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The Niger delta basin is a major hydrocarbon
producing provinces. The remaining oil reserves for the basin were estimated at
approximately 20 billion barrels (TPC, 1995) Although the oil resources of
the basin are substantial, the gas resources are more abundant. This
characteristic of the Niger delta is consistent with numerous analogs in the
hydrocarbon habitat of worldwide basin. A major contributor to this
characteristic is the high input of terrigenous source rocks that are preserved
by the rapid sedimentation rate generally associated with deltaic deposition.
INTRODUCTION
During the initial portion of the project, three
project areas in the Niger delta were designated for characterization of the
petroleum system(s). The project focused on the late/middle Miocene and
Pliocene/late Miocene depo-belts in which the project areas are located.
The elements and/or processes of the petroleum system characterized will conform
to those outlined by Ekweozor and Daukoru (1994) in their published synthesis of
the older Paleogene Depo-belt I. Areas selected for study during the
initial phase are the following project areas:
Area 1 - comprises a portion of the northern end of the late/middle
Miocene Depo-belt (Depo-belt VI of Ekweozor and Daukoru, 1994).
Area 2 - comprises a large portion of the north-central portion of
the Pliocene/late Miocene Depo-belt (Depo-belt VII of Ekweozor and Daukoru,
1994).
Area 3 - comprises the eastern portion of the Pliocene/late Miocene
Depo-belt (Depo-belt VII of Ekweozor and Daukoru, 1994).
The general question posed for this study was:
“Why or how does the Niger delta petroleum system work or not work for the
accumulation of oil in this highly gas-prone basin?” The elements or
processes analyzed in attempting to answer this question are as follows:
(1) Source and maturity,
(2) Migration,
(3) Trap
(4) Seal,
(5) Reservoir,
(6) Pressure regimes, and
(7) Play concepts.
Many of these elements must be evaluated interactively, thereby producing a
dynamic and integrated interpretation. Many questions can be posed in
relation to these elements; therefore, an inventory of the hydrocarbon habitat
for each depo-belt studied is necessary. Some questions can apparently be
answered while others cannot or the answer is implied. As in many similar
types of studies, analogs and “back-in” analyses must be used. This is
especially true when a complete database is not available.
It was envisioned that a second phase of the
study would characterize the petroleum system of other project areas, especially
in studying the areas of the Plio-Miocene depo-belt not included in this portion
of the study. Additionally, other factors for study during the second
phase would be addressed, including the relationships between depth to top of
oil-generative window and depth to abnormal pressure zone.
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