南海北部湾盆地乌石凹陷成藏主控因素与成藏模式

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

乌石凹陷发育优质烃源岩,具备优越的烃源条件,为油气的富集成藏提供了重要的前提。通过对乌石凹陷成藏主控因素深入分析,提出乌石凹陷不同构造单元的两种成藏模式。自古近纪以来,一方面乌石凹陷沉积多套不同类型的砂岩储集体,与上覆泥岩形成良好的储盖组合;另一方面,凹陷内主干断裂的发育演化不但控制了前期烃源岩的差异性沉积,同时还控制了后期已生成油气的运聚格局。在这一背景下,断裂活动与砂岩的沉积充填形成复杂的油气输导体系,加之长期差异性的油气生成控制了油气的空间分布,形成了乌石凹陷东区源内横向运移-垂向有限调节与乌石凹陷中区近源垂向运移-横向有限调节两种不同的油气成藏模式。乌石凹陷这一成藏特征的发现对后期勘探部署具有指导意义。

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.