Aspects of the Petroleum Systems in the Southeastern Niger Delta, Nigeria

Olumuyiwa A. Olawoki, Simeon Bolaji Famakinwa

The Niger Delta of Nigeria, West Africa is a series of thick, shore-parallel, southward-migrating subbasins with significant temporal and spatial connotations. The sedimentary packages are diachronous but could be packaged into a basal marine Akata Formation, middle paralic Agbada Formation and top continental Benin Formation. Numerous unconformities subdivide the Agbada into the Biafra, Rubble, Qua Iboe and D-1 members.

Eight classically-defined petroleum systems are identified in the southeastern Niger Delta. They are the Akata-Biafra, Akata-Rubble, Akata-Qua Iboe, Akata-D1, Biafra-Biafra, Biafra-Rubble, Biafra-Qua Iboe and Biafra-D1 (?) systems. They are all hypothetical, Type III-dominated, and vertically-drained petroleum systems. The Akata-Biafra (?) and the Biafra-Biafra (?) are the most prolific and widespread.

Preliminary biomarker characterization work shows that the oils are largely terrestrial in origin and Tertiary in age, based on the high oleanane content. Kerogen type is dominantly Type III, TOCs about 1.5% and HI in the 50-200 range. Thermal maturity data, supported by geochemical modelling indicate hydrocarbon generation to be in the early to main generation phase. The high Pristane/Phytane ratios (>1.8) and stable carbon isotope values are suggestive of oils generated under oxidizing conditions.

One-dimensional basin modelling (BMod) indicates the top of maturity window (main phase 25% TR) to be generally between 8,500^prime and 10,500^prime deep. It is as shallow as 8000^prime in areas of high heat flow (~63HFU) and as deep as 16,000^prime in areas of relatively low heat flow (-45HFU). This variation appears to be related to the sand/shale ratios.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995