Formation evaluation and geomechanical modelling of the Middle Jurassic Lower Safa reservoir of the Shushan Basin, Western Desert, Egypt: implications for reservoir development and completion optimization

This study presents a comprehensive reservoir geomechanical characterization of the Middle Jurassic Lower Safa sandstones from the Shushan Basin, Egypt. Petrographical thin sections, SEM, XRD, routine core analysis, wireline logs, downhole measurements and drilling data were integrated to characterize the studied reservoirs. The reservoir is composed of mesoporous quartz arenites with dominantly primary intergranular porosity, and exhibits an isotropic pore system with 7–14% effective porosity and ≤1 mD permeability. Cementation (silica and clay) and mechanical compaction were identified as the primary diagenetic factors reducing the reservoir quality. The reservoir exhibits a low shale volume, high hydrocarbon saturation and a hydrostatic pore pressure gradient. The relative gradients of in situ stresses indicate a normal to strike-slip faulting stress regime. Based on the ‘C-quality’ breakouts from multi-arm caliper log analysis, the maximum horizontal stress azimuth is interpreted as N140°E. Utilizing the stress-based model, the risks of wellbore instability, depletion-induced reservoir instability and sand production were assessed. The assessment indicated the possibility of production-induced shear failure at a depleted pore pressure magnitude of 1000 psi, which can be considered the abandonment pressure. The hydraulic fracturing simulation confirmed the presence of a stress barrier that would restrict the vertical propagation of fractures into the overburden/underburden during stimulation. The horizontal wells drilled along a NE–SW azimuth offer higher sand-free critical drawdown and therefore this is considered the preferred lateral azimuth to minimize sand production risk. The sensitivity of collapse pressure, fracture initiation pressure and sand-free critical drawdown pressure was assessed for various wellbore trajectories, rock-mechanical property and depletion magnitudes.