Abstract: Regional Fault Pattern Study - Sonam/Ajapa Area Offshore Western Niger Delta

K. A. Kanu, J. E. Glass, P. C. Okoro, A. A. Adeogba, A. G. Nunns, T. L. Heidrick, H. Xiao

A total of 900 sq km² of high quality 3D data was used to interpret structural trends: an inner trend containing the Mefa, Meji and Ajapa oil fields and a younger outer trend containing the large Sonam condensate field. Each trend is bounded by a large, regional down-to-the-coast fault system on the northeast and its associated counter-regional fault to the southwest.

Hydrocarbon accumulations are contained within rollover anticlines adjacent to the main seaward-dipping fault trends. However, our data shows that structural geometries within each trend are highly three-dimensional. Anticlinal end closure is achieved by changes in fault detachment level and displacement, which generally occur near major fault junctions. Thus, significant accumulations are associated with first-order high-relief accommodation zones. In the absence of such first-order closure, we cannot rely upon the systems of relatively small faults that occur on seaward dipping flanks and in areas of crestal collapse. Detailed 3D mapping, supported by drilling results, shows that such faults do not link strongly together, thereby allowing leakage of hydrocarbons around fault tips an up relay ramps between faults.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France