ABSTRACT
The data of Ubiaja and illushi area that fall within to and longitude to were interpreted qualitatively and quantitatively. The qualitative interpretation revealed that the area is intensely faulted with major anomalies (faults) trending in the northeast and southwest directions.
Standard Euler , source parameter imaging (SPI), analysis and modelling (forward and inverse) methods were employed in the quantitative interpretation aimed at determining the depth or thickness of the sedimentary basin, magnetic susceptibilities and type of mineralization prevalent in the area.
The results obtained by employing SPI have shown the minimum to maximum depths of 258.2 m to 3497.7 m of anomalous source bodies.
Applying standard deconvolution method for the structural index (SI), the depth obtained for SI = 0.5 ranges from 1377.3 m (outcropping and shallow magnetic bodies) to 2510.9 m (deep lying magnetic bodies).
For SI = 1, the depth to magnetic source ranges from 1482.0 (outcropping and shallow magnetic bodies) to 3003.3 m (deep lying magnetic bodies).
For SI = 2, the depth to magnetic source ranges from 1627.8 m (outcropping and shallow magnetic bodies) to 2984. 3 m (deep lying magnetic bodies); and for SI = 3, the depth ranges from 1853.9 m (outcropping and shallow magnetic bodies) to 3089.9 m (for deep lying magnetic bodies).
The spectral depth obtained revealed two source depths, shallow and deeper. The deeper depth ranges from 1114.085 m to 3978.874 m with an average value of 2105.014 m, while the shallow depth ranges from 163.836 m to 460.057 m with an average value of 295.708 m.
The results from forward and inverse modelling for profiles 1, 2, 3 and 4 showed depths of 4118 m, 3611 m, 2964 m and 5489 m respectively.
From the results of susceptibility values obtained, profiles 1 and 2 with susceptibility value of 0.0100 is underlain by a body associated with group of minerals like hematite, gneiss, granite or gabbro. Profile 3 with susceptibility value of 0.0613 is typical of igneous rock porphyry.
Profile 4 with susceptibility value of 0.0288 is typical with minerals like slate and hematite. The depth obtained from the four methods show thick sediment but on an average, the sedimentary thickness of the area is fairly sufficient for hydrocarbon accumulation.
TABLE OF CONTENTS
Title page i
Dedication ii
Certification iii
Acknowledgments iv
Table of contents v
List of Tables ix
List of figures x
Abstract xii
CHAPTER ONE: INTRODUCTION
1.1 Background of the Study 1
1.2 Operation of Magnetic Survey 2
1.3 Applications of Aeromagnetic Surveys 3
1.4 Location and Geology of the Study Area 4
1.5 Geologic Setting 6
1.6 Stratigraphy 7
1.7 The Earth’s Magnetic Field and its Anomalies 8
1.8 Magnetic Field of the Earth 10
1.8.1 The Earth’s main Field 10
1.8.2 Temporal Variation of the Earth’s Magnetic Field 12
1.9 Magnetism of rocks and minerals 13
1.9.1 Thermoremanent magnetization 16
1.9.2 Detrital magnetization 16
1.9.3 Chemical remanent magnetization 16
1.9.4 Isothermal remanent magnetization 16
1.9.5 Viscous remanent magnetization 16
1.9.6 Dynamic remanent magnetization 17
1.10 Geomagnetic Components 17
1.11 Objectives of the study 18
CHAPTER TWO: LITERATURE REVIEW
2.1 Review of Previous Aeromagnetic Survey carried out in Anambra Basin
and other basins 19
CHAPTER THREE: MATERIALS AND METHODS
3.1 Theory of Magnetic Force 24
3.2 Magnetic Field Strength, H 24
3.3 The Magnetic Potential 25
3.4 Magnetic Susceptibility (k) 25
3.5 Magnetic instruments 26
3.6 Airborne Magnetometers 27
3.6.1 Proton precession magnetometer 27
3.6.2 Fluxgate magnetometer 30
3.6.3 Optically pumping magnetometer 32
3.7 Gradiometer 33
3.8 Aeromagnetic Data Filtration 33
3.8.1 Polynomial fitting 33
3.8.1.1 Regional-residual separation 34
3.8.2 Derivatives 34
3.8.2.1 Vertical derivative 34
3.8.2.2 Horizontal derivative 35
3.8.3 Reduction to pole 35
3.9 Method of Data Analysis 35
3.10 Sorting and Arrangement of Data 36
3.11 Interpretation 36
3.11.1 Qualitative interpretation 36
3.11.2 Quantitative interpretation 37
3.12 Spectral Analysis 37
3.12.1 Derivation of depth to basement from power spectrum 40
3.13 Source Parameter Imaging (SPI) 41
3.14 Euler-3D deconvolution method 42
3.15 Forward and inverse modelling 42
3.16 Softwares used in this work 42
3.17 Source of Data 44
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 Data Analysis and Results 45
4.2 Qualitative Interpretation 45
4.2.1 Total intensity (TMI) 45
4.2.2 The reduction to pole 46
4.2.3 The upward continuation 47
4.2.4 Residual anomaly from polynomial fitting of degree 1 and 2 48
4.2.5 Regional anomaly from polynomial fitting of degree 1 and 2 50
4.2.6 First horizontal derivative 52
4.2.7 First vertical derivative 53
4.2.8 Rose diagram (circular histogram) 54
4.3 Quantitative Interpretation 55
4.3.1 Source parameter imaging (SPI) method 55
4.3.2 Standard Euler deconvolution method 56
4.3.3 Spectral analysis result 59
4.3.3.1 Plots of spectral depths (logarithm of energy against frequency) 60
4.3.3.2 2-dimensional (2D) and 3-dimensional (3D) plots of the deeper depth 70
4.3.3.3 2-dimensional (2D) and 3-dimensional (3D) plots of the shallow depth 72
4.3.4 Forward and inverse modeling (using potent software) 73
4.4 Discussion of Results 80
CHAPTER FIVE: CONCLUSION AND RECOMMENDATION
5.1 Conclusion 85
5.2 Recommendation 86
REFERENCES 87
INTRODUCTION
1.1 Background of the Study
Minerals and hydrocarbon play vital roles in the socio-economic development of a country
. Before the colonial era to the era of the 1960‘s, the search for mineral deposits and hydrocarbon has been a major business challenge in Nigeria.
It is no doubt that the foundation or basis of the Nigerian economy has been the solid minerals and now the booming oil sector since over 80% of the nation economy depends greatly on it (Obiora et al., 2015).
Since all the exploitation of hydrocarbon in Nigeria is mostly done in the Niger delta, it will benefit the country if other sedimentary basin such as the Anambra basin is explored.
Anambra basin where Ubiaja and Illushi fall is one of those basins being suspected to have hydrocarbon and solid minerals prospect.
Magnetic method is a geophysical survey technique that exploits considerable differences in the magnetic properties of minerals with respect to the ultimate objective of characterizing the earth‘s subsurface.
The technique requires the acquisition of measurements of the amplitude of the magnetic field at discrete points along survey lines distributed reg
ularly throughout the area of interest (Horsfall, 1997).
REFERENCES
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Agagu, O.K., Fayose E.A. and Petter, S.W. (1985). Stratigraphy and sedimentation in the Senonian Anambra Basin of the Eastern Nigeria. Journal of Mineral Geology, 22: 25 – 36.
Agagu, O.K. and Adhijie, C.I. (1983). Tectonic and sedimentation framework of the Lower Benue Trough Southeastern Nigeria. Journal of African Earth Sciences, 1: 267 – 274.
Akanbi, E.S. and Fakoya, A.D. (2015). Regional Magnetic Field Trend and Depth to Magnetic Sourec Determination from Aeromagneti Data of Maijuju Area, North Central, Nigeria. Physical Science International Journal, 8(3): 1 – 13.
Ali, I., Olatunji, S., Nwankwo, L.I., Akoshile, C.O., Johnson, L.M. and Ellino, F. (2012). Geophysical Modeling of potential hydrocarbon traps in the lower Niger Delta, offshore West Africa. Archives of applied science Research 4(2): 863-874.
Amajor, L.C. (1989). Grain size characteristics and geologic controls on bed load sediments: A case study from the Imo River in South-eastern Nigeria. Journal of African Earth Science. 9: 507 – 515.
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