Stress-induced permeability evolution mechanism of hydrate-bearing sediments from pore-scale perspective

Carbon dioxide replacement during natural gas hydrate (NGH) exploitation facilitates natural gas extraction and CO2 sequestration. Clarifying the relationship between NGH reservoir parameters and permeability is crucial for enhancing production efficiency. In this study, sandy hydrate-bearing sediments (HBSs) with varying hydrate saturations were generated under low-temperature, high-pressure conditions with in-situ X-ray CT scanning. Permeability measurements during effective confining pressure compression and swelling explored stress-sensitive mechanisms at the pore scale. Results show: 1) Hydrate distribution heterogeneity significantly influences permeability; samples with low hydrate saturation (Sh = 32.95 %) exhibited gas permeability 3–5 times higher than those with medium to high saturation (Sh > 56 %). 2) Permeability decreases nonlinearly with increasing effective confining pressure, following a modified Kozeny-Carman equation (R2 = 0.8590 for compression, 0.7775 for swelling). 3) Compression and swelling processes induce distinct microstructural changes, with high Sh samples showing enhanced structural stability and permeability recovery. 4) PIV analysis reveals that hydrate presence reduces HBSs deformation under stress, with higher saturations leading to more uniform displacement distributions (variation <0.05 mm). This study advances understanding of the interactions between hydrate saturation, effective stress, and permeability, providing a theoretical basis for improving NGH extraction strategies and maintaining HBS stability.