A NEW EXPLOITATION METHOD FOR GAS HYDRATE IN SHALLOWSTRATUM: 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.