The effective stress of marine sediments frequently shifts owing to natural or anthropogenic factors, and a broad spectrum of processes fundamentally require accounting for sediment responses to such changes. Marine sediments hosting natural gas hydrates have been regarded as a prospective energy reservoir, and depressurization-driven production efficiency hinges largely on the effective absolute permeability of hydrate-bearing strata. Yet, how this permeability evolves during depressurization remains unresolved, and whether pore-hosted hydrates impede or enhance it remains ambiguous. This study probes the permeability response of hydrate-bearing sands to cyclic loading through isotropic compression/swelling and water flow tests. Results reveal that methane hydrate presence curbs the void-ratio decline yet amplifies the effective-void-ratio reduction during isotropic loading. The effective absolute permeability of hydrate-bearing sands declines with rising hydrate saturation and increasing mean effective stress, and permeability stress sensitivity intensifies at higher hydrate saturations and lower mean effective stresses. The introduced model accurately predicts void-ratio changes during isotropic loading and unloading. Coefficients for strengthening, normal filling, and enhanced filling effects are introduced and quantified to disentangle the positive and negative influences of methane hydrate, with the negative filling effect exceeding the positive strengthening effect by one order of magnitude for quartz sands.

Natural gas hydrates in marine sediments undergo phase transitions under non-equilibrium conditions, making it challenging to accurately measure the permeability characteristics of hydrate-bearing sediments using experimental methods. In this study, pore network modeling is utilized to simulate the hydrate formation process and investigate the single-phase and two-phase permeability of hydrate-bearing sediments, and a comparative analysis was performed on consolidated and unconsolidated sediment samples. The results revealed the evolution of effective permeability as a function of hydrate saturation, and quantitative relationships were observed for the water retention curves and gas-water relative permeability, emphasizing the influence of pore structure and hydrate distribution on flow behavior. On the basis of the simulation results, predictive methods for irreducible water saturation, maximum water saturation, and key parameters in the van Genuchten and Brooks-Corey models for hydrate-bearing sediments are proposed. The findings provide deeper insights into gas-water flow dynamics in hydrate-bearing sediments and offer valuable guidance for hydrate resource exploitation, the assessment of environmental risks associated with hydrate dissociation, and the evaluation of carbon sequestration potential.

Cross-scale studies in geomechanical and hydrological systems employ a variety of approaches, either experimental, simulation or theoretical, each characterized by corresponding scale-specific methodologies. This perspective identifies and discusses challenges encountered at various scales, ranging from molecular to field scale, and examines issues related to integrating these scales. It highlights discrepancies in resolution and data compatibility, emphasizing the necessity for improved scale transition techniques. Insights and recommendations are proposed for future research to enhance multiscale modeling frameworks. These suggestions are crucial for bridging knowledge gaps on geological systems and improving the analyses accuracy for better engineering applications or earth system modelling.