An Enriched Approach for Modeling Multiscale Discrete-Fracture/Matrix Interaction for Unconventional-Reservoir Simulations

Abstract

Summary Unconventional reservoirs after formation-stimulation treatments are always characterized by complex fracture networks with a wide range of length scales and topologies. Accurate simulation on multiscale discrete-fracture/matrix interaction during transient productive flows for such reservoirs is challenging but important for reservoir evaluation, optimization, and management. In this paper, we present a new enriched and explicit method for simulation on multiscale discrete-fracture/matrix modeling (EE-DFM) on structured grids to decouple the mesh conformity between the porous media and the fractures. A hybrid structured EE-DFM is first introduced, and enrichments for different scales of fracture segments are proposed to locally enrich the conventional approximation space for representing the pressure solution surrounding multiscale fracture networks. By appropriately selecting an asymptotic function to locally enrich the conventional approximation space, typical behavior of fluid flux around features in fractured media, such as discontinuities and singularities, can be directly captured. Simulation on complex multiscale fracture networks is achieved by using the superposition principle of the enrichments without introducing additional degrees of freedom and while maintaining computational efficiency. We demonstrate the accuracy and flexibility of the method by performing a series of case studies and comparing the results with simple analytical solutions as well as with conventional numerical solutions. The results of long-term well-performance case studies are used to show the good computational efficiency of the proposed method when the complexity of fracture networks is increased. The potential of the proposed method to be incorporated into the multicontinuum concept for solving nonlinear gas transport in a shale reservoir is presented. The present study provides a promising framework for real-field multiscale discrete-fracture models for unconventional-reservoir simulations.