Lawrence Berkeley National Laboratory

We present an extended multiple interacting continua (Ex-MINC) model of fractured rock masses that uses Oda's crack tensor theory to upscale the hydraulic and mechanical properties. The Ex-MINC concept includes separate connected continua representing active fractures, inactive fractures, and matrix to represent the fracture-matrix system. The crack tensor theory was used to calculate the stress-dependent permeability tensor and compliance tensor for individual grid blocks. By doing this, we transformed a discrete fracture network model into a grid-based continuum model. The Ex-MINC model was verified against an existing analytical solution, and the entire Ex-MINC/crack tensor model approach was applied to a benchmark test (BMT) related to coupled stress, fluid flow, and transport through a 20- × 20-m model domain of heavily fractured media. This BMT was part of the international DECOVALEX project for the development of coupled models and their validation, thus providing us with the opportunity to compare our results with the results of independent models. We conducted the coupled hydraulic and mechanical modeling with TOUGHFLAC, a simulator based on the TOUGH2 multiphase flow code and the FLAC3D geomechanical code. The results of our simulations were generally consistent with the results of the other independent modeling approaches and showed how inactive fractures impeded solute transport through the fractured system by providing an additional fracture surface area as an avenue for increasing fracture matrix diffusion.