Abstract: N¹² formation of Wunan Oil Field is a set of sand-shale thin interbedding deposit, forming some sand sheets and lenticular bodies. Those sand bodies are the main target horizons of Wunan Oil Field. The grain size of reservoir rock is relatively fine, mainly fine sand and fine sandstone. Calcite of rock is well cemented and high in content. The diagenetic stage of the studied reservoir is from the late A period of early diagenesis to the early B period of early diagenesis. Hydrocarbon source rock released a large amount of organic acid in the late A period of early diagenesis, forming the secondary porous development zone in the sandstone. The reservoirs pores are mainly residual intergranular pores and intergranular dissolved pores. The physical properties of reservoir are poor. The porosity of the reservoir is low to super-low while the permeability is super-low to ultra-low, belonging to the scope of compact sandstone. Thanks to the effect of compactness on the mudstone and sandstone interbedding under the background of saline lake basin sedimentation, the fluids were drained into sandstone from mudstone, leading to cementation of calcite in the rock. This is the main factor for rock compactness in the research zone.