POLYCYCLIC EVOLUTION AND PETROLEUM ACCUMULATION IN THE WEST OF CHINA

Regional tectonic framework of the vast northwest area identified by 2 lithosphere fractures of Eerqisi-Deerbugan and Kangxiwa-Longmucuo-Lancangjiang is composed of polycyclic orogenic belt and ancient continental segment with different size and characteristics in the Kasakstan and Ancient China continental segments,belt-like in the south and north,block-like in the east and west.Bounded with early Hercynian movement,late Hercynian movement and middle Yanshan movement,regional tectonic framework and basin evolution can be divided into 4 cycles: the Sinian-Middle Devonian open-close cycle,under Ancient Asian Ocean environment;the Late Devonian-Middle Permian open-close cycle under Ancient Tethys Ocean environment;the Late Permian-Late Jurassic cycle under Tethys Ocean environment and the basin cycles since Cretaceous under present ocean environment.According to cycle characteristics and evolution degree,the west basins can be divided into 6 types such as mild conversion and polycyclic basin,etc.In this paper,the complicated space distribution of source generated in different stages,and the course of multi-stage hydrocarbon generation,chargement and accumulation in complicated deposition and thermal systems are discussed.The previous concept and content of multiple petroleum system are improved;a concept of petroleum accumulation unit is proposed and used in the summarization of accumulation element and course in different part of multiple petroleum system.Static condition and dynamic course of accumulation in 2 basins are analyzed based on dissection of previous reservoirs.An accumulation model is made.Petroleum accumulation in the west basins is characterized by multi-source and multi-stage.Formation,destruct and reformation of 2 types of various cause reservoirs and capping system result in sets of reservoir and cap.In different zone,types of trap compound horizontally and vertically.A general summary of "regional control of the Ancient Asia and Tethys→polycyclic basin evolution and changing superposition transformation→multi-facies oil and gas from multisource and multi-stage hydrocarbon generation→types of multiple petroleum accumulation belt in multiple petroleum system" is put forward.