2D vs 3D geomechanical modelling comparison to influence pore pressure and fracture gradient analysis

Geomechanical modeling can be an important tool in constraining pore pressure and fracture gradients in exploration wells, especially in areas of salt tectonics. Full 3D modeling can be time consuming and impractical for planning so knowing that 2D modeling can achieve similar results can be significant. We predict the stress and strain description around a salt structure from the West African Coast using a 3D static geomechanical model and compare the results to a 2D model. The 3D model uses the present-day basin geometry and a series of inputs (pore pressure, material properties assuming poro-elastic behavior for sediments and visco-plastic behavior for salt, boundary constraints and initial vertical to horizontal effective stress ratios). The 2D model uses geometry from the 3D model and the same input parameters. Both models predict similar sediment and salt displacements and stress ratio reduction above the salt structure although the displacements and stress ratio reduction are larger in the 2D model. The results of our analysis indicate that 2D geomechanical models, if selected correctly, can represent more complex 3D geometries. In addition, less computationally expensive 2D model allow a more complete sensitivity analysis and the identification of the mechanism of stress / pore pressure reduction.