Stress-dependent hydraulic permeability in hydrate-bearing sediments: A novel analytical model

The development of natural gas hydrates (NGHs) has drawn significant attention owing to their potential as a promising unconventional energy resource. However, during NGHs production, hydrate-bearing sediments (HBS) experience changes in the effective stress, resulting in nonlinear variations of pore structure that make porous fluid flow behavior difficult to predict. The diversity among different hydrate occurrence patterns further complicates pore structure evolution and hydraulic permeability characterization. To address these challenges, this study proposes a theoretical permeability model for HBS under different effective stresses. The model explicitly incorporates key mechanisms that have not been fully represented in previous studies, including diverse hydrate occurrence patterns, complex pore structures, and HBS deformation responses under isotropic as well as laterally confined compression conditions. Quantitatively, the proposed model accurately reproduces the experimental elastoplastic evolution of the void ratio, with coefficients of determination generally exceeding 0.9. Furthermore, the simulation results reveal that, compared with pore-filling (PF) and patchy (PA) hydrates, wall-coating (WC) hydrates exhibit higher permeability and can even exert a beneficial effect on effective absolute permeability (i.e., an effect ratio greater than one) under relatively high effective stress (e.g., greater than 3 MPa) and low hydrate saturation (e.g., less than 0.3), as demonstrated in the sensitivity analysis. This distinction underscores the critical role of hydrate morphology in controlling flow characteristics. These findings not only deepen the understanding of the coupled mechanisms between hydrate occurrence and effective stress, but also provide a theoretical foundation for evaluating long-term hydrate reservoir productivity.