The Agbami structure is in a lower slope environment outboard
of the modern shelf slope break in a Miocene-to-recent depobelt
where structure is dominated by detachment folds, shale ridges
and toe thrust anticlines induced by upslope extensional growth
faulting on the outer shelf margin.
According to ChevronTexaco officials, Agbami itself is a northwest/southeast
trending doubly plunging thrust-faulted, detachment-fold anticline
that's 20 miles long. The structure is characterized by crestal
extensional faulting of the Pleistocene to upper Miocene sequences
over middle Miocene to Paleocene strata that were thrust-faulted
and later uplifted by a shale-cored detachment fold.
Oligocene and earliest Miocene sediments deposited over the
Akata shale Formation were middle to lower bathyal shales and
basin floor fans with broad areal distribution. Isochron and isopach
mapping indicates a major lower Miocene sediment fairway across
the crest of the Agbami structure, with the presence of basin
floor fan sands likely.
Regional paleoenvironmental and palinspastic reconstructions
of the Agbami area support unconfined sheet-like basin floor fan
deposition throughout the lower and part of the middle Miocene.
Biostratigraphy and facies analyses of the Agbami 1 and 2 wells
have confirmed bathyal environments within the middle Miocene
slope channel, slope fan and basin floor fan facies. As the shelf
prograded outward, depositional loading induced structural folding,
beginning about 12.5 million years ago. This has resulted in bathymetric
features that channelized subsequent sedimentation, leading to
channel-levee type deposition.
AAPG
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