Yan'an Delta is located in the southeastern part of Shanbei slope in Ordos Basin and contains several oil reservoirs.Chang 4+5 and Chang 6 are the main pay zones.According to sedimentary facies

reservoir-seal assemblage and distance from source

this paper established several hydrocarbon accumulation patterns.The superimposed channel sandbodies in the delta are the major migration pathways for the hydrocarbon

and they provided conditions for long distance lateral and vertical migration of hydrocarbons.According to the distance between source and reservoir and the ability of oil accumulation

the reservoirs can be divided into three types

i.e

proximal accumulation

distal accumulation and pro-ximal dissipation.The former two types of accumulation areas have better oil enrichment conditions as the hydrocarbon migration and/or sealing conditions are favorable

while the later is limited in hydrocarbon accumulation capacity despite its shortest distance to oil source due to the migration of hydrocarbons to structural high.According to the migration pathways'quality and reservoir location

the accumulation pattern of Yan'an Delta are divided into five types

i.e.the proximal accumulation pattern with main migration pathways

the distal accumulation pattern with main migration pathways

the proximal accumulation pattern with sub-migration pathways

the distal accumulation pattern with sub-migration pathways and the proximal dissipation pattern.