Study On The Characteristics And Model Of Natural Gas Accumulation In The Northern Tectonic Belt Of Kuqa Depression

Based on the full use of outcrop profile,drilling data,etc,through the methods and technologies of petroleum geology and oil and gas geochemistry,this dissertation analyzes the evaluation of source rocks in the northern structural belt of Kuqa Depression,the genesis and analysis of natural gas geochemical characteristics,reservoir characteristics,oil and gas filling time,fault caprock combination characteristics and their influence on reservoir formation.Based on this analysis,the reservoir forming types of gas reservoir solution are divided,the differences of main controlling factors of different gas reservoir types are analyzed,three reservoir forming models are established,and the favorable exploration direction is pointed out.It is of great significance for the future exploration and development of oil and gas reservoirs in Kuqa depression.The main research results are as follows:（1）Aiming at the problem of gas generation potential of source rocks,the hydrocarbon generation potential of source rocks in the northern structural belt of Kuqa depression is evaluated by integrating organic geochemical experimental analysis such as total organic carbon（TOC）experimental test,rock Eval pyrolysis analysis of source rocks,vitrinite reflectance（Ro）of source rocks,chloroform asphalt"A"extraction of source rocks and maceral composition of source rocks.The results show that the mudstone,carbonaceous mudstone and coal-bearing source rock developed in the northern structural belt of Kuqa depression have high abundance of organic matter.The organic matter types of Triassic and Jurassic are mainly type III andⅡ₂,the maturity（Ro）ranges from 0.8%to 1.8%,and the maximum hydrocarbon generation intensity of source rocks exceeds 70×10⁸m3/km2,Jurassic coal rock and Triassic lacustrine mudstone have high gas production rate and good gas generation,which can provide sufficient natural gas for the generation of gas reservoir.（2）In view of the origin and source of natural gas,combined with the composition of natural gas and the results of alkane carbon isotope test,the genetic type of natural gas is distinguished,and the measured gas composition is directly compared with the methane carbon isotope value(δ¹³C₁)in the thermal simulation results of source rock.The results show that methane is the main hydrocarbon component of the gas reservoir in the northern structural belt of Kuqa depression,while the content of heavy hydrocarbon is low.Alkane carbon isotopes of natural gas from Dibei gas reservoir,Tuziluoke gas reservoir,Tugeerming gas reservoir and Wucan 1 gas reservoir shows positive carbon isotope sequence as a whole,but local inversion occurs.The mixing of natural gas from different sources and stages is the reason for the carbon isotope inversion of natural gas in the northern structural belt of Kuqa Depression.The gas source analysis shows that the natural gas of Dibei gas reservoir,Tuziluoke gas reservoir and Tugeerming gas reservoir is mainly generated by the coal-bearing source rock in Yangxia sag.The natural gas of Wucan 1 gas reservoir mainly comes from Jurassic source rocks in Baicheng sag.Triassic source rocks also provide certain gas sources for four gas reservoirs in the northern structural belt of Kuqa Depression.This result provides a basis for the study of reservoir forming characteristics and process.（3）Aiming at the problem of whether the reservoir is densified or not,the physical properties of ahe formation,Yangxia formation,Kezilenuer formation,Jidike formation and Shushanhe formation in the northern structural belt of Kuqa Depression are tested by helium porosimeter and permeability measuring device,and the pore evolution history of tight reservoir is restored by pore quantitative evolution method.The results show that the porosity and permeability of Ahe and Shushanhe formation belong to tight sandstone reservoir,while Yangxia formation,Kezilenuer formation and Jidike formation are not tight sandstone reservoirs.The Ahe formation reservoir was densified at 8Ma,while the Shushanhe formation reservoir was densified at 6Ma.This result provides a basis for studying the relationship between reservoir densification and oil and gas charging time.（4）Aiming at the controversial issue of the accumulation period and accumulation time of gas reservoirs,a combination of petrology of inclusions,microthermometry,K-Ar dating of authigenic illite,quantitative fluorescence of reservoir particles（QGF）and quantitative fluorescence of extracts（QGE-E）and other experimental methods,combined with the process of tectonic evolution history,integrated the comprehensive research methods of oil and gas charging time and stages.The results show that early oil charging and late gas charging are the main features,and the oil and gas charging of Dibei gas reservoir occurred at 20 Ma and 5 Ma.In the Tuziluoke reservoir,oil charging occurred19Ma ago and natural gas charging occurred 2Ma ago in the late stage.The oil and gas charging of Tugeerming gas reservoir occurred at 18 Ma and 3 Ma.The oil and gas charging of Wuan 1 gas reservoir occurred at 10 Ma and 3 Ma.（5）It is aimed at the problem that the spatial and temporal matching relationship of the fault-caprock combination in the northern structural belt of the Kuqa Depression is not clear.The evolution history of caprocks and faults is analyzed using the method of strata paleo-thickness restoration,extension/compression rate variation,growth index method and structural equilibrium profile method.Based on this,combined with the degree of the fault cutting caprock in the drilling data,the temporal and spatial matching relationship between the fault and caprock is revealed.The period when the mudstone caprock of the Yangxia Formation has sealing ability and the period when the fault has conductivity matches is E_1-2km,N₁j,N₁k,and N₂k depositional period;E_1-2km,N₁j,N₁k,and N₂k depositional period matches the period when the mudstone caprock of the Kezilenuer Formation has sealing ability and the period when the fault has conduction ability;Qigu Formation+Qiakemake Formation mudstone caprocks have sealing ability and faults have conduction ability matching the N₁j,N₁k,and N₂k depositional period.The critical fault connection thickness of the Yangxia Formation fault-cap rock combination is about 150～170m,the critical fault connection thickness of the Kezilenuer Formation is about 105～120m,and the Qigu Formation+Qiakemake Formation closed natural gas is about 105～120m.The critical disconnect thickness is about 120～130m.This result lays a foundation for the study of natural gas accumulation process.（6）The thesis aims at the classification of natural gas reservoirs in the northern structural belt of Kuqa Depression.Through the anatomy of typical gas reservoirs and the comparison of reservoir forming characteristics,three types of gas reservoirs are divided:structural lithologic reservoir,tight sandstone reservoir and structural reservoir.The main differences of the reservoir forming characteristics of the three types of sandstone gas reservoirs are as follows:（1）the filling power is different.The filling of tight sandstone oil and gas reservoirs is mainly overpressure filling,while the structural lithologic oil and gas reservoirs and structural oil and gas reservoirs are mainly buoyant filling;（2）The physical properties of reservoirs are different,and the tight sandstone reservoir is densified,while the reservoirs of structural lithologic reservoir and structural reservoir belong to conventional sandstone reservoir;（3）The preservation conditions are different.The preservation conditions of tight sandstone reservoir depend on the"dessert area"in tight sandstone reservoir,the preservation conditions of structural lithologic oil and gas reservoir depend on the distribution of structural traps and reservoir heterogeneity,and the preservation conditions of structural oil and gas reservoir mainly depend on the sealing ability of cap rock in structural trap.This result provides a basis for the analysis of main controlling factors and the establishment of reservoir forming model.（7）Aiming at the problem of establishing gas reservoir forming model,based on the classification of gas reservoir types and the analysis of main controlling factors,three reservoir forming models in the northern structural belt of Kuqa Depression are established,which are structure lithologic gas reservoir forming model,tight sandstone gas reservoir forming model and structural gas reservoir forming model.The main controlling factors of structural lithologic reservoirs are:preservation conditions and trap factors;The main controlling factors of tight sandstone gas reservoir are:high-quality source rock provides sufficient material basis,provides the power of overpressure filling,and widely distributed tight sandstone reservoir.The main controlling factors of structural oil and gas reservoirs are:good source rock conditions,reservoirs with good physical properties,good fault caprock combination characteristics,fault transportation conditions and structural trap conditions.Different from structural lithologic oil and gas reservoirs,this type has higher requirements for reservoir porosity and permeability conditions.