In order to determine the current status of the reservoir in the Chang 8 oil layer, the basic characteristics of the reservoir and the diagenetic and sedimentary processes were investigated through methods such as thin section analysis and scanning electron microscopy. In the context of overall low permeability, it is found that higher production rates are observed in some oil wells located in areas of relatively high relative permeability. By understanding the enrichment patterns in the study area, factors contributing to the decrease in rock porosity are analyzed. The results indicate that the Jiyuan area has favorable reservoir development in underwater distributary channels and estuarine bar deposits, with the center of the sand bodies exhibiting the best reservoir properties. Therefore, the Chang 8 oil layer is found to have good reservoir and permeability performance, including intergranular pores, intergranular pores with dissolved pores, and dissolved pores with intergranular pores. On the other hand, the combination of dissolved pores and micropores as well as micro-pores alone is found to have poor flow performance. The reservoir space predominantly composed of extremely small micro-pores is observed to have low connectivity, resulting in lower internal surface area, flow resistance, and poorer reservoir and flow performance.