Tectonic Evolution And Its Control On Hydrocarbon Accumulation In Tainan Sag

Tuha Basin is one of the most petroliferous basin and a typical multi-cycle superimposed basin which is located between Bogda Mountain in the north and Jiaoluotage mountain in the south. Therefore the tectonic stress field is complex and structural features of each period are different, which has an important influence on hydrocarbon accumulation of each period. Tainan Sag is a structure unit of Tuha Basin, the Permian and Triassic System of which are important exploring field. As a result, it is of great significance to recognize structure evolution and its control on oil accumulation in Tainan Sag for the guidance of oil-gas exploration of Permian and Triassic System in Tainan Sag.Because of Huoyanshan fault making the footwall structure complex and seismic quality bad, the paper established triple fault combination mode and discover three big fault zones: Huoyanshan basement fault zone, Lubei fault zone, Lunan fault zone and Kubei fault zone. These fault zones separate the sag into eight structure unit.According to tectonic evolution sections, there are five periods of tectonic evolution, which are fault depression stage during Early-Middle Permian, thrust reverse stage during Late Permian, strong thrust fold stage during Triassic, stable sedimentation during Jurassic-Miocene and adjustment reconstruction stage during Pliocene to the present.Paleostructure of the Permian and Triassic system during hydrocarbon accumulation period are restored. The control of tectonic evolution on oil accumulation of the Permian and Triassic system in Tainan Sag shows in three respects: â‘ Paleostructure in depositional stage controls the distribution of sedimentary system. Tainan Sag was west high and east low during Early-Middle Permian and west low and east high since Late Permian, which influence the source direction. â‘¡Paleostructure before hydrocarbon accumulation period offer benefit trap for oil to accumulate in Tainan Sag. There are back thrust anticline traps in Lukeqin fault horst zone, reverse fault block traps in the footwall of Huoyanshan basement faults, Lubei and Kubei faults and anticline-unconformity traps in Huoyanshan fault horst zone. â‘¢Paleo structure during hydrocarbon accumulation periods controls dominant migrating channel. There are seven structure ridge in the Permian connecting from source area to Tainan Sag which controls dominant migrating channel of oil. There are two structure ridge in Triassic in Lukeqin fault horst zone.