Slip length of methane flow under shale reservoir conditions: Effect of pore size and pressure

Effect of Surface Type on the Flow Characteristics in Shale Nanopores

“…In this work, to weed out the effect of random roughness of the wall structure to the gas transport, a full atomic smooth structure of three graphite layers is used to represent the organic nanopores in shale reservoir (as shown in Figure 3). Such a simplified method is widely used in the MD simulations which are focused on the research of geofluids adsorption and flow performance in shale organic pores [15,[21][22][23]45]. The dimension of the graphene layers in x-and y-direction are L x = 20:27 nm and L y = 10:07 nm, respectively, and such a box size is enough to make the transport behavior of the gas molecules reach a steady state in the NEMD simulation.…”

“…The bulk density and the viscosity cannot represent the physical properties actually since the distribution of the gas confined in nanopore may be inhomogeneous [16,17]. In another aspect, as the mean free path of methane molecules changes to be comparable to the pore size in such tiny pores [18][19][20], the traditional Darcy Law may be invalidated and make the prediction of shale gas flow be challenging [6,21,22].…”

“…When the pore size is enough large, Kn is sufficiently small and lower than 0.001; the fluid flow is assumed as continuum flow and could be described by the no-slip condition combined with the Navier-Stokes equation [25,26]. The Poiseuille flow under slit-like pores could be predicted as the following [22,23]:…”

“…Furthermore, to have an accurate understanding of gas transport characteristics in nanoporous/microporous media, the molecular dynamic (MD) simulation is also widely applied to understand the gas flow behaviors, as summarized and depicted in one recent review by Yu et al [39,40]. The nanochannels are generally used to mimic the fluids flow confined in shale nanoporous media in these MD simulations [22,41,42]. Since the shale organic matter is mainly composed of carbon atoms and the pore wall is hydrophobic; thus, the graphene sheets, carbon nanotubes, and arrayed carbons are abstracted as organic pore wall materials in numerous previous work [39].…”

“…Employing parallel carbon walls to model the complex organic pore structure, Chen 2 Geofluids et al investigated the pressure-driven shale gas flow behavior; they found that the velocity profiles translate from plug-like to parabolic when the pore width increases from 2 nm to 10 nm [41]. The similar carbon structure was also used to study the slip behavior of shale gas by Nan et al [22]. Recently, the slit-like pore confined in amorphous kerogen structure was constructed and used to reveal the transport behavior of geo-fluids.…”