Upscaling Reactive Transport and Clogging in Shale Microcracks by Deep Learning

Fracture networks in shales exhibit multiscale features. A rock system may contain a few main fractures and thousands of microcracks, whose length and aperture are orders of magnitude smaller than the former. It is computationally prohibitive to resolve all the fractures explicitly for such multiscale fracture networks. One traditional approach is to model the small‐scale features (e.g., microcracks in shales) as an effective medium. Although this fracture‐matrix conceptualization significantly reduces the problem complexity, there are classes of physical processes that cannot be accurately upscaled by effective medium approximations, for example, microcrack clogging during mineral reactions. In this work, we employ deep learning in place of effective medium theory to upscale physical processes in small‐scale features. Specifically, we consider reactive transport in a fracture‐microcrack network where microcracks can be clogged by precipitation. A deep learning multiscale algorithm is developed, in which the microcracks are upscaled as a wall boundary condition of the main fractures. The wall boundary condition is constructed by recurrent neural networks, which take concentration histories as input and predict the solute transport from main fractures to microcracks. The deep learning multiscale algorithm is first employed in specific scenarios, then a general model is developed which can work under various conditions. The new approach is validated against fully resolved simulations and an analytical solution, providing a reliable and efficient solution for problems that cannot be upscaled by effective medium models. Key Points We propose a hybrid framework for modeling reactive transport and clogging in multiscale fracture networks Microcracks are upscaled by deep learning while main fractures are described by theory‐based modeling, ensuring a two‐way coupling The framework provides a reliable and efficient upscaling method without relying on the existence of macroscopic equations