塔里木盆地天然气中氮地球化学特征与成因

Geochemical characteristics and genesis of nitrogen in natural gas from Tarim Basin

通过统计分析塔里木盆地103个天然气样品,发现塔里木盆地天然气主要存在两种成因类型,即油型气和煤成气,且氮气含量在油型气中明显高于煤成气。在台盆区产自古生界地层的塔中、东河塘、哈得和中生界的轮南地区为异常高氮气天然气,氮气含量大于20%;新生界地层与塔西南和库车坳陷的中生界地层产出的天然气氮气含量最低(<5%),主要为煤成气;塔北地区,天然气氮气含量变化较大,低含量氮气主要为煤成气,而高氮气含量天然气为油型气,在高氮气含量的油型气中,不同热演化阶段氮气来源不同,其含量也不相同。雅克拉天然气高氮气含量可能是来源于高演化形成的氮气与少量深部气体的混合。

Statistical measurements of 103 gas samples from the Tarim Basin indicate that the oil-type gas and the coal-derived gas dominate the basin and that the former contains much more nitrogen than that of the latter. The gas with abnormal high concentration of nitrogen （ more than 20 % ） occurs in the Paleozoic gas reservoirs of Tazhong, Donghetang, and Hade regions, and the Mesozoic gas reservoirs of Lunnan region （ in the Paleozoic craton area）. The gas with the lowest N2 content （N2 〈5 % ） are mainly coal-derived and are distributed in the Cenozoic strata of the basin and the Mesozoic strata of southwestern Tarim and Kuqa depressions. In the Tabei area, the N2 contents in natural gas are considerably varied. Gases with low nitrogen concentration are mostly coalderived ;while those with high nitrogen concentration are often oil-type gas, in which the origins and contents of nitrogen are changed with the different thermal stages of sapropelic source rocks. The nitrogen molecular in Yakela gas may be explained by the mixture of organic nitrogen formed by sapropel-type kerogen during overmature stages and a little amount of inorganic nitrogen derived from deep crust.