Reserve Estimation from Geoelectrical Sounding of the Ewekoro Limestone at Papalanto, Ogun State, Nigeria.

Abstract

Formed consequent to the opening of the South Atlantic in the early Cretaceous, the Dahomey Basin is an arcuate coastal Sedimentary Structure, the on-shore part of which underlie the coastal plain sands of Southwestern Nigeria and Benin and is limited eastward by the Okitipupa basement ridge among other localities. Papalanto (long. 3⁰13⁰E and Lat. 6⁰54⁰N) harbours one of the largest surface outcrops of Ewekoro Limestone that easily attracts attention. 17 Schlumberger array Vertical Electrical Sounding (VES) were done in Papalanto to determine the overburden to and thickness of the Limestone and to quantitatively estimate its reserve. Results which were buttressed by some well information reveal a thick overburden of between 3m and 16m made up of silt, clay, sand and shale. The thickness of the limestone is between 3m and 40m: (the thickest being at Fashola, VES 17) averaging about 28m. The reserve was therefore calculated to be 7.7 x 10⁸ m³ for the limestone deposit at Papalanto.

Key words: Vertical Electrical Sounding, Reserve estimation, Limestone thickness, Schlumberger array, Geoelectric layer.