A reassessment of hydrocarbon prospectivity of the chad basin, Nigeria, using magnetic hydrocarbon indicators from highresolution aeromagnetic imaging

Abstract

High resolution digital aeromagnetic data acquired by the Nigerian Geologic Survey Agency (NGSA) over a part of the Chad Basin, Nigeria, were analyzed to investigate the hydrocarbon prospectivity of the basin using various magnetic hydrocarbon indicators. The digital aeromagnetic data were processed to produce total magnetic intensity and residual magnetic maps, and further transformed into Reduced-to-the-Equator map to remove the asymmetry associated with low latitude magnetic anomalies. Horizontal, vertical, and tilt derivatives, and 3D Euler deconvolution analyses were used to map the geometry and depth of basement rocks. Intra-sedimentary magnetic anomalies with possible association with hydrocarbon occurrence were enhanced by the application of band pass filters. The derivative maps revealed parallel to sub-parallel trending NE-SW, NW-SE and E-W lineaments probably caused by fracture zones in the basement underlying the study area, some of which propagate as faults into the overlying sedimentary formations. The thickness of the sediments in the study area ranged from 1.5 km in the north-eastern region, 6.0 km in the south-eastern region to 7.0 km in the eastern region. The band-pass filtered map displayed some magnetic aureoles (circular magnetic low surrounded on all sides by magnetic high), often associated with hydrocarbon seepages. These aureoles characterize the deepest parts of the basin in the east-central and south-western parts, far removed from the existing exploratory wells that are mostly dry. It was concluded that the east-central and south-eastern parts of the basin investigated with a combination of favorably thick sedimentary formation, faults, fractures and magnetic aureoles probably represented areas of better potential for hydrocarbon exploration and were thus recommended for detailed seismic surveys.

Keywords: Chad Basin, Hydrocarbon Prospectivity, High-resolution Aeromagnetic Imaging, Magnetic Hydrocarbon Indicators.