鄂尔多斯盆地中东部上古生界天然气地球化学特征

The Geochemical Characteristics of Upper Paleozoic Natural Gases in the Central and Eastern Parts of the Ordos Basin

鄂尔多斯盆地是我国第二大含油气盆地,天然气勘探前景广阔。该盆地中东部上古生界天然气中烃类组分以高CH4含量(>85%)为特征,C2+含量小于10%,干燥系数(C1/Cn)多大于90%,反映了以"干气"为主、"湿气"为辅的特征。非烃组分主要是CO2和N2,微含H2、He等。上古生界天然气的δ13C1值一般大于-36‰,大部分在-35‰^-30‰之间,δ13C2多在-27‰^-22‰之间,δ13C3多为-27‰^-21‰,δ13C4为-26‰^-20‰,δDCH4值为-185‰^-162‰,与下古生界天然气有差异。研究认为,鄂尔多斯盆地中东部上古生界天然气主要属于煤成气。

The Ordos Basin was the second largest hydrocarbon-bearing basin in China. It had good oil and gas exploration prospects. The Upper Paleozoic natural gases in the central and eastern parts of Ordos Basin were predominated by methane (>85%) and minor C+2 contents (less than 10%). The dryness coefficients (C1/Cn) were generally more than 0.90. Their non-hydrocarbon components were mainly CO2 and N2, and contain trace H2, He. This indicates the characteristics of major dry gases and minor wet gases. The δ13C1 values of Upper Paleozoic natural gases are generally more than -36‰, mainly among -35‰～-30‰. The δ13C2, δ13C3, and δ13C4 values of most natural gases are among -27‰～-22‰, -27‰～-21‰, and -26‰～-20‰, respectively. Their δD values are -185‰～-162‰. These characteristics of carbon and hydrogen isotope ratios are different from those of Lower Paleozoic natural gases. It is suggested that the Upper Paleozoic natural gases in the central and eastern parts of the Ordos Basin are mainly coal-formed gases.