Abstract
Solute transport is important in a variety of applications regarding flow in porous media, such as contaminant groundwater remediation. Most recent experimental studies on this process focus on field-scale or centimeter-scale data. However, solute spreading and mixing are strongly influenced by pore-scale heterogeneity. To study this, we developed a novel methodology to quantify transient solute concentration fields at the pore scale using fast laboratory-based microcomputed tomography. Tracer injection experiments in samples with different degrees of pore-scale heterogeneity (porous sintered glass and Bentheimer sandstone) were imaged in 3D by continuous scanning at a time resolution of 15 s and a spatial resolution of 13.4 μm. While our calibration experiments indicated a high uncertainty (1σ) on the concentration in single voxels due to imaging noise (± 27% of the total concentration range), we show that coarse gridding these values per individual pore significantly lowers the uncertainty (± 1.2%). The resulting pore-based tracer concentrations were used to characterize the transport by calculating the solute's arrival time and transient (filling) time in each pore. The average velocities estimated from the arrival times correspond well to the interstitial velocities calculated from the flow rate. This suggests that the temporal resolution of the experiment was sufficient. Finally, the pore-based transient filling times, the global concentration moment and the global scalar dissipation rate calculated from our experiments, indicated more dispersion in the sandstone sample than in the more homogeneous sintered glass. The developed method can thus provide more insight in the influence of pore-scale heterogeneity on solute transport.
| Original language | English |
|---|---|
| Pages (from-to) | 9279-9291 |
| Number of pages | 13 |
| Journal | Water Resources Research |
| Volume | 55 |
| Issue number | 11 |
| DOIs | |
| Publication status | Published - Nov 2019 |
Funding
): ‘Saturated solute transport micro‐CT dataset in sintered glass and Bentheimer sandstone’. Tescan XRE is thanked for the use of the reconstruction software Acquila and Marijn Boone (Tescan XRE) for the help with setting up the experimental workflow. Giovanni Porta is thanked for the helpful discussion on the quantification of mixing. We thank Maartje Boon and two anonymous reviewers for their useful comments on this work. The authors gratefully acknowledge UGCT (the center for X‐ray tomography at Ghent University) for the use of the micro‐CT scanner facilities. The Ghent University Special Research Fund (BOF‐UGent) is acknowledged for the financial support to the Centre of Expertise UGCT (BOF.EXP.2017.007). Tom Bultreys is a postdoctoral fellow of the Research Foundation–Flanders (FWO) and acknowledges its support under grant 12X0919N. The micro‐CT data can be found in the Digital Rocks Portal repository (Prodanovic et al.,
Keywords
- fast microcomputed tomography
- pore-scale imaging
- solute transport