Geohydrodynamic properties of hydrogeological units in parts of Niger Delta, southern Nigeria

We used geophysical and laboratory techniques to study the geohydraulic properties of the geological units in the Niger Delta of southern Nigeria. Our main objective was to investigate the distribution of the geohydrodynamic parameters and to establish the interrelationships among them in the study area for effective characterisation of hydrogeological units. Measurements on the core samples aided in the estimation of effective porosities. The hydrogeological units' bulk resistivities measured from 1-D resistivity data constrained by nearby boreholes and the formation pore-water resistivities measured in the laboratory were used in computing the hydrogeological unit formation factor resistivity. Integration of field and laboratory measurements in conjunction with regression analysis of the data led to the determination of the hydrodynamic coefficients of the hydrogeological units. The graphs and the contour maps generated from the data show the variations and the interrelationships among the parameters. A theoretical model for the porosity-resistivity formation factor relation which conforms to Dakhnov's formulation, obtained for similar sediment with different grain sizes in another geological province has been developed based on the measured data. A good approximation with error of the mean square of 2.48 and standard deviation of 1.5 was obtained between the experimental aquifer formation factor F and the predicted aquifer formation factor Fm. Generally, the results of our study reveal good correlations with similar studies carried out in literatures at different places. The juxtaposition of contour maps which show variations of geohydraulic parameters in a continuum is worthwhile. The changes in geohydraulic parameters are influenced by size of grains, magnitude of pore sizes and shapes, pore-water and formation conductivities, facies changes and anisotropy of aquifer sediments. Our results have not really shown any interaction between freshwater and saltwater within the potential aquifers despite the proximity of the salt water within the area.