Application of Geophysical Well Logging in Investigation of Salt–Water Intrusion in Parts of Lagos State, Southwestern Nigeria

Abstract

The salineation of freshwater aquifer units with the view of assessing groundwater quality in parts of Lagos State areas has been investigated in this study. The objectives task was achieved via exploring the potential of borehole geophysical method. The obtained suites of geophysical well logs covering the west – east and south – northeast directions were subjected to lithostratigraphic correlation analysis using the Petrel software. Based on the analysed results, five aquifer units characterized the study area with thickness ranging from > 5 m to 205 m were delineated. Further analysis established that saline water aquifer, brackish water sand, fresh water sand with resistivity values in the range of 0 – 60 ohm-m, 60 – 80 ohm-m and > 80 ohm-m, respectively at the depths of 10 – 165 m were delineated using the resistivity well log tool along the lithostratigraphic sequence. It was evidenced from the analysis that saline water often occurred greatly at depth of 10 – 160 m and the depth at which fresh water can occur in the area is greater than 200 m along the east – west and 0 – 200 m in the southwest – northeast sections.  This study concludes that borehole geophysical wireline logs can be effectively relied upon in the delineation of aquifer units and assessment of groundwater quality in the investigated area.

Keywords: Geophysical, Well Log Analysis, Aquifer, Salt-water Intrusion, Lagos State.