Microscale effect of microvadose in shale reservoirs

Nanopore structure characterization for organic-rich shale using the non-local-density functional theory by a combination of N2 and CO2 adsorption

“…In nanopore structures, physisorption filling may be regarded as the primary physisorption process at the micropore scale (diameter, D < 2 nm), and surface coverage takes place on the walls of mesopores (2 nm < D < 50 nm) or open macropores (D > 50 nm), which causes mono-multilayer adsorption and pore condensation [5,14,16,19e21]. Micro-scale effects such as slippage and adsorption/desorption also significantly influence the gas flow in nanopore channel systems [22]. Therefore, the investigation of nanopore systems can provide a better understanding of the gas storage and migration pathways in shales.…”

Shale Gas Transport in Nanopores: Contribution of Different Transport Mechanisms and Influencing Factors

“…Javadpour et al pointed out that the diameter of the main flow pore of shale gas reservoirs in North America is between 4 and 200 nm. Yang et al , measured the diameter of the main flow pore of marine shale in Sichuan Basin to be 5–200 nm using field-emission electron microscopy and CT. Ning et al measured the pore diameter of shale samples collected from Sichuan Basin to be approximately 10–300 nm by combining field-emission SEM and nitrogen adsorption and high-pressure mercury injection experiments. Because of the large number of nanopores in shale gas reservoirs, gas flow through these reservoirs exhibits obvious microscale flow characteristics, and the flow transport mechanism, which mainly includes viscous flow, the slippage effect, boundary Knudsen layer effect, gas adsorption/desorption balance, and surface diffusion, is extremely complex. , Moreover, because the velocity at the wall surface is not zero when the gas flows in micro-/nanopores, the slippage effect is produced.…”

“…Knudsen number ( K n ) refers to the flow characteristic control parameter of shale gas in nanopores and is defined as the ratio of the mean free path of the gas to the characteristic length of the flow domain . Studies have shown that gas flow in the nanopores of shale gas reservoirs mainly occurs in the slip flow and transition flow regimes, where 0.001 < Kn < 10. , The slippage effect should be considered when 0.001 < Kn < 0.1; the Navier–Stokes equation combined with boundary slip correction is feasible for describing gas flow under this condition. ,,− When 0.1 < Kn < 10, the continuum hypothesis fails, and the Burnett equation can be used to describe the gas flow . Considering the complex transport mechanisms and multiscale flow characteristics of shale gas reservoirs, conventional numerical simulation methods cannot accurately describe the microscopic flow behaviors of shale gas.…”

“…Researchers have recently acknowledged the benefits of the lattice Boltzmann method (LBM) in unconventional gas flow simulation, and a large amount of research work incorporating this method has been published. ,,,,− The research object of LBM is the fluid micelle, which is larger than single molecules but smaller than particles in the continuum hypothesis. Thus, the method has mesoscale characteristics.…”

“…29 Studies have shown that gas flow in the nanopores of shale gas reservoirs mainly occurs in the slip flow and transition flow regimes, where 0.001 < Kn < 10. 11,18 The slippage effect should be considered when 0.001 < Kn < 0.1; the Navier−Stokes equation combined with boundary slip correction is feasible for describing gas flow under this condition. 14,16,30−32 When 0.1 < Kn < 10, the continuum hypothesis fails, and the Burnett equation can be used to describe the gas flow.…”