25th International Meeting on Organic Geochemistry IMOG 2011

P-259
Stable carbon isotopes of coal-derived alkane gases in China
Jinxing Dai, Yunyan Ni, Xiaoqi Wu, Shipeng Huang, Fengrong Liao
Research Institute of Petroleum Exploration and Development, PetroChina, Beijing, China (corresponding
author:djx@petrochina.com.cn)
There were six main coal-forming periods in China
including Carbonaceous, Permian, Triassic, Jurassic,
Cretaceous and Tertiary, and each period had
corresponding coal measures. Hydrocarbons
generated from these coal measures were dominated
by gas, with subordinate amounts of oil. Coal-derived
gas played a key role in the Chinese natural gas
industry. To date, coal-derived gas accounted for over
65% of the total proved gas reserves and 65.6% of
the annual gas production in China. In the past 30
years, we collected 500 primary gas samples which
were sourced from the Carbonaceous coal measures
in the Junggar Basin, Permian coal measures in the
Ordos Basin (Figure 1), Triassic coal measures in the
Sichuan Basin, Jurrasic coal measures in the Tarim
Basin, Cretaceous coal measures in the Songliao
Basin and Tertiary coal measures in the Yingqiong
Basin. 1600 carbon isotopic data (� 13 C1-4) were
determined and main characteristics of these coalderived
gases were as follows:
1. Patience (2003) proposed that � 13 C of coal-derived
methane ranges from - 38‰ --22‰, however,
coal-derive methane in China has much wider
variance, -43‰--23‰. This is due to the multistages
of reservoir formation of coal-derived gases in
China. The Chinese coal-derived gases have � 13 C2 of
- 28‰ --15.7‰, � 13 C3 of - 43‰ --23‰, and
� 13 C4 of -43‰--23‰.
2. The Chinese coal-derived gases are characterized
by a normal carbon isotopic distribution pattern
whereby gases become more enriched in 13 C with
increasing molecular mass among the C1-C4 alkanes
(� 13 C1