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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.


Related in: MedlinePlus

(a) Voxel velocity distributions and (b) probability of molecular displacements P(ζ) for time td = 0.015 for two images of Estaillades limestone. Computations on a 3503 image with a voxel size of 7.7 µm (labeled Estaillades in Table1) are compared to the results from a 6503 image with a voxel size of 3.3 µm (Estaillades high resolution in Table1).
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fig11: (a) Voxel velocity distributions and (b) probability of molecular displacements P(ζ) for time td = 0.015 for two images of Estaillades limestone. Computations on a 3503 image with a voxel size of 7.7 µm (labeled Estaillades in Table1) are compared to the results from a 6503 image with a voxel size of 3.3 µm (Estaillades high resolution in Table1).

Mentions: [39] We explore the effect of image resolution in Figures 11a and 11b where we compare the velocity fields and propagators for Estaillades for the 3503 image with a voxel size of 7.7 µm and the 6503 Estaillades higher-resolution image with a voxel size of 3.3 µm. The velocity fields are virtually identical with, perhaps, more slow-flowing regions identified in the higher-resolution image. There is very little difference in the predicted propagators. Improving the image resolution allows more of the pore space to be captured, although there is still unresolved microporosity. However, there is, with finite computational resources, a trade-off between resolution and total system size. One cannot both resolve microporosity and run simulations on an image that spans several characteristic lengths, and which is therefore representative of core-scale transport.


Insights into non-Fickian solute transport in carbonates.

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

(a) Voxel velocity distributions and (b) probability of molecular displacements P(ζ) for time td = 0.015 for two images of Estaillades limestone. Computations on a 3503 image with a voxel size of 7.7 µm (labeled Estaillades in Table1) are compared to the results from a 6503 image with a voxel size of 3.3 µm (Estaillades high resolution in Table1).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig11: (a) Voxel velocity distributions and (b) probability of molecular displacements P(ζ) for time td = 0.015 for two images of Estaillades limestone. Computations on a 3503 image with a voxel size of 7.7 µm (labeled Estaillades in Table1) are compared to the results from a 6503 image with a voxel size of 3.3 µm (Estaillades high resolution in Table1).
Mentions: [39] We explore the effect of image resolution in Figures 11a and 11b where we compare the velocity fields and propagators for Estaillades for the 3503 image with a voxel size of 7.7 µm and the 6503 Estaillades higher-resolution image with a voxel size of 3.3 µm. The velocity fields are virtually identical with, perhaps, more slow-flowing regions identified in the higher-resolution image. There is very little difference in the predicted propagators. Improving the image resolution allows more of the pore space to be captured, although there is still unresolved microporosity. However, there is, with finite computational resources, a trade-off between resolution and total system size. One cannot both resolve microporosity and run simulations on an image that spans several characteristic lengths, and which is therefore representative of core-scale transport.

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.


Related in: MedlinePlus