ABSTRACT
This research was aimed towards the assessment of geothermal potential part of Borno Basin north-east Nigeria using aeromagnetic and aeroradiometric data. Regional/Residual separation was performed on the total magnetic intensity map using polynomial fitting, and the residual map was divided into nine spectral blocks of which the log of spectral energies were plotted against frequency. Centroid depth and depth to top boundary obtained was used to estimate the Curie point depths, which were further used in computing the geothermal heat flow of the study area reveals that the curie point depth ranges from 9.74 km to 21.68 km with an average value of 15.71 km. The geothermal gradient, vary between 26.75 oC/km and 59.55 oC/km. The results shows that the heat flow values of the study area vary between 71.09 mW/m2 and 150.07 mW/m2, low values of 65 mW/m2 to 90 mW/m2 are located at the Northeastern and Northwestern part of area (Awiam and Bajoga) and higher value of 100 mW/m2 to 150 mW/m2 can be located at most part of the southcentral part (Dukku and Bajoga). This shows that the geothermal heat flow varies between 67.41 mWm-2 and 150.07 mWm-2. The aeroradiometric data covering the study area was also analysed to estimate the radiogenic heat contribution. The radioactive heat production values vary between 1.25 µW/m2 and 2.03 µW/m2 with an average of 1.43 µW/m2. The estimated heat flow value of 80 mW/m2 to 100 mW/m2 obtained around Awiam, Dukku (north/western), and Nafada and Bajoga (Northeastern and southeastern) region of the study area makes the area to be of favourable for geothermal exploration.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background of the Study
Geophysics is a very powerful and dynamic tool of exploration and consistently used in reconnaissance surveys. There are many geophysical survey methods, which include gravity, magnetic, radiometric, seismic, electrical resistivity etc. Each of the above survey method has a unique operative physical property like density, magnetic susceptibility, radioactivity, propagation or velocity of seismic waves and electrical conductivity of the Earth (Kearey et al., 2002). These methods were used to investigate the subsurface geology of an area of interest. Some of these methods can still be applied by flying the geophysical equipment namely magnetic, electromagnetic, gravity and radiometric. Airborne geophysics is an effective way for surveying a very large area quickly for regional exploration.
The quest for renewable energy sources as a means of alternative energy to carter for the dwindling rate of power supply, which will meet up with the current population growth and industrial development in Nigeria, has necessitated the need for this survey. A high resolution Aeromagnetic and Aeroradiometric data over part of Borno Basin, an extension of the Nigeria part of Chad Basin, has been analysed and interpreted quantitatively with the aim of investigating the study area for possibility of geothermal potentials by estimating the Curie point depth and the heat flow of the study area based on a reconnaissance for geothermal energy.
The Curie point (bottom of magnetic source) is the point within the earth crust at about the temperature of 580 °C where magnetic properties of rocks disappears and magnetic minerals show paramagnetic susceptibility (Khojamli et al., 2016).
Depending on the geology and rock mineral contents, Curie point temperature varies from area to area. It is therefore normal to expect minimum Curie point depth (CPD) at the regions which have geothermal potential, young volcanisms and a thin crust (Aydın and Oksum, 2010). The assessment of the disparities in the CPD of a particular region can give a preliminary and appreciated information about the area temperature distribution at a depth and the geothermal energy potential of the subsurface (Tselentis, 1991).
In some part of Nigeria; Ikogosi in Southwest and Wikki in the North Central, there are geological evidence of warm spring and hot spring respectively, which have signs of good indication for geothermal energy potential. The aeromagnetic and airborne radiometric data of part of Borno Basin based on a reconnaissance survey was used to assess the geothermal energy potentials in the study area.
1.2 Statement of the Research Problem
Presently, there is an inconsistent supply of power in the country, because the hydroelectricity needs constant supply of water and we experience a two-season period (rainy and dry) in Nigeria. During dry season, hydroelectric dams usually have low level of water for our power plant to function well. Household generators are noisy hazardous with high emission of carbon dioxide into the atmosphere.
Other power sources that have been explored are unreliable, very expensive to maintain and in most cases are hazardous to the environment. The availability of geothermal energy which results from radioactive decay of minerals within Earth’s core are readily utilised by several countries of the world. However, in Nigeria quite a little of this energy alternative source is known. This is even with the existence of the known potential entities such as; Ikogosi warm spring (37 0c) in Ondo State, Wikki warm spring (39 0c) in Bauchi State and Rafin- Ruwa warm spring (45 0c) in Plateau State.
1.3 Justification for the Study
Assessing the geothermal potential in Borno basin will help determine areas of good geothermal energy to augment and boost power supply in the study area. In addition, keen interest on the importance and uses of geothermal energy, which is a non-fossil fuel energy source, is very important in the quest to boost Nigeria’s current grid. Quite importantly, almost all aspect of human life require energy.
1.4 Aim and Objectives of the Study
The aim of this study is to assess the geothermal potential in part of Borno basin using
Aeromagnetic and Aeroradiometric data. The objectives of the study are to:
i. produce and interpret the composite total magnetic intensity (TMI) map and the ternary concentration maps of the radionuclide elements (Uranium, Thorium and Potassium).
ii. separate the composite (total magnetic intensity) map into regional and residual components.
iii. use spectral analysis to reveal Curie point depth, geothermal gradient and Heat flow.
iv. interpret the radiometric data for possible radiogenic heat contribution.
v. delineate areas suitable for geothermal exploration and exploitation.
This material content is developed to serve as a GUIDE for students to conduct academic research
ASSESSMENT OF GEOTHERMAL POTENTIAL IN PARTS OF BORNO BASIN NORTH-EAST NIGERIA USING AEROMAGNETIC AND AERORADIOMETRIC DATA
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