Integrated detection of micro-pore structures and macro-mechanical responses for hydrate-bearing sediments

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.