Detachment-Style Folding in the Outer Fold and Thrust Belt of the Niger Delta

The Niger Delta outer fold and thrust belt is the compressional toe of a linked extensional-compressional system. It contains a wide variety of structural styles that have been interpreted using models of fault-propagation and detachment folds, as well as simple- and pure-shear fault bend folds.

Interpretations of the first order kinematic evolution of the compressional part of the Niger Delta are mainly based on regional scale balanced structural restorations that attempt to match the amount of extension updip on the shelf with the amount of shortening in the deep water. Our experience shows, however, that the charge and distribution of hydrocarbons are mainly controlled by the architecture and kinematic evolution of the individual folds, examples of which have not been reported.

We present a 3-dimentional kinematic model of a singular detachment fold, whose evolution has been studied using a combination of depth converted seismic data and structural modeling, including 2D and 3D structural restorations, isopach mapping, area balancing etc. Our model indicates that the shape (i.e., amplitude, wavelength, symmetry) of the structure is defined by a number of local factors, including the geometrical and mechanical properties of the deformed layers as well as those of the underlying detachment. Implications of this structural model for the petroleum system will be discussed.