| Oil and gas resources are indispensable strategic resource in human life.As an important supplement and component of oil and gas resources,oil sand provides an important guarantee for national economy,social development and national security.Based on theories and methods of sedimentology,petrology,oil sand geology,geochemistry,and geophysics,and on previous geological reports and published literatures,as well as a lot of achievements from oil sand related projects the author participated,this thesis systematically investigates the sedimentary system,the detailed characteristics and the accumulation conditions of oil sand reservoir in the Junggar basin.Finally,the main controlling factors and accumulation rules of oil sand are discussed.The relevant research is of great scientific significance for understanding the regional oil sand accumulation law and the future exploration and development of oil sand.The following achievements are obtained from this research:(1)Sedimentary facies have an obvious influence on the macroscopic distribution of oil sand reservoir.The underwater distributary channel in the front of braided river delta,sand sheet,and the microfacies sand bodies in braided river island is the best facies belt for oil sand reservoir,which are developed in large areas with large sedimentary thickness and good reservoir property and permeability.By contrast,the alluvial fan gravel braided river channel,underwater distributary channel of fan delta front and braided river channel have poor reservoir storage ability.Sedimentary microfacies such as interdistributary bay and littoral shallow lake are not conducive to the development of oil sand reservoirs.(2)The oil content of oil sands depends on the lithology,physical property and heterogeneity of reservoirs.The lithology of Qingshuihe Formation is mainly composed of fine sandstone,while that of Qigu Formation,Badaowan Formation and Kelamayi Formation are mainly of medium sandstone.There is a positive correlation between the permeability and porosity.It is found that the permeability of oil sand is positively correlated with its porosity,and oil content is positively correlated with the permeability of oil sand.The porosity and permeability are the highest in the fine sandstone reservoir,followed by those of medium and coarse sandstone reservoir.Accordingly,the oil content is the highest in the oil sand of Qingshuihe Formation,followed by that of the Badaowan Formation,Qigu Formation and Karamay Formation.(3)The accumulation of oil sand is strongly influenced by the tectonic activities,and the distribution of oil sand reservoir is controlled by the fault and unconformty.The destruction of the original reservoir by tectonic activity is conducive to the formation of oil sand,but on the other hand,continuous tectonic uplift is not conducive to the preservation of oil sands with high oil content.The fault system can be used as both the transport channel of original oil and the barrier layer of oil sands accumulation.The oil sands with high oil content are primarily distributed in the vicinity of the drainage fault and the unconformity surface of the marginal slope zone,with the highest oil content accumulating in the "criss-cross" of faults.Furthermore,the oil sands generally have high oil content and large scale near the overlapping area of unconformity surface.(4)The accumulation of oil sand is highly correlated to the burial depth,and shallow burial depth is not essential but favorable for oil sand formation.The depth of oil sands in the Wuerhe,Baijiantan,Heiyoushan,and Hongshanzui area are respectively 130 m,160 m,100 m,and 50 m.It is thought that oil sand with high oil content is distributed in depth of 30 m to 150 m in the studied area.The oil sands of each group are characterised by homogeneous rhythm and local accumulation with the increase of buried depth.(5)The main controlling factors of oil sand accumulation are abundant oil sources,matched migration channels,favorable reservoirs,serious destruction and good preservation conditions,and emphasis should be focused on the destruction,reservoir conditions and preservation conditions.The high-quality source rocks of Fengcheng Formation,Wuerhe Formation,and Jiamuhe Formation in Mahu depression provides oil source conditions for oil sand mineralization.The migration channels of fault,unconformity as well as blanket sand are matched and interconnected to form an effective dispersal system and control the migration path of oil sands.The sedimentary microfacies and physical conditions controls the degree of heterogeneity of reservoir sand bodies and determines the quality of oil sand accumulation.The comprehensive destruction of biodegradation and oxidation by water washing controls the geochemical properties of oil sands.The four kinds of reservoir and cap combination as well as four types of cap formation control the preservation conditions of oil sands and directly affect the oil content of oil sands.(6)Oil sand is a typical destructive reservoir,and oil sand accumulation is the coupling process of "oil-transportation-storage-breaking-preserve".The oil sands are developed in the ultra-stripping belt in the northwest margin of the Junggar Basin.Along the migration channel,conventional oil,heavy oil and oil sand occurs transitionally,forming a Z-shaped migration and accumulation,and the accumulation model belongs to a complex slope migration type.Verticaly,the oil sands are mainly distributed in the middle Triassic Kelamayi Formation,lower Jurassic Badaowan Formation,upper Jurassic Qigu Formation and lower Cretaceous Qingshuihe Formation.Horizontally,the oil sands in the studied area are mainly distributed in the Wuerhe,Baijiantan,Heiyoushan and Hongshanzui area.The oil sands of Qingshuihe Formation and Qigu Formation are mainly developed in Wuerhe area,the oil sands of Qigu Formation and Badaowan Formation are mainly developed in Baijiantan area,and those of Badaowan Formation and Karamay Formation mainly in Heiyoushan area.The oil sands in Wuerhe area are the "sweet spot" of the study area. |
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