Geothermal Gradient, Heat Flow and Curie Point Depth as Key Indicators of Hydrocarbon Maturity in Parts of Southern Nigeria: Insights from Aeromagnetic Data

Abstract

This study evaluates the use of Curie-point depth (CPD), geothermal gradient, and heat flow as regional indicators of hydrocarbon maturity across parts of southern Nigeria using aeromagnetic data. Eight magnetic sheets covering the southeastern onshore Niger Delta, Calabar Flank, and adjoining Basement Complex were processed, and the residual magnetic field was divided into 40 overlapping spectral blocks. Radial power-spectrum analysis was used to estimate the depths to the top and centroid of magnetic sources, from which CPD, geothermal gradient, and heat flow were calculated. CPD ranges from 23.27 to 83.15 km, with a mean of 60.36 km. The geothermal gradient ranges from 6.98 to 24.93°C/km, with a mean of 10.30°C/km, while heat flow ranges from 17.44 to 62.33 mW/m², with a mean of 25.74 mW/m². Blocks 2, 4, 7, and 29 show intermediate CPDs and moderate thermal conditions that may be comparatively favourable for oil maturation. Blocks 8, 9, and 18 exhibit shallower CPDs and higher thermal parameters, suggesting more advanced maturity and possible gas-prone conditions. Blocks 19, 32, 35, and 36 display deeper CPDs and lower thermal parameters, indicating comparatively cooler and potentially under-mature conditions. The results demonstrate the value of aeromagnetic CPD analysis for regional thermal screening, while recognising that the interpretations remain indirect and require confirmation using borehole, seismic, and geochemical evidence.