Major developments of coal-formed gas exploration in the last 30 years in China

Since its formation in China 30 years ago, the theory of coal-derived gas has not only opened a new field of coal-derived gas exploration, but also increased the proved reserves of coal-derived gas from 1/10 to 7/10 in the total gas of China; the nation's proved gas reserves rise sharply from 2 264×108 m3 to 6.4×1012 m3; the annual production of gas rises from 137.34×108 m3 to 760×108 m3; and the nation's coal-derived gas fields (reservoirs) increases from less than 10 (excluding Taiwan) to 124. After briefing the major developments of China's coal-derived gas exploration, this paper concentrates on the exploration development of coal-derived gas in Ordos Basin, Tarim Basin and Sichuan Basin where large numbers of coal-derived gas fields have been discovered. With carbon isotopic data of alkane gases, it also demonstrates that some gas fields of controversial origin (Jingbian, Kekeya and Akemomu gas fields) are of, or predominantly of, coal-derived gas, and that a few gas reservoirs (Wolonghe, Naxi, Hejiang gas fields) in the Xujiahe Formation coals of Sichuan Basin are oil-associated gas.