旋转射流冲蚀天然气水合物试验及数值模拟研究

为探究适合南海天然气水合物特点的高效开发模式，对比分析了淹没围压条件下锥形射流和旋转射流冲蚀天然气水合物沉积物的成孔规律。首先，利用 LS-DYNA软件，建立了旋转/锥形射流冲蚀天然气水合物沉积物的拉格朗日–欧拉（ALE）流固耦合模型，分析了淹没、围压条件对旋转/锥形射流冲蚀天然气水合物沉积物效率的影响；然后，利用自主设计研制的天然气水合物生成及射流冲蚀可视试验装置，进行了天然气水合物沉积物生成及冲蚀试验，天然气水合物二次生成后，在冲蚀坑中注石膏，测量冲蚀孔孔深及孔径。对比分析数值模拟和室内试验结果发现:围压在增强天然气水合物沉积物强度的同时，抑制了射流扩散能力，降低了射流冲蚀天然气水合物沉积物的效率；在无围压和围压5 MPa条件下，旋转射流冲蚀天然气水合物沉积物体积分别是锥形射流的1.8和1.7倍。研究结果表明，对于泥质粉砂储层天然气水合物沉积物，旋转射流在保证冲蚀孔孔深的同时，具有比锥形射流更强的扩孔能力，这为固态流化法开采天然气水合物提供了依据。 

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.