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

Abstract

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.