Basin Evolution and Geochemical Modeling
Sedimentology and Sequence Stratigraphy of Syn-rift Nukhul and Asl formations, Suez Rift, Egypt
Research by Dr Ian Carr, Professor Rob L. Gawthorpe, Dr Christopher A.L. Jackson, Dr Ian. Sharp and Dr Ali Sadek
Introduction:
The project used the exceptionally well exposed Nukhul and Asl Formations in the Suez Rift to develop 4D high resolution sequence stratigraphic concepts and models for shallow marine depositional systems which can be applied at both exploration and production scales in the subsurface, particularly in rift basins (e.g. North Sea, Gulf of Suez).
Aims:
The specific aims of the project were as follows:
Document facies, facies stacking patterns and stratal geometry from shallow marine depositional systems in the early syn-rift (Nukhul Formation) and rift climax (Asl Formation) and determine geometry of facies bodies, the length scales of facies transitions, and the reservoir quality.
Develop detailed, process-based facies models for the Nukhul and Asl shallow marine successions and compare with existing facies models in the literature, which are largely dominated by examples from the Western Interior Seaway.
Produce high-resolution sequence stratigraphic interpretations of shallow marine (and associated) depositional systems based on key stratal surfaces and determine variability of contemporaneous stratal units.
Integrate sequence stratigraphy with analysis of structural development, sediment sources and basin physiography to establish whether sequence variability is systematic and relates to one or more of the major controls (3D) and how controls and sequences change with time (4D) as a result of fold/fold growth and lateral propagation.
Development of sequence stratigraphic models for shallow marine successions with particular emphasis on variability of stratal surfaces and stratal units around growing faults/folds and pragmatic application to subsurface data sets at both the exploration and production scales.
Methods:
Sedimentological and stratigraphic data was collected by:
(1) mapping key stratal surfaces and lateral and vertical facies transitions in the field;
(2) compiling 35 detailed graphic logs and correlation panels;
(3) recording depositional geometries and facies transitions on large scale photomosaics.
Results to date:
The rift-climax Asl Formation is interpreted to have been deposited in a shoreface environment. Tidal sandwaves were developed by currents passing through transfer zones between fault segments. Fault-linkage caused the shoreface and tidal units to be incised by a conglomeratic delta. Flooding and downshift surfaces display typical characteristics of shallow marine key stratal surfaces. The Nukhul Formation is interpreted to have been deposited in a shoreface and estuarine setting. The estuarine deposits can be divided into three associations, tidal inlet, estuary funnel and estuary channel. The estuary deposits show atypical key stratal surfaces. Flooding surfaces commonly have coarse-grained sandstones of the tidal inlet association passing abruptly up to mudstones of the estuary funnel association. Downshift surfaces commonly have mudstones of the estuary funnel association overlying sandstones of the tidal inlet association. These results show the importance in developing a robust facies model prior to sequence stratigraphic interpretation based on key stratal surfaces.