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Insights into non-Fickian solute transport in carbonates.

Bijeljic B, Mostaghimi P, Blunt MJ - Water Resour Res (2013)

Bottom Line: Mostaghimi, and M.Blunt (2013), Insights into non-Fickian solute transport in carbonates, Water Resour.Res., 49, 2714-2728, doi:10.1002/wrcr.20238.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth Science and Engineering, Imperial College London London, UK.

ABSTRACT
[1] We study and explain the origin of early breakthrough and long tailing plume behavior by simulating solute transport through 3-D X-ray images of six different carbonate rock samples, representing geological media with a high degree of pore-scale complexity. A Stokes solver is employed to compute the flow field, and the particles are then transported along streamlines to represent advection, while the random walk method is used to model diffusion. We compute the propagators (concentration versus displacement) for a range of Peclet numbers (Pe) and relate it to the velocity distribution obtained directly on the images. There is a very wide distribution of velocity that quantifies the impact of pore structure on transport. In samples with a relatively narrow spread of velocities, transport is characterized by a small immobile concentration peak, representing essentially stagnant portions of the pore space, and a dominant secondary peak of mobile solute moving at approximately the average flow speed. On the other hand, in carbonates with a wider velocity distribution, there is a significant immobile peak concentration and an elongated tail of moving fluid. An increase in Pe, decreasing the relative impact of diffusion, leads to the faster formation of secondary mobile peak(s). This behavior indicates highly anomalous transport. The implications for modeling field-scale transport are discussed. Citation: Bijeljic, B., P. Mostaghimi, and M. J. Blunt (2013), Insights into non-Fickian solute transport in carbonates, Water Resour. Res., 49, 2714-2728, doi:10.1002/wrcr.20238.

No MeSH data available.


Voxel velocity distributions for Mt Gambier limestone and Estaillades limestone. Mt Gambier limestone has a narrow spread of velocities, while Estaillades limestone has a wide spread of velocities. This results in a different shape of propagators (stagnant concentration regions, elongated mobile tails) and hence the different nature of transport. The lines indicate diffusive cutoffs at Pe = 10, 50, 200, and 700 for which the time taken to traverse a voxel by advection is 100 times longer to that traversed by diffusion for Mt Gambier limestone. The arrow shows that diffusive cutoff decreases with an increase in Pe. The solid line shows the velocity distribution in a single circular tube, representing the homogeneous limit.
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fig10: Voxel velocity distributions for Mt Gambier limestone and Estaillades limestone. Mt Gambier limestone has a narrow spread of velocities, while Estaillades limestone has a wide spread of velocities. This results in a different shape of propagators (stagnant concentration regions, elongated mobile tails) and hence the different nature of transport. The lines indicate diffusive cutoffs at Pe = 10, 50, 200, and 700 for which the time taken to traverse a voxel by advection is 100 times longer to that traversed by diffusion for Mt Gambier limestone. The arrow shows that diffusive cutoff decreases with an increase in Pe. The solid line shows the velocity distribution in a single circular tube, representing the homogeneous limit.

Mentions: [36] We can explain the complex non-Fickian transport behavior of propagators described in Figures 9 by looking at the velocity distribution curves in Figure 10. The exemplars taken are Mt Gambier limestone for a narrow spread of velocities and Estaillades limestone for a wide spread. Note that they are different in both low-velocity regions where diffusion is the only mechanism of transport leading to largely immobile solute, and the high-velocity region that produces the elongated tail of fast-moving solute. These characteristics define the nature of transport revealed by the different shapes of the propagators.


Insights into non-Fickian solute transport in carbonates.

Bijeljic B, Mostaghimi P, Blunt MJ - Water Resour Res (2013)

Voxel velocity distributions for Mt Gambier limestone and Estaillades limestone. Mt Gambier limestone has a narrow spread of velocities, while Estaillades limestone has a wide spread of velocities. This results in a different shape of propagators (stagnant concentration regions, elongated mobile tails) and hence the different nature of transport. The lines indicate diffusive cutoffs at Pe = 10, 50, 200, and 700 for which the time taken to traverse a voxel by advection is 100 times longer to that traversed by diffusion for Mt Gambier limestone. The arrow shows that diffusive cutoff decreases with an increase in Pe. The solid line shows the velocity distribution in a single circular tube, representing the homogeneous limit.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3814002&req=5

fig10: Voxel velocity distributions for Mt Gambier limestone and Estaillades limestone. Mt Gambier limestone has a narrow spread of velocities, while Estaillades limestone has a wide spread of velocities. This results in a different shape of propagators (stagnant concentration regions, elongated mobile tails) and hence the different nature of transport. The lines indicate diffusive cutoffs at Pe = 10, 50, 200, and 700 for which the time taken to traverse a voxel by advection is 100 times longer to that traversed by diffusion for Mt Gambier limestone. The arrow shows that diffusive cutoff decreases with an increase in Pe. The solid line shows the velocity distribution in a single circular tube, representing the homogeneous limit.
Mentions: [36] We can explain the complex non-Fickian transport behavior of propagators described in Figures 9 by looking at the velocity distribution curves in Figure 10. The exemplars taken are Mt Gambier limestone for a narrow spread of velocities and Estaillades limestone for a wide spread. Note that they are different in both low-velocity regions where diffusion is the only mechanism of transport leading to largely immobile solute, and the high-velocity region that produces the elongated tail of fast-moving solute. These characteristics define the nature of transport revealed by the different shapes of the propagators.

Bottom Line: Mostaghimi, and M.Blunt (2013), Insights into non-Fickian solute transport in carbonates, Water Resour.Res., 49, 2714-2728, doi:10.1002/wrcr.20238.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth Science and Engineering, Imperial College London London, UK.

ABSTRACT
[1] We study and explain the origin of early breakthrough and long tailing plume behavior by simulating solute transport through 3-D X-ray images of six different carbonate rock samples, representing geological media with a high degree of pore-scale complexity. A Stokes solver is employed to compute the flow field, and the particles are then transported along streamlines to represent advection, while the random walk method is used to model diffusion. We compute the propagators (concentration versus displacement) for a range of Peclet numbers (Pe) and relate it to the velocity distribution obtained directly on the images. There is a very wide distribution of velocity that quantifies the impact of pore structure on transport. In samples with a relatively narrow spread of velocities, transport is characterized by a small immobile concentration peak, representing essentially stagnant portions of the pore space, and a dominant secondary peak of mobile solute moving at approximately the average flow speed. On the other hand, in carbonates with a wider velocity distribution, there is a significant immobile peak concentration and an elongated tail of moving fluid. An increase in Pe, decreasing the relative impact of diffusion, leads to the faster formation of secondary mobile peak(s). This behavior indicates highly anomalous transport. The implications for modeling field-scale transport are discussed. Citation: Bijeljic, B., P. Mostaghimi, and M. J. Blunt (2013), Insights into non-Fickian solute transport in carbonates, Water Resour. Res., 49, 2714-2728, doi:10.1002/wrcr.20238.

No MeSH data available.