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.