Multiphase Flow Model of Gas Hydrate Production Wellbore Based on Double-Layer Continuous Pipe

In order to research the hydrate decomposition behaviors and multiphase flow characteristics during hydrate mining, a full transient non-isothermal gas-liquid-solid multiphase flow model was established. The model considered the heat and mass transfer due to hydrate phase transition. The calculated results of the model are in good agreement with the measured data of MWD. The model is used to analyze the changes of wellbore temperature and pressure, hydrate decomposition rate, and the volume fraction of each phase over time during the hydrate particles transportation. The numerical simulation results show that: within 2 h before mining, the hydrate decomposition rate is relatively slow, and the volume fraction of each phase in the wellbore changes little; with the increase of time, the volume fraction of each phase in the wellbore varies significantly; it arrives stable state after about 5 h of mining. Meanwhile, the gas volume fraction of the wellhead reaches about 40%. In addition, at the position of the downhole lift pump, the solid-liquid volume fractions both undergo significant mutations. These research results have a particular reference value for the in-depth understanding of the behavior of multiphase flow in hydrate mining.