A Model for Multiphase Flow in Wellbore During Solid Fluidization Exploitation of Natural Gas Hydrate
In order to study the decomposition of hydrates and the multiphase flow characteristics of wellbore during the transportation of hydrate slurry,based on the mass,momentum and energy conservation equations of gas-liquid-solid phase,considering the interphase heat and mass transfer caused by hydrate decomposition,com-bined with the technological characteristics of double-layer coiled tubing in producing hydrates,a full transient nonisothermal gas-liquid-solid multiphase flow model under hydrate phase change conditions was built.The model was verified using MWD measured temperature data.The variations of wellbore temperature,wellbore pressure,hydrate decomposition rate and volume fraction of each phase with production time during the transportation of hy-drate slurry were analyzed using the model.The simulation results show that within 2 hours before exploitation,the decomposition rate of hydrates is relatively slow,and the volume fraction of each phase in the coiled tubing changes relatively little.As the production time prolongs,the volume fraction of each phase in the coiled tubing changes significantly.After about 5 hours of exploitation,a stable state is reached,the gas-phase volume fraction at well-head reaches about 40%.Moreover,there is a significant change in the solid-liquid phase volume fraction at the location of the downhole lifting pump.The research results are referential for a deeper understanding of the multi-phase flow law in the process of hydrate development,and contribute to the further development of hydrate extrac-tion technology.
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