The Minami-Nagaoka Gas Field, located approximately 10 kilometers southwest of Nagaoka City in Niigata Prefecture, is one of Japan's largest onshore natural gas fields in terms of reserves. The natural gas in this field--the deepest in Japan--is contained in volcanic rock at depths of 4,000 to 5,000 meters below ground.
Development of this large gas field began in the late 1970s. While exploring for natural gas stored in green tuff (layers of green tuffaceous rock) in Niigata Prefecture, INPEX confirmed the presence of gas in the green tuff west of Nagaoka City in 1976 marking the discovery of a promising gas deposit. After further exploration and various technical studies, the company decided to develop the field in 1981 with the drilling of production wells and the construction of plants (natural gas production and processing facilities). In 1984, we completed construction of the Koshijihara Plant, one of the largest in Japan, and began production.
The natural gas produced at the Minami-Nagaoka Gas Field is processed at the plant and then marketed to city gas operators and industrial customers based along INPEX's natural gas trunk pipeline network.
| Contract area (block) | Project status | Gas processing capacity | Venture company (established) | Investment |
|---|---|---|---|---|
| Koshijihara Plant | In operation | 4.2 million Nm3per day | INPEX JAPAN, LTD. (Oct. 1, 2024) |
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| Oyazawa Plant | In operation | 1.66 million Nm3per day | INPEX JAPAN, LTD. (Oct. 1, 2024) |
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Koshijihara Plant (Niigata Prefecture)
The Koshijihara Plant in Niigata Prefecture has been in operation since September 1984. With a gas processing capacity of 4.2 million normal cubic meters per day, the plant has one of the largest outputs in Japan. The facility uses the proven "OASE® method," a process also used at the Oyazawa Plant for removing carbon dioxide found in the natural gas produced from the Minami-Nagaoka Gas Field.
Oyazawa Plant (Niigata Prefecture)
Following the development of the Koshijihara area, the Oyazawa Plant has been in operation since October 1994 to establish a supply base to meet the growing demand for natural gas in Japan. The plant has a gas processing capacity of 1.66 million normal cubic meters per day. The plant was the first in Japan to adopt the "OASE® method," a process to remove carbon dioxide contained in natural gas that is economically superior and limits corrosion.
