Fracture characteristics and hydrocarbon accumulation of western steep slope in northern sag of Miaoxi

Northern sag of Miaoxi is a loop-shape sag in the east of Bohai bay basin.The western steep slope belt in profile presents different combination features,and develops different boundary fracture structure types(simple type and compound type).The compound fracture structure includes seat type,horsetail type,cascade type and complex fault terrace zone.Under the fracture control,different structural styles have been developed,namely normal drag structure,reserve drag structure and rolling anticline structure.The formed trap types include fault nose,fault block,inverse traction anticline and the rolling anticline.The hydrocarbon migration and accumulation are controlled by fracture structure,while the horsetail and cascade structure type are advantageous to vertical hydrocarbon channeling.Affected by Poping,the migration ability of seat structure type is poor.Therefore,the reasonable matching between fracture structure and trap matching is the key to the formation of hydrocarbon enrichment blocks.