Characteristics and hydrocarbon enrichment rules of transfer zone in Fushan Sag,Beibuwan Basin

The Fushan Sag is a secondary tectonic unit in the southeastern coast of the Beibuwan Basin which is located in the northwestern of the South China Sea.Based on the interpretation of the 3D seismic data and the contrast of tectonic characteristics between the western and eastern area,a transfer zone is found in the centre of the sag.The transfer zone was mainly developed in the Palaeogene Liushagang Formation and located above the Huachang low uplift at the intersection of the western and eastern areas.Two extensional structure systems were developed respectively at two lateral sides of the transfer zone.There were significant differences on the strike of faults and structure styles between the two systems.The formation of the transfer zone was caused by the existence of strike-slip process with the development of flower structure.The transfer zone is the entrance of source and controls the distribution of sand and deposition system through the counseling function of regulation faults.The deep antithetic fault system is favorable to form various kinds of traps and control the most petroleum accumulation distribution.The complex structure system contributes to the formation of the fault block reservoir and fault-nose pool and improves the quality of sandstone reservoir.The transfer zone holds distinct hydrocarbon accumulation with two oil resources and various types of reservoir.In all,the transfer zone has a good control effect on hydrocarbon accumulation and has good prospects for hydrocarbon exploration.