Empirical Study of Permeability-Porosity Relationships in the Benin Formation Aquifer, Delta State

The Benin Formation constitutes the primary aquifer in Delta State and the Niger Delta region, yet the empirical relationship between porosity and permeability in this sequence, critical for groundwater flow modelling and well yield estimation, has not been rigorously established from representative core sample datasets. This study empirically derives permeability-porosity relationships for the Benin Formation in Delta State using measurements on core samples recovered from exploration boreholes. Core samples spanning a depth range of thirty to three hundred metres were subjected to helium porosity measurement using a core holder and grain volume porosimeter, while permeability was determined by steady-state air permeameter measurements at several confining stress levels to account for stress-dependent effects on fractures. Pore size distribution was characterised by mercury injection capillary pressure measurements on a subset of samples. Scanning electron microscopy provided information on pore geometry and diagenetic pore-filling minerals. Statistical regression analysis was applied to test power law, exponential, and Kozeny-Carman model fits to the porosity-permeability dataset, with regression performance evaluated by R-squared and root mean square error statistics. The study identifies a bimodal relationship attributable to two populations of samples differentiated by clay content, with high clay samples exhibiting disproportionately reduced permeability relative to porosity. Derived empirical equations and clay content correction factors are proposed for use in regional groundwater flow models. Keywords: permeability, porosity, Benin Formation, empirical relationship, aquifer characterisation.