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根据油气分异聚集原理，一般来说，在同一构造内是气在构造高部位，油在构造低部位富集，而桥口构造则与之相反，呈“上油下气，顶油边气”的分布状态。为搞清该区油气分布规律，建立了油气运移模式，得出了如下主要认识：该区下第三沙三段，沙四上段为主要生油层，东邻的葛岩集洼陷为主要生油气区；早期洼陷中生成的油气在泥岩欠压实作用产生的压差作用下，向构造高部位运移，聚集形成沙三段油气藏，后期由于断裂活动强烈，油气沿断

OILAND GAS MIGRATION MODE OF QIAOKOU STRUCTURE IN THE DONGPU SAG

??Acconding to the differential accumulation theory,oil is generally concentrated at the bottom of structures.But the one in Qiaokou structure appears the contrary distribution pattern of "gas under oil and top oil with edge gas." In order to clarify the oil-gas distribution,an oil-gas migration model is set up by studying shale under compaction,fluid potential,oil physical variation,the geochemical characteristics of the oil and source rock and the relationship between petroleum and structures.The conclusions are following:??The Tertiary Sha 3 member and Sha 4 upper member in the area are the main oil source beds.Gegangji depression to the east is the main oil-gas source area.??The hydrocarbon generated in the depression at the early stage has migrated and accumulated to the upper section of the structure to form Sha 3 member oil-gas reservoir under the differential pressure caused by shale undercompaction.The secondary oil-gas reservoirs of Sha 1 and Sha 2 members were formed as the violent rifting at later stage made hydrocarbon migrate along faults.??Litun fault with an intenser sealling,located on the east side of the structure,was formed earlier mainly generating gas at later stage.The generated gas sealed by Litun fault formed Sha 3 gas reservoir with fault-stratum trap in the deep place in the east to make the oil-gas appear the distribution of "gas under oil and top oil with edge gas".