Evolution Of Structure-Deposition And Characteristics Of Hydrocarbon Accumulation In Mesozoic Of Zhanhua Sag

Petroleum exploration status at present and its developing trend showed that the keyfactor to realize strategic production replacement is to emphasize exploration in difficultareas such as reconstructed basin and residual basin. Mesozoic is residual basin in Jiyangdepression. Compared with Tertiary in Kainozoic, Mesozoic is more complicated instructure with low exploration and investigation degree, but existing exploration resultstill indicated big potential. By way of integrated geology, geophysics and fluctuationanalysis of sedimentary basin, based on stratigraphic division and correlation, the paperreestablished Mesozoic prototype basin in Zhanhua sag for the first time. Sedimentaryfeature and reservoir character were studied systematically, and character of oil-gasreservoir and its control factors were analyzed. The paper divided exploration units moredetailed, and clarified reservoir types and features in different superposition unit. Thischanged blindfold concurrent exploration to purposeful exploration.Mesozoic in Zhanhua sag can be divided into Fangzi formation, Santai formation ofJurassic and Mengyin formation, Xiwa formation of Cretaceous. Angular unconformity orparallel unconformity was discovered between either two adjacent formations. Regionalangular unconformity was found between Jurassic and Cretaceous. Distribution ofMesozoic basin was controlled by bottom fault strike to NW-SE. Evolution of the basinexperienced 2 creation periods and 3 structural alterations. It is flexural basin extended tonortheast in early and middle Jurassic, then changed into rift basin controlled bystrike-slip movement in late Jurassic and early Cretaceous, and at last the basin upliftedwholly during late Cretaceous. Superposed with Cenozoic, the sedimentations can bedivided into 4 structural superposition units: unit uplift in Mesozoic and Cenozoic, unitdepressed in Mesozoic and Cenozoic, unit uplift in Mesozoic and depressed in Cenozoic,and unit depressed in Mesozoic and uplift in Cenozoic.Mesozoic in Zhanhua sag is continental sedimentation featured by alluvial fan～fluvial (alluvial plain) ～delta～lacustrine system. The basin experienced 2 cyclictransgression and regression. Sedimentary facies and unconformity surface are factorscontrolling development of reservoir bed. Xiwa formation is the most favorable reservoirbed, and Mengyin formation and Santai formation are in the second place. Good reservoiris mainly pebbled sandstone and sandstone in fluvial facies and delta facies influence byunconformity and fault.There are 2 kinds with 6 types of oil gas reservoir. Different reservoir combinationswere developed in different structural superposition units. Self-generation self-storagestratigraphic gas reservoir combination and Cenozoic-generation Mesozoic-storageunconformity oil-gas reservoir combination developed in unit depressed in Mesozoic andCenozoic. Self-generation self-storage stratigraphic gas reservoir combination,Cenozoic-generation Mesozoic-storage unconformity oil-gas reservoir combination andCenozoic-generation Mesozoic-storage structural oil-gas reservoir combination developedin unit uplift in Mesozoic and depressed in Cenozoic. Self-generation self-storagestratigraphic gas reservoir combination, Cenozoic-generation Mesozoic-storageunconformity oil-gas reservoir combination and Cenozoic-generation Mesozoic-storagestructural oil-gas reservoir combination developed in unit depressed in Mesozoic anduplift in Cenozoic. Reservoir forming conditions in unit depressed in Mesozoic and upliftin Cenozoic and unit uplift in Mesozoic and depressed in Cenozoic are the most favorable,and they are important exploration orientation in the future.