Coupled Geomechanics and Flow in Fractured Porous Media

The effects of geomechanics on the reservoir response can be important, and this is especially true for naturally fractured formations. Modeling the mechanical deformation of naturally fractured formations poses significant numerical challenges, and accurate coupling between mechanical deformation and flow adds to the challenge. We describe a simulation framework for coupled mechanics and flow based on a Discrete Fracture Model (DFM). An important aspect is that the mechanics and flow problems share the same unstructured DFM grid. The geomechanical model is based on the classical Biot theory. The Barton-Bandis model is used to describe the fracture mechanical response. For the flow problem, we use Darcy’s law and mass conservation for slightly compressible fluids. The fractured formation is discretized using DFM, which leads to complex unstructured grids. Three standard elements (hexahedrons, tetrahedrons and wedges) are used to represent the volumes of the matrix, and the fractures are represented using lower dimensional objects (triangles or quadrangles). The Galerkin finite-element method is used for the mechanics, and a DFM finite-volume method is used the flow equations. Two different coupling strategies are considered: the fully implicit method and the fixed-stress sequential-implicit scheme. Several examples of fractured porous media are used to illustrate our methodology.