A general algebraic multiscale framework is presented for fractured porous media, which enables the treatment of fractures with multiple length scales and wide ranges of conductivity contrasts. To this end, fully integrated local basis functions for both matrix and fractures are constructed. These basis functions are employed to construct the multiscale coarse system for both matrix and fractures, and then interpolate the coarse solutions back to the fine-scale reference system. Combined with a second stage fine-scale solver, here, ILU(0), our development leads to an iterative multiscale strategy for heterogeneous fractured media, allowing for error reduction to any arbitrary level, while honoring mass conservation after any multiscale finite volume stage. In order to maintain generality, it is shown that when each fracture network is modeled using a single coarse grid cell, our formulation automatically reduces to that proposed by Hajibeygi et al. (2011). However, in order to facilitate the treatment of general ranges of conductivity contrasts and deviation term norms, we introduce the ability to refine the coarse grid to more than one cell per network. Our experiments show that this flexibility results in a significant improvement on convergence properties. This added degree of flexibility is made possible through an algebraic formulation, which leads to a multi-stage multiscale conservative linear solver for multiphase flow in fractured media.

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