准噶尔盆地南缘天然气中N_2地球化学特征及成因分析

Geochemical Characteristics of Nitrogen and It′s Genesis in Natural Gas,Southern Margin of Junggar Basin

通过统计分析准噶尔盆地南缘155个天然气样品组分和碳同位素数据,发现天然气中的N2主要富集在新近系沙湾组、古近系紫泥泉子组和北天山山前的浅部地层中。天然气组分和碳同位素表明,N2和烃类气体为同源生成,均来自有机质处于高—过成熟阶段的侏罗系煤系地层,没有大气渗入和岩浆—火山气体的混入。N2含量与储层年龄和地层埋深有关,随着地层由老到新,埋藏由深至浅,N2逐渐富集。高含氮天然气主要受运移作用控制,是天然气垂向运移的结果,新地层和北天山山前浅部地层中赋存的天然气受到微生物降解。

According to statistics of 155 gas samples from the southern margin of Junggar basin,the N2-enriched gas is mainly distributed in the neogene Shawan Formation,Palaeogene Ziniquanzi Formation and the shallow layers of the north Tianshan piedmont.Chemical and carbon isotopic compositions of the natural gas indicate both N2 and hydrocarbon gases in the natural gases are derived from the Jurassic coal in the southern margin of Junggar basin and not from atmosphere and mantle-volcanic gas.The N2 content in natural gas is relative to reservoir age and buried depth of gas reservoir,the content of N2 is increasing with reservoir age chances from old to young and buried depth from deep to shallow.The relatively high N2 content is controlled by vertical migration of gas.Natural gas is degraded by microbe in the neogene Shawan Formation,Palaeogene Ziniquanzi Formation and the shallow layers at the north Tianshan piedmont.