Three‐dimensional Lattice Boltzmann simulation of gas‐water transport in tight sandstone porous media: Influence of microscopic surface forces

Abstract

A three-dimensional two-phase Lattice Boltzmann model was developed and validated for the fundamental phenomena of gas-water transport in tight porous media considering microscopic forces, namely, the electrostatic and solid-liquid intermolecular forces. The thickness of the water film adhering to the porous media surface was calculated based on the principle of thermodynamic equilibrium and the gas-water electrostatic potential energy. The Lattice Boltzmann model simulations focused on the effects of the microscopic forces and water film thickness on the gas-water transport in tight porous media. The fluid flow in the porous media was simulated under different conditions for the characteristic length, interfacial tension, and displacement pressure gradient. The results confirmed that the gas-water transport is strongly affected by the microscopic forces in tight porous media and that the transport process is accompanied by a high seepage resistance. The seepage resistance is more pronounced in the case of smaller pores because the adhering water film is thicker and more stable. During the transport process, the water film may disintegrate under certain conditions, which would enhance the gas flow in the porous media. However, it is difficult to effectively improve the gas flow by increasing the displacement pressure gradient under microscopic forces; this can be attributed to the accumulation of water or increased seepage resistance dictated by the interfacial tension, which occurs more frequently with smaller pores. This paper provides a promising new perspective for efficiently improving the Lattice Boltzmann model for transport trends considering microscopic forces. K E Y W O R D S bounded water film, gas-water two-phase transport, Lattice Boltzmann model, microscopic surface force, tight sandstone gas reservoir | 1925 HU et al. egge (s) The position of the gas leading edge (x/L) The interfacial tension: 0.020 N/m The interfacial tension: 0.025 N/m The interfacial tension: 0.030 N/m The interfacial tension: 0.035 N/m The interfacial tension: 0.040 N/m 0 5 10 15 20 0 0 .2 0.4 0 .6 0.8 1 The breakthrough time of the leading edge (s) The position of the gas leading edge (x/L) The interfacial tension: 0.020 N/m The interfacial tension: 0.025 N/m The interfacial tension: 0.030 N/m The interfacail tension: 0.035 N/m The interfacial tension: 0.040 N/m

Pore Water and Its Multiple Controlling Effects on Natural Gas Enrichment of the Quaternary Shale in Qaidam Basin, China

“…Pore water forms a water film on the pore surface, which is usually from a few nanometers to tens of nanometers in thickness. The thickness of the pore water film is related to factors such as porosity and rock particles [46]. The calculation of water film thickness in pores involves concepts such as capillary pressure, formation pressure, and separation pressure (Figure 7).…”

A Simplified Lattice Boltzmann Boundary Conditions for Gas Transport in Self-Affine Microchannels with an Inherent Roughness of in a Tight Reservoir

“…According to the Knudsen number Kn, there are four main mass transfer mechanisms for gas in porous media [8]: continuous flow (Kn < 0.01), where Darcy's law is still applicable; slip flow (0.01 < Kn < 0.1), where the slip effect should not be neglected; transition flow (0.1 < Kn < 10), where the rarefaction effect must be taken into account, and the continuum assumption is nearly invalid; and free molecular flow (Kn > 10) where molecular-wall collisions mainly dominate the gas flow. The Knudsen number in the nanopores of a tight sandstone gas reservoir matter ranges from 0.001 to 1 [9]. Therefore, the multiple flow mechanisms of slip flow and continuous flow for tight sandstone gas exist simultaneously, a factor that should be carefully investigated.…”