Petrophysical and hydrogeological characterization of coastal aquifer using geophysical logs in Lekki Peninsula, Lagos, Nigeria

Abstract

The coastal aquifers of Lekki Peninsula, Lagos are increasingly threatened by saline water invasion. In this study, the characterization of the petrophysical properties of the coastal aquifers in Lekki Peninsular through analysis of geophysical logs was carried out. The methodology involved editing, interpolation, depth shifting and normalization of gamma ray and resistivity logs from twelve water wells. Log analysis was employed to map aquiferous units and determine their petrophysical properties which include clay volume, porosity, permeability, water resistivity, total dissolved solid and water quality. These properties were further subjected to cross plot analysis. The results identified three aquifers. Aquifer 1 is mostly unconfined shallow phreatic aquifer characterized by 11–35% porosity. The TDS ranges from of 4.63 mgL−1 – 50.33 mgL−1. The intermediate Aquifer 2 is characterized by significant thickness (25–75 m), clay volume (0.22–0.54) excellent porosity (16–27%), permeability (99–110 mDarcy), water resistivity (25–175 Ωm) and total dissolved solids of <30.00 mgL−1. The deep Aquifer 3 lies at 153–255 m depth and has total dissolved solids value of 10.63 mgL−1 and 26% porosity. Cluster analysis shows 67% of wells that penetrated Aquifer 2 encountered saline to brackish water while 40% found aquitard with poor petrophysical properties. Water wells in the study area should target aquifer 3 as Aquifer 2 is prone to saltwater intrusion due to over-pumping. This study furnishes information that enables sustainable future exploration, exploitation, monitoring and management of groundwater reserve in Lekki Peninsula.