Discrimination of abiogenic and biogenic alkane gases

• Published in: Science in China. Series D, Earth sciences Vol. 51; no. 12; pp. 1737 - 1749
• Main Authors: Dai, JinXing, Zou, CaiNeng, Zhang, ShuiChang, Li, Jian, Ni, YunYan, Hu, GuoYi, Luo, Xia, Tao, ShiZhen, Zhu, GuangYou, Mi, JingKui, Li, ZhiSheng, Hu, AnPing, Yang, Chun, Zhou, QingHua, Shuai, YanHua, Zhang, Ying, Ma, ChengHua
• Format: Journal Article
• Language: English
• Published: Heidelberg SP Science in China Press 01.12.2008
• Subjects: Earth and Environmental Science; Earth Sciences; alkane gas; discrimination; biogenic; carbon isotope; helium isotope; abiogenic
• ISSN: 1006-9313; 1862-2801
• DOI: 10.1007/s11430-008-0133-1

We have combined the analytical data of the carbon isotope distribution pattern, R/Ra and CH 4 / 3 He values of abiogenic and biogenic (referring to the thermogenic and bacterial or microbial) alkane gases in China with those of alkane gases from USA, Russia, Germany, Australia and other countries. Four discrimination criteria are derived from this comparative study: 1) Carbon isotopic composition is generally greater than −30‰ for abiogenic methane and less than −30‰ for biogenic methane; 2) Abiogenic alkane gases have a carbon isotopic reversal trend (δ 13 C 1 > δ 13 C 2 > δ 13 C 3 > δ 13 C 4 ) with δ 13 C 1 > −30‰ in general; 3) Gases with R/Ra >0.5 and δ 13 C 1 − δ 13 C 2 >0 are of abiogenic origin; 4) Gases (methane) with CH 4 / 3 He⩽10 6 are of abiogenic origin, whereas gases with CH 4 / 3 He⩽10 11 are of biogenic origin.