Approaches for modelling gas flow in clay formations as repository systems

Modelling of transport phenomena in disturbed as well as in undisturbed portions of clay formations is more complex than that of most other host rocks used as geological repository for intermediate and high level radioactive wastes. Darcy’s Law provides the basic formulation for gas movement either dissolved in liquid phase or as free phase together with liquid phase. However, the restrictions of the Darcy formulation for modelling the fluid flow in clay formations are reported. The dominating effect of the capillary forces, the local and global heterogeneities, the interactions of percolating fluids with clay minerals are some of the features limiting the direct application of Darcy formulation. Physical and numerical approaches have been made for more representative formulations of gas movement in clay formations. An executive compilation of the modelling efforts of gas transport in clay formations as well as in bentonite based buffer materials for radioactive waste disposal is presented. Modelling concepts are evaluated and compared. Their implementations and the degree of validations are summarized.