The Evaluation of Anisotropic Properties of Parts of Ijebu-Igbo, Southwestern, Nigeria, Using Azimuthal Resistivity Survey (ARS) Method

Abstract

This research was carried out to determine the anisotropic properties of parts of Ijebu Igbo, southwestern Nigeria which falls within the southwestern Basement Complex of Nigeria and it is underlain by migmatite gneiss and older granites. Physical parameters (water temperature, pH, salinity and total dissolved solid (TDS)) of 107 hand dug wells were measured. Thirty Azimuthal Resistivity Survey (ARS) were investigated along four azimuths; 00, 450, 900, and 1350. An Ohmega terrameter was used for resistivity measurement in which the Schlumberger configuration was employed with a maximum electrode spacing (AB/2) of 100m. The results showed that the physical parameters fall within the WHO standard. The iterated curves revealed 4 (KH and QH) to 5 (QQH and AKH) geoelectric layer curve types. The bedrock resistivity values range from 1467.3Ωm to 27,457Ωm with overburden thickness range of 0.6m to 61.5m. The anisotropic polygons showed N-S, E-W and NW-SE, and NE-SW directions. The co-efficient of anisotropy for all the stations varies from 1.09 to 1.61 with a mean of 1.2. Areas with low bedrock resistivity, thick overburden, presence of two interconnected anisotropy polygon directions and high co-efficient of anisotropy indicate intense fracturing, thus, a potential sites for the drilling of water borehole.