Experimental and Numerical Simulation Study of Natural Gas Hydrate Erosion by Swirling Jet

In order to explore an efficient development mode suitable for the characteristics of natural gas hydrate in the South China Sea, the hole forming law of submerged conical jet and swirling jet on natural gas hydrate sediments under confining pressures were compared and analyzed. Firstly, the Lagrangian-Eulerian (ALE) fluid-solid coupling model was established with LS-DYNA software to analyze the influence of submerged and confining pressure environment on the erosion efficiency of the two types of jets on natural gas hydrate sediments. The experiments for natural gas hydrate generation and jet erosion were carried out based on a self-designed visual experimental device. After the secondary generation of natural gas hydrate, gypsum was injected into the erosion hole to measure the depth and size of erosion hole. Through comparative analysis of numerical simulation and experimental results, it is concluded that the confining pressure can increase the strength of natural gas hydrate sediments while inhibiting the diffusion ability of jet, and can reduce the jet erosion efficiency. In the environments without confining pressure and with a confining pressure of 5 MPa, the volume of natural gas hydrate sediments eroded by swirling jet is 1.8 and 1.7 times that of conical jet, respectively. The results show that, for the natural gas hydrate deposits in argillaceous silt reservoirs, the swirling jet has a stronger hole-expanding ability than the conical jet while ensuring the depth of the erosion hole. This study provides a theoretical basis for the production of natural gas hydrate by solid fluidization method.