四川盆地天然气的碳同位素特征

CARBON ISOTOPE CHARACTERISTICS OF NATURAL GAS IN THE SICHUAN BASIN, CHINA

四川盆地发育 10多个产气层系、6套主要气源岩。文中研究了不同地区不同产层的碳同位素组成特征。大多数气样的δ1 3C具有正碳同位素系列 (δ1 3C1 <δ1 3C2 <δ1 3C3<δ1 3C4 ) ,显示出有机成因特征。一些样品中甲乙烷碳同位素倒转 (δ1 3C1 >δ1 3C2 )可能是由于不同源岩或不同成熟度的气混合的结果。盆地中相同成熟度油型气的δ1 3C比煤成气的轻。CO2 的δ1 3C也具有生物成因的特征。

There are over ten gas producing beds and six main gas generating rock intervals in the Sichuan Basin in the middle of China. In this paper, carbon isotopic data of natural gas from different regions and reservoirs were studied. The δ 13 C value of most gas samples show the pattern of δ 13 C 1<δ 13 C 2<δ 13 C 3<δ 13 C 4, indicating their biogenic origin. Samples with δ 13 C 1>δ 13 C 2 might be a mixture of gases from different source rocks or of different maturity. The δ 13 C value of humic gas is more negative than that of sapropelic gas. The δ 13 C value of the analyzed CO 2 indicates it is of biogenic origin.