Methane hydrate is often called “fiery ice.” Methane hydrate looks like an ice, and starts burning when an open flame is brought close to it; hence the name. Only water is left after combustion. It is a strange substance.
Note that the natural methane hydrate – existing in areas surrounding Japan – that MH21 aims to develop is not purely a white agglomeration like artificial methane hydrate. Since methane hydrate exists in between the sand particles of sandy sediments as shown in the photo below, the methane hydrate-bearing layers do not appear white but rather look similar to soil.
What is methane hydrate?
Water molecules form a cage-like structure in a certain temperature and pressure environment. This cage-like structure encaging methane molecules is called methane hydrate. Methane is the primary component of natural gas, and the development of methane hydrate follows almost the same procedure as that for natural gas.
Although it is called gas hydrate generally, MH21 habitually uses the term methane hydrate since almost 100% of natural hydrate distributed in Japan contains methane.
A small cage composed of the crystalline structure of methane hydrate
Green: methane molecule Red: water molecule
Water molecules form the cage-like structure and methane molecules are contained in it.
So, how much methane is contained in methane hydrate?
For example, 1 m³ of methane hydrate dissociates to approximately 160 – 170 m³ (at 0ºC and 1 atmosphere) of methane gas, although the exact amount varies depending on the measuring environment.
Conversely, methane hydrate can involve the methane of approximately 160 – 170 times its own volume. Aside from the development of natural methane hydrate, studies are now being conducted, by utilizing the above property, in an attempt to transform natural gas that consists primarily of methane that has been hydrated to decrease its volume, and ensure better transportation efficiency. (Reference: JOGMEC (Japan Oil, Gas and Metals National Corporation) website)
We live in an environment where the pressure is 1 atmosphere and water freezes at 0℃. Under a pressure of 1 atmosphere, methane hydrate can exist only in a low temperature of -80℃ or below. When the temperature is 0℃, it can exist only under a high pressure of 23 atmospheres or above. Low temperature and high pressure. Methane hydrate requires a “Low temperature and High pressure” environment in order to exist.
The areas that permit the existence of methane hydrate on the Earth are limited to (1) permafrost zones in polar regions, and (2) layers within several hundred meters from the seafloor of an ocean with a depth of 500 m or deeper.