鄂尔多斯盆地天环北段白云岩体成因及储集性能

鄂尔多斯盆地西缘天环北段白云岩体总面积约1×104km2,最大厚度431m。马家沟组中每个地层段均不同程度地发育有白云岩。富晶间孔的粉细晶白云岩及其充填物中Fe、Mn含量显著高于其它碳酸盐岩,而Sr含量平均值低于其它碳酸盐矿物。δ18O的值出现较大负值,并且跨度较大,说明白云岩体的成因并非单一模式。据碳氧同位素值计算的古盐度指数均小于120,说明在白云岩形成期间有淡水的加入。该白云岩体的成因应具有双重因素,即早期的混合水成因和晚期的热水成因。据推测:热水成因白云岩约占60%,混合水成因白云岩约占40%。

Origin and Reservoir Characteristics of Dolostone in Northern Tianhuan Depression, Ordos Basin

Dolostone covers about 10,000km2 with the largest thickness of 431m in northern Tianhuan Depression,Ordos basin.It developed to some extent in the deferent beds of oil-paying Majiagou Formation.The content of Fe and Mn is several timesas higher in aplitic dolostone as that in other carbonates, but the content of Sr is lower than that in other carbonates. The δ18Oput up high negative values and spans wide,which means that not dolostones are genetic from a single pattern.Based uponanalysis of paleosalinity index (<120), the formation of dolostones is related with either mixed water or hot water. About 60%of dolostone was genetic from hot water during early period and the other 40% of it from mixed water during the late period.