Integrated Geophysical-Petrophysical Modelling for Characterising Fractured Basement Reservoirs in Northern Nigeria

This study develops an original integrated geophysical-petrophysical modelling framework for characterising fractured basement reservoirs in northern Nigeria, addressing the emerging exploration concept of hydrocarbon accumulations in basement rock fracture systems beneath the sedimentary basins. Fractured basement reservoirs have been discovered in several West African countries, and recent seismic imaging has revealed potential basement involvement in some Nigerian exploration blocks. The characterisation of such reservoirs requires an integration of seismic, potential field, and petrophysical methods that has not been systematically developed for the Nigerian geological context. This study develops a conceptual and computational modelling framework that links seismic reflection and refraction imaging of fractured basement to potential field signatures of rock property changes, borehole geophysical characterisation of fracture systems, and petrophysical modelling of fractured basement porosity and permeability. Theoretical relationships between seismic velocity, fracture density, fluid content, and resistivity are derived from effective medium theory adapted for Nigerian basement rock types. Field testing applies the framework to available data from three exploration blocks in northern Nigerian sedimentary basins. Integrated interpretation identifies two drill-ready basement targets. Geomechanical modelling predicts fracture aperture sustainability and permeability under in-situ stress conditions. Findings reveal that integrated geophysical signatures diagnostic of productive fractured basement (low seismic velocity anomaly plus magnetic contrast plus low-resistivity anomaly) occur in only 8 percent of basement surface area, representing a highly selective targeting criterion. The study provides an original exploration model for fractured basement reservoirs in Nigerian sedimentary basins and recommends drill testing of the identified targets.

Keywords: fractured basement reservoir, geophysical-petrophysical modelling, northern Nigeria, effective medium theory, exploration framework.