Genetic Classification and Hydrocarbon Potentiality of Passive Rift Basins

The concept and genesis of rift basins were deeply studied since 1890s, but most of them were focused on the active rift basins, and less on the genetic mechanism and classification of passive rift basins. Based on the exploration practice in the passive rift basins in the Central-Western African region and the analogy study on the active and passive rift basins, this paper analyzed the geodynamic mechanisms and basin forming processes of the two types of rift basins. The author summarized that the passive rift basin was formed by the crustal extension induced by non-mantle upwelling, and five types of passive rift basins were divided based on the basin forming stress field, such as intra-cratonic extensional passive rift basin (ICE Passive Rift), post-orogenic extensional rift passive basin (POE Passive Rift), strike slip fault related passive rift basin (SSF Passive Rift), collision-induced extensional passive rift basin (CIE Passive Rift) and extensional passive rift basin at the trailing edge of thrust belt (TET Passive Rift). According to the statics, there are 93 main passive rift basins in the world, including 42 ICE Rifts which were mainly distributed in the northern part of North Sea and North Africa, 18 POE Rifts which were mainly distributed in the Central Asia Orogenic Belt, Tethys Orogenic Belt and Cordillera Orogenic Belt, 13 SSF Rifts which were mainly distributed on both sides of the Central African Shear Zone and the San Andreas Shear Zone in North America, 10 ICR Rifts which were mainly distributed around the Tethys Belt and 10 TET Rifts which were mainly distributed within the Tethys belt. According to the results of CNPC’s internal global oil and gas resources assessment in 2016, the total discovered oil and gas reserves of the main passive rift basins in the world account for 25.3% of the total discovered reserves in the rift basins, the undiscovered oil and gas resources are 15.69 billion tons of oil equivalent which are 15.7% of the total undiscovered resources in the rift basins. Although many passive rift basins in the world have been highly explored, there are also some basins with large undiscovered resources and low exploration degree, such as Melut, Bongor, East Niger basins in Africa, Cuyo basin in South America, Cauvery basin in Indian East Coast, Menam basin in Southeast Asia and Canning basin in Australian.