The goal of “carbon peak and neutrality” is driving China's energy system to accelerate transition to clean, low-carbon development. As an important new clean energy source, natural gas hydrate (NGH) exhibits high energy density, wide distribution, and substantial resource potential. Therefore, accelerating its industrial production is key to achieving a reduction in pollution and carbon emission. NGH production involves Thermal-Hydrological-Mechanical-Chemical (THMC) multi-physical field coupling. Traditional experiments and production tests fail to fully reveal underlying mechanisms, making numerical simulation—with high functionality, flexible methods, and low cost—an essential research tool. This study systematically reviews theories, technologies, and applications of numerical simulation for natural gas hydrate production to provide theoretical support for safe, efficient extraction and advance the translation of simulation technologies to engineering practice. Specifically, it clarifies evolution laws of seepage parameters (e.g., porosity, permeability) during hydrate dissociation; identifies evolution of mechanical parameters (e.g., shear strength, cohesion) with hydrate saturation, revealing the core mechanism by which hydrates dominate reservoir mechanical property evolution via decomposition behaviour; outlines approaches to constructing THMC multi-physical field coupling models; summarizes functions and advantages of major global simulators (e.g., TOUGH+Hydrate, SuGaR-TCHM), and validates applications at typical pilot sites. Current numerical simulation research has limitations: multi-phase flow models insufficiently account for continuous pore structure evolution and impacts of hydrate saturation on relative permeability; characterization of mechanical properties and sand production risk responses in unconsolidated clayey silt sediments is inadequate; and capacity to predict long-term mechanical stability risks (e.g., land subsidence, submarine landslides) induced by production is limited. Future work should establish “micro-macro” cross-scale parameter models, refine elastoplastic constitutive models for clayey silt sediments, and develop integrated geological engineering simulation tools to advance simulation technologies from mechanistic interpretation to engineering decision support.

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.

CO₂ is now considered as a novel heat transmission fluid to extract geothermal energy. It can be used for both energy exploitation and CO₂ geological sequestration. Here, a 3-D, “two-spot” pattern well model is developed to analyze the mechanism of CO₂-water displacement and heat extraction. To obtain a deeper understanding of CO₂-geothermal system under some more realistic conditions, heterogeneity of reservoir’s hydrological properties is taken into account. Due to the fortissimo mobility of CO₂, as long as the existence of highly permeable zone between the two wells, it is more likely to flow through the highly permeable zone to reach the production well, even though the flow path is longer. The preferential flow shortens circulation time and reduces heat-exchange area, probably leading to early thermal breakthrough, which makes the production fluid temperature decrease rapidly. The analyses of flow dynamics of CO₂-water fluid and heat may be useful for future design of a CO₂-based geothermal development system.