Mesozoic Basin Evolution And The Exploration Of The Pre-Tertiary Petroleum In The Area Of Bohai Bay Basin

The Mesozoic basin of Bohai Bay basin experienced complicated geological development and serious reconstruction, and the research foundation is unsubstantial, that restricts the resources assessment and the exploration of the pre-tertiary oil and gas of Bohai Bay basin to some extent. So the restoration of the prototype basin of each structural period in Mesozoic, and the analyzing of the forming, evolution and the reconstruction, furthermore making certain the superimposition relationship of each structural period basin is the key to the exploration of the pre-tertiary petroleum of Bohai Bay basin.According to the unconformities, the Mesozoic of Bohai Bay basin can be divided into five structural sub-layers: lower to middle Triassic, upper Triassic, lower to middle Jurassic, upper Jurassic to lower Cretaceous, upper Cretaceous, then the characteristics of the lithology and the distribution were ascertained. Through the research on the evolution of the terrestrial peripheral orogenes, the deep faults and the geodynamics mechanism in Mesozoic, the geodynamics background of the basin evolution in Mesozoic were ascertained. On the basis of above analysis, through the detailed interpretation of the seismic sections, the activities of the main faults in Bohai Bay basin were studied using the fault activity velocity, and the development characteristics of the Mesozoic faults were ascertained. Furthermore, combined with the analysis of balanced cross section, extension ratio and the structural style of each structural period in Mesozoic, the Mesozoic structural characteristics in the area of Bohai Bay basin were analyzed. On the basis of above research, the Mesozoic basin evolution in the area of Bohai Bay basin can be divided into five periods: early to middle Triassic, a large-scale interior basin; late Triassic, the area of Bohai Bay basin was extruded and uplifted undergoing denudation; early to middle Jurassic, some small intermontane basin developed in the earlier period, from the middle to later period the drape-like deposition developed; late Jurassic to early Cretaceous fault basin developed mainly, various types of basin developed in various area, such as detachment rift, extension rift, inversion rift and strike-slip and pull-apart rift; late Cretaceous, the area of Bohai Bay basin uplifted wholly, only deposited in few lower area. Combined with the evolution in Paleogene, the superimposition relationship of each structural period in Mesozoic and Cenozoic were ascertained, the superimposition unit were defined in this thesis. Bohai Bay basin can be plot out into three large kinds and six small kinds of superimposition units. On the basis of above research, analyzed the petroleum conditions of pre-tertiary, studied the petroleum conditions of different kinds of superimposition, the difference of petroleum conditions of pre-tertiary of different kinds of superimposition units were summarized. Finally, the advantageous exploration areas were brought out on the side of the plot of the superimposition units: for Paleozoic, the superimposition units ofâ…¡2 andâ…¡4 are best, the superimposition ofâ… is better in case the Jurassic and Cretaceous deposited thinly and the reconstruction later was weak; for Mesozoic, the superimposition units ofâ… andâ…¡2 are best, the superimposition ofâ…¡3 is better in case the source rocks had come into the hydrocarbon-generation threshold, the reconstruction later was weak and the combination of reservoir and cap rocks was good.