轮古西地区奥陶系碳酸盐岩古岩溶储层碳、氧同位素地球化学特征

中—下奥陶统鹰山组碳酸盐岩古岩溶储层是塔里木盆地轮古西地区的主要油气产层 .为了弄清储层的成因类型、储层古岩溶过程中的流体性质和古水文条件 ,为预测和评价此类储层提供有关的地球化学信息 ,讨论了储层形成过程中记录的碳、氧稳定同位素特征 .结果表明 :轮古西地区奥陶系鹰山组碳酸盐岩古岩溶储层中的δ13C和δ18O值的变化范围较大 ,δ13C值为 -0 .70‰～ -6.5 0‰ ,平均值 -1 .76‰ ;δ18O值为 -3 .75‰～ -1 7.1 0‰ ,平均值 -9.42‰ .碳酸盐岩基质、冲积岩和方解石胶结物的δ13C和δ18O分布具有一定的差异 .三类样品的δ18O值均具有明显偏负特征 ,表明在碳酸盐岩成岩过程中受到大气成因的淡水影响 ,反映了当时的风化壳岩溶成岩环境 .冲积岩样品的δ13C值的偏负程度较高 ,其物源可能来自石炭—二叠系地层

Geochemistry characteristics of carbon and oxygen isotopes of Ordovician carbonate palaeokarst reservoir in the western region of Lungu,Talimu Basin

The study of the geochemical characteristics of carbon and oxygen isotopes of Ordovician carbonate reservoir in this area can provide geochemical information for understanding the genetic types, the fluid properties and the palaeohydrologic condition of karst reservoirs, and evaluating the reservoirs. The analyses of 26 matrix material samples, 6 cementing matter samples and 6 karst samples from the depth of 5 600～5 900 m show that, there is great variation of δ~(13)C and δ~(18)O values of the carbonate palaeokarst reservoir. The variation ranges and the average values of δ~(13)C and δ~(18)O are -0.70‰～-6.50‰, -3.75‰～-17.10‰ and (-1.76)‰, -9.42‰respectively. The distributions of δ~(13)C and δ~(18)O values of carbonate matrixes, alluvial rocks and calcite cements are different. The negative of δ~(18)O values of three kinds of samples show that the process of carbonate diagenesis is affected by meteoric fresh water, which indicates the weathering crust karst diagenesis environment at that time. The much more negative δ~(13)C values of alluvial rocks also indicates that their provenance is probably Carboniferous—Permian formation.