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Nanoscale simulation of shale transport properties using the lattice Boltzmann method: permeability and diffusivity.

Chen L, Zhang L, Kang Q, Viswanathan HS, Yao J, Tao W - Sci Rep (2015)

Bottom Line: Correction of the intrinsic permeability is performed based on the dusty gas model (DGM) by considering the contribution of Knudsen diffusion to the total flow flux, resulting in apparent permeability.The correction factor over a range of Knudsen number and pressure is estimated and compared with empirical correlations in the literature.Specifically, we found that most of the values of correction factor fall in the slip and transition regime, with no Darcy flow regime observed.

View Article: PubMed Central - PubMed

Affiliation: 1] Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, China [2] Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA.

ABSTRACT
Porous structures of shales are reconstructed using the markov chain monte carlo (MCMC) method based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analysis of the reconstructed shales is performed, including porosity, pore size distribution, specific surface area and pore connectivity. The lattice Boltzmann method (LBM) is adopted to simulate fluid flow and Knudsen diffusion within the reconstructed shales. Simulation results reveal that the tortuosity of the shales is much higher than that commonly employed in the Bruggeman equation, and such high tortuosity leads to extremely low intrinsic permeability. Correction of the intrinsic permeability is performed based on the dusty gas model (DGM) by considering the contribution of Knudsen diffusion to the total flow flux, resulting in apparent permeability. The correction factor over a range of Knudsen number and pressure is estimated and compared with empirical correlations in the literature. For the wide pressure range investigated, the correction factor is always greater than 1, indicating Knudsen diffusion always plays a role on shale gas transport mechanisms in the reconstructed shales. Specifically, we found that most of the values of correction factor fall in the slip and transition regime, with no Darcy flow regime observed.

No MeSH data available.


Methane concentration distributions in the reconstructed shale.
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f2: Methane concentration distributions in the reconstructed shale.

Mentions: When the character length of a system is comparable to or smaller than the mean free path of the gas molecules, collisions between molecules and the solid wall are more frequent than that between gas molecules, leading to the Knudsen diffusion process. The Knudsen diffusivity in a local pore is30where M (kg mol−1) is molar mass, R the universal gas constant and T (K) temperature. dp (m) is the effective pore diameter and is determined by the 13 direction averaging method26. The effective Knudsen diffusivity Dk,eff, taking into account the pore size distributions as well as structural characteristics of a porous medium, is predicted by the LB mass transport model (See Methods). Fig. 2 shows the simulated 3D distribution of methane concentration in the reconstructed structure Sample 1. It can be seen that the diffusion process is greatly affected by the local void space, showing very complicated concentration distributions. The effective Knudsen diffusivity can be determined based on the concentration fields predicted (See Methods). The ratio between Dk,eff and D0 is 0.0212, 0.0197, 0.0380 and 0.0130 for Samples 1–4, respectively. With D0 as 5.44 × 10−6 m2s−1 (the Knudsen diffusivity with dp = 25 nm and T = 383 K), Dk,eff for Samples 1–4 is 1.25 × 10−7 m2s−1, 1.17 × 10−7 m2s−1, 2.25 × 10−7 m2s−1 and 7.71 × 10−8 m2s−1, respectively.


Nanoscale simulation of shale transport properties using the lattice Boltzmann method: permeability and diffusivity.

Chen L, Zhang L, Kang Q, Viswanathan HS, Yao J, Tao W - Sci Rep (2015)

Methane concentration distributions in the reconstructed shale.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4308705&req=5

f2: Methane concentration distributions in the reconstructed shale.
Mentions: When the character length of a system is comparable to or smaller than the mean free path of the gas molecules, collisions between molecules and the solid wall are more frequent than that between gas molecules, leading to the Knudsen diffusion process. The Knudsen diffusivity in a local pore is30where M (kg mol−1) is molar mass, R the universal gas constant and T (K) temperature. dp (m) is the effective pore diameter and is determined by the 13 direction averaging method26. The effective Knudsen diffusivity Dk,eff, taking into account the pore size distributions as well as structural characteristics of a porous medium, is predicted by the LB mass transport model (See Methods). Fig. 2 shows the simulated 3D distribution of methane concentration in the reconstructed structure Sample 1. It can be seen that the diffusion process is greatly affected by the local void space, showing very complicated concentration distributions. The effective Knudsen diffusivity can be determined based on the concentration fields predicted (See Methods). The ratio between Dk,eff and D0 is 0.0212, 0.0197, 0.0380 and 0.0130 for Samples 1–4, respectively. With D0 as 5.44 × 10−6 m2s−1 (the Knudsen diffusivity with dp = 25 nm and T = 383 K), Dk,eff for Samples 1–4 is 1.25 × 10−7 m2s−1, 1.17 × 10−7 m2s−1, 2.25 × 10−7 m2s−1 and 7.71 × 10−8 m2s−1, respectively.

Bottom Line: Correction of the intrinsic permeability is performed based on the dusty gas model (DGM) by considering the contribution of Knudsen diffusion to the total flow flux, resulting in apparent permeability.The correction factor over a range of Knudsen number and pressure is estimated and compared with empirical correlations in the literature.Specifically, we found that most of the values of correction factor fall in the slip and transition regime, with no Darcy flow regime observed.

View Article: PubMed Central - PubMed

Affiliation: 1] Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, China [2] Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA.

ABSTRACT
Porous structures of shales are reconstructed using the markov chain monte carlo (MCMC) method based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analysis of the reconstructed shales is performed, including porosity, pore size distribution, specific surface area and pore connectivity. The lattice Boltzmann method (LBM) is adopted to simulate fluid flow and Knudsen diffusion within the reconstructed shales. Simulation results reveal that the tortuosity of the shales is much higher than that commonly employed in the Bruggeman equation, and such high tortuosity leads to extremely low intrinsic permeability. Correction of the intrinsic permeability is performed based on the dusty gas model (DGM) by considering the contribution of Knudsen diffusion to the total flow flux, resulting in apparent permeability. The correction factor over a range of Knudsen number and pressure is estimated and compared with empirical correlations in the literature. For the wide pressure range investigated, the correction factor is always greater than 1, indicating Knudsen diffusion always plays a role on shale gas transport mechanisms in the reconstructed shales. Specifically, we found that most of the values of correction factor fall in the slip and transition regime, with no Darcy flow regime observed.

No MeSH data available.