Water-soluble natural gas

Japanese: 水溶性天然ガス - すいようせいてんねんガス

Natural gas is a type of gas that is combustible, consists mainly of methane, and is produced together with associated water. In the case of marine gas, associated water contains seawater from the time of deposition, so its salinity is close to that of seawater.
[Cause]
When organic remains are deposited on the bottom of a sea or lake in an oxygen-poor environment, bacteria break them down and produce methane. This methane combines with water to form hydrates, which are buried underground instead of dissipating. As the methane is buried deeper, its temperature rises, and it becomes methane gas again, dissolving in the surrounding water and becoming soluble natural gas.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

天然ガスのうち，可燃性で，メタンを主成分とし，付随水とともに産出するものをいう。付随水は，海成の場合は堆積当時の海水を取り込むので，塩分濃度が海水に近い値である。
［成因］
　海底または湖底に有機物の遺骸が酸素の乏しい環境で堆積すると，これをバクテリアが分解してメタンを発生させる。このメタンが水と結合して水和物となるので，散逸せずに地中に埋没する。これが埋没深度の増大とともに温度上昇し，再びメタンガスとなり周辺の水に溶けて水溶性天然ガスとなる。

出典　株式会社平凡社世界大百科事典第２版について　情報

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