced in map and seismic sections, without significant thickening or change in style across these features (Samuel et al., 2003).
High-resolution 3D seismic has been used to study the shallow section in order to evaluate the evolution of slope systems and facies distribution. The entire study area is characterised by slope channels, mass transport complexes, faulting, and, more locally, by sediment waves, pockmarks and gas chimneys. The succession can be divided into distinct packages separated by well defined continuous seismic facies interpreted as hemipelagic drapes. The delineation of these draping facies allows the sequences identified to be placed into relative chronological order. A number of distinct seismic facies can be identified, and assigned sedimentological interpretations based on internal characteristics and analogues with published data.
Channels are not common on the present-day seafloor, but become extremely abundant in the subsurface. Sizes vary greatly, from small channels presumably representing single sequence channels to large channels that may have been exploited over multiple 4 th order sequences on the upper slope. Re-incision is extremely common and results in only partial preservation of "original" channels. Evolutionary trends in internal/external geometry, vertical stacking patterns and key intra-channel architectural elements reflect the interplay of local controls (slope gradients, flow properties, pre-existing topography, and sediment supply) and regional controls (sea level).
This study provided new insights into deep water clastic systems and collaboration with industry has provided access to a unique dataset. It is hoped this research will allow the generation of models which will improve the understanding of deeper hydrocarbon prospective systems.
This work is being continued by Dr Dorthe Hansen in phase 2 of the offshore slope systems theme.