Observations of 3-D transverse dispersion and dilution in natural consolidated rock by X-ray tomography

- We have developed a new core flood test for the characterization of transverse dispersion and dilution in three dimensions in natural-rock media.
- Dt were calculated using three different methods: (1) fitting to an analytical solution, (2) from the second-central moment and (3) from the dilution index.
- Dt decreased with distance due to flow focusing.
- Sub-linear behavior of Dt with Pe was observed in the power law regime.
- The reactor ratios were high confirming the homogeneity of the Berea sandstone.

Recent studies have demonstrated the importance of transverse dispersion for dilution and mixing of solutes but most observations have remained limited to two-dimensional sand-box models. We present a new core-flood test to characterize solute transport in 3-D natural-rock media. A device consisting of three annular regions was used for fluid injection into a cylindrical rock core. Pure water was injected into the center and outer region and a NaI solution into the middle region. Steady state transverse dispersion of NaI was visualized with an X-ray medical CT-scanner for a range of Peclét numbers. Three methods were used to calculate Dt: (1) fitting an analytical solution, (2) analyzing the second-central moment, and (3) analyzing the dilution index and reactor ratio. Transverse dispersion decreased with distance due to flow focusing. Furthermore, Dt in the power-law regime showed sub-linear behavior. Overall, the reactor ratios were high confirming the homogeneity of Berea sandstone.