Main Factors Controlling Differential Enrichment Of Hydrocarbons In The Foreland Basins In The Southern Zone Of The Asia Segment Of The Tethys Realm

With public literatures,commercial data for fields and reservoirs,and unpublished scientific research reports as the data base,and the plate tectonics,basin dynamics and petroliferous basin analysis as the guiding theories,this study conducted an integrated petroleum system analysis and discussed the inter-relationships among the tectonic and depositinal evolution of foreland basins in the southern zone of the Asia segment of the Tethyan Realm,essential geological elements,and oil and gas enrichment with a focus on the main factors controlling the difference of oil and gas enrichment in the study area.The results show that:(1)the study area has experienced five stages of tectono-sedimentary evolution,which are pre-Proto-Tethyan syn-rift stage,Proto-Tethyan to Paleo-Tethyan intra-cratonic sagging stage,Neo-Tethys syn-rift stage,Neo-Tethys passive continental margin stage and foreland basin stage.The three typical basins in the study area have the characteristics of"different time and synchronal sequence".(2)The Silurian petroleum system,Jurassic petroleum system,Cretaceous/Paleogene composite petroleum system and Paleogene petroleum system are the main systems developed in the study area.The former three petroleum systems are all developed in the Zagros Basin.In contrast,the dominant petroleum system is the Cretaceous/Paleogene composite system in the Potwar Basin and Paleogene system in the Assam Basin;(3)494 oil fields and 143 gas fields have been discovered in the study area,with proven and probable recoverable reserves of 3038.04×10~8boe.The distribution of oil and gas resources is highly uneven.The Zagros Basin not only hosts the largest share of the discovered oil and gas reserves,accounting for 98.23%of the total in the study area,but also has the highest oil and gas reserves abundance,which is53.97×10~8boe/km~2,much higher than 4.03×10~8boe/km~2in the Potwar Basin and7.75×10~8boe/km~2in the Assam Basin;(4)The differential enrichment of oil and gas in the study area is mainly controlled by four factors:the quality and distribution of source rocks,reservoir petro-physical properties and scale,the development and distribution of traps and regional cap beds,and the effects of tectonic deformations in a particular basin.