Pore-scale modelling of gas flow in porous media

Description

Although the unconventional gas has accounted for 67% of the natural gas resources, its production contributed only 14% of global gas supply in 2012 [1]. Understanding of gas transport in unconventional reservoirs is still challenging for experimental and theoretical studies due to its extremely small permeability and complex nanoscale geometry. To predict the gas permeability through ultra-tight porous media where the Knudsen number (Kn) is large, gas rarefaction effect which enhances permeability should be taken into account. The Darcy’s law was first extended to slip regime (Kn < 0.1) in Klinkenberg model by considering the Navier-Stokes equation with gas slip on the pore surface [2]. Recently, a few models have been proposed to further expand Klinkenberg correction for all regimes by implementing the second-order slip flow boundary condition [3] or the so-called Knudsen diffusion mechanism [4]. However, these core-scale models include empirical parameters determined by fitting with numerical or experimental data. In modelling pore-scale flows, the gas kinetic theory approach is indispensable to simulate gas flow in the transitional regime (0.1 < Kn < 10). As Direct Simulation Monte Carlo (DSMC) method is extremely expensive for simulating low-speed flows in tight porous media, the kinetic model equations, which are simplified version of the Boltzmann equation, can be solved providing reliable results with reasonable computational cost. In the present work, gas flows through samples of porous media is simulated directly by solving the BGK kinetic equation [5] using Discrete Velocity Method (DVM) and Lattice Boltzmann method (LBM). The numerical data are compared with commonly used core-scale models, see Figure 1. The results show that the discrepancy between these models and the kinetic solution is small in the slip regime, and it varies in the transitional and free molecular regimes depending on the value of empirical parameters.

Period	9 May 2017
Event title	9th International Conference on Porous Media and Annual Meeting
Event type	Conference
Conference number	9th
Location	Rotterdam, NetherlandsShow on map
Degree of Recognition	International