Liquid–Solid Coupled Internal Flow Field Analysis of Natural Gas Hydrate Spiral-Swirling Downhole In Situ Separator

This study aims to solve the problem of the recovery efficiency of natural gas hydrate being affected by a large amount of mud and sand in the solid fluidization mining of natural gas hydrate. Therefore, a new method for the separation of in situ sediment and natural gas hydrate in a spiral-swirling downhole is proposed, and the corresponding numerical simulation model is established to realize the analysis and verification of key flow field parameters such as flow velocity, pressure, sediment, and natural gas hydrate phase distribution. The results show that the flow velocity field of the mixed slurry presents an ‘M’-shaped symmetrical distribution, and the slurry near the wall of the separator can obtain a larger flow velocity, which is beneficial to the separation of mud–sand and natural gas hydrate. The static pressure field shows an axisymmetric distribution that decreases first and then increases, indicating that the pressure of the mixed slurry increases with the increase in the radial position, and the closer to the wall, the greater the static pressure of the mixed slurry. Near the wall of the separator, the volume fraction of the sediment phase reaches the maximum. In contrast, the volume fraction of the natural gas hydrate phase reaches the minimum, which confirms the separation effect of the sediment and the natural gas hydrate. The results show that the separation of sediments and natural gas hydrate can be realized, thereby improving the exploitation efficiency of natural gas hydrate. The designed spiral cyclone coupling separator provides a new solution to solving the problem of sand removal in natural gas hydrate exploitation.