Pore-scale permeability calculation using CFD and DSMC techniques

Numerical experiments are performed to evaluate the capability and examine the computational costs and tradeoffs of numerical and analytical approaches for apparent gas permeability calculation. Considering the dominance of capillary force in pore-level microstructures, two-phase distribution maps are constructed within micro- and nano-scale media using a quasi-static pore morphology-based technique. At each equilibrium step, the gas saturation profile is extracted to conduct single phase flow simulations and predict the gas effective permeability. To investigate the effect of gas slippage on the accuracy of the results, both Computational Fluid Dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) techniques are applied in a wide range of gas pressures. The results reveal that the continuum theory is valid for a specific pore size and gas pressure range and its accuracy is strongly dependent on the Knudsen number value. DSMC simulation case studies demonstrate that in case of proper medium characterization, a tuned Klinkenberg correlation is capable of providing satisfying predictions within both slippage and transition flow regimes.