The Explanation on the Turnover of Carbon Isotopic Compositions of Hydrocarbon Series of Natural Gases in the Northern and Central Tarim Basin

Key words: 
• the Northern and central tarim basin /
• natural gases /
• turnover of carbon isotopic compositions of hydrocarbon series

Abstract: Abstract the carbon isotopic compositions of hydrocarbon series were measured from natural gases in the Northern and central tari m basin . any local turnover phenomena,e.g. δ¹³c₁ ＞δ¹³c₂＞δ¹³c₃ or δ¹³c₁ ＞δ¹³c₂＞δ¹³c₃＞δ¹³c₄，exist in the carbon isotopic compositions of hydrocarbon series. they suggests thathydrocarbons of the natural gases may be mainly biogenic in the Northern and central tarim basin. ost of natural gas samples have the turnovers of δ¹³ c₃ ＞δ¹³ c₄ from the Northern Slope Zone in the Luntai uplift,and the cause of the turnovers may be that these natural gases were mixed less amount of sapropelic hydrocarbons. according to δ¹³c₁values of natural gases and whether they have the δ¹³c₁ ＞δ¹³c₂ turnover,natural gases in the central tarim basin can be divided in to two groups. Natural gases of the first group have heavy δ¹³c₁ values,bet ween -2l.l %"-30.7 %，and the¹³c₁＞δ¹³c₂turnover,such as tz26(0)well,tzl03(c_Ⅱ）well and tzl03(c_Ⅲ）well ；the others have light δ^l3c₁，δ^l3c₂ values,with -4l.0 %"-43.7 %，and -38.8 %"-39.6 %，respectively,without the δ¹³c₁ ＞δ¹³c₂ turnover,such as t24sp-3(c_Ⅲ），tz4-8-30(c_Ⅲ），tz-l(0)and tz45(0)well. t may suggest that less amount of abiogenic hydrocarbons was contained in natural gases of the first group,and that natural gases in the central tarim basin have two genetic types. all the natural gases do not exist turnover of carbon isotopic compositions fromthe Lunnan Lower- uplift,suggesting that they may come from the same source.