准噶尔盆地南缘异常天然气地球化学特征及其成因

Origins and geochemical characteristics of unconventional natural gas in south margin of Junggar basin

利用天然气成因判别Whiticar图版研究准噶尔盆地南缘独87井、南安1井和齐34井天然气成因类型,结论与乙烷和丙烷碳同位素判识结果相矛盾。在分析研究区南安1井八道湾组、齐34井中、下侏罗统和独87井中新统储层天然气组分和碳同位素组成特征的基础上,对异常天然气成因进行分析。南安1井甲烷含量为84.58%,齐34井甲烷含量为97.38%,两者均为干气;独87井甲烷含量仅为77.09%,为湿气。独87井碳同位素变化比较复杂,出现δ13C1>δ13C2,δ13C2<δ13C3且δ13C3>δ13C4局部碳同位素倒转现象;齐34井天然气为δ13C2>δ13C3>δ13C4的局部碳同位素倒转;南安1井没有出现碳同位素倒转,为正碳同位素特征。南安1井和齐34井天然气因受到细菌降解作用,其组分含量和碳同位素发生变化;独87井天然气δ13C1变重是上覆盖层封盖能力较差、甲烷发生漏失所致。据此对Whiticar图版进行了必要的补充修正,可以对细菌降解和甲烷漏失次生作用进行有效识别,避免对天然气母质类型认识上的误差。

Based on study of the component and its carbon isotope of natural gas samples from the J1b reservoir of Nanan-1 well,the J2-1reservoir of Qi-34 well and the N1reservoir of Du-87 well in the south margin of Junggar basin,we suggest that these natural gases arecoal-related gas herein.But the natural gases sample data from the J1b reservoir of Nanan-1 well and the J2-1reservoir of Qi-34 wellare distributed at the region where natural gas originated from Type Ⅱ kerogen often locates in the Whiticar chart board.Natural gascarbon isotope and natural gas components show that,the secondary action should alter C1/C2+3and δ13C1.In view of the geological back-ground of south margin of Junggar basin,the genesis of unconventional natural gas from Nanan-1 well and Qi-34 well and Nanan 1well is bacterial degradation,which resulted in C1/C2+3increase and δ13C1lightening,but the genesis of unconventional natural gas fromDu-87 well is methane leakage effect.According to the distribution region of the unconventional natural gas,the different developmentdirection of bacteria degradation gas and the coal-related gas leakage in methane component are pointed out.The research conclusionis a necessary supplement to the Whiticar chart board,and makes the Whiticar chart board more practical in the research work aboutnatural gas.