The unconformity characteristics and stratigraphic reservoir-forming model of Chezhen sag

Affected by teetogenesis,there were several struc- tural elevations and depositional breaks in Chezhen sag. At present,six periods of main stratigraphic unconformi- ties are preserved.For the different fracture systems and reservoir forming conditions between Trertiary system and pre-Tertiary system,Chezhen sag has binary geologic structure,and the hydrocarbon accumulation and reser- voir-forming were chiefly controlled by the widely dis- tributed Yanshan unconformity surface.The unconformi- ty may improve the reservoir physical property of the un- derlying formation,which can act as the channels of the hydrocarbon lateral transportation,form the stratigraphic traps and provide the location for the hydrocarbon accu- mulation.There are three types of stratigraphic hydrocar- bon reservoirs in Chezhen sag,namely the buried hill hy- drocarbon reservoir(the basement hydrocarbon reser- voir),the stripped hydrocarbon reservoir and the onlap hydrocarbon reservoir,separately developing in the differ- ent oil-bearing series and having different forming char- acteristics and distribntion rule of hydrocarbon reservoir. For the preferable exploration potential,the stratigraphic stripped hydrocarbon reservoirs and onlap hydrocarbon reservoirs should be the main exploration direction for Chezhen sag in the future.