Integrated Geophysical and Petrophysical Characterization of the Coastal Plain Sands: A Case Study from Upenekang, Akwa Ibom State

Abstract

This study presents an integrated subsurface evaluation of a borehole located in Upenekang, Ibeno (Akwa Ibom State), utilizing a combination of Vertical Electrical Sounding (VES) and downhole geophysical logging to characterize the subsurface of Upenekang, Ibeno.The primary objective was to delineate the local lithostratigraphy and evaluate the petrophysical potential of the target aquifers within the Coastal Plain Sands.The lithological sequence reveals a transition from superficial clays to prolific sand aquifers extending from approximately 35 m to 90 m. Correlation with the spontaneous potential (SP) and resistivity logs confirmed this interval as a clean, permeable formation characterized by significant positive resistivity separation, indicating high permeability and active fluid invasion. Resistivity data at depth greater than 200m suggest a vulnerability to saltwater intrusion, while geotechnical analysis of the overburden identifies potential settlement risks in upper clay units. Petrophysical modeling using Archie’s Law yielded estimated porosities ranging from 30% to 42% within the primary sand unit. A Pickett Plot analysis demonstrated that the data points align closely with the 100% water saturation line, suggesting a high-quality, freshwater-saturated reservoir. These findings confirm the depth interval of 35–90 m as the most viable target for high-yield groundwater abstraction, with a secondary, lower-permeability aquifer identified in the silty sand units below 118 m. Also, study reveals one of the weaknesses of VES known as principle of suppression. This integrated approach validates the accuracy of surface geoelectrical models against direct borehole measurements.

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