Water/Methane Two-Phase Flow in the SiO2 Nanoslit Can Be Well Described via the Deformed Water Layer Model: A Molecular Simulation Study

The intricate flow processes in nano-pores pose limitations on the extraction of resources such as shale gas and gas hydrates. To observe water/gas two-phase flow in nano-pores, we employed molecular dynamics simulations on water/methane two-phase flow in a hydrophilic SiO2 nanoslit, and obtained high-quality data by applying the "pump method" and "nano-manometer." This study revealed the variation in phase distribution during flow process, and assessed the impact of water phase distribution on methane gas flow. We proposed the "Deformed Water Layer (DWL) model" based on physical mechanisms, which can precisely describe methane relative permeability and forecast the critical water saturation for forming water lock. Our results suggest a two-stage transition in methane gas permeability with increasing water saturation within nano-pores, governed by spatial deformation of water phase. This phenomenon underscores that maintaining a reduced groundwater saturation is imperative to facilitate superior gas permeability and enhance recovery efficacy.