Micro-pore structures determine the macro-mechanical behaviors of porous media, whereas their quantitative linkages remain ambiguous owing to the limitations of test techniques, especially for hydrate-bearing sediments. This study proposes an integrated approach that combines low-field nuclear magnetic resonance high-frequency detection with triaxial shearing, enabling the in-situ simultaneous monitoring of both the macro-mechanical parameters and micro-pore structures. The device, which consists of a high-pressure specimen vessel, a low-field nuclear magnetic resonance measurement module, a temperature and pressure control module, and a data acquisition module, allows the real-time acquisition of transverse relaxation time distribution and magnetic resonance images during triaxial loading, facilitating the detection of pore water distribution and crack development. Preliminary verification illustrates the high reliability of the device. Under relatively low strain, the signal intensity ratio of micropores rises with a transverse relaxation time of less than 10 ms, while that of macropores decreases gradually. Conversely, the signal intensity ratios for both micropores and macropores present the opposite tendency with the strain exceeding 5.1%. Besides, with the axial strain rising from 0 to 15%, there is an increase of about 16.9% in the peak area of macropores. Randomly distributed cracks observed under triaxial shearing correspond to the increasing peak area and signal intensity ratio of macropores, which is verified by comparing the magnetic resonance and computerized tomography images. This method provides a new possibility for characterizing the failure processes of hydrate-bearing sediments and establishing macro-to-micro equivalent relationships, enhancing the applications for porous media containing phase-reversible agents.

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.