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PROJECT AREA I
The Project Area I study area comprises most of
the northern end of the late/middle Miocene Depo-belt and includes the CPIRL/Atlas
block OML 109. This portion of the depo-belt is one of the most highly
petroliferous province in the delta. Middle/late Miocene hydrocarbon
reserves are estimated at 5.3 billion barrels of oil and 6 trillion ft3 of gas
(about 6.3 billion BOE) or total hydrocarbon resources of 11.6 billion BOE in or
adjacent to the study area. Generally, these oil reserves are concentrated
in the eastern and central sectors of the depo-belt.
The hydrocarbon resources (oils) of the Study
Area I indicate several oil families with varying maturities. This is
indicative that multiple source rocks generated the reservoired oils. The
characteristics of the oil families indicate a wide variation in the
depositional environment of the source rocks that generated these oils.
Although the maturities of the oils vary, they range from least mature to medium
maturity indicating that generation and/or migration occurred during early to
main phase of the generative cycle. The variations in maturity of the oils
indicate that multiple or continuing phases of generation and migration supplied
these oils. Oil reservoirs appear to be most abundant over the inboard
portion of the depo-belt, while gas reservoirs appear to be most abundant over
the outboard portion. The concentration of oil resources in the inboard
portion of the depo-belt appear to be indicative of early structure formation in
this portion of the depo-belt, an efficient upper seal for the petroleum system
(Mefa shale/clay), and efficient fault conduits for the migration of
hydrocarbons from multiple source rock sequences. In the outboard portion
of the depo-belt, the structures appear to be more compartmented, to have longer
basinward flanks, and complications of shale (clay) diapirism.
PROJECT AREA II
Project Area II comprises north-central portion
of the Pliocene/late Miocene Depo-belt. In the depo-belt adjacent to the
study area, presently discovered late Miocene to early Pliocene hydrocarbon
reserves are estimated at 750+ million barrels of oil and 1.5+ trillion ft3 of
gas (about 1.6 billion BOE) or a total of 2.35 billion BOE. Generally,
these reserves are concentrated in the east-central sectors of the depo-belt.
The two oil families were identified with varying
maturities ranging from mid to less mature. Characteristics of oil
families identified indicate a transitional environment of deposition for the
source rocks generating the oils. The oil maturities indicate that the
oils were generated and/or migrated during the early to mid phase of the oil
generative-window. The range of maturities also indicates that the oils
were generated or migrated during multiple or continuing phases. As in the
preceding study area, the occurrence of oil reservoirs is more abundant in the
inboard portion of the depo-belt with gas reservoirs more abundant in the
outboard portion of the depo-belt. The hydrocarbon resources of this
portion of the Pliocene/late Miocene depo-belt are not as rich as in the eastern
portion of the depo-belt (see Project area III). In a number of areas in
the Plio-late Miocene depo-belt, the zone of abnormal pressure is higher than
the zone of thermal maturity indicating the onset of oil generation.
Available data indicates that occurrences of oil reservoirs in this zone are
rare.
PROJECT AREA III
Project Area III lies in the eastern end of the
Pliocene/late Miocene depo-belt and includes the offshore Cameroon Rio del Rey
sub-basin. This portion of the Pliocene/late Miocene depo-belt is a highly
petroliferous province and is one of the richest in the delta. Lower
Pliocene/Upper Miocene-reservoired hydrocarbon reserves are estimated at over
6.3 billion barrels of oil and 6+ trillion ft3 of gas (over 6.3 billion BOE) or
total hydrocarbon resources of over 12.6 billion BOE. Generally, these
reserves are spread across the entire width of the depo-belt.
Seven oil families ranging from lowest to highest
input of higher land plant debris have been identified in or circa to the
project area. The great variations in oil families is indicative that
multiple source rock sequences with varying environments of deposition
contributed to the oil resources of petroleum system in this portion of the Plio-late
Miocene depo-belt. The concentration of low-oil maturity in the eastern
portion of the depo-belt indicates that these oils were most probably generated
and/or migrated during the earliest oil-generative phase. More mature oils
to the east at Isongo and to the northwest on the outboard trend of the late/mid
Miocene depo-belt indicate that these hydrocarbons were generated and/or
migrated from more mature source rocks during the mid-to-late phase of the oil
generative cycle (multiple pulses).
The presence of two transgressive clay units, the
early-late Miocene Afam and late Miocene Qua Iboe, offer a competent and
wide-ranging upper seal for the hydrocarbon system of the eastern study area.
These regressive clays cove a major portion of the eastern late-mid Miocene and
Plio-late Miocene depo-belts. The regressive clays play a significant part
in the development of stratigraphic and/or combination strati-structural play
concepts in these portions of the depo-belts.
The distribution of oil reservoirs across the
entire Plio-Miocene depo-belt (not concentrated in specific regimes of the depo-belt
as in Area 1 and Area 2) can be explain by: 1) the presence of multiple
regressive clay seals; 2) the multiplex of system tracts providing reservoirs
and multiple source rocks; 3) the complexity of diapiric tectonics providing an
abundance of structures; 4) multiple fault systems providing a wealth of
migration conduits; and 5) the stratigraphic effects associated with the incised
valley (Afam and Qua Iboe) system tracts. These structural, stratigraphic,
and geochemical factors highly impact the petroleum system of the project area. |
