Building 3D Geomechanical Models - Some Practical Aspects of Mesh Generation and Boundary Conditions

Abstract

The optimal exploitation of conventional and unconventional reservoirs is strongly affected by the tectonic stress field. Amongst others, wellbore stability, orientation of hydraulically induced fractures and - especially in fractured reservoirs - permeability anisotropies depend on the recent in situ stresses. This state of stress in a reservoir can be substantially modified by faults as well as lithological changes and contrasts in rock mechanical properties (e.g., Zoback, 2007; Fjaer et al., 2008). In some fault-controlled reservoirs, for instance, local stress orientations differing by up to 90 from the regional trend have been reported for individual fault compartments (Yale, 2003). Any robust prediction of stresses and fracture networks in a reservoir has to incorporate the specific reservoir geometry, the ambient stress field and the mechanical properties of lithologies and faults. An appropriate numerical technique to account for complex reservoir geometries and inhomogeneous material distributions is the Finite Element (FE) Method. The improved workflow presented can be used to build 3D geomechanical FE models and is applicable to both large-scale regional as well as detailed submodels of the reservoir. It allows to maintain the full geometrical complexity of the reservoir and to study stress perturbations in relation to faults and lithological changes.