舞阳、襄城盐湖盆地未熟油地球化学特征、判别标志及成因

GEOCHEMICAL CHARACTERISTICS, IDENTIFICATION INDEX AND ORIGIN OF THE IMMATURE OILS FROM WUYANG AND XIANGCHENG BASINS,HENAN,CHINA

通过对舞阳、襄城凹陷原油及烃源岩样品的有机地化分析 ,研究了该区未熟油地球化学特征、判别标志及成因类型。认为盐湖盆地原油具“两高、两低”特征 ,族组成上表现为饱和烃含量较低 ,“非烃 +沥青质”含量较高。正烷烃呈双峰态分布 ,OEP值 >1。具植烷优势 ,Pr/Ph <0 .2 5。萜烷以伽玛蜡烷含量高 ,Tm/Ts >1。脱羟基维生素E普遍存在 ,其分布型式主要有倒“V”字型和不对称“V”字型。根据C2 9甾烷 2 0S/ (2 0S +2 0R) ,C2 9甾烷 ββ/ (ββ +αα) ,C3 2 藿烷 2 2S/ (2 2S +2 2R)等成熟度参数 ,认为原油属于未熟油。伽玛蜡烷、脱羟基维生素E及碳同位素组成特征反映原油属咸水湖相、盐湖相成因。

Geochemical characteristics, identification index and origin of immature oils are investigated in terms of organic geochemical analyses of crude oils and source rocks from the Wuyang and Xiangcheng basins. Crude oils from the basins are characterized by the low contents of saturated hydrocarbons and the great abundances of non hydrocarbons and asphaltenes. N alkanes in the oils display a bimodal carbon number distribution with an odd over even predominance. The ratio of pristine/phytane is less than 0.25 while the phytane/C 18 n alkane ratio is greater than 4. The extended tricyclic terpenes, identified in a lower concentration, are distributed in carbon number from C 20 to C 26 , and the ratio of Ts/Tm is greater than unity. The PAHs are dominated by phenanthrene series and subordinately by naphthaline series. Decarboxyl vitamin E is widely spread with the 5 configurations of δ, 6 methyl MTTC, β, γ and α. The ratios of 20S/(20S+20R) and ββ/(ββ+αα) of C 29 steranes (0.12-0.23, 0.20- 0.26 , respectively), 22S/(22S+22R) of C 32 homohopanes (0.36-0.48), β/γ of Dehydroxyltocopherols (0.07-0.39) and MDR(4 MSF/1 MSF) (0.41-1.85) show immature characteristics of the crude oils analyzed, which is proposed to have originated in the saline lacustrine environment.