Abstract:Reservoirs of the Eocene Pinghu Formation in Xihu sag was deeply buried with low permeability and high heterogeneity. Genesis and distribution of the “sweet points” in such low permeability reservoir were still unclear, which made it hard to increase the reserves in this area. Complicated diagenesis is the key factor to solve this problem. In order to study the diagenesis and analyze the genesis of the low permeability reservoirs in this area, reservoirs in Pinghu Formation in different areas, different formation, and different facies were compared in detail. Reservoir quality differences, affecting factors, and genesis mechanism of high quality low permeability reservoirs were clarified. It is found that secondary dissolution and microfacies are significant factors affecting the reservoir distribution. Diagenisis including cement and dissolution and facies including tidal flat and delta make the reservoir quality divide into different levels. Weak cementation with strong dissolution, weak cementation with medium dissolution, and medium cementation with medium dissolution facies in tide channel, sand flat, distributary channel, and mouth bar developed high quality reservoirs. Tide channel sand bodies in Ping-4 and Ping-5 section in Kongqueting west and Baowuting are reservoir sweet points. Distributary channel sand bodies in Ping-2 and Ping-3 section in Kongqueting east and Tuanjieting are other reservoir sweet points. Study achievements are bases for the prediction of favorable reservoir distribution and are directions for hydrocarbon exploration and development.