Lithological Investigation at Tombia and Opolo Using Vertical Electrical Soundings and Pseudo Tomogram

Francis Omonefe, Edeye Ejaita, Eteh Desmond Rowland

Niger Delta University, Wilberforce Island, Amassoma, Nigeria

Abstract:-Vertical electrical soundings (VES) was carried out in Opolo and Tombia all in Yenagoa local government area, Bayelsa state, Nigeria to understand the resistivity distribution of its subsurface which serves as a tool in investigating subsurface lithology. All VES sounding were stacked together to generate 1D pseudo tomogram and was subsequently interpreted. The interpreted VES curve results shows that Opolo consists of three layers within the depth of investigation. Sandy clay with mixture of silt make up the first layer (Top layer) with resistance value ranging from 24-63Ωm. The second layer is made up of thick clay with very low resistivity values ranging from 3-19Ωm. The third layer is sandyclay with its resistance value ranging from 26-727Ωm.Tombia also reveals that the area is in three layers within the depth of investigation. Sandy clay with a mixture of fine sand made up the first layer (Top soil) with its resistance values ranging from 40-1194Ωm. The second layer is made up of fine sand with resistivity value ranging from 475-5285Ωm. The third layer is made up of sandy clay/sand with its resistance value ranging from 24-28943Ωm.The results of the 1D pseudo tomogram also reveals that Tombia and Opolo consists of three layers within the depth of investigation and pseudo tomograms serves as a basis tool for interpreting lithology and identifying lithological boundaries for the subsurface.

Keywords: VES, Tomogram, 1D, Resistivity, Yenagoa.

I. INTRODUCTION

Geophysical Exploration is a fundamental part of geophysics in geosciences which gives us an insight of subsurface features based on the physical properties of the earth. With this study, scientists and researchers have been able to determine different changes in depth, such as rheological behavior, electrical and magnetic properties, among others, thus allowing greater knowledge about the structure of the land. Geo-electric methods are widely used in engineering research, geophysics, geology and hydrology, geological engineering and environmental studies. Some of them have been developed to study complex heterogeneous structures. Finite differences (FD), finite elements (FE), integral equations, and analytical methods and approaches were developed to find 2D / 3D structures. 1D approximation method is often used to solve forward and inverse problems as explained by Koefoed and Mallick (1979).

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