流体包裹体中气体碳同位素测定新方法及其应用

A NEW METHOD IN ASSAYING GAS ISOTOPES IN FLUID INCLUSION AND THE WAY OF APPLICATION

陈孟晋 胡国艺

Chen Mengjin Hu Guoyi

采用热爆裂法和真空球磨法提取流体包裹体中CO和CH等多种气体,以灵敏度较高的Delta S仪器测定其碳同位素值。由于热爆裂法产生CO影响CH碳同位素测定,而真空球磨法不会改变气体的性质,因此,真空球磨法提取的气体反映真实古流体的性质,测定的碳同位素值比较可靠。采用该种方法对鄂尔多斯盆地中部气田奥陶系储层方解石脉中包裹体的烃类气体进行了碳同位素测定,结果表明,烃类气体δC分布在-2.673%～-4.360%,δC分布在-2.253%～-2.580%,δC分布-2.141%～-2.626%,其组成具有上古生界天然气的特征,并与下古生界天然气差别较大;推测鄂尔多斯盆地中部气田下古生界天然气成藏期有两期,早期可能主要以上古生界煤型气来源为主。

The methods of pyrolysis and vaccum ball grinding are used to obtain carbon dioxide, methane and other gasses. Then, the carbon isotope values of theses gases can be assayed by a higher sensitive apparatus(Delta S). CO resulting from the pyrolysis can affect the assaying of isotope value whereas the method of vacuum application can't change nature of gasses, therefore, gases extracted by the vacuum ball grinding can reflect the nature of true ancient current and it's more reliable for assaying isotopic value. This method has been used to isotopic assay hydrocarbon gas in inclusions from the Ordovician reservoir calcite veins in central gas field of Ordos basin. The results show that the values of δC distribute between -2.673% and -4.360%. The values of δC are from -2.253%～2.580%. The values of δC are from -2.253%～2.580%. The characteristics of gas from the fluid inclusion show that the gas generated from coal is very different from the gas in gas fields. It is speculated by the author that there would have been at least two stages for the formation of the low Paleozoic natural reservoirs in central gas field of Ordos basin, coal type gas was probably dominant at the earliest stage.

10.11743/ogg20020407