Analysis and interpretation of high-resolution aeromagnetic data for depth estimation and geothermal energy exploration around the middle benue trough, Northcentral Nigeria / Eko Gerald Ejiga

Eko , Gerald Ejiga (2022) Analysis and interpretation of high-resolution aeromagnetic data for depth estimation and geothermal energy exploration around the middle benue trough, Northcentral Nigeria / Eko Gerald Ejiga. PhD thesis, Universiti Malaya.

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Abstract

The geothermal energy potentials of areas around the Akiri and Awe hot springs in the Middle Benue Trough (MBT) of Northcentral Nigeria was assessed using high resolution aeromagnetic data (HRAD). The data, acquired by airborne magnetic survey, was processed, and analyzed for basement depth delineation, structural assessment, Curie point depth (CPD) estimation, as well as geothermal gradient and crustal heat flow determinations. Applying the scaling/fractal method based on correlated distribution of magnetic sources, yielded a basement depth/sediment thickness ranging from 1.8 – 6.3 km, and CPD between 14.3 – 23.3 km, with an average of 18.7 km. The scaling exponent ranging from 0 – 2 was calculated based on the various lithologies of the area. The conventional centroid method based on uncorrelated distribution of sources was however, tested in the region for the purpose of comparison and substantiation of results, and found to have over-estimated the CPD by an average of 7.2 km per block window. The CPD is the depth at which ferromagnetic minerals losses their magnetic properties to become paramagnetic and no magnetic response can be captured beyond this depth. It serves as a proxy for direct crustal temperature measurement due to several constraints associated with borehole measurements, like huge cost of drilling and limited depth of penetration. The geothermal gradient and crustal heat flow obtained varies from 24.9 to 40.6 ℃/km with an average of 31.9 ℃/km and, 62.2 to 101.4 mW/m2 with an average of 79.7 mW/m2 respectively. The forward modelling together with derivative analysis indicate that the Cenozoic magmatism in the MBT was far more extensive than revealed by surface mapping, with numerous emplacements of volcanic intrusions into the Cretaceous sediments. The major orientation of the geologic structures in the area is in NE–SW, aligned with the axis of the Benue Trough. Other minor trends are in NW–SE, N–S, E– W directions signifying multiple episodes of tectonic regimes across geologic time. The shallow CPD and ensuing high heat flow obtained in the central to southwest portion, together with imprints of several volcanic intrusions, as well as presence of deep fault planes which could have served as conduits for heat transfer, indicate the presence of probable anomalous geothermal energy potential in the area. This potential is found to be more concentrated near the hot springs. The energy generation capacity of Nigeria is grossly inadequate and these geothermal resources, if effectively exploited could address the energy needs of the country while at the same time safeguarding the environment from excessive pollution as the case with other non-renewable energy source.

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