Carbon and hydrogen isotopic composition and generation pathway of biogenic gas in China

作     者：SHEN Ping WANG Xiaofeng XU Yin SHI Baoguang XUYongchang 

作者机构：The Key Laboratory of Gas Geochemistry Chinese Academy of Sciences Lanzhou 730000 China 

出 版 物：《Chinese Journal Of Geochemistry》 (中国地球化学学报)

年 卷 期：2009年第28卷第2期

页      面：119-124页

核心收录：

学科分类：070704[理学-海洋地质] 0709[理学-地质学] 081803[工学-地质工程] 07[理学] 0707[理学-海洋科学] 08[工学] 0818[工学-地质资源与地质工程] 

基　　金：supported by the National Natural Science Foundation of China (Grant No. 40703001) 

主　　题：碳同位素组成 生物气藏 二氧化碳 重氢 中国 气藏描述 醋酸发酵 古水介质 

摘      要：The carbon and hydrogen isotopic composition of biogenic gas is of great importance for the study of its generation pathway and reservoiring characteristics. In this paper, the formation pathways and reservoiring characteristics of biogenic gas reservoirs in China are described in terms of the carbon and hydrogen isotopic compositions of 31 gas samples from 10 biogenic gas reservoirs. The study shows that the hydrogen isotopic compositions of these biogenic gas reservoirs can be divided into three intervals: δDCH4-200‰,-250‰δDCH4-200‰ and δDCH4-250‰. The forerunners believed that the main generation pathway of biogenic gas under the condition of continental fresh water is acetic fermentation. Our research results showed that the generation pathway of biogenic gas under the condition of marine facies is typical CO2-reduction, the biogenic gas has heavy hydrogen isotopic composition: its δDCH4 values are higher than-200‰; that the biogenic gas under the condition of continental facies also was generated by the same way, but its hydrogen isotopic composition is lighter than that of biogenetic gas generated under typical marine facies condition: -250‰δDCH4-200‰, the δDCH4 values may be related to the salinity of the water medium in ancient lakes. From the relevant data of the Qaidam Basin, it can be seen that the hydrogen isotopic composition of biogenic methane has the same variation trend with increasing salinity of water medium. There are biogenic gas reservoirs formed in transitional regions under the condition of continental facies. These gas reservoirs resulted from both CO2-reduction and acetic fermentation, the formation of which may be related to the non-variant salinity of ancient water medium and the relatively high geothermal gradient, as is the case encountered in the Baoshan Basin. The biogenic gas generating in these regions has light hydrogen isotopic composition: δDCH4-250‰, and relatively heavy carbon isotopic composition. There is a fairly stro