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Salient Geological Aspects of Deep Offshore Nigeria, West Africa

Obaje, Ibikunle J.1
1 Department of Petroleum Resources P.M.B., Lagos, Nigeria.

The renewed drive to aggressively explore the Nigeria deep offshore off Gulf of Guinea in the West African Margin has proven the deep water zone as one of the world’s largest petroleum provinces.

The availability of high resolution combination of Post Stack Time Migration (PSTM) and Pre-stack Depth Migration (PSDM) regional seismic data and integrated proprietary exploration and production datasets revealed several discrete depositional, stratigraphical and structural episodes in the development of the main Tertiary Niger Delta and Deepwater zone.

In this paper, we shall examine attributes of the deepwater fans using high resolution regional PSTM, PSDM and integrated proprietary datasets to characterize the reservoirs and provide a clearer picture of the environment of deposition and overall architectural reservoir styles and proffer new play ideas and robust subsurface field development strategies.

The Nigeria deep offshore probably developed from a simple Stratigraphy and complex imbricate structures with sediment loading and structuration onto major litho units occurring from the Cretaceous Times. Active ‘structuration’ and sedimentations were prominent from the Oligocene with varying intensities from Miocene through Pliocene due to eustatic changes and gravity driven processes which developed the varying trap mechanisms and associated reservoir facies and geometries from the Slope through the Basin floor.

Comparatively, the Nigeria deep offshore is an extension of the Niger Delta which is typically a regressive sequence of clastic sediments developed in a series of offlap cycles. All deep wells in the basin document a tripartite lithostratigraphic succession in which the regressive sequence is demonstrated. Three main lithistratigraphic units are common on the Niger Delta. In the eastern portion, the characteristic marine Akata Mobile Shale which is relatively the oldest unit maintained a regional continuity from the onshore Niger Delta to the deepwater from the Eocene to Oligocene Times and thinned out in the western portion as the main Cretaceous sediments regressed basinward and strongly rifted to create the sag basin while the Agbada and Benin Formations being the younger units (probably from Miocene to Recent) could not be said to have continued into the deepwater due to the complex deepwater geological processes that ensued from the Shelf through the Slope to the Basin floor since the Oiligocene Times.


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