Modelling of Flow Induced Shear Failure in Poro-elastic Fractured Media

A finite volume based numerical modeling framework using a hierarchical fracture representation has been developed to compute flow induced shear failure. To accurately capture the mechanics near fracture manifolds, discontinuous basis functions are employed which ensure continuity of the displacement gradient across fractures. With these special basis functions, traction and compressive forces on the fracture segment can be calculated without any additional constraints, which is extremely useful for estimating the irreversible slip based on a constitutive friction law. Unlike other models, here asymptotic dilation of fracture aperture due to shear failure is considered. To solve the resulting linear system, a sequential approach is used, that is, first the flow- and then the mechanics problems are solved. The new modeling framework is very useful to predict seismicity, permeability- and flow evolution in geological reservoirs. This is demonstrated with numerical simulations of enhancing a geothermal system. Novelties of this approach are (i) that due to the special basis functions only one additional degree of freedom per fracture segment is introduced (opposed to four in the XFEM method) and (ii) achieving consistent coupling with the flow solver using asymptotic aperture relaxation.