A Next-Generation Reservoir Simulator as an Enabling Technology for a Complex Discrete Fracture Modeling Workflow

Abstract

Abstract We present an innovative workflow for reservoir characterization, gridding, discretization, and simulation of discrete fractures embedded within a single-porosity continuum. This discrete fracture modeling (DFM) workflow provides the capability to realistically model the impact of fractures on recovery without incurring the simplifying assumptions of traditional dual-porosity models. We represent the matrix of the unstructured DFM using 3D polyhedral cells including tetrahedra, pyramids, and prisms. The fractures are represented as polygonal interfaces between matrix cells. The workflow is enabled by a next-generation reservoir simulator that is designed for robust solution of unstructured grid models. The simulator supports parallel computation on distributed and shared memory machines without manual user intervention. The efficiency of the simulator is due primarily to a parallel linear solver that is designed specifically for unstructured grids. This results in a very efficient and robust reservoir simulator for highly heterogeneous DFMs. We demonstrate the practicality of this technology by performing a design of experiments (DoE) study that involves a suite of sector models representing multiple discrete fracture realizations of an actual carbonate reservoir. We also show the feasibility of a full-field simulation including over ten thousand discrete fractures, more than a hundred wells, and 3.65 million simulation cells. These simulations are challenging due to the high contrast in matrix and fracture properties, multiphase flow, and the inclusion of complex physics (e.g., rapid gravity segregation in fractures, first- and multi-contact miscibility). The successful application of the DFM workflow is largely due to the availability of the next-generation technology for reservoir modeling. We could not perform this work using existing simulation technologies designed for structured grids. Our DFM work facilitated the understanding of recovery mechanisms and contributed to business decisions toward optimal development of the carbonate reservoir.