Abstract:Based on the analysis of general thin-section, casting lamella, scanning electron microscope, X-ray diffraction and other analysis methods, the diagenesis of Paleogene Huagang Formation in Huangyan tectonic belt of Xihu Sag is studied in detail. The result shows that feldspathic-lithic quartz sandstone is the main sandstone type with medium maturity of texture and component. The vitrinite reflectance and paleogeotemperature reveal that diagenetic stage of reservior is at middle diagenetic A stage. Compaction, cementation, metasomatism and dissolution are recongnized, which are main types of diagenesis in sandstone reservoir. Compaction and cementation are typical destructive diagenesis, which destroy most primary pores and a large volume of secondary pores are filled by carbonate cements, whereas the dissolution developed in study area produces a lot of secondary pore, which forms the secondary pore zone at a depth of 3500 meters and improves the reservoir physical properties effectively.