A Coupled Model for Upscaling Water Flow in a Shale Matrix System from Pore Scale to Representative Elementary Area Scale.

Abstract

Understanding water transport in pore structures is essential for studying the impact of water leakage on oil and gas development in shale reservoirs. Previous apparent liquid permeability models have focused on describing the flow mechanism and paid less attention to the quantification of multiscale porous media within real samples and the convenience of numerically calculating multiscale flow-solid coupling. This study presents a multicomponent, multiscale pore spatial model by combining a representative elementary area (REA)-scale shale matrix grid model and fractal conical micropipe bundle model, facilitating quantification of the complex pore space in shale. The well-researched water-transport behavior in nanopores was then increased to describe REA-scale shale. The results show that the fractal conical micropipe model is more suitable for describing the heterogeneous pore structures of shale components than the fractal capillary bundle model. Wettability and fluid viscosity are key factors affecting the permeability enhancement of organic matter (OM) and inorganic matter (IOM), respectively. The degree of influence of OM heterogeneity on the total permeability of REA-scale shale depends on the total organic carbon content and permeability contrast between OM and IOM. Finally, an empirical model describing the macroscopic apparent liquid permeability of shale matrices was established that could quantify the effects of scale and porosity and permeability heterogeneity on permeability in shale matrices. The findings of this study can help us to better understand pore systems and fluid flow phenomena in shale matrices.