Integrated Characterization and Forecasting of Overpressure Mechanisms in the ‘Nge’ Field, Offshore Niger Delta: Insights from Rock Properties – Seismic Velocity Cross-Plot Analysis

The overpressure mechanisms in the NGE Field, located offshore in the Niger Delta, were investigated using a cross-plot analysis of rock properties and seismic velocities. Overpressure, which is primarily caused by disequilibrium compaction and unloading mechanisms, poses significant challenges during hydrocarbon exploration and drilling operations in the region. Wireline log data (sonic, density, resistivity, and gamma-ray logs) and 3D seismic data were employed to delineate overpressure zones and estimate their magnitudes using Eaton’s and Bowers’ methods. These data sources collectively provide critical insights into pore pressure, compaction, fluid saturation, lithology, and structural context, which are essential for accurate delineation of overpressure zones. Three distinct overpressure zones A, B and C were identified across the NGE X, Y, and Z wells, with depths ranging from 7,600 to 12,700 feet. The primary cause of overpressure in zones A and B is disequilibrium compaction, indicated by deviations from the normal velocity trend, with pressure values slightly above normal levels, typically around 0.5 to 1.0 psi/ft. In contrast, unloading due to tectonic stress is responsible for the high overpressure in zone C, where pressures can exceed 1.5 psi/ft. The results demonstrate that faults, particularly major growth faults in the region, played a critical role in overpressure development, with wells drilled across fault planes exhibiting higher overpressure magnitudes. The need for integrating seismic and well log data for accurate pore pressure prediction is therefore emphasized in this study, highlighting the importance of understanding overpressure mechanisms for safer and more efficient hydrocarbon exploration in the complex geological settings of the Niger Delta.