MAIN CONTROLLING FACTORS AND ACCUMULATION MODELS OF HYDROCARBON IN WUSHI SAG, BEIBU GULF BASIN, SOUTH CHINA SEA

The Wushi sag, characterized by high quality oil-gas source rocks, has excellent hydrocarbon source conditions for oil and gas accumulation. Through analysis of the controlling factors of hydrocarbon accumulation in the sag, the authors put forward two kinds of accumulation models for the different tectonic units of the Wushi sag. Since Paleogene, multiple sets of different types of sandstone reservoir and overlying mudstone have formed as good reservoir-cap assemblages in the Wushi sag on the one hand; and on the other hand, the major fractures controlled the migration-accumulation pattern of generated oil and gas. The deposition of sandstone together with the faulting formed a complex oil and gas transporting system. The long-term different generation of oil and gas controlled distribution of oil and gas in space. As the results, there formed two different hydrocarbon accumulation models:lateral migration and limited vertical adjustment within the source area in the eastern Wushi sag and vertical migration-limited horizontal adjustment near the source area in the central WuShi sag.