Take the Upper Triassic regional erosion surface as sequence boundary

the Jurassic and Triassic terrigenous clastic systems in Yanchang oil province could be divided into upper sequence and lower sequence.The lower sequence (Upper Triassic)is composed of a transgressive system tract(TST)and a highstand system tract(HST).The Upper sequence (Juassic)includes a lowstand system tract(LST)overlain by a transgressive system tract(TST)and a highstand system tract(HST).Three assemblage types can be distinguished according to the disposal relationship of source reservoir cap rock assemblage:1.lithologic reservoirs

characterized by source rocks in the lower part and reservoirs in the upper part

formed during rapid subsidence with high accommodation space.The Chang 7 lacustrine facies and Chang 6 deltaic facies in the lower part of the Lower sequence are the best oil reservoir dispose;2.lithologic structural reservoirs with source rocks in the upper part and reservoirs in the lower part

and self sourced reservoirs developed in the upper part of the lower sequence represented by Chang 2+3 and Chang 1 meandering/anastomosing system. It is the second excellent oil reservoir dispose in the study area.3.structural lithologic reservoirs with source rocks in the lower part and reservoirs in the upper part associated with self sourced reservoirs developed in the upper sequence of fluvial facies(Yan 10-Yan 1 submembers).The hydrocarbon pool forming in reservoirs needs good structural trap due to poor lateral seals.