Pore-network modeling of flow in shale nanopores: Network structure, flow principles, and computational algorithms

Hydrocarbons in subsurface nanoporous media, such as shale, are promising energy resources to compensate for the shortage of conventional reservoirs. Pore-network modeling serves as a valuable tool for simulating microscale fluid transport and elucidating flow physics in porous media. However, traditional pore-network models have failed to capture features of spatial structure and fluid flow in unconventional shale rock. This work presents a critical review of pore-network modeling of single-phase and two-phase flow in shale rock. Pore-network modeling advances of shale are reviewed based on three major parts: network morphology and geometries, flow principles in nanocapillaries, and pore-network computational algorithms. First, based on key geological features of shale rock, we analyze network topology, multiscale network, pore geometries, and network representativeness of shale pore-network models. Then, we discuss four important aspects that may influence flow principles of fluids in nanocapillaries: gas and liquid slippage, sorption and diffusion behavior, hydrocarbon thermodynamics, and the presence of water. Finally, we present pore-network modeling methods used for flow simulations in shale rock, including quasi-static and dynamic algorithms. We hope that this review could shed light on fundamentals of pore-network modeling of shale rock.