Structure of the Cenozoic bottom unconformity zone in Jizhong depression and its significance on hydrocarbon accumulation

The bottom unconformity of Cenozoic is well developed in Jizhong Depression.As the favorable place of dissolution,the unconformity zone has the function to serve as the hydrocarbon migration pathway and accumulation place.The structure of the Cenozoic bottom unconformity zone is studied by means of geological and geophysical method.The space structure of unconformity zone includes three parts: water flooded layer,weathered clay and semi-weathered rock,flow pore below the unconformity is mainly composed of pores,caves,and fractures,while layered permeable body above the unconformity mainly consists of pores.The semi-weathered rock can be divided into vertical vadose zone,horizontal underflow zone and deep karst zone,hydrocarbon migration and accumulation occurred mainly in vertical vadose zone and horizontal underflow zone.The development of unconformity zone can improve physical property of carbonate reservoir,form favorable migration pathway,reservoir-cap rocks assemblage and unconformity trap,which has great significance in hydrocarbon migration and accumulation.