Abstract: Conducting research on gas migration processes in buffer materials under multi-physics coupling conditions holds both theoretical and practical significance for ensuring the safety of deep geological repositories. Studies reveal that gas migration in buffer materials sequentially undergoes ultra-low permeability and gas breakthrough stages, characterized by gas dissolution-diffusion and significant gas seepage, respectively. The breakthrough mechanisms are categorized into capillary, mechanical, and interfacial breakthrough. To achieve continuous measurement of gas flux throughout the process and identification of breakthrough patterns, experimental setups have evolved through constant-volume, K0 confined, isotropic stress-controlled, and triaxial stress-controlled configurations. The newly developed triaxial testing system enables ultra-low flow rate measurement at 1/10 000 mL/min while incorporating eddy current sensing technology for real-time monitoring of localized volumetric changes in specimens, thereby facilitating breakthrough mode identification. Given the absence of characterization indices in empirical models and quasi-continuum theory-based theoretical models, researchers have established a conceptual model to identify gas breakthrough patterns based on the principle of preferential touching of breakthrough pressure curves. Future research should prioritize gas breakthrough testing methods with short testing cycle and high measurement accuracy, development of generalized breakthrough pattern identification models, and parameter scaling across different scales.

Key words: buffer materials, gas breakthrough pattern, gas migration experimental system, multi-field coupling, identification of breakthrough pattern