Abstract: The high water production rate of Yanchang Formation reservoirs in Ordos Basin is one of the main problems in the fine exploration of oilfield. The Chang 4+5₁ Reservoir in the Baibao-Nanliang Area is taken as the research object. Through the comparative analysis of source rock conditions, sand body types, reservoir characteristics, fracture characteristics, and shielding conditions, the enrichment rules of oil reservoirs are discussed. The results show that the Baibao Area is distributed in the lower delta plain and the near source part of delta front, and the sand body type is mainly underwater distributary channel with large thickness, high permeability, and long lateral extension. Due to the large-scale connectivity sand body with good physical properties, the crude oil migrated laterally to the high part of the structure under the action of buoyancy, resulting in the oil-bearing core producing water. Low amplitude structure is a favorable exploration target in this area. Nanliang Area is distributed at the end of the delta front, mainly composed of mouth-bar sand body. The sand body is relatively isolated, the physical properties are relatively poor and the lithology changes frequently. It is difficult for crude oil to migrate laterally due to the good conditions of authigenic traps in isolated sand bodies. Sand bodies with smooth vertical migration channels and good reservoir physical properties are favorable exploration targets in this area.

Key words: Baibao-Nanliang, differential accumulation, enrichment law, lithologic reservoir, Chang 4+5₁ Reservoir