北京下苇甸地区寒武系张夏组鲕粒滩成岩演化与勘探前景

Diagenetic Evolution and Exploration Prospect of Oolitic Bank in Cambrian Zhangxia Formation at Xiaweidian Area,Beijing

成岩作用及成岩演化序列控制着鲕粒滩储集空间的发育。下苇甸地区寒武系张夏组主要为鲕粒滩微相。通过野外实测、薄片观察、X衍射等方法,阐明了下苇甸地区寒武系张夏组鲕粒滩的主要成岩作用类型和成岩序列,并对张夏组鲕粒滩的勘探前景进行了展望,得出如下结论:(1)对下苇甸地区张夏组鲕粒滩储集性能有明显影响的成岩作用主要包括压实-压溶、胶结作用、白云石化作用等。除此之外,硅化作用主要以围绕鲕粒的硅化套形式出现;(2)鲕粒白云石化主要发生在同生成岩阶段,白云石晶间孔是鲕粒滩主要的储集空间。早-晚成岩阶段主要以鲕粒滩的压实-压溶作用为主,造成了粒间孔隙的急剧减少;(3)鲕粒滩压溶产生的缝合线及其伴生的溶蚀孔隙与白云石晶间孔构成的疏导-储集复合体系是鲕粒滩可能的油气储集空间,在证实中新元古界烃源岩供源的前提下,华北寒武系张夏组是一套潜在的勘探新层系,值得研究和探索。

Diagenesis controls the development of the storage space of oolitic banks,and their different diagenetic sequences determine the physical properties of the final reservoir.The Cambrian Zhangxia Formation at Xiaweidian occurs mainly in the oolitic bank facies in the carbonate platforms.In this study,based on outcrop descriptions,thin section observations and XRD,we discuss the major diagenetic types and sequence,and exploration prospect of the Zhangxia Formation.We conclude that:(1)Major diagenetic processes that affect the reservoir quality of oolitic bank include compaction,pressure dissolution,cementation and dolomitization.Silicification occurs mainly as silicide around the ooids;(2)Dolomitization of ooids mainly occurs in the syngenetic diagenetic stage,dolomite intercrystal pores are the main reservoir space of the local oolitic bank.The eogenetic and telogenetic diagenetic stage is mainly based on the compaction and pressure dissolution of the oolitic bank,resulting in a sharp porosity drop;(3)Migration and storage complex system,composed of the stylolite and dolomite intercrystal pores,is a possible storage space in the local oolitic bank.In the provision that the hydrocarbon supplying ability of the Proterozoic source rocks is confirmed,the Zhangxia Formation represents a new potential sequence for exploration,and warrants further investigation.