Relationship Between Thrust Fault Architecture, Pressure Cell Stacking and Hydrocarbon Leakage in the Deep Offshore Niger Delta

Livinus Nosike¹, Christopher Wibberley², Jean-Loup Montenat³, Christophe Jardine², and Yves Pacalin^2
1Géosciences Azur, University of Nice Sophia Antipolis/TOTAL France, Pau, France
²TOTAL France, Pau, France
³TOTAL Congo, Pointe Noire, Congo

Several indicators of fluid leakage including pockmarks, submarine pingoes and mud volcanoes have been observed on the seabed in the deep offshore Niger Delta where the NE-SW gravitational sliding/displacement of blocks result in imbricate thrust structure. But the link between these leakage features and the tectonic processes are yet to be properly understood. Previous IFREMER and TOTAL’s in-house studies have shown that gravity loading by the sediment weight alone is not sufficient to explain the observed expulsions, which Wetness and Total Scanning Fluorescent (TSF) tests show are from depth. The existence of regional seals suggest that expulsion of fluids originating from depth could only be possible (1) by breaching of the caprock due to overpressure build-up, or (2) by fractures and faults formed by structural processes.

We have interpreted the shallow leakage features and used both 3D-seismic and well data to link them to the active/inactive tectonic processes. The architecture of the major thrust, and its extrados faults, was highlighted from map and section views to show how it controls the leakage patterns in the presence of other overpressure-related factors. To describe why some faults or caprocks leak while others do not, we investigated how dynamic and static conditions affect hydraulic fracturing and up-fault leakages. We propose a conceptual “relative scenarios” model to show that the combined effect of anticlinal and up-fault leakages within each stratigraphic layer varies with the nature of the fault-flanking fold, thus explaining both vertical and lateral stacking of geopressure cells in the deep offshore context.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery