盐城凹陷凝析油地球化学特征

运用碳同位素、气相色谱、色谱 质谱、流体包裹体技术 ,研究了盐城凹陷凝析油地球化学特征 ,并与永安凹陷永 7井凝析油、下扬子海相原油进行了对比。该凝析油碳同位素为 -2 8 8‰～ 3 0 5‰ ,全油色谱中含有一定的长链正构烷烃 ,Pr/Ph为 1 5 6,三环萜烷含量高 ,伽玛蜡烷含量低 ,重排甾烷含量高 ,C2 9甾烷 >>C2 7甾烷 >C2 8甾烷。石蜡指数、庚烷值表明原油为高成熟凝析油 ,甲基菲指数MPI表明原油为未熟—低熟原油 ,C2 9甾烷 2 0S/ (2 0S+2 0R)值表明原油为成熟原油。这种成熟度的差异可能与不同成熟度原油的混合作用有关。油气主要充注时间为 6～ 1 5Ma。凝析油的主体可能源于泰州组烃源岩 ,凝析油的形成与蒸发分馏作用密不可分

GEOCHEMICAL CHARACTERISTICS OF CONDENSATE OIL IN THE YANCHENG SAG

Using isotope, GC,GC/MS, inclusion techniques, the geochemical characteristics of condensate oil are described and compared with those of condensate oil from Yong-7 well in the Yong'an Sag and marine oils in the Lower Yangtze Region. The δ 13C values of whole oil are about -28.8‰～-30.5‰. In the whole oil chromatogram, the condensate oil contains a significant amount of long alkanes. The features of biomarkers in the condensate oil are presented as follows: Pr/Ph about 1.56, high tricyclic terpane, low gammacerane, high C 27 diasterane, C 29ααα20 R sterane>> C 27ααα20 R sterane> C 28ααα20 R sterane, and high PI1, PI2 values of condensate oil suggest the oil reached the overmature stage. Low MPI of the condensate oil suggests it is the product of unmature to low-mature stage. C 29 sterane 20S/(20S+20R) values of the condensate oil indicate it belongs to mature oil. The difference among maturity parameters may be attributed to the mixing of oils with different maturities. The time of hydrocarbon charging ranges mainly from 15Ma to 6Ma. The condensate oil may come largely from the Taizhou Formation. The formation of condensate is ascribed to the process of evaporative fractionation.