Deep Plays in the Eastern Niger Delta: The Role of Oblique Slip in Predicting Reservoir and Traps Distribution

Abstract

The Cenozoic wave dominated Niger Delta has been regionally divided in two main lobes separated by the regional NE-SW Charcot Fracture zone. The western edge of the west lobe is delimited by the Chain Fracture Zone while the eastern edge of the East lobe by the Fernando Po Fracture Zone, a regional NE-SW lineament related with the opening of the Gulf of Guinea and the Equatorial Atlantic. The high depositional rate of the Niger Delta strongly influenced the structural styles, as the majority of the observed deformational structures are related to gravity driven sin-depositional processes (i.e. activation or re-activation of growth faults). Other styles of deformation, mainly located in the offshore Niger Delta, consist of thin skinned deformation: fault-bend fold, fault propagation folds, detachment folds and complex imbricate thrust system. The presence of the Akata Fm, a thick level of unconsolidated shale underneath the main sand prone reservoir succession of the Agbada Fm, represents an important regionally extensive detachment level thus supporting the interpretation of thin-skinned deformation. In the Eastern Niger Delta, at the border with Cameroon, gravity-driven and thin-skin deformations have been historically used as reference to build structural subsurface models. In this study, however, oblique slip/transpressive faults and related structural elements have been mapped at different scale, ranging from regional 2D lines, field scale 3D surveys and reservoir scale where they are likely controlling pressure depletion at production scale. A detailed sequence seismic stratigraphic analysis of 2D and 3D seismic data, reveals the presence of a high number of regionally extensive unconformities. Their genesis is likely controlled by the interplay between sediment-driven subsidence and reactivation of complex fault blocks delimited by both regional and local structures with a large range of orientation. This resulted in a reservoir facies complex which, contrarily to other area of the delta dominated by laterally continuous shoreface sandstone, consist of heterogeneous assemblage of tidal channels, lagoon, barrier sands and limited shoreface. Understanding the deformation history of the Fernando Po Fault Zone, is therefore critical to reconstruct the kinematic evolution of this area and predict different styles of deformation and therefore hydrocarbon trapping mechanisms in the Easternmost Niger Delta and neighboring western Cameroon.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018