Relationship Between Gas Accumulation and Structural Characteristics of Extensional-Shear Fault System in Yakela Fault Block

Through interpretation of 3D seismic data,the extensional-shear fault system in the Neogene in Yakela fault block has two main features of blocks distributed along east-west and zones distributed along north-south,which develops four fault structural styles,including stepladder fault structure,tilted fault block structure,graben-horst block structure and negative flower shaped structure.There are four trap structural styles associated with extensional-shear fault system,namely fault nose and faulted anticline,tilted fault block,reverse drag anticline and horst.The traps formed by the extensional-shear faults,whose main active period are Suwiyi-Jidike epoch of neogene,well match the periods of hydrocarbon formation reservoirs.The hydrocarbon vertical migration along the extensional-shear fault appears clearly in the process of hydrocarbon accumulation in Cretaceous and Tertiary,but lateral sealing of the extensional-shear fault is vital in the process of pools of petroleum accumulation.