塔里木盆地天然气地球化学特征与成因类型研究

通过统计分析塔里木盆地的234个天然气样品指出：该盆地的天然气主要以烃类气体为主(烃类气体含量为80%以上,占样品总数的84%);古生界和中生界天然气中的非烃气体N₂含量高于新生界，且N₂与烃类气体（C _1-4）之间存在正相关性；古生界和中生界天然气主要为油型气，而新生界天然气则为煤成气，且δ¹³C₂和δ¹³C₃存在一定的正相关性;³He/⁴He值一般为n×10^-8数量级，表现为壳源特征，且³He/⁴He值与天然气类型没有明显关系;古生界和中生界天然气的⁴⁰Ar/³⁶Ar值整体上要略高于新生界(这与形成天然气母质中K丰度有关)。根据以上地球化学参数判定塔里木盆地天然气以有机成因类型为主。

Geochemical Characteristics and Genesis of Natural Gas in Tarim Basin

According to statistical measurement of 234 gas samples, natural gas in the Tarim basin is dominant hydrocarbon gas, in which more than 80% of hydrocarbon gases accounts for 84% of all the samples. The contents of non|hydrocarbon gas (N2) in the Paleozoic and Mesozoic are higher than those in Cenozoic, with the positive correlation of nitrogen and hydrocarbon gases (C1|4). Based on carbon isotope fractionation of hydrocarbon gases, the natural gases in Paleozoic and Mesozoic are mostly classified as oil|type gas, whereas gas in Cenozoic is coal|type gas derived from humic matters. A positive correlation between δ¹³C₂ and δ¹³C3 in natural gas from the Tarim basin suggests that natural gases were mainly derived from the thermal decomposition of organic matters. The noble gas isotopes (3He/4He) in the order of n×10^-8 indicate natural gas in the Tarim Basin is of crust origin, in which there is no correlation between ³He/⁴He ratios and types of natural gases. The little higher ratios of⁴⁰Ar/³⁶Ar in Paleozoic and Mesozoic than those in Cenozoic resulted from the different K abundance in source rocks. In combination with the geochemical information above, the natural gas is of thermal genesis, mostly derived from organic matters in the Tarim basin. [JP]