Theoretical Investigation of Gas Reservoir Geomechanics and Its Implications for Well Productivity in the Deepwater Niger Delta

The interplay between geomechanical deformation and fluid flow in deepwater Niger Delta gas reservoirs influences well productivity, reservoir compaction behaviour, and long-term field development performance, yet integrated geomechanical-reservoir simulation frameworks validated for deepwater Niger Delta conditions are absent from the published literature. This study conducts a theoretical investigation of gas reservoir geomechanics and develops an original coupled geomechanical-reservoir simulation framework for deepwater Niger Delta applications. The theoretical framework is built on poroelasticity theory extended to account for the stress-sensitive permeability and porosity characteristic of deepwater turbidite sandstone reservoirs, incorporating a constitutive model for the highly compressible weakly cemented sediments prevalent in the study environment. The coupled simulation framework is implemented by integrating ECLIPSE reservoir simulation with ABAQUS finite element geomechanical modelling through an iterative coupling scheme, with coupling efficiency optimised through a novel asynchronous coupling algorithm. The framework is applied to a synthetic reservoir model representative of deepwater Niger Delta turbidite geometry and rock properties, with parameters calibrated against published data from analogous deepwater West African reservoirs and rock mechanics laboratory data from Niger Delta core samples. The study's original theoretical contributions include: a stress-dependent porosity and permeability model for weakly cemented deepwater Niger Delta sandstones, a compaction drive production contribution model specific to the studied sedimentary context, and a well trajectory optimisation framework that maximises productivity while managing geomechanical risk from sand production and wellbore instability. Findings demonstrate that neglecting geomechanical effects in production forecasting leads to systematic overprediction of late-life well productivity by 15 to 25 percent. Recommendations include mandatory geomechanical screening for all deepwater Niger Delta gas development wells and incorporation of the coupled framework into standard field development plan requirements. Keywords: geomechanics, reservoir simulation, deepwater Niger Delta, poroelasticity, well productivity.