Natural gas is divided into natural gas dissolved in water, which is dissolved in groundwater, and non-associated natural gas, which is stored as compressed gas in the anticlinal structures of geological stratums. Natural gas dissolved in water is found in Japan mainly in Chiba and Niigata prefectures. While its volume of production per well is small compared to non-associated natural gas, its gas in place is abundant. In addition, the groundwater in which the natural gas is dissolved also contains iodine, making them unique gas fields, even from an international perspective.
On the other hand, non-associated natural gas fields are found mainly in Niigata, Akita and Hokkaido prefectures. Non-associated natural gas accounts for 83% of the gross amount of natural gas produced domestically in Japan.
Natural gas is primarily composed of methane, and also contains ethane, propane, and butane. Japanese natural gas contains very few impurities, such as sulfur. It is used for not only city gas and fuel for power generation, but also as the raw material for manufacturing chemicals such as Methanol , Ammonia, and acetylene. Of the gross amount of natural gas produced in Niigata, about 57% is used within the prefecture; of this, 53% is used for city gas and fuel for power generation, and 16% is used for chemical industry raw material and fuel.