松辽盆地深层天然气碳同位素反序及形成机理探讨

Discussion on the reverse order of carbon isotope series of the deep gas in Songliao Basin and its mechanism

松辽盆地深层天然气碳同位素反序现象十分普遍,对其成因的认识一直存在分歧。全面分析、总结了松辽盆地深层昌德、徐深、升平、长岭4个具有碳同位素反序现象的烷烃气组分以及碳同位素组成,结果认为深层烷烃气组分与同位素值不具备典型无机成因气特征,其负碳同位素系列不能作为鉴别无机成因气的充分条件。深层煤成气与无机气混合作用可能是碳同位素反序的首要因素,运移过程中的扩散分馏是导致混源模拟与实际测量值出现偏差的主要原因,且制约着盆地深层天然气组分及碳同位素值垂向变化。此外,盆地深层单纯无机成因气组分与碳同位素组成是准确估算深层非生物成因气含量的关键,其研究具有重要理论意义与应用价值。

Carbon isotope in reverse order is usually observed in deep gases of Songliao Basin,but there has been a long disagreement about its mechanism.Multi-analysis has been performed for the alkane gas composition and carbon isotope composition of deep gases from Changde,Xushen,Shengping and Changling gas reservoirs in Songliao Basin showing reverse order of carbon isotope.The result indicates that the composition and isotope value of deep alkane gas do not have the characteristics of typical abiogenic gas,and only negative carbon isotope series is not sufficient to identify inorganic origin.The hybridization of deep coal gas and inorganic gas probably contributed to carbon isotopic reversal in the first place.The difference between simulation and measurement is primarily caused by diffusive fractionation during migration,which also controlled the vertical variation of deep gas composition and carbon isotope value in the basin.In addition,pure abiogenic gas composition and carbon isotope composition are key parameters for accurate estimation of inorganic gas content in the deep formation of the basin.The result of this research is of important theoretical significance and application value.