Prediction of geohydraulic pore pressure gradient differentials for hydrodynamic assessment of hydrogeological units using geophysical and laboratory techniques: a case study of the coastal sector of Akwa Ibom State, Southern Nigeria

Abstract

We used borehole-constrained geophysical measurements and laboratory analyses of water samples and hydrogeological unit samples to estimate the basic petrophysical parameters required in the Kozeny-Carman-Bear’s equation. This led to the estimation of hydraulic conductivity, permeability and tortuosity. The evaluation of hydraulic pressure gradient differential and the hydraulic pressure differential was possible through Darcy’s law. Our main objective was to assess the effect of hydraulic pressure gradient differential and that of the hydraulic pressure differential on the hydrodynamic coefficients of economically hydrogeologic units of the study area. The specific constants of water such as density, dynamic viscosity and acceleration due to gravity were all employed in estimating some of the parameters as required in the empirical relations used. Graphical relations were used to predict the generic behaviour between permeability and its dependence, and hydraulic pressure gradient and hydraulic pressure differentials respectively. The results of our analyses show that in arenaceous hydrogeologic units like sands characterised by interconnected/communicating pores, hydraulic pressure differential will be high as the thickness of the saturated unit increases—the precondition for high hydrodynamic activity in the saturated medium. Again, in argillaceous materials, the hydraulic pressure gradient differential is high as it is caused by poor geofluid thickness penetration due to little or no communication between pores. This reduces the hydrodynamic coefficients like porosity and permeability in such hydrogeologic units. The observation of these hydraulic energy parameters in hydrogeologic units could be the physical basis for predicting groundwater flow and a guide to designing geofluid flow modelling programmes in saturated subsurface.