Abstract: Natural gas hydrate decomposition is a complicated process involving heat and mass transfer and phase transitions. We established a three-dimensional mathematical model for the gas hydrate decomposition by depressurization taking factors such as heat conduction, heat convection, gas-liquid two-phase flow, and hydrate decomposition kinetics into consideration. The effects of the bottom hole pressure, initial hydrate saturation, and absolute permeability of the reservoir on the decomposition results were analyzed using numerical simulation. The results showed that the lower the bottom hole pressure is, the faster are the gas production rate and the reservoir temperature and pressure decrease. When the initial saturation of the gas hydrate is relatively large, the decomposition rate of the early stage is faster, but that of the later stage is slower. When it is too high, it will inhibit the decomposition of the gas hydrate. The absolute permeability has little impact on the gas production; however, when the permeability is too low, the production efficiency will be lower. Therefore, a combination of the depressurization method and other methods can be used.

Key words: natural gas hydrate, depressurization, mathematical model, parameters, temperature field, stress field