苏丹福拉凹陷转换带特征及其与油气的关系

Transfer zone character and its relationship to hydrocarbon in Fula Sag,Sudan

Muglad盆地位于中非苏丹共和国南部,是在中非剪切带剪切应力场背景下形成的被动裂谷盆地。福拉(Fula)凹陷位于Muglad盆地东北部,面积约5000km2。福拉凹陷转换带位于中部构造带,是重要的含油气构造带。该转换带开始形成于早白垩世第一裂谷期,在晚白垩世第二裂谷期,断裂再次活动,转换带基本定型;在古近纪,第三裂谷期对整个转换带构造格局没有大的影响,仅发育了一些调节小断层,使转换带构造复杂化。转换带对油气聚集的影响贯穿油气成藏的整个过程。转换带可以形成有利于油气聚集的构造或圈闭;转换带将沉积区分成彼此分隔的洼陷,控制富含有机质沉积物或储集砂体的分布;转换带密集发育的断裂系统为油气的运移和聚集提供通道。

Muglad Basin, southern Sudan, is a passive rift basin resulted from the extensional tectonics of the dextral shear stress field in the Central African Trans-current Slip Zone. Fula Sag of 5000km^2 is located in northeastern Muglad. Fula Transform Zone in the middle structural zone is formed during the first rifting phase in Early Cretaceous. During the second rifting phase in Late Cretaceous, faults reactive and the zone is finalized. During the third rifting phase in Paleogene, the tectonic framework of the zone isn＇t changed and only small accommodation faults are developed. The effect of the zone to hydrocarbon accumulation exists in the whole reservoir-forming process. The transfer zone may form structures or traps that are prone to hydrocarbon migration and accumulation. It controls the distribution of organism-rich sendiments or sandbodies by dividing the depositional area into isolated subsags. The dense faults in the zone provide channel for hydrocarbon migration and accumulation.