Natural gas hydrate (gas hydrate for short) is an ice-like crystalline substance distributed in deep-sea sediments or terrestrial permafrost, which is formed by natural gas and water at high pressure and low temperature. Because it looks like ice and can burn when it meets fire, it is also called "combustible ice" or "solid gas" or "gas ice".

The methane content of natural gas hydrate accounts for 80% ~ 99.9%, the combustion pollution is far less than that of coal, oil and natural gas, and the global reserves are enough for human use 1000, so it is regarded as an alternative energy source for oil and natural gas in the future by all countries.

Natural gas hydrate exists in the sediments of deep seabed (polar region) and 400-650m (equatorial region) below several hundred meters to100-250m, where the pressure and temperature conditions can make natural gas hydrate in a stable solid state [1].

At present, more than 30 countries and regions have carried out research, investigation and exploration of "combustible ice", and great progress has been made in mining experiments in the last two years. China plans to drill natural gas hydrate in China in 20 15, which will greatly promote the exploration and development process of "combustible ice" in China.