中国有机烷烃气碳同位素系列倒转的成因

CAUSATION OF PARTLY REVERSED ORDERS OF δ^(13) C IN BIOGENIC ALKANE GAS IN CHINA

所谓烷烃气碳同位素系列是指依烷烃气分子中碳数顺序递增 ,δ1 3C值依次递增或递减。递增者称正碳同位素系列 ,递减者叫负碳同位素系列。当烷烃气的δ1 3C值不按正、负碳同位素系列规律 ,排列出现混乱时 ,谓之碳同位素系列倒转。致使倒转的原因有有机烷烃气和无机烷烃气的混合 ;煤成气和油型气的混合 ;同型不同源气或同源不同期气的混合和烷烃气中某一或某些组分被细菌氧化。倒转可由其中一种原因 。

The δ 13 C values change in a regular manner with the increase of hydrocarbon gas molecular weight, i.e. change in normal order or reverse order.The normal order is δ 13 C 1<δ 13 C 2<δ 13 C 3<δ 13 C 4,and the reverse order is δ 13 C 1> δ 13 C 2>δ 13 C 3>δ 13 C 4.Partly reversed order is also common in gas samples from different basins in China,such phenomenon can be attributed to one or several of the following reasons:(a)Mixing of biogenic gas and abiogenic gas;(b)Mixing of gases from sapropelic sources and humic sources;(c)Mixing of gases from two source rock intervals of the same type but of different maturity;(d)Mixing of gases from one source rock interval of varying maturity.