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Reservoir Risk Assessment by Means of Integrated Hinterland Drainage to Basin Analysis for the Cainozoic Interval of the Cameroon to Namibian Offshore

Mohd Ali, Amita 1; Van Heiningen, Pieter 2; Watkins, Carl 3
1 Subsurface Technology, Petronas Research, Kuala Lumpur, Malaysia.
2 Reservoir Unit, Fugro Robertson, Netherlands, The Hague, Netherlands.
3 Basin Study, Fugro Robertson, UK, Llandudno, United Kingdom.

A drainage study conducted on the Greater Congo and adjacent drainage basins along the Cameroon to Namibia coast (FIG.1) has provided insight into the spational and temporal character and stratigraphical variation of sediment input points at the coast. In addition, shelf and deep-water seismic interpretation has revealed large scale sediment bodies, channels and erosion surfaces which can be correlated to the identified input points.

The aim of this study is to reduce the deepwater reservoir risk of the Cameroon to Namibia margin by defining continental drainage and subsequent sediment transport over time, with a view to determine timing and character of sediment input to the shelf. Understanding palaeo drainage is vital in being able to explain the spatial and temporal variations in shelfal sediment thickness and depocentres.

The morpho-tectonic evolution of the Hinterland has been investigated in GIS by means of topographic modelling and image enhancement of SRTM and Landsat data. This allowed the identification of drainage and landscape characteristics that provide the basis for a new interpretation of drainage evolution. Available thermochronological data in parts of the study area have been reviewed and incorporated in the reconstruction of hinterland denudation scenarios.

The research further indicates that since the opening of the South Atlantic the configuration and geometries of the drainage basins have changed substantially. Flow reversal events, development of wind gaps and deformation of macro-scale drainage basin geometries are amongst the most important results. The presence of water gaps demonstrates that the hydrological and geomorphological situation of the hinterland in question is still dynamic, contrasting with the common perception of an old and considered stable topography for Central West Africa.

Large scale channels limited to the Miocene to Recent suggest shelf uplift and sediment bypass to deep water. Present day Congo sedimentation occurs in deep water, as a result of sediment bypass, facilitated by the landward extent of the Congo Canyon. Spatial variation is controlled by a combination of changes to both basin outlets, regionally dominated by the Southward shift of the Congo outlet and relative sea level variations. Sediment load delivered to the West African Shelf is derived from the erosion of Precambrian igneous and metamorphic lithologies as well as Carboniferous and Cretaceous clastics.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009