Modeling geomechanical effects on the flow properties of fractured reservoirs

Conventional modeling of fractured reservoirs treats fracture permeability and porosity as static (or pressure-dependent) data. Recent attempts at coupling geomechanics focused on the permeability, but used crude empirical relations and treated the fluid flow as single porosity. This study takes advantage of joint mechanics theory to develop general, rigorous coupling between fluid flow equation and deformation of fractured media. Both porosity and permeability coupling is considered. Arbitrary orientation and spatial distribution of fractures in naturally fractured reservoirs is likely to create a complex flow path that must be represented using full tensor permeability field. This complexity further increases when the fractures are treated as deformable and different fracture sets deform differently. As a result, spatial distribution of full tensor permeability becomes stress-dependent and may also experience variation in principal directions in time. The formulation developed here, captures all the variations involved. The theory was implemented in an iteratively coupled reservoir and geomechanical simulator with the ability to handle variable full tensor permeability.; The geomechanical part of the simulator uses the equivalent continuum approach, considering both rock and fracture deformation properties. Multiple sets of fractures with any dip and strike angle can be defined. The nonlinear stiffness of fractures varies with the effective stress according to a law typical for joints. In addition to the stress field, the overall deformation is obtained considering the pore pressure provided from the flow module. The resulting pseudo-continuum stiffness matrix equations were verified by comparing with models using explicit modeling of fractures and analytical anisotropic poroelasticity theory. The main novelty of this work is that the geomechanics solution is decomposed into matrix and fracture parts and used to compute their dynamic porosity and permeability separately. This approach captures rigorously the effect of fractured media deformation on the dual porosity flow part of the coupled system using the decomposed strain components of each media, and allows the permeability and porosity variations to be based on measurable joint properties. Flow model then carries on with these new properties using a 27-point discretization technique of Multi Point Flux Approximation (MPFA) developed in this study for handling full tensor permeability. New deformation is then obtained using new pore pressures in an iterative manner.; The main issue studied was the variation in the permeability of the fracture system. The examples show that fracture deformation has a significant effect on productivity or injectivity, and that anisotropy of the permeability tensor develops from deformation. The results provide an initiative for implementing the case of full tensor permeability in a efficient way so that this feature could be used routinely.