Characteristics and Origins of Stable Carbon Isotope in Coalbed Methane of China
QIN Yong; TANG Xiu-yi; YE Jian-ping ; JIAO Si-hong(College of Mineral Resource and Environment Sciences, CUMT, Xuzhou, Jiangsu 221008, China;Huainan Institute of Industry, Huainan, Anhui 232000, China;No. 1 Branch, China National Administration Bureau of
The distribution of the stable carbon isotope of coalbed methane (CBM) in China was systematically generalized in the aspects of area, geological era, and coal rank. The origin of CBM was discussed. In general, the carbon isotope is more extensively distributed and lighter in composition than that of the normal natural gas, and approaches to or falls in the range of the normal humic-type gas during the anthracite period.The δ13C1 in the CBM from the first stage of desorption is lighter than that from the secondary stage. The carbon isotope composition of the CBM in the middle-high rank coal reservoirs from most parts of China is controlled mainly by the isotope fractionation under the thermodynamical mechanism, and the addition of the CBM desorption- diffusion-migration effect to the mechanism might be the important reason why the carbon isotope is relatively light.