塔里木盆地若羌油苗的地球化学意义

Geochemical Significance of the Ruoqiang Oil Seepage in Tarim Basin

若羌油苗是塔里木盆地东南地区首次发现的油苗。详细研究了该油苗的地化特征,认为若羌油苗生物标记化合物组合特征不同于塔里木盆地已发现原油的地化特征,具有盐湖相特征:油苗饱和烃气相色谱图上nC14~nC26出现明显偶碳优势;植烷优势明显,Pr/Ph为0.29~0.35,Ph/nC18为0.94~0.99,Pr/nC17为0.38~0.43;伽马蜡烷丰度非常高,且比C29藿烷峰还高;C35升藿烷丰度明显高于C34升藿烷。原油成熟度较低,Ro在0.70%~0.73%之间。推测油源母质类型为Ⅰ-Ⅱa型有机质,较柴达木盆地第三系盐湖相好。若羌油苗的发现和地化特征预示塔东南地区可能存在一套盐湖相、并能生成工业油流的生油岩。

Ruoqiang oil seepage is the first discovery of oil seepage in the east-south of Tarim Basin. The article researches on the geochemical characteristics of Ruoqiang oil seepage in detail and figures that the combination characteristics of the biomarkers in the Ruoqiang oil seepage is different from the crude oil discovered in Tarim before while possesses the characteristics of brine lack facies. The gas chromatogram of saturated hydrocarbon reveals the even carbon advantage obviously from nC14 to nC26; phytane advantage is distinct, Pr/Ph is 0. 29-0. 35, Ph/nC18 is 0. 94-0. 99, Pr/nC17 is 0. 38-0. 43; The abundance of gammacerane is much high, even higher than C29 Hopane apex; and the abundance of C35 Hopane is higher than the C34 Hopane apparently too. The crude oil maturity is lower relatively and Ro is between 0. 70% -0. 73%. Therefore, it is supposed that the organic types of the source rock is Ⅰ-Ⅱ1and it is better than the tertiary brine lake deposition of Qaidam Basin. Both the discovery of Ruoqiang oil seepage and its geochemical character predict that the east-south area of Tarim may produce a set of brine lack facies oil source rocks which possess the ability of forming industrial oil flow.