Geophysical mapping of the occurrence of shallow oil sands in Idiopopo at Okitipupa area, South-western Nigeria

Abstract

Oil sands are known to be an alternate source of energy and of great economic value. To map the occurrence of shallow oil sand deposits in Idiopopo, Okitipupa area in Ondo state southwestern Nigeria, vertical electric sounding (VES) in 11 stations along 3 profiles were carried out using the Schlumberger configuration. Apparent resistivity value obtained ranged from (135.7 ± 0.05) ohm-m to (4592.6 ± 0.05) ohm-m. The resistivity curves obtained for each VES location were interpreted using partial curve-matching and computer iterated techniques and it revealed the presence of 4 and 5 geoelectric layers. Interpretation of the geo-electric parameters obtained indicates the possible presence of
oil sand in the fourth layer of VES 8 with a resistivity value of 164.9 ohm-m at a depth of about (16.50 ±
0.05) m and thickness of (39.03 ± 0.05) m. Also, VES locations 5 to 8 (profile one) all indicate the possible presence of oil sands in the fifth layers with a resistivity value of less than (725.0 ± 0.05) ohmm at a mean depth of (39.05 ± 0.05) m. However, due to the depth of probe more information about these layers could not be ascertained. It is recommended that further geophysical survey techniques like VES with increased electrode spacing and/or 2D resistivity method should be employed to effectively map the oil sands especially along profile one.

Key words: Geo-electric, oil sand, Idiopopo, South-western Nigeria, vertical electric sounding, resistivity.