Natural gas hydrate production involves complex mass/heat transfer, phase transformation, and multiphase seepage processes, where permeability critically influences exploitation efficiency and sediment stability. This review summarizes progress in permeability evolution in hydrate-bearing sediments, covering: multiphase seepage theories involving absolute and relative permeability models; pore-scale methods, including Lattice Boltzmann, Pore Network models, CFD simulations, and microfluidic experiments, for investigating the effects of hydrate morphology and pore heterogeneity; core-scale experiments, such as seepage tests and X-ray CT, for quantifying permeability changes with hydrate saturation and stress sensitivity; site-scale scenarios involving pilot tests and numerical models are challenged by fluid migration prediction and reservoir stability. Key findings show hydrate dissociation induces dynamic pore structure changes and complex multiphase interactions, with existing models oversimplifying heterogeneous pore structures and hydrate distributions. Critical research gaps include: inadequate characterization of pore structure evolution during hydrate nucleation/dissociation; unclear gas-water flow mechanisms in deformable sediments; lack of multiscale correlation and coupled modeling for permeability-stress-phase change interactions. Addressing these offers critical insights for optimizing extraction, reducing energy use, and ensuring reservoir stability, enabling safe and efficient exploitation of natural gas hydrates as a strategic clean energy resource.

The exploitation of natural gas hydrates is in essence the process of hydrate dissociation from the solid phase into the gas and liquid phases, which is a complex problem involving phase transition and gas-water multi-phase flow. Permeability is a useful parameter for characterizing the flow capacity of sediments, and the pore-structure changes caused by hydrate dissociation make this parameter characterized by spatial and temporal evolution. Clayey silt sediments form the hydrate accumulation reservoir in the South China Sea, whose lithological characteristics (shallow buried deep, poor permeability, and low cementation) are unfavorable to fluid flow, leading to difficulties in the production prediction of clayey silt hydrate-bearing sediments. In this paper, the mutual feed-back mechanism between pore-structure and permeability during hydrate dissociation was clarified using the lattice Boltzmann model method. Core-scale seepage experiments were carried out to validate the dynamic evolution of permeability relationship. The permeability calculation module of Tough+Hydrate code was developed to quantitatively describe the evolution of this relationship, and the first hydrate production test in the Shenhu area was evaluated to validate the applicability of pore- and core-scale study at the site scale. This study clarifies the dynamic evolution mechanism of permeability during hydrate dissociation, and establishes a permeability evolution model in a S-shape suitable for clayey silt hydrate-bearing sediments.