渤海中部古近系沙河街组有利砾岩类储层特征

渤海湾盆地是我国重要的含油气盆地,其中古近系沙河街组发育储集性较好的砾岩储层。通过对储层岩石薄片显微鉴定、物性分析、扫描电镜分析、阴极发光分析等,明确了沙河街组有利的砾岩储层的岩石学、储集性和成岩作用特征。砾岩类型多样,其中云质砾岩的储集性最好。砾岩储层物性较好,平均孔隙度为16.1%,平均渗透率为217.93m D。主要孔隙类型为原生孔,原生孔类型主要为砾石间残余原生孔和生物碎屑体腔孔,其次是溶蚀孔。砾岩储层成岩作用类型与砾岩填隙物成分关系密切,以砂岩为主要填隙物的成岩作用中有显著的长石溶蚀作用,以碳酸盐岩为主要填隙物的则具有多期白云石和方解石等胶结物,最有利的成岩作用是早期白云石衬垫和长石的溶蚀作用。

High-quality conglomerate reservoirs from the Palaeogene Shahejie Formation in central Bohai Bay Basin

The Bohai Bay Basin is an important petroliferous basin in eastern China, where the conglomerate reservoirs with good reservoir quality are well developed in the Palaeogene Shahejie Formation in central Bohai Bay Basin. In the light of microscopic examination, physical property, scanning electron microscopy (SEM) analysis and cathodoluminescence images, the present paper focuses on lithology, reservoir capacity and diagenesis of the favourable conglomerate reservoirs in the Palaeogene Shahejie Formation. In a variety of conglomerates, the dolomitic conglomerates have the best reservoir quality, with an average porosity of 16.1% and an average permeability of 217.93 mD. The porosity types are composed dominantly of the primary pores and secondly of the dissolved pores. The primary pores contain intergranular residual primary pores and visceral foramen in bioclastics. The diagenetic types of the conglomerate reservoirs generally depend on the interstitial compositions in the conglomerates. The dissolution of feldspar may be apparently visible in the diagenesis of the sandstone-filled conglomerates, whereas the multiphase dolomite and calcite cements tend to occur in the diagenesis of the carbonate-filled conglomerates. The favourable diagenesis is represented by the early dolomite padding and feldspar dissolution.