Effect Of The Tibetan Plateau Uplift On The Hydrocarbon Accumulation Of Cenozoic Qaidam Basin

Qaidam Basin is the only continental petroliferous basin in Tibet Plateau that has discovered large-scale reserves,built oil and gas fields.However,the control of the uplift of Tibet Plateau on oil and gas accumulation in Qaidam Basin has not been thoroughly analyzed.Therefore,it is of great theoretical significance and exploration value to study the relationship between the uplift of the Tibet plateau and the formation of oil and gas pools in Qaidam basin,which can not only promote the new understanding of uplift and basin control and reservoir control,enrich the theory of petroleum geology in plateau basins,but also contribute to the oil and gas exploration in plateau basins.Based on basin analysis,structural geology and petroleum geology,this paper aims at the scientific problems in the formation of Qaidam Basin and hydrocarbon accumulation,summarizing the rules of basin,hydrocarbon and reservoir formation.The controlling effect of the Tibet plateau uplift on the formation of the Qaidam basin is studied from the characteristics of the Tibet plateau uplift,and the controlling effect of the Tibet plateau uplift on the formation of oil and gas in the Qaidam basin is explored.The paper has achieved the following results.It is suggested that the formation and evolution of Qaidam Basin have the characteristics of "two stages","three center migration" and "differential compression-differential subsidence-differential denudation".Based on the study of the Meso-Cenozoic structural evolution of Qaidam Basin,the "two-stage" evolution model of the early Cenozoic partial scattered small fault depression and the late unified open large depression is established;Based on the comparison of sedimentary structural characteristics of different depressions,the differential evolution and regular migration characteristics of Cenozoic sedimentation center,sedimentation center and salt lake basin center are proposed;It is suggested that "differential compression-differential subsidence-differential denudation" is a significant feature of the formation and evolution of Qaidam Basin;It is pointed out that the evolution of Qaidam Basin is controlled by the uplift mechanism of "multi-stage,non-uniform and unequal velocity" of the Tibet Plateau.It is pointed out that the uplift of Tibet Plateau is the decisive factor for the late accumulation of oil and gas in Qaidam Basin."Late generation" : the uplift of the plateau has resulted in shortening and thickening of the basin crust,weakening of mantle baking and occurrence of cooling events have resulted in a decrease in geothermal gradient,slowing down the thermal evolution of source rocks and causing a delay in hydrocarbon generation;"Late trap" : The strong characteristics of the late uplift of the plateau resulted in the development of many large late tectonic zones in the basin,while the stages of uplift resulted in the final adjustment and shaping of the early structures from the late structures.Since Neogene,intense compression deformation has taken place,resulting in late formation or setting of different types of structural traps in different structural units,zones and different strata."Late migration" : the tectonic movement caused by the strong uplift of the plateau in the late period is not only conducive to the formation of new late-stage faults,but also can cause late-stage activities of some pre-formed faults,which are effective late-stage migration channels.At the same time,the abnormal high pressure generated by the strong compression in the late period also provides sufficient power for high-efficiency migration in the late period.It is the "three late" mechanism under the control of Tibet plateau uplift that determines the late accumulation characteristics of oil and gas in Qaidam basin.By analyzing the reservoir forming conditions and main controlling factors of four large oil and gas areas of 100 million tons in north Kunlun,Yingxiuling,Dongping and sebei,four late reservoir forming models are constructed: "contemporaneous structure,late finalization,fault step relay,late complex reservoir formation" in Kunbei area,"structural multi-stage superimposition,fault relay,late complex reservoir formation" in Yingxiongling area,"early and late structural superimposition,fault direct transmission,late complex reservoir formation" in Dongping-Jiandingshan area,"late structure,late hydrocarbon generation,self generation and self storage,late reservoir formation" in Tainan-Sebei area.A new scheme for classification of buried hills in Qaidam Basin is put forward,and evaluation and optimization criteria for buried hill zone are put forward.The basin buried hills are divided into four types: thrust controlled,strike slip controlled,paleogeomorphic and composite.According to the character of the controlled faults,the buried hills are further divided into 11 subtypes according to the characteristics of the paragenetic,syngenetic and epigenetic.The buried hill structural belt is divided into 3types: thrust controlled(fault controlled),paleouplift controlled(uplift controlled)and thrust and paleouplift controlled(fault uplift co controlled)Type);the evaluation and optimization criteria of "fault uplift sag" buried hill zone are established,and it is pointed out that Lenghu and Dafengshan areas are favorable directions for further exploration in buried hill area.