Abstract: Shale samples from the lower third member of the Shahejie Formation of the Palaeogene in Dongying Sag were taken for a sedimentation characterization,a classification of lithologic facies and microfacies and an analysis of planar and vertical distributions of the shales of semi-deep and deep lacustrine facies through a centimeter-scale core description,thin section identification and X-ray diffraction analyses of the samples.Such means as observations of SEM images and laser confocal microscope and experiments of low-temperature nitrogen adsorption were also resorted to study the genesis,types,morphology,size and distribution of pores and fissures in the samples.The results show various types of minerals and the fine-grained sediments being regarded previously as high-quality source rocks are largely carbonates.It also indicates that there are various pore and fissure types and the pores are of multi-scales and have complicated structures.The shale reservoirs with different types of microfacies differ in micro-structures.The controlling effect of sedimentary microfacies upon the micro-structure of reservoirs is mainly displayed in compositions and fabric of minerals,and deposition and preservation of organic matters,which further affect the types and structures of pores.The shale reservoirs developed in flat and semi-deep lacustrine facies are found to contain high content of organic matters,various types of rocks and brittle minerals dominated by calcite.They also harbor pores and fissures of various types.With fairly connected open pores,the reservoirs are considered to be potential exploration targets in the sag.

Key words: pore, reservoir microscopic structure, microfacies, shale, Dongying Sag, Bohai Bay Basin