Abnormal carbon and hydrogen isotopes of alkane gases from the Qingshen gas field, Songliao Basin, China, suggesting abiogenic alkanes?

作者：Liu, Quanyou^*; Dai, Jinxing; Jin, Zhijun; Li, Jian; Wu, Xiaoqi; Meng, Qingqiang; Yang, Chun; Zhou, Qinghua; Feng, Zihui; Zhu, Dongya

来源：Journal of Asian Earth Sciences, 2016, 115: 285-297.

DOI：10.1016/j.jseaes.2015.10.005

• Qingshen gas field
• Thermogenic gas
• Abiogenic alkanes
• CO2 reduction
• Magmatic activity

It is great debate that the alkane gases of abiogenic origin would constitute a major portion of the commercial accumulation of the Qingshen gas field, Songliao Basin, China. In this study, abiogenic gases characterized by heavy delta C-13(1) values, reversal of the usual carbon isotopic trend of C-1-C-5 alkanes, very narrow variation in delta H-2(C1) values, and low CH4/He-3 ratios associated with high R/Ra values (>1) were identified. The hydrocarbon gas in the Qingshen gas field is a mixture of thermogenic alkanes derived from Cretaceous mudstone (type I kerogen) or Jurassic coal (type III kerogen) and abiogenic alkanes (mainly CH4) from mantle degassing. A quantitative estimation of abiogenic alkanes contribution to the Qingshen gas field is made based on a delta C-13(1) vs. delta C-13(2) plot: about 30-40% of alkane gases in the Qingshen gas field, along with its helium, are estimated to be derived from the mantle via magmatic activity. Particularly, the abiogenic formation of CH4 generated from the reduction of CO2 by hydrothermal activity may contribute. Our study suggests that abiogenic alkane gases in certain geological settings could be more widespread than previously thought, and may accumulate into economic reservoirs.

• 出版日期2016-1-1
• 单位中国石油化工股份有限公司石油勘探开发研究院; 中国石油天然气股份有限公司勘探开发研究院