The decomposition process of gas hydrate in sediments is actually the dynamic phase transition process of solid hydrate in sediments after absorbing heat decomposition. According to the phase equilibrium characteristics of gas hydrate, there are three basic development methods, including heating, chemical injecting and depressurization. Currently, there is no good commercial software used to simulate heat transmission and mass transfer in the gas hydrate decomposition process. So in this paper, based on typical gas hydrate sediment in South China Sea, microcosmic, mesocosmic (fractal theory) and macrocosmic scales are respectively used to successfully reveal the heat and mass transfer mechanism of three basis development methods. Molecular dynamics simulation shows heat injection is the best method for heat and mass transferring, and chemical injecting is better than depressurization. Fractal theory is successfully used to describe the complex structure of the porous sediments with gas hydrate occurrence, and can realize the prediction of heat and mass transfer law of hydrate dissociation in porous media. Macrocosmic numerical simulation of depressurization for gas hydrate sediment in South China Sea shows gas hydrate reservoir geological model has a large influence on the gas hydrate decomposition, and permeability and hydrate saturation of the upper cover layer have great effect on gas hydrate decomposition. It is poor development efficiency for only depressurization development and the problem of water drainage should be paid attention during development process.

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