Clay-rich geological formations are considered as host rocks for deep geological disposal of radioactive waste. Over the long term, gas will be produced and will migrate through the surrounding geological formation. Gas transport mechanisms have been investigated in laboratory tests. However, the effects of material heterogeneity remain insufficiently explored. This paper presents a stochastic analysis of two-phase flow in clays under gas injection, incorporating spatially correlated porosity. The study evaluates the effects of sample size, gas injection pressure, and the choice between two-dimensional (2D) and two-dimensional (3D) conditions on the statistical outputs, including mean behaviour and variability. The results indicate that larger samples exhibit reduced variability in the degree of saturation and gas permeability due to enhanced averaging effects. Moreover, the variation in results is higher under high gas injection pressure compared to low gas injection pressure. In addition, the variability of results is significantly reduced in 3D simulations compared to 2D, with high-permeability regions more likely to form continuous pathways under 3D conditions, emphasising the necessity of accounting for 3D effects. The findings indicate that sample size is a critical factor in experiments, as it influences the number of tests required to achieve results within a desired level of accuracy. ... Read more

Gas flow along localized dilatant pathways is considered as an important gas transfer mechanism in saturated plastic clays such as Boom clay. The process involves micro-fracturing of the pore space at rising gas pressures, gas flow and possibly sealing of the newly-created pathways.

Modelling gas flow along localized dilatant pathways presents a number of challenges associated with: (1) the very strong coupling between the hydraulic and mechanical aspects of the problem, (2) the microscopic scale of the process and (3) the important influence of material heterogeneities on the process dynamics.

This contribution presents a review of existing theoretical and numerical frameworks for damage, strain localisation and fracture of clay materials. In particular, it addresses the suitability of these approaches as a basis for the development of new modelling framework for gas flow along localized dilatant pathways.

The research was carried out within the WP GAS of EURAD (2019 - 2024). ... Read more