甲烷簇同位素在鄂尔多斯盆地靖边气田气源对比中的应用

鄂尔多斯盆地靖边气田的天然气成因一直存在争议，其来源是以上古生界煤成气为主还是以下古生界油型气为主仍然没有定论。本研究拟通过近几年发展起来的新技术——甲烷簇同位素分析方法的应用对靖边气田的气源进行判识，主要采取以下两种路径:（1）热力学研究表明在同位素平衡状态时，甲烷的簇同位素是仅与温度有关的函数，故通过靖边气田天然气样品的甲烷簇同位素测试分析即可反演出其形成温度。结合盆地区域埋藏史和热史研究，即可以判断天然气的来源与成因；（2）对靖边气田不同区块天然气样品、气源为上古生界石炭-二叠系的煤成气样品、以及气源为下古生界奥陶系的油型气样品均进行甲烷簇同位素测试分析。通过对靖边气田与后两者的天然气甲烷簇同位素变化特征的对比研究来探讨靖边气田的气源问题。最后，综合分析两种方法所得结论，对靖边气田的气源进行判识，为鄂尔多斯盆地下一步勘探方向的确定提供新的理论依据。

The gas genesis of Jingbian gas field in Ordos basin has been controversial. It is still not clear whether the source is coal-derived gas from the upper Paleozoic or oil-derived gas from the lower Paleozoic. This study intends to identify the gas source of Jingbian gas field through the application of methane clumped isotope analysis method, a new technique developed in recent years. The following two approaches are mainly adopted: (1)Thermodynamic study shows that the clumped isotope of methane is a function only related to temperature at the isotopic equilibrium state, so the formation temperature can be determined by the test and analysis of the clumped isotope of methane in gas samples from Jingbian gas field. Then, the origin of natural gas can be determined by combining the study of regional burial history and thermal history; (2)Methane clumped isotope analysis was carried out on gas samples from different blocks in Jingbian gas field, coal-derived gas samples from carboniferous Permian system in upper Paleozoic, and oil-derived gas samples from ordovician system in lower Paleozoic. The gas source problem of Jingbian gas field is discussed by comparing the methane clumped isotope variation characteristics between Jingbian gas field and the latter two. Finally, the gas source of Jingbian gas field is judged and identified through analyzing the conclusion obtained by the two methods comprehensively, which provides a new theoretical basis for the determination of the next exploration direction of Ordos basin.