SUBSURFACE GEOLOGICAL MAPPING USING VERTICAL ELECTRICAL SOUNDING (VES) AND 2D ELECTRICAL RESISTIVITY IMAGING SURVEYS: CASE STUDY OF FUPRE SOUTHERN NIGERIA.

Electrical resistivity imaging (ERI) and vertical electrical sounding (VES) surveys were carried out over a football field at the Federal University of Petroleum Resources, Effurun (FUPRE), and Delta State, Nigeria. The main purpose of the geophysical surveys was to characterize the subsurface geological of the study area for better understanding of the subsurface lithology underlying the area. For this purpose, seven Vertical Electrical Soundings (VES), and four (4) 2D Electrical Resistivity Tomography (ERT) traverses were established for electrical resistivity measurements. The results of the VES and ERT surveys show that the subsurface strata are composed of four (4) subsurface geologic lithologies identified as clayey sand, fine sand, fine-to-coarse sand, and coarse/dry sand, with resistivity values of (201.9-285.4) Ω-m, (424.2-476.9) Ω-m, (564.5-909.4) Ω-m, and (1023.3- 4239.0) Ω-m respectively, all were mapped at different depths. In addition, the geo-electrical resistivity result was validated with borehole data from drillers’ log. Correlating the borehole data from driller log with the VES result of VES 1 to 7, it was observed that the coarse sandy layers delineated predominantly within the third layer of VES 1, 2, 3, 4, 5, 6, and 7 at depth of 41.90 m, 22.90 m, 13.1 m, 30.10 m, 35.70 m, 51.2 m, and 15.2 m respectively, identified as potential aquifer layers were as well delineated at depth between 12.192 and 15.240 m in the borehole log. These depths were consistent with the depth of coarse sand observed in VES 3 and 7 interpretations. By using a combined method, the subsurface geological strata, their thicknesses, and the consistency of each stratum have been better defined