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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Deepwater Nigeria Play Characterization
By
Shell Exploration and Production
Houston, Texas
Deepwater Nigeria is divisible into eight major structural
plays: eastern and western minibasins, eastern and western
fold belts, eastern and western thrust belts, and the relatively
unstructured transform margin. Each play is characterized by a
unique set of play criteria, including predominate
trap
type, lead
density, field size distribution, gas fraction
and success rate. Discovered probable recoverable
volumes from all plays total 10.8 billion
barrels of oil equivalent (BBOE) with
65% of the volume being oil.
Minibasin plays in the eastern and western
portions of deepwater Nigeria cover areas of
6,000 and 15,500 sq km, respectively. Water
depths range from 200 to 1,500 m. The minibasins are complex
extensional basins that have a high density of relatively small
traps along shale diapir flanks and faults. Twenty-one structures
have been drilled in these plays, resulting in 3.5 BBOE of probable
recoverable volumes. Although a few of the wells are dry, the
commercial success rate is the lowest of the proven plays with
hub volumes discovered in only two of the basins, the Bonga-
Aparo Basin in the west and the Usan Basin in the east. Hub
volumes have been discovered in channel-over-nose structural
-stratigraphic
traps on larger, simpler structures. Wells finding
technical success volumes are predominantly along steeply-dipping
diapir flank structures. Although past discoveries have
predominately seen oil, the gas fraction most likely comprises at
least 50% of the future play volumes.
The fold plays in the eastern and western portions of deepwater
Nigeria cover 9,200 and 10,000 sq km, respectively. Water depths
range from 1,500 to 2,000 m. The fold plays are characterized
by a small number of very large simple traps. An estimated total
of 7.1 BBOE has been discovered by 18 wells with a 50%
commercial success rate. The wells have
proved one of the largest global deepwater
field size distributions with a mean discovery
volume of 475 MMBOE. The eastern fold
play is characterized by relatively simple anticlines
with Middle to Lower Miocene basin
floor reservoirs. The western fold play targets
predominantly channel-over-nose structural
-stratigraphic
traps in Middle to Lower
Miocene reservoirs. The low density of large traps resulted in
rapid creaming of the plays.
Thrust plays cover 35,000 sq km, half the structured play area in
deepwater Nigeria. Thrust plays are subdivisible into three
segments: inner and outer thrust belts in the western and an eastern
outer thrust belt. The outer thrust belts are toe-of-slope compressional
trends coincident with the main phase of extension along
the coast to the outer shelf. The western inner thrust belt is probably
an older fold/thrust system
reactivated by shale diapirism from
the Upper Miocene to the present. Due to extreme
structural
complexity and low
trap
retention, the western inner thrust belt
has been tested by only one well, a dry hole. The outer thrust belt
plays include nearly 200 en-echelon seaward- and landward-dipping
thrust structures in water depths of 2,000 to 3,000 m. A
majority of the structures have present-day seafloor bathymetric
expression.
Trap
retention coupled with charge and migration
risks as well as ultra-deepwater depths make this a technically
challenging play.
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