A revisited compositional 2-phase flow model for gas transport at various scales in heterogeneous porous structures in a deep geological radioactive waste disposal facility

There is a considerable challenge in modelling gas transport at different (spatial-time) scales in the saturated-unsaturated heterogeneous porous structure of a deep geological high-level radioactive waste disposal facility (HLW-DF). Inconsistencies in the conceptual physical two-phase flow models and uncertainties in the input parameters of such models (lack of knowledge, spatial variability…) can lead to misunderstanding of physical phenomena occurring in a HLW-DF, which may affect its performance during the post-closure phase. Therefore, there is a need for developing new physical approaches, and to account for uncertainties, in order to enhance the mathematical modelling of compositional two-phase flow models applied to gas migration in a HLW-DF. The purpose of this work is twofold: (i) to study the sensitivity to gas entry pressure, as a parameter in the hydraulic properties of clay-based materials, on the modelling of gas transport in a state of near full water saturation, and (ii) to analyze the propagation of uncertainty of the input parameters of gas transport models at various scales. Based on the codes iTOUGH2 (Finsterle et al., 2007) and TOUGH2-MP (Zhang et al., 2008), three test problems are studied in this work.