Pattern and dynamics of methane/water two-phase flow in deep-shale illite nanoslits

Abstract

The development of deep shale gas is critical for the sustainable growth of unconventional energy resources. Deep shale formations are characterized by a high illite content, which necessitates a thorough understanding of the structural and flow dynamics of methane and water within illite nanoslits. In this study, molecular dynamics simulations were employed to examine the flow characteristics of methane and water in slit-shaped illite nanopores. The investigation sheds light on the effects of water saturation, acceleration, and pore size on two-phase flow behavior. The results reveal that water molecules preferentially adsorb onto the illite channel surface. As water saturation increases, the water phase evolves into various forms, including water films, water bridges, and water locks, ultimately trapping methane in nanobubbles encased by the water phase. The presence of water significantly reduces the flow space available for methane. With increasing water saturation, the methane density peaks near the channel walls decrease, and the density distribution curves transition into parabolic profiles. The methane flow flux decreases notably as water saturation increases, especially from 0% to 40%. When the S_w reaches 40%, the methane flow flux is reduced by 84% compared to methane single-phase flow. Additionally, the flow fluxes of both water and methane increase with larger pore sizes in illite slits. These findings are expected to provide valuable insights for developing deep shale gas reservoirs, optimizing hydraulic fracturing designs, and improving production performance predictions.