Abstract: The relations among the geological factors of composite petroleum system are set forth from the view point of petroleum system in Santanghu basin. Three petroleum systems exist which can be divided into upper, middle and lower sections. The middle petroleum system, the most important one, is characterized by single source, multi-reservoir and multi-stage pools. The hydrocarbon source comes from Lucaogou formation(Permian), including two stages of reservoirs due to early Indosinian movement and late Y anshan movement, dominated by the former. The major hydrocarbon distribution area is Permian hydrocarbon-generating center surrounded with Heidun-Niujuan -Mazhong zone ir Malang sag. V ertical and short- distance lateral hydrocarbon migrations are suggested and accompanied with high-filling capacity. The major reservoirs are Lucaogou formation in Permian and Xishanyao formation in Jurassic,with high efficiency in drainage and accumulation, being the most important petroleum system for its abundant hydrocarbon resources. The upper petroleum system's hydrocarbon comes from Xiaoquangou formation in Triassic, where the key stage of forming reservoirs is late Yanshan movement episode, lasting from Middle-I ate Triassic to the end of Cretaceous, while the preservation stage in from Late Cretaceous to present. The hydrocarbon is mostly distributed within the scope of matures source rock in Triassic of Tiaohu sag, and centered in Lower Jurassic vertically.

Key words: (Santanghu basin), Petroleum System, Oil and gas reservoir formation, Oil generation time, Migration time, 0il and gas migration, Oil and gas accumulation belt