Large scale oil reservoirs have been discovered in the second section of the Upper Uerhe Formation in the ST1 oil field and the first section of Upper Wuerhe Formaton in the ST2 oil field of Shawan sag, which have favorable conditions for the accumulation of oil and gas. Based on seismic, logging, core and geochemical data, a systematic study was conducted in this area. The underwater distributary channel sand body in the front of the fan delta is the main reservoir of the Upper Wuerhe Formation. The sedimentary environment and diagenesis are the basis for the formation of larger matrix pores that make up the front edge reservoir. The development of fractures and abnormal high pressure to improve physical properties is the key to the development of high-quality reservoirs even under larger burial depths in the western slope. Hercynian movement caused the northwest to uplift, and at the meantime, the sand and gravel deposits of the Xiazijie and Fengcheng Formation were extensively eroded at the bottom boundary of the Upper Wuerhe Formation. Therefore, an unconformity erosion surface of 1180 km2 was formed. The sand and gravel deposited beneath the erosion surface and the fault system together formed the oil and gas transport grid, providing advantageous channels for oil and gas migration.