Genetic Types of the Alkane Gases in Giant Gas Fields with Proven Reserves over 1000×108m3 in China

By the end of 2011, 20 giant gas fields with proven reserves over 1000×10 8 m 3 had been discovered in 7 sedimentary basins in China. Based on the molecular and the carbon isotopic compositions of the alkane gases in these gas fields, in combination with the δ 13 C 1 -δ 13 C 2 -δ 13 C 3 and δ 13 C 1 -C 1 /C 2+3 identification diagrams, the origin of the alkane gases in these 20 giant gas fields are discussed: the alkane gases in Sulige, Daniudi, Yulin, Zizhou, Wushenqi, Hechuan, Guang'an, Anyue, Yuanba, Xinchang, Kela2, Dina2, Dongfang1–1and Kelameili giant gas fields are mainly coal-derived; the alkane gases in Tazhong1 and Datianchi giant gas fields are oil-derived; the alkane gases in Tainan giant gas field are bacterial gases; the alkane gases in Jingbian giant gas field are mixed gases mainly composed of coal-derived gases supplemented with a small quantity of oil-derived gases; the alkane gases in Puguang giant gas field are mixed gases mainly composed of oil-derived gases supplemented with a small quantity of coal-derived gases; the alkane gases in Xushen giant gas field are mixed gases mainly composed of abiogenic gases supplemented with a small quantity of coal-derived gases. The study on the genetic types of the alkane gases in these fields is not only of great scientific importance to the gas correlation, gas accumulation research and the optimization of the exploration targets, but also to the acceleration of the Chinese natural gas industry.