INVESTIGATION OF GEOTHERMAL ENERGY POTENTIAL USING AEROMAGNETIC AND AERO-RADIOMETRIC DATA OVER PART OF KADUNA STATE

ABSTRACT

The study focuses on both quantitative and qualitative analysis of high resolution aeromagnetic data for the estimation of geothermal potential in parts of Central Nigeria Basement Complex and correlating the results from the analysis of radioactive concentration data of the study area. The study area covers a total of 6050 km2. Two aeromagnetic sheets were used to cover the major towns; Kaguru and Geshere. The study areas are bounded by latitude 100 00′ N to 100 30′ N and longitude 7o 30′ E to 8o 30′ E. The aeromagnetic data subjected to Fourier analysis and spectrum analysis of 10 blocks were carried out to determine the curie depth within the study area. The spectral depth method was employed in evaluating the geothermal parameters. The region found to have a shallow curie point depth of 12 km and the highest Curie point depth of 56 km are located within the North Central regions and South Eastern parts of the study area respectively with an average value of 30.46 km. The heat flow of the study area has values ranging from 30 mW/m2 to 160 mW/m2 with an average value of 80.60 mW/m2. The North-Central region surrounded by Wugana, Kaguru, New Kwasam and also the Western edge of the study area records high and anomalous heat flow values ranging from 105 mW/m2 to 160 mW/m2. The geothermal gradient also has values ranging from 8 0C/km to 50 0C/km with an average of 25.19 0C/km of the study area. Correlating this result with the analysis of radiometric result from Ternary map shows that the region of high concentration of Potassium, Thorium and Uranium contents correspond to the regions  of  relatively  high  heat  flow  and  geothermal  gradient  at  the  North-Central portion of the study area.

CHAPTER ONE

1.0       INTRODUCTION

1.1       Background to the Study

Geothermal energy is the heat energy that is originated naturally from the earth interior mainly by the disintegration of radioactive elements like uranium, thorium and potassium. Geothermal energy is a durable and renewable energy source which can be used  to  generate  electricity  for  space  heating  and  cooling,  cooking,  industrial application,  swimming,  agricultural  application  and  heat  pumps.  Recently,  more attention has been given to it due to its ample benefits like; inexhaustible power supply, environmentally friendly, low emission of greenhouse gases, and it is globally available. All these make the geothermal energy a very vital contributor to the global energy productions in an environmentally friendly way (Sui et al., 2019).

As the pollution and emission of toxic gases and harmful radiations from the industries today causes detrimental effect to our environment and human life, the demand for renewable and clean energy sources become our prime focus. The utilisation of renewable energy sources has provided us with a clean alternative source of energy and has reduced the emission of greenhouse gases. Due to its inexhaustible supply, energy generated from geothermal resources has become the leading source of energy. Electricity production from geothermal sources has increase to a great extend for the

past 20-25 years with an increase of the power generation from 1300 mW in 1975 to 10,715 mW in 2012 (Bu et al., 2012).

Geothermal energy is considered as one of the most favorable expectation and dependable energy resources. It is hardly affected by the weather and always available to provide reliable and steady output. Future growth is expected that geothermal energy reach more than 3% of the global electricity demand by 2050 (Geothermal, 2018).

The geothermal energy source is the heat energy extracted from the earth. About  4.5 billion years ago, this heat is radiated from the centre of the earth from a depth more than 6400km and Scientific prediction has shown that about 42 million megawatts (MW) of Geothermal energy coming out from the centre of the earth into its surface is mainly by conduction (Geothermal Energy Association, 2018). In addition, the geothermal energy source usually ranged from the shallow reservoir to the ultra-deep reservoir  at  a  depth  of  thousands  kilometer  in  the  earth  subsurface.  Geophysical methods play a vital role in geothermal exploration since many objectives of geothermal exploration can be achieved by these methods. The geophysical surveys are directed at obtaining indirectly from the surface or from the shallow depth, the physical parameters of the geothermal system (Keller, 1981).

A geothermal system is made up of four main elements: a heat source, a reservoir, a fluid which is the carrier that transfers the heat, and a recharge area. The heat source is generally a shallow magmatic body cooling and most at time molten. The volume of rocks  from  which  heat  can  be  extracted  is  called  the  geothermal  reservoir,  which contains hot fluids describing as hot water, vapor and gases.

A geothermal reservoir is usually surrounded by colder rocks that are hydraulically connected with the reservoir. Hence water may move from colder rocks outside the reservoir (recharge) towards the reservoir where hot fluids move under the influence of boney forces towards a discharged area.

Geothermal reservoir is much hotter than surface hot springs; it can reach a temperature of more than 350 0C, and are very powerful sources of thermal energy. If geothermal reservoir are very close to the surface, then the possibility of reaching these geothermal sources of energy is by drilling wells, sometimes about two miles deep. Hot water and steam are pumped to the surface at a temperature between 120 °C and 370 0C. In geothermal power plants, we utilise the natural hot water and steam from the earth to turn turbine generators to produce electricity (Keller et al., 1981).

Despite the numerous advantages of geothermal energy production, there are some few disadvantages encountered from generating power from geothermal power plants. The disadvantages  of  geothermal  energy  are;  the  location  of  the  geothermal  plant  is restricted, they can trigger earthquake and it is also a very expensive source of energy.

1.2 Statement of the Research Problem

Geothermal technology is one of the alternative energy sources that much attention has not been given to in Nigeria. The geothermal potential in Nigeria has been exposed from the analysis of sub surface temperature distribution of rock mass from oil and gas bore hole wells data within sedimentary basins (Abraham, 2013). In spite of the outcome, no further steps have been taken by the government, and the power sector continues to suffer. Therefore, it is considered necessary for Nigeria to develop its thermal energy source through the introduction of geothermal power plant to meet the needs of the power sector in the country.

1.3 Aim and Objectives of the Study

The aim of the research is to investigate the geothermal potential in parts of central Nigeria Basement Complex by correlating the result of Aeromagnetic data with the result of Aero-radiometric data within the study area.

The objectives are to:

i.      estimate the depth to the top and centroid depth of magnetic sources.

ii.      determine the Curie point depth, the geothermal gradient and heat flow of the study area.

iii.      interpret the concentration of radioactive elements within the study area.

iv.      delineate possible site for geothermal exploration.

1.4       Justification of the Study

Application of Curie point can be of great advantage when considering the area for exploration of geothermal energy. A shallow Curie point and high heat content is of great advantage. The result from this work will help to ascertain the viability of the area of study for geothermal energy exploration. This will help to boost the economy of the nation and social wellbeing of the environment.

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