Parametric sensitivity to gas-entry pressure in 2-phase flow models in a deep geologic disposal of radioactive waste

Abdellah Amri (1) , Zakaria Saadi (1) , Rachid Ababou (2) , Magdalena Dymitrowska (1)

1 IRSN/PSE-ENV/SEDRE/UEMIS - Unité d'expertise et de modélisation des installations de stockage
2 IMFT - Institut de mécanique des fluides de Toulouse

After closure of a deep geological disposal (DGD), some gases will be generated through a number of processes. As gas concentration rises, a separate gas phase may be formed. If gas pressure exceeds gas entry pressure, a 2-phase flow may occur, potentially resulting in a decrease of the repository performance [1]. Therefore, a demonstration of the long-term safety of the repository requires a good characterization of hydraulic properties of its host rock and engineered barriers near full water saturation. A number of studies have focused on air-entry pressure (Pe) as a parameter to correct the classical van Genuchten-Mualem (VGM) model used in unsaturated soil hydrology for water retention and permeability curves [2], [3]. However, numerical simulations with gas-entry pressure effects in 2-phase flows are not available. In this work, a new approach is developed, consistent with experimental measurements of hydraulic properties of clay host rock and clay-based materials. As a first step, the RETC code [4] is modified by implementing a modified VGM model [3] accounting for gas-entry pressure, and by introducing gas permeability in addition to water permeability and water retention curve. All these hydraulic properties are combined in a single objective function. Figure 1 shows the resulting simultaneous fit to data of hydraulic properties of the argillaceous layer of Callovo-Oxfordian (COx) rock which has been chosen by Andra as a possible host-rock for deep geological disposal of intermediate-level long-lived and high-level radioactive wastes in eastern France. To use this new model with gas-entry pressure parameter, modifications were necessary in the TOUGH2 code [6]. Thus, the capillary pressure is set as primary state variable instead of gas saturation. After numerical verification of the revised version of TOUGH2, the Andra's PGZ1 experiment [7] is modeled (Figure 2). The preliminary results show that a non-zero gas entry pressure leads to considerably higher gas pressures than those simulated by the classical model with Pe=0 while keeping all other materials parameters unchanged.

Domaines: Mécanique des fluides [physics.class-ph]

Abdellah Amri, Zakaria Saadi, Rachid Ababou, Magdalena Dymitrowska. Parametric sensitivity to gas-entry pressure in 2-phase flow models in a deep geologic disposal of radioactive waste. 8th international Clay Conference 2022, Jun 2022, Nancy, France. ⟨hal-04483757⟩