煤型气碳同位素演化二阶段分馏模式及机理

A two stage model of carbon isotopic fractionation in coal gas

天然气中甲烷Ｃ 同位素组成是判识其母质类型和演化程度最有效的方法之一。国内外学者对煤型气δ１３ Ｃ１ 与演化程度（ Ｒｏ） 之间的关系做过大量的工作， 取得了重要成果， 但由于其研究对象的局限性，对其完整的同位素演化分馏特征尚需进一步完善。由于我国含煤盆地广布，源岩的成烃演化完整而系统，使得系统研究其演化成为可能。本文通过我国不同盆地、不同时代和不同成烃演化的煤型气甲烷Ｃ 同位素组成和源岩演化程度（ Ｒｏ） 的研究， 在大量资料分析的基础上， 通过数学处理， 回归出煤型气Ｃ 同位素组成演化的二阶段分馏模式并对其分馏机理进行了探讨。这一结果对煤成烃，特别是低演化阶段煤成烃的勘探开发具有重要意义。

Carbon isotopic composition of methane in natural gas is one of the most effective indicators to identify the type of source rock and the stage of its evolution. The relationships between δ13C1 of coal gas and Ro(vitrinite reflectance) of the relevant source rocks have been studied extensively in the world and important results have been obtained. But owing to the limitation of the object of individual research, the comprehensive model of isotopic fractionation during the evolutions of gas and source rock needs to be further developed. Because of the widespread coal seam and the completeness of hydrocarbon generation and evolution of the source rocks in China, systematic study of the whole evolution is possible. In this paper, through the studies of carbon isotopic composition methane in coal gas and the evolution degree of relevant source rocks in different evolution stages and different geological age of source rocks in different basins in China, the two stage model of carbon isotopic fractionation of methane in coal gas was obtained by using the mathematical regression and the analysis of a lot of other information. The mechanism of this fractionation was probed as well. This model will play an important role in exploring and developing coal gases, especially those generated at lower evolutionary stages.