Keywords: 
• Sanzhao depression

Abstract: To study migration horizons downward of oil from K1qn source rock in Sanzhao depression The mechanism and condition of oil migration downward was studied. It was considered that two conditions in F,Y oil lagers, they are ①enough high overpressure and ②T2 faults connected k1qn source rock and F,Y oil lagers. Oil from k1qn source rock can migrate downward into F,Y oil layer in the end of K1n, K2m, and E sedimentary period under the action of overpressure. The migration distance downward of oil from k1qn source rock in Sanzhao depression was studied by the principle of pressure seal. The migration distance downward of oil from k1qn source rock is generally more than 500 m, the maximum thickness of F,Y oil lagers is only 500 m, it indicates that oil from K1qn source rock can migrate downward into all F,Y oil layers. There is oil from top of F oil layer to bottom of Y oil layer now, and oil reservoirs found in F,Y oil layers of Sanzhao sag distribute in the migration areas downward of oil from K1qn source rock. It indicates that the migration horizon downward of oil from K1qn source rock controls the oil accumulation horizons, the migration areas downward of oil from K1qn source rock controls oil accumulation areas. The migration areas downward of oil from K1qn source rock and its around should be favorable areas for oil exploration in F,Y oil lagers of Sanzhao depression.