一种新的海洋浅层水合物开采法——机械-热联合法

天然气水合物是国家的战略能源之一.天然气水合物分解相变使其开采难度高于常规化石能源.国际天然气水合物试验性开采表明通过降压、注热等方法难以满足商业化开采的需求，尤其在水合物位于浅层、软土情况下，持续稳定且高效率的热量供给是其瓶颈.天然气水合物机械-热联合开采是一种新概念模式，即通过粉碎水合物沉积物通过管道输运并在内部分解，这样既增加了传热的表面积，又利用海水热量和对流传热提高了能量供给效率.分析表明:利用该方法开采时水温过高会导致水合物分解过快而产生不稳定流，温度过低又导致水合物二次生成或结冰；水流流速既要能使被粉碎的水合物沉积物颗粒悬浮和流动，又不能导致流动失稳.为了实现高效安全的机械-热水合物开采，经过初步分析提出原位水合物地层粉碎的颗粒直径设定在0.1~1.0 cm之间，控制水流速度为0.22~0.67m/s，温差保证在5K以上，混合物中水的体积分数大于0.85. 

A NEW EXPLOITATION METHOD FOR GAS HYDRATE IN SHALLOW STRATUM:MECHANICAL-THERMAL METHOD

Gas hydrate is one of the national strategic energy resource. The endothermic chemical dissociation and phase transformations make its exploitation differ from those of the fossil energies. A continuous, stable, and high effcient heat supply is the critical problem to commercial production of gas hydrate. The combined mechanical-thermal gas hydrate exploitation is affinew conceptual method, crushing gas hydrate-bearing sediments into small bodies to increase the surface area of heat transfer, and utilizing the heat of seawater and convective heat transfer to enhance the efficiency of energy supply. Through the feasibility analysis, the results show that relative high temperature leads to the rapid dissociation of gas hydrate, and the fluid flow becomes unstable, while low temperature leads to the reformation of gas hydrate or freezing. In order to achieve effcient and safe exploitation of gas hydrate, the diameter of crushing bodies of in-situ mining hydrate-bearing sediments ranges from 0.1 cm to 1.0 cm, the seawater injection velocity ranges from 0.22m/s to 0.67m/s, the temperature difference is greater than 5 K, and the volume fraction of water in the mixed water and grains of hydrate sediments exceeds 0.85. The combined mechanical-thermal hydrate exploitation is affinew potential technology for effcient production of gas hydrate stratums.