Research On Oil Shale Characteristics And Metallogenic Mechanism Of Cenozoic Fault Basins In Eastern Northeast Region

Oil shale is a kind of important alternative source of energy,which can be used to obtain shale oil and relevant products through dry distillation, generate electricity, keep warm and transport as fuel, and produce building materials, cement and chemical fertilizer, or extract chemical product and metal from the burned waste residue (undergoing oil refining and power generation).Currently, with the increasing demand for energy resources, oil shale has aroused the people's great attention by the world owing to its enormous, potential and comprehensive value. And a meridian of oil shale exploitation is triggered again. However, behind the quick growing up of oil shale industry, enormous disharmony exists. At present, oil shale is discovered often by outcrop and drilling exploration due to weak metallogenic theory. We can not predict regularity of oil shale formation, and proceed reasonable resource evaluation of oil shale through analogy method. On this background, paper focuses on studying the metallogenic mechanism of oil shale.The basic theory of oil shale has never been studied systematically in China. In the thesis, thanks to the poor data of previously published, we choose Cenozoic Fushun Basin, Huadian Basin and Yilan Basin ,which have representative metallogenic mechanism and favourable research condition, in eastern Northeast region as target areas for investigating metallogenic mechanism of fault basin. Moreover, during the study of domestic oil shale, we utilized comprehensively sedimentology, sequence stratigraphy, palaeolimnology, palaeoclimatology, geochemistry, palaeontology and gitology in order to determine metallogenic mechanism of rift basin.According to comprehensive analysis including Sr/Ba ratios, palaeontologic fossils (Gastropoda, Shell, Frog, etc.), TiO2/K2O ratios, and the characteristic of clay mineral assemblage, the study reveals that oil shale members in Fushun Basin and Yilan Basin are deposited in freshwater lake environment, oil shale members in Huadian Basin are deposited in brackish lake environment, whereas coal-bearing and oil shale members in Yilan Basin are deposited in lacustrine bog environment with mildly brackish water. Organic types of oil shale in target areas consist of the types I, II1 and II2 kerogen. Among them, the type I kerogen is developed in Huadian Basin and low-grade area in Fushun Basin, the type II1 kerogen is developed in high-grade area in Fushun Basin, coal-bearing members and oil shale members in Yilan Basin, and the type II2 kerogen is only developed in oil shale members in Yilan Basin. In brief, Oil shale in fault basin in China is characterized by hybrid origin.Based on mineral features of rocks , geochemical ratios of elements (Ni/Co and Sr/Ba ratios, lanthanonδEu, and positive anomaly of Ce), facies indicator, organic geochemical characteristics (organic matter types, normal paraffin hydrocarbons and isoprenoid), it is confirmed that oil shale in target areas is deposited in semi-deep-deep lake, shallow lake and lacustrine bog environment.The research on the equilibrium among the organic matter imput,organic preservervation,inorganic matrix dilution of the three basins indicates that the organic matter of the oil shale has three origins: self-productivity of lake,terrigenous organic matter and aquatic plant. And oil shale has three preservervation forms: water body stratified , fast accumulation of organic matter and water-enclosed .Import of inorganic matrix play a role of dilution in the process of oil shale formation. Optimum organic enrichment occurs where production is maximized and destruction and dilution are minimized. However, frequent gravity flow is unfavorable to the oil shale formation. That is why the depositional environments of Fushun and Yilan Basins is the same, but their oil shale quality is different (Fu shun oil shale with high oil yield but Yilan oil shale with low oil yield).Above regularities are not only reveals the conditions of oil shale enrichment, but also will be an inspiration for the hydrocarbon source rock research, for that oil shale is the best hydrocarbon production potential of the source rocks.According the analysis of palaeoclimate, palaeosedimentary environment and palaeotectonics of oil shale formation, there are some rules as follows: palaeoclimate and palaeotectonics are the most important controlling factors. The palaeoclimate of the brackish lake controls the oil yield and thickness according affecting the lake chemical nature and lake level. Brackish lake forms in the semiarid, subhumid, and low precipitation climate and the climate fluctuation directly controls the lake level goes up and down. The flood times controls the oil shale layers, and the flood scale controls the oil yield and the thickness. From the first to the last flood, oil yield and the thickness begins ever higher and thicker separately. The oil yield and the thickness change little in early high system tract, and begin decrease in the late high system tract. The palaeoclimate of the fresh lake controls the oil yield and thickness according affecting the productivity of lake and organic preservervation. In the Warmth and humid climate, nutritive substance come from the land by the abundant precipitation accelerate the lake productivity greatly. The organic matter is well preserved in the stable stratification deep lake. So the oil shale formed in the fresh lake often has big thickness and middle oil yield. While there is a abnormal occurrence in Yilan basin with low oil yield for the frequent gravity flow. Basin-controlling faults and synsedimentary faults control the thickness and oil yield of oil shale. Those rules of mineral-formation conditions will provide theory references for the later resource evaluation and oil shale mineralization prediction.Based on the sequence stratigraphy theory, this is the first time to study the oil shale metallogenic in the sequence stratigraphy framework. In the chrono-stratigraphic unit, oil shale mainly distribute in the Transgression system tract and High system tract,and is controlled by integrated factors include climate, tectonics, fluctuation of lake horizon and so on.Oil shale in the Transgression system tract has the following features: thin-medium thickness, poor-medium oil yield, mixed tape II1-II2 kerogen. Oil shale in the High system tract has the following features: medium-thick thickness, medium-high oil yield, predominantly tape I kerogen. Among those conditions, the climate is the mainly controlling factor. This oil shale mineralization mechanism of the faulted basin will enrich the whole oil shale metallogenic theory greatly.In the Transgression system tract and High system tract, different basins express different mineralization characteristics for different oxidizing-reducing atmosphere, production condition, water chemistry condition and so on. This paper covers palaolake research, which further indicates the distribution regulation of thickness, oil yield, and associated mineral of oil shale in the Transgression system tract and High system tract of every basin. Among those conditions, water chemistry is the major controlling factor for the different mineralization rules of the three Basins. Whereas, paper proposes three mineralization models: freshwater lake mineralization model, brackish lake mineralization model, salt water lake mineralization model. These models will be important to oil shale resource evaluation and multi-purpose exploitation.