Modeling Crustal Structures of Southern Nigeria Basins from Aeromagnetic Data: Implication on Hydrocarbon Prospectivity

Southern Nigeria has major and minor sedimentary basins. This study covers parts of 5 sedimentary
basins in southern Nigeria, this includes the Niger Delta, Benue Trough, Calabar Flank, Mamfe basin
and Lower Benue Trough. Aeromagnetic data has been used by many authors worldwide in
evaluation of subsurface basin configuration. This study covers parts of five basins (Niger Delta,
Calabar Flank, Anambra Basin, Mamfe Basin, and Lower Benue Trough) in Nigeria. The study utilized
twenty aeromagnetic maps on a scale of 1:100,000. The maps were digitized manually along flight
lines and a total of 16,689 data points obtained. The data was processed using computer techniques
including map merging, reduction to pole, polynomial and power spectrum filtering for residual and
regional anomaly separation, and forward and inverse 2.5D Saki modeling. Results obtained from
power spectrum depth analysis indicate depth to magnetic sources vis – a –vis sediment thickness
from the Niger Delta area (2.75 km - 3.75 km), Anambra basin (1.5 km – 2.6 km), Calabar Flank (1.3
km – 2.3 km), Mamfe basin (2.0 km – 3.4 km), and Lower Benue Trough (1.5 km – 3.2 km). Also,
depth to basement results from forward and inverse modeling indicate the Niger Delta has thickness
of sediments ranging between 1.0 km- 8.0 km, Anambra basin (1.4 km – 2.7 km), Calabar Flank (0.8
km- 2.5 km), Mamfe Basin (1.0 km – 2.7 km), and Lower Benue Trough (1.4 km – 2.7 km). Also,
results from modeled number of intrusives indicate that the Calabar Flank has five intrusives, Niger
Delta has four intrusives, Mamfe basin has six intrusives, Anambra basin has five intrusives, and
Lower Benue Trough has four intrusives. The implications of the increased number of intrusives are
that generated hydrocarbons might be converted to gas, this is more likely in areas around Calabar
Flank, Mamfe basin and Anambra basins, given the high number of occurrence of intrusives within
these areas. Whereas areas around the Niger Delta and Lower Benue Trough with significantly
increased depth and lower number of intrusive are less prone to excessive heat from the intrusive and
may produce more oil. The study support further exploration activities within the Niger Delta and
Lower Benue Trough areas. The significance of this study is the wide range appraisal of the basin
architecture and configuration of the offshore and inland basins in Southern Nigeria. The Niger Delta
basin areas of Portharcourt, Bonny with sediment thickness of about 8.0km and less occurrence of
intrusives has the highest hydrocarbons exploration potentials. The Bansara area within the Mamfe
basin has (2.6 km) sediment thickness that could generate hydrocarbons given that another condition
is favourable, but the presence of numerous intrusives may make the area prone to excessive heat
and may produce more gas than oil. The Anambra basin and the Lower Benue Trough have a
moderate depth of sediments thickness(2.5km) and less number of intrusives, these areas came
second to the Niger Delta among the studied basins for good prospects in hydrocarbon exploration
investigations. It is concluded that this study reveals the order of preference of the choice of
investigating the hydrocarbon prospective potentials of Southern Nigerian basins using the potential
field magnetic method, it is recommended that other geophysical methods such as gravity, and
seismic be used to identify possible hydrocarbon habitats within the Southern Nigeria Basins.