OIL SOURCE AND HYDROCARBON MIGRATION PROCESS IN QIANGTANG BASIN,QINGHAI-TIBET PLATEAU

The oil seepages from the formations of J₂b in West Longeni,J₃s in Angdaercuo,J₃s in West Changliang and J₃s in the area of No.114 Anduo road maintenance squad as well as the J₂x hydrocarbon-rich shale in Biluocuo and the J₃s dark-gray limestone in the area of No.114 road maintenance squad are characterized by high rearrangement sterane content,low pregnane,triclene and gammacerane contents,high ratio of Pr/Ph as well as heavy carbon-isotope.The oil seepages in the formations of J₂b in West Longeni and J₃s in Angdaercuo originate from the J₂x lagoon-phase hydrocarbon-rich source rock in their corresponding areas.The oil seepages in the formations of J₃s in the areas of No.114 Anduo road maintenance squad and West Changliang originate from the J₃s platform facies dark-gray limestone and hydrocarbon-rich shale.There are "light active oil" and "solid bitumen" in the oil-bearing dolomite in center of the basin and in the J₃s lime-rubble rock in No.114 Anduo road maintenance squad area.The solid bitumen is product of the first hydrocarbon migration and accumulation.The fluorescent light active oil is product of the second or third hydrocarbon migration and accumulation causing by reburial or tectogenesis.They have undergone two or more hydrocarbon generation and migration processes.