Load-balanced parallel simulations for embedded discrete fracture model on non-conforming staggered 3D unstructured grids

Abstract

Recently, embedded discrete fracture model (EDFM) using non-conforming staggered 3D unstructured grids was presented for the numerical simulation of fluid-flows in large-scale complex fractured porous media. In this paper, we implement load-balanced parallel simulations for this approach on distributed memory systems. A load-balanced domain decomposition algorithm is presented to partition matrix grids and embedded fracture grids uniformly. We classify all grid connections on the boundary of subdomains to five types and illustrate corresponding inter-processor connections. A packaged inter-processor communication approach is implemented based on message passing interface (MPI) to improve communication efficiency for this simulation method. A two-phase parallel simulator is developed, and block coupled method is adopted to assemble the equations discretized in matrix and grid domains using two-point flux approximation (TPFA) finite volume method. The load-balanced algorithm is tested by nonuniformly distributed fracture networks. The performance and scalability are also tested on 1024 CPU cores by two complex fracture network models with up to 25 million matrix grids and 11 million embedded fracture grids. The results show satisfactory parallel efficiency and scalability.