中文摘要：

乙烷碳同位素是天然气成因类型判别的重要指标,在天然气成因类型判别和气源岩研究中发挥了重要作用,其主要依据是：1腐殖型有机质比腐泥型有机质富集13C,腐殖型烃源岩比腐泥型烃源岩有机质的碳同位素值更高;2乙烷碳同位素受成熟度的影响很小,很好地继承了天然气母源有机质的碳同位素组成特征。但是,国内外一些地区天然气的研究表明：1部分腐泥型有机质具有异常高的碳同位素值,其形成的天然气会表现出煤成气的碳同位素组成特征;2成熟度对天然气的乙烷碳同位素值存在较明显影响,低成熟天然气通常具有很低的乙烷碳同位素值,无论其来源于腐泥型烃源岩还是腐殖型烃源岩,通常表现出油型气的乙烷碳同位素组成特征。因此,在应用乙烷碳同位素判断天然气成因类型时,需要考虑烃源岩形成的沉积环境、烃源岩原始有机质的碳同位素组成及天然气的成熟度等因素,才能够正确、合理地判断天然气成因类型。

英文摘要：

Carbon isotope composition of ethane has been considered as a very useful index for discrimination of natural gas genetic type,due to the following aspects.（1）Humic organic matters are much more enriched in 13 C than sapropelic source rock,so its carbon isotope is heavier than of that of sapropelic matter;（2）Maturity has little influence on carbon isotope composition of ethane,so it inherits the carbon isotope characteristics of its parent source.However,some research results showed that some sapropelic organic matters have abnormal heavy carbon isotopic composition,and ethane carbon isotopic composition of gases from this type is similar as gases from humic type.Meanwhile,maturity does have distinct influence on carbon isotope of ethane.Low-mature stage gas is generally enriched in 12 C whether it originated from humic or sapropelic source rock,and has a similarcarbon isotopic character of gas from oil-type gases.As a consequence,factors of the deposition environment of source rocks,the original carbon isotope composition of its organic matter and the maturity of the natural gases should be considered comprehensively in applying carbon isotopic composition of ethane to distinguish the genetic type of nature gas.