Curie point depth and heat flow estimations for geothermal energy exploration in parts of southern Nigeria’s inland basins

In the ongoing quest to improve power supply in Nigeria and boost economic activities, new forms of environmentally friendly, carbon-neutral energy sources are being prioritized. Geothermal energy, whose exploration in diverse geological settings initially relies on geophysical methods, is one of such promising avenue. In this study, high resolution aeromagnetic data were acquired over Afikpo, Oban Massif and up-dip Niger Delta areas in Nigeria to evaluate the prospectivity of geothermal energy. To fully tap into the rich information contained in the high resolution aeromagnetic data and further our understanding of the geothermal energy potential, we have performed spectral analysis on the acquired data. Firstly, the reduced-to-equator of the residual field of the aeromagnetic data was segmented into several overlapping blocks. Using the centroid method, the average depth to the top of the magnetized crust, Z_t, was first estimated by linear fitting to the high wave number portion of the power spectrum of the aeromagnetic data. Afterward, the depth to the centroid of the magnetized crust, Z_o, was computed by linear fitting to the low wave number portion of the radially averaged power spectrum. Thereafter, the depth to the bottom of the magnetized crust was calculated from Z_b = 2Z_o – Z_t. These results were validated using forward modeling of the spectral peak. On the basis of the obtained results, the Curie point depth (CPD) varies from 12 to 35 km. The Curie temperature of magnetite was used to estimate the geothermal gradient and heat flux in the study area. Results show that the northeastern and southeastern parts of the study area, with shallow CPD’s, high geothermal gradient and heat flux, possess huge potential for geothermal energy resource, which could be harnessed to improve power supply in Nigeria.