Geoelectric Tomography Study of Hydrocarbon Spill at IJEDODO Area, Abule Ado, Lagos

Geo-tomography study has been undertaken to determine the level of pollution occasioned by hydrocarbon spill at Ijedodo section of petroleum pipeline route at Ijedodo area of Abule Ado, Lagos. The field study involved the electrical resistivity tomography method using Dipole-Dipole electrode configuration. Traverse length of 1,870 m was occupied with electrode separations of 10 m and inter-dipole separation factor (n) varied from 1 to 8. The study area is underlain by the Dahomey Sedimentary Basin. The data are presented as field and theoretical pseudosections alongside 2-D resistivity structure. 2-D Resistivity Structure output presents inversion of the field data to obtain a model utilized for subsurface characterization. Observed high resistivity values are attributable to resistive sand units while low values obtained are diagnostic of conductive clay units. However, anomalously high resistivity values recorded are attributable to hydrocarbon invasion of some pore spaces. Dipole-Dipole field and theoretical pseudosections generated for the segment show predominance of conductive (clay) materials interspersed with slightly resistive (sand) materials beneath the southern half (1000 m) of the investigated segment. An isolated conductive feature (clay) was delineated beneath hydrocarbon pollution point. Finite Difference Method (FDM) inversion section of the investigated section however presents low resistivity materials (presumably clay) constituting the top segment within 180 – 970 m to depth of about 23 m. The section presents anomalously high resistivity constituents (diagnostic of severe hydrocarbon impact) at the lower segment in areas around 390 – 940 m and 1740 – 1870 m.