Geomechanical and Structural Investigations of Production-Induced Stress Changes in Reservoir Sands in Part of Niger Delta Nigeria
Abstract
Hydrocarbon production reduces pore-fluid pressure and increases the effective stress acting on the grain framework of reservoir rocks. This process induces reservoir deformation, compaction, and stress redistribution, often manifesting as fault reactivation, surface subsidence, wellbore instability, and 4D seismic time shifts. In this study, we present a geomechanical and structural interpretation of production-induced stress changes in the Kolo-Creek Field, Coastal Swamp Niger Delta, Nigeria. The analysis integrates 3D seismic interpretation, geomechanical evaluation, well-log analysis, and production data. Time-lapse seismic surveys acquired in 1997 (base) and 2009 (monitor) show clear 4D responses with a root-mean-square repeatability ratio (RRR) of 0.38, indicating excellent survey repeatability. The seismic interpretation reveals fault reactivation and fracturing associated with production-induced stress changes. Geophysical well logs from seven wells were used to delineate and correlate three reservoir zones (Sand A, Sand B, and Sand C). Petrophysical analysis indicates low shale content ranging from 7.74–37.44%, high porosity values between 0.19 and 0.36), and excellent permeability varying from 375–3327 mD, which is consistent with high-quality, coarse-grained sandstones. Production and pressure data provided by SPDC show a decline from 1592.55 to 400.34 bbl/day and from 4766 to 3103 psi over 12 years, respectively, corroborating with the geomechanical interpretation. The integration of geomechanics with seismic and structural analysis demonstrates the influence of reservoir stress changes on fault behavior and reservoir performance, providing insights to optimize production and manage risks in similar deltaic settings. This study could lead to Wellbore Stability Management; Using stress change predictions to guide well placement and drilling orientation, minimizing risks of shear failure, casing deformation, and production losses.