Spectral Analysis of Aeromagnetic Data using Fourier Transform for Geothermal Energy Potential Assessment-Case Study of Niger Delta, Southern Nigeria

The aeromagnetic survey contour map of the study area, sheets 310, 311, 319 and 320 was obtained from the publication of the Nigerian Geological Survey Agency (NGSA, airborne geophysical series, 1976) was published on a scale of 1:100,000. The contoured aeromagnetic maps were digitized in ArcGIS to estimate the total field intensity values of the study area. The observed regional magnetic anomaly of the study area was refined by the introduction of a plane polynomial surface. The deep heterogeneity of the earth crust of the regional map of the study area was observed to be trending in the NE-SW direction. The power spectrum is extracted from a two-dimensional Fourier Transform estimated from the residual total magnetic field intensity values. This was done by subjecting the residual magnetic data to computerized method of filtering by spectral analysis. The result presents a delineation of the sub-surface sources (the Curie-point isotherm depth and thickness). In addition, the depth to the causative bodies was estimated by calculating the slope of each graph (deep and shallow origins). The estimated geothermal gradient and heat flow for the study area varies between 44.46 and 101.088 C/km for the geothermal gradient and correspondingly between 111.72 and 252.71mW/m2 for the heat flow which is a primary observable factor for geothermal exploration. The general trend shows that the area with the highest heat flow value (252. 71mW/m2) corresponds to the area with the highest geothermal gradient and vice-versa and also area with shallow Curie-point depth has high heat flow. Heat flow in values greater than 80 – 100mW/m2 are indicative of significant geothermal potential. Hence, the high potential regions are recommended for more detailed study in view of exploration.