SOURCE:

Faculty: Physical Sciences
Department: Applied Geophysics

CONTRIBUTORS:

Ikumbur B. Emmanuel
Onwuemesi A. G.

ABSTRACT:

An investigation of geothermal energy potential of Parts of the Middle Benue Trough, Nigeria, has been carried out using aeromagnetic and aeroradiometric data obtained from the Nigerian Geological Survey Agency (NGSA), Abuja. The study area lies on latitudes 7030lN to 9000lN and longitudes 8030lE to 10000lE. It consists of nine square blocks of map sheet (210, 211, 212, 231, 232, 233, 251, 252 and 253). The softwares used were Surfer 32 and Microsoft Excel. The methods involved in aeromagnetic analysis include production of the total magnetic intensity (TMI) anomaly map and separation of the contoured TMI map into regional and residual anomaly by fitting a linear surface to the aeromagnetic data using a multiple regression technique. The aeromagnetic data was analysed using spectral method to obtain depths to top (Zt), centroid (Zo) and bottom (Zb) of the magnetic sources. In analysing the radiometric data, the nine radiometric data sheets were contoured to produce one map for each of the three radiometric elements of K, Th and U. From the radiometric heat calculations, a single radiometric heat map was produced. The results from aeromagnetic analysis show that the depth to top of magnetic sources in the study area ranges between 0.76 and 4.46 km with an average of 2.14 km; while the depth to centroid ranges between 7.29 and 19.6 km with an average of 14.21 km. The depth to bottom of magnetic sources corresponds to the Curie point depth (CPD) in the study area which is the depth at which magnetic rocks lose their magnetism. Lineament analysis using the lineament map and rose diagram showed the main structural trend in the study area to be north-east to south-west (NE-SW), while minor ones trend east to west (E-W) and NNE-SSW directions. The spectral method was used to estimate the CPD, geothermal gradient, and geothermal heat flow in the study area. The results show that the CPD varies between 12.70 and 37.22 km, with an average of 26.29 km; the geothermal gradient varies between 15.58 and 45.670C/km, with an average of 23.580C/km; and the geothermal heat flow varies between 38.9 and 114.17mW/m2, with an average value of 58.94mW/m2. From the aeromagnetic analysis method, two mathematical models were established to show the relationship between geothermal heat flow and CPD; geothermal heat flow and geothermal gradient. From the graphs, it is shown that the geothermal heat flow in the study area increases with a decrease in CPDs; while the geothermal heat flow increases with an increase in geothermal gradient. The modelled equations for the study area were Q = 0.1135Z2 – 8.3879Z + 196.48 (for geothermal heat vs CPD) and Q = 2.5Z + 0.0002 (for geothermal heat vs geothermal gradient). The geothermal heat flow values around Shendam, Lafia, Akiri, Ibi, Makurdi and Akwana fall between 60 and 100mW/m2 which is the acceptable standard for geothermal heat flow potentiality. The radiometric heat analysis shows high heat concentration in the same areas where there is high geothermal heat deduced from magnetic analysis. Therefore, areas with high geothermal heat flow which corresponds with high radiometric heat are areas that are geothermally active and can be utilized for geothermal energy production. Areas of high geothermal energy potential in the study area include Shendam, Lafia, Akiri, Ibi, Makurdi and Akwana.