Beyond multiple-continuum modeling for the simulation of complex flow mechanisms in multiscale shale porous media

Abstract Simulation of mass transfer in shale porous media continues to challenge the hydrocarbon recovery industry due the involved complex porous media transport mechanisms and complicated porous structures. In this paper, we present a new multiscale approach to improve the simulation of gas flow in shale porous media based on a coupled triple-continuum and discrete fracture model. Gas transport in shale formations entails porous media flow through matrix (which contains organic and inorganic matters) and fractures. The fractures consist of small-scale natural fractures and large-scale artificial fractures from hydraulic fracturing. In the triple-continuum model, kerogen matrix, inorganic matrix and natural fractures are modeled as three superimposed continua. The hydraulic fractures are handled by discrete fracture model. Using a framework via the multiscale mixed finite element method, our methodology couples the triple-continuum model and discrete fracture model in a rigorous and systematic approach. The method can capture the small-scale features of gas flow through multiscale basis functions calculated based on the triple-continuum background. We go beyond multiple-continuum modeling by enabling explicit discrete fracture representation in our multiscale framework. As a result, our approach could avoid some oversimplified assumptions made in conventional triple-continuum models and enjoy explicit fracture treatment with high computational efficiency. Numerical aspects of the new approach are detailed with examples demonstrating its efficiency and accuracy for simulating gas flow in shale porous media with multiscale porous features.