Professional Evaluation of Geomechanical Modelling Approaches for Compaction and Subsidence Prediction in Producing Niger Delta Offshore Fields

Reservoir compaction and associated seabed subsidence are significant operational and structural engineering concerns in high-porosity, weakly consolidated Niger Delta offshore fields where reservoir pressure depletion drives porosity reduction and vertical strain in the overburden. This study professionally evaluates geomechanical modelling approaches for compaction and subsidence prediction applicable to producing fields in the Niger Delta offshore. The study reviews one-dimensional, pseudo-three-dimensional, and fully coupled three-dimensional reservoir-geomechanical modelling approaches, assessing the computational complexity, data requirements, and predictive accuracy of each approach based on published validation studies from analogue West African fields. Constitutive soil models evaluated include linear elastic, Cam-Clay, and Modified Cam-Clay plasticity models, with the Modified Cam-Clay model providing superior compaction predictions for the high-porosity sands characteristic of Niger Delta Agbada Formation reservoirs. Integration of geomechanical models with Eclipse reservoir simulators using the ABAQUS coupling methodology is reviewed for implementation feasibility in the Nigerian operator context. Application of a coupled geomechanical model to an anonymised producing Niger Delta field demonstrates that primary reservoir depletion of 1,200 psi produces maximum seabed subsidence of 0.35 metres at the field centre, with implications for riser design and FPSO mooring tolerances. Validation against high-precision repeat bathymetric surveys is recommended as a mandatory model calibration step. Keywords: geomechanical modelling, compaction, subsidence, Niger Delta offshore, reservoir pressure depletion.