徐家围子断陷无机成因气证据及其份额估算

Geochemical characteristics of abiogenic gas and its percentage in Xujiaweizi Fault Depression,Songliao Basin,NE China

松辽盆地徐家围子断陷发育各种成因天然气,其无机成因烷烃气具有典型的负碳同位素系列(1δ3C1>1δ3C2>δ13C3>1δ3C4),并且甲烷碳同位素组成大于-30‰,R/Ra大于0.5。根据二源混合(无机成因气与热成因气的混合)模拟计算结果,无机成因气端元组分与煤成气或油型气混合后,大部分混合气都需要无机成因气所占比例高于80%才能发生负碳同位素系列,混合气的甲烷碳同位素组成远远偏重于徐家围子断陷无机成因甲烷的碳同位素组成主峰值。因此,认为徐家围子断陷无机成因烷烃气不可能完全是二源混合的结果。另外,煤成气与油型气之间的混合模拟说明有机成因气之间的混合无法产生负碳同位素系列,进一步佐证了徐家围子断陷深层天然气负碳同位素系列的无机成因。

Gases with different origins occur in the Xujiaweizi Fault Depression.Among them,the abiogenic gases have a typical carbon isotopic reversal trend(δ13C1>δ13C2>δ13C3>δ13C4),the carbon isotope of methane is greater than-30‰,and the R/Ra greater than 0.5.According to the simulative calculation with two-source mixing(mixture of abiogenic gas and thermogenic gas),when the end composition of abiogenic gas being mixed with coal-derived gas or oil-derived gas,it will require an amount of abiogenic gas more...