Hydrocarbon Accumulation Patterns and Characteristics of the Cretaceous Reservoirs in Jianghan Basin

The Cretaceous filling in Jianghan Basin was a set of alluvial fan and river flat sedimentary system with low exploration degree and wide distribution areas.Although it was lack of source rocks itself,it had favorable reservoirs and seals.Based on research of exploration practice,it is indicated that in the upper Triassic-lower Jurassic system,lower Xingouzui Formation of The Eogene and Qianjiang Formation source rocks feed the Cretaceous reservoirs with hydrocarbons through unconformities,faults,and sand bodies,form accidentally-sourced secondary accumulation.And there are three hydrocarbon-accumulation patterns,the first pattern is the Cretaceous reservoirs with hydrocarbons migrating through unconformities from the Upper Triassic-Lower Jurassic coal measure source rocks(old-bed generation and new-bed storage);and the second and third are the Cretaceous reservoirs with hydrocarbons migrating through faults from the lower Xingouzui Formation and from the Qianjiang Formation source rocks,respectively(new-bed generation and old-bed storage).The updipping fault-barrier,reverse nose-shape structures are favorable for the first pattern,and the depression-ramp-fault-uplift configuration is favorable for the other 2 patterns.