Abstract:

Caohu Sag is located in the northern extensional part of Manjiar Depression,North Tarim.The main source rock is the Cambrian Ordovician carbonate rock,and the major period of oil generation in Cambrian was in Middle Caledonian Late Hercynian period;that of Ordovician was Hercynian Yenshan period.The source rock of the above mentioned periods used to generate and expel large amount of oil and gas.The oil and gas migrated respectively in Late Paleozoic Early Jurassic and Early Miocene Quaternary along Cambrian and Ordovician sediments to the west,north and east sides.The northern and eastern parts of the sag uplifted intensively during late Hercynian,the erosion lasted for 40 Ma.As a result,not only the Permian sediments there were eroded completely,but also the oil and gas that had generated before escaped along faults.That is why more than ten wells drilled there are all dry.As for the Carboniferous and Triassic traps formed on the slope between Caohu sag and Ackule uplift,they should be taken as targets of oil and gas exploration since they formed earlier,underwent small damage,oil and gas there have seldem escaped.

Key words: Caohu Sag, petroleum system, source rock, oil gas migration, exploring direction