Abstract: Since the formation of Juanquanzi member in Laojunmiao structure has the features of high water cut and low displacement efficiency,the study of pore structure becomes the key to enhanced oil recovery. A variety of experimental test methods were used to study the pore structure and influencing factors of Paleogene Oligocene clastic reservoir in Juanquanzi member of Baiyanghe Formation,such as casting thin section observation,SEM analysis,capillary pressure testing and so on. The result shows that the reservoir lithologies are mainly lithic sandstone and feldspathic lithic sandstone,with high debris content,low maturity of composition and texture. Reservoir spaces are mainly residual intergranular pores and intergranular dissolved pores. The reservoirs can be divided into four types according to pore structure characteristics,and type Ⅰand type Ⅱhave relatively good reservoir property,with permeability above 10 mD. The capillary curves have significant platforms,and coarse skewness. There is a positive correlation between reservoir properties and the concentration of pore throat and the proportion of rough throat. The layer analysis shows that the layer L was in alkaline diagenetic environment,there were a large amounts of clay minerals and calcite cements contained in intergranular pores,and the well sections with weak cementation have good reservoir properties. The acid diagenetic environment of layer M inhibited the cementation,parts of primary pores were preserved,and the dissolution effect by acidic fluids promoted the formation of high quality reservoirs in M layer. The research results can provide geological basis for later effective exploitation.

Key words: pore structure, diagenesis, Jianquanzi member, Baiyanghe Formation, Jiuxi Basin