Overview and consistency of migration experiments in clay

An overview is given about the types of migration experiments in clay and their corresponding mathematical models aimed to determine: (1) the product ηR of the diffusion accessible porosity η and the retardation factor R, and (2) the apparent dispersion coefficient D. An example shows that not all set-ups allow to estimate values for these parameters. An important concern is consistency.Consistency requires a good correlation between the diffusion accessible porosity η (fitted from migration experiments) of tritiated water and the independently measured water content. Column migration experiments (pulse injection type) on compact clay cores taken at different depths in the Ypres Clay Formation, confirm this correlation and lead to the expected value of the grain density, showing that nearly the entire porosity of the clay is accessible for water diffusion.Another requirement for consistency is that different experimental set-ups lead to the same value for the migration parameters. The average values of the apparent diffusion coefficient of dissolved silica obtained with different types of tests in Boom Clay are, respectively, 6 × 10−13 m2/s (in-diffusion, 25 °C), 2 × 10−13 m2/s (percolation, 25 °C) and 9 × 10−13 m2/s (combined glass-dissolution/diffusion, 30 °C). The values of the product ηR are around 60–70 (in-diffusion) and between 100 and 150 (percolation). Using fit results from the combined glass-dissolution/diffusion experiments with other results, leads to ηR values ranging from 40 to 90. The values of the migration parameters obtained from different types of experiments and the corresponding models are consistent.