Jurassic Tectonic Evolution And It's Control Over Hydrocarbon Accumulation In The North Margin Of Qaidam Basin

Based on the comprehensive research on petroleum geology in the northern margin of Qaidam basin, this paper analysed the regional geology, the coupling mechanism between Jurassic strata and regional structure, and established the tectonic-sedimentary and buried characteristics. Combining with tests and data, the paper revealed the trend of temperature gradient, and the hydrocarbon generation evolution of Jurassic source rocks; at the same time, we studied the tectonic evolution and its control over sedimention and oil-gas, revealing the region, time, depth and phase which were benefical to hydrocarbon generation. All these can be considered in oil and gas exploration.Research area is located in the northeast of Qaidam basin, that is, west of Hongshan. The tectonic development, combination form, distribution, scale and deformation characteristics are various in different areas, but there are some common grounds, compressional structure (compression-shear) is the main character. The area formed the tectonic framework of uplift and depression interphase from the basement, which was controlled by the three groups of faults with strike of NWW-NW, NE-NNE and nearly NS. The evolutions of Altyn fault belt, Qilian orogenic belt and east Kunlun orogenic belt are related to surrounding plates movement, and all the 3 orogenic belts controlled the evolution of the basin.Based on the analysis of seismic sections, results of tests and regional tectonic setting, tectonic evolution of Mesozoic and Cenozoic is divided into five stages: fault sag stage in early- middle Jurassic; depression stage in late Jurassic– Cretaceous; uplift-erosion stage in late Cretaceous; depression stage in Paleogene; squeezed sag in Neogene. Controlled by the extension of and postorogenic phaseand self sedimentary loading, the Jurassic was formed, but the complexty of structure was the result of later activities and reformation. The depocenter atrophied and transferred from SW to NE controlled by structure activities.Since deposition, Jurassic source rocks have experienced two stages of tectonic and burial history, which were Yanshan stage and Himalayan stage. Different buried stage and depth lead the difference of hydrocarbon generation evolution in various structure belts, most of areas have one hydrocarbon generation stage, and only some have two. The Himalayan stage (E3-N1) with great depth and high maturity of source rocks is the main hydrocarbon generation stage.The activities of Yanshan stage and Himalayan stage controlled the sedimention of Jurassic sourcks, formation of traps and migration channels, which formed the reserviors based on the rational allocation of time and space. Based on the research, we can see that hydrocarbon generation center and structure avtivities are the key factors which control the reservoirs. Hydrocarbon generation center determined the scale of oil field; structure avtivities can destory the reservoirs and lead the oil-gas dissipation. Therefore, the relatively stable structure area near the Hydrocarbon generation center could be the best exploration target.