Abstract: The major factors controlling the enrichment of tight oil in the 7th oil layer group of the Triassic Yanchang Formation(Chang 7 oil layer group)in Fuxian-Ganquan area,Ordos Basin,were investigated from multiple perspectives of outcrop,core,logging and laboratory testing,combined with such dynamic data as production tests.The results show that the high-quality source rocks of Chang 7 oil layer group are developed well and widely and are characterized by large thickness,high organic richness,favorable type of kerogen and moderate maturity,thus provide an abundant oil source for tight oil enrichment and control the oil-water contact of the Chang 7 tight oil reservoirs.The Chang 7¹ and Chang 7² sub-layer groups in the Chang 7 oil layer group together with the underlying source rocks make up a source-reservoir assemblage characteristic of closeness between the underlying source rock and overlying reservoir.The analysis of diagenetic facies shows that quality diagenetic facies of reservoir controls the zones of tight oil enrichment.There is multi-phase oil charging in the tight oil reservoirs.During the early charging stages,the wettability of the reservoir rock was turned from water wet to mixed wettability with oil charging,leading to the formation of preferential channels for oil migration and accumulation,which determines the pathway and scope of oil migration and accumulation in the major pool-forming period,and to a certain extent constrains the distribution of the Chang 7 tight oil reservoirs.Baffles and barriers of various sizes compartmentalize the reservoirs into a network structure with intense heterogeneity,leading to differential fluid flow and complex oil-water contact in the sandstone.Meanwhile,the shelter of tight layers can also play a role in controlling the accumulation of Chang 7 tight oil.All the factors mentioned above collectively determine the limited distribution of tight oil,the complexity of water-oil contact and the coexistence of oil wells and water wells.

Key words: diagenetic facies, heterogeneity, multi-phase charging, tight oil, Yanchang Formation, Triassic, Ordos Basin