Tectonic Deformation Characteristics And Petroleum Geological Significance Of Peninsula Lake Area In Qiangtang Basin,Northern Tibet

As the most important oil and gas basin in Qinghai-Tibet Plateau,the Qiangtang basin has always been a hot topic in the geological study of the Qinghai-Tibet Plateau.The formation of the basin has undergone several tectonic movements.The collision between the Qiangtang and the Lhasa block in late Mesozoic,and the collision of the India and Eurasian plate in Cenozoic both have great influence on the tectonic pattern,and the formation and preservation of oil and gas of the basin.Therefore,the tectonic movements and the problem of hydrocarbon accumulation and preservation become the key to hydrocarbon evaluation in the basin.In this paper,combined with the results of two-dimensional seismic reflection,the field survey of the structures was carried out on the area of Peninsula Lake in northern Qiangtang.The division of tectonic units and tectonic layers in Peninsular Lake area was carried out to find out the characteristics of the deformation of study area,so as to explore the influence of tectonic events on structural deformation and their relationship with oil and gas.According to the characteristics of the surface structure and their distribution in different times,the study area is divided into three tectonic units,namely,the Yin Tian Lake fold belt,the Wujieliang-Qiangrenwenzaka fault fold belt,and the YinlongcuoDonghu fault fold belt.According to the structural elements in the study area,the direction of the mean principal compressional stress axis of the fold and fault is NNW or SN,which indicates that during the deformation process,the study area is mainly squeeze by the stress of North-South dirction,which is consistent with the stress state of the Qinghai-Tibet Plateau.The collision of the Qiangtang and Lhasa in the late Mesozoic caused strong deformation of the basin.The large trap structurs formed by Jurassic folds are basically stereotyped in this tectonic event,and the time is exactly the same as the first time of the formation of oil and gas.Besides,in the study area,the anticlines of Jurassic are large andvertical.Compared with the synclines,the wings of the anticlinesare usually tightly closed.It is beneficial to the preservation of oil and gas,and also,it provides a favorable trap structure for the next time of the formation of oil and gas.In the early Cenozoic,the collision of India and Eurasian plate produced multi-stage deformation.But the deformation is relatively weak,and after the Miocene,the basin is dominated by the overall uplift.Therefore,the tectonic movement has little transformation to the study area.Besides,compared with the time of the tectonic event,the second time of the formation of oil is late,so,the deformation has limited effect on the reservoir.Comprehensive analysis shows that the area of Peninsula Lake is a favorable area for the formation and preservation of oil and gas in the North Qiangtang.