Geophysical Interpretation of Abakaliki And Bansara Area, Lower Benue Trough Nigeria Using Airborne Gravity Data

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ABSTRACT

The Geophysical Airborne gravity data of Abakaliki and Bansara area of Lower Benue Trough Nigeria was interpreted qualitative and quantitative in order to determine the sedimentary thickness/depth to basement and the possibility of hydrocarbons accumulation in the area and also to determine the density contrast and different rock types or rock bearing minerals present in the area. Source Parameter Imaging (SPI) and Forward and Inverse modeling techniques were employed in quantitative interpretation. It was found that bouguer gravity anomaly value of Abakalilki and Bansara ranges from -14.7 mGal to 12.8 mGal while the residual anomaly ranges from -12.6 mGal to 11.4 mGal. The SPI depth ranges from -1002.5 to -7733.3 m. This depths show thick sediment that is feasible for hydrocarbon accumulation. The depths of forward and inverse modeling for profiles 1-6 were estimated to be -2328, -1777, -1404, -2431, -1513 and -2036 m respectively with their respective density values of 2.550, 2.700, 1.980, 2.630, 2.550 and 2.700 g/cm3. These indicate that the presence of limestone, marble, graphite and granite causes the anomaly observed in the area.The study area has revealed potentials for mineral deposits, which could serve as raw material for many factories and industries in Nigeria.

TABLE OF CONTENTS

Title Page i

Approval page ii

Dedication iii

Acknowledgement iv

Table of contents v

List of figures viii

List of Tables ix

Abstract x

CHAPTER ONE

1.1 . Introduction 1

1.2. Aims and objectives of the study 4

1.3 Location and Geology of the area 4

1.3.1 Lower Benue Trough 4

CHAPTER TWO 2.1 Literature Review 7

CHAPTER THREE 3.1 Source of Data 14

6 3.2 Basic theory of gravity 14

3.2.1 The Gravity method 14

3.2.2 Gravity units 16

3.2.3 Gravity Formula 16

3.2.4 Instrumentation 17

3.2.4.1 Relative Gravimeters 17

3.2.4.2 Absolute Gravimeters 18

3.2.5 Reduction of observation 19

3.2.5.1 Terrain corrections 20

3.2.5.2 Tidal correction 20

3.2.5.3 EÖtvÖs correction 21

3.2.5.4 Latitude correction 22

3.2.5.5 Elevation correction 22

3.2.5.6 Free Air correction (FAC) 23

3.2.5.7 Bouguer correction 23

3.2.6 Rock densities 24

3.3 Materials 27

3.4 Methodology 27

7 3.4.1 Merging and gridding of the data 27

3.4.2 Polynomial fitting 27

3.4.3 Derivatives 28

3.4.3.1 First vertical derivatives (FVD) 28

3.4.3.2 Second vertical derivatives (SVD) 29

3.4.3.3 Horizontal derivatives (HD) 30

3.4.4 Forward and inverse modelling 30

3.4.5 Source parameter imaging (SPI) 32

CHAPTER FOUR 4.1 Data analysis and Results 34

4.1.1 Bouguer gravity map 34

4.1.2 Residual and Regional Bouguer map 35

4.1.3 Derivatives 36

4.1.4 Source parameter imaging (SPI) 38

4.1.5 Forward and inverse modeling 39

4.2 Discussion and Results 45

CHAPTER FIVE

5.1 Conclusion 46

8 5.2 Recommendations 46

References

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Geophysical Interpretation of Abakaliki And Bansara Area, Lower Benue Trough Nigeria Using Airborne Gravity Data

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