Effect of nano-confinement on high pressure methane flow characteristics

High pressure gas flow in shale nanoporous media plays an important role in shale gas recovery. The objective of this work is to study the effect of confinement on high pressure methane flow in nanoscale pores. We used dual control volume grand canonical molecular dynamics for different temperatures and pore sizes and compared our results with conventional hydrodynamic equation. We observed that when pore size is larger than 2 nm, flux increases with pore size. But when pore size is less than 2 nm, flux shows varying behaviors depending on the pore size due to methane molecular configurations and structures under different nano-confinements. We also observed that enhancement over the prediction from Hagen-Poiseuille equation can be more than two orders of magnitude in nanopores of around 1 nm pore size. Similar to previous computer simulation and experiments on liquid flow in nanopores, the dependences of the enhancement factor ε and the calculated slip length Ls on the pore sizes show discontinuity within three distinct regions: R1) pore size less than 0.8 nm; R2) between 0.8 and 1.0 nm; and R3) larger than 1.0 nm. Within R2 and R3, ε and Ls monotonically decrease with pore size. The methane molecular flux, enhancement factor, and calculated slip length increase from 328.15 K to 368.15 K, but remain comparable for 368.15 K and 408.15 K.