Abstract: The Upper Triassic Bagung Formation clastic rocks in the North Qiangtang Depression are the key strata of reservoirs in the Qiangtang Basin. The study shows that the overall compositional maturity and structural maturity of the sandstone in the Bagung Formation are medium and low, the dissolution pores are the main reservoir space, and the pore structure is characteristic of small pore throat radius, poor sorting and poor connectivity. Dissolved pore space is the main pore type, and the pore structure shows poor sorting, fine roaring channel and poor connectivity. Sedimentary factors are the main factors controlling the quality of the reservoir. The sands formed in the microphase of the diversion channel are formed with strong hydrodynamic force and transported far away, and their thickness is larger and the primary pores are more developed, and the acidic dissolution is more developed in the later stage because of the strong compaction resistance and more intergranular pores are retained. The chlorite lining inhibits the formation of intergranular siliceous cement, the fracture development improves the reservoir properties, and the unique acidic medium environment of the coal system also promotes the formation of secondary pores.

Key words: North Qiangtang Depression, Bagung Formation, tight sandstone, reservoir characteristic, controlling factor