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Table of Content

    25 March 2002, Volume 23 Issue 1
    THEORY PROGRESS OF NATURAL GAS GEOLOGY AND STRATEGY OF GAS EXPLORATION
    Wang Tingbin
    2002, 23(1):  1-7.  doi:10.11743/ogg20020101
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    Major progress in the study of natural gas geology since the 6th five year plan are as follows: 1.put forward the geological theory of transformation from coal basin into gas(oil) basins; 2.put forward the multi source,multi stage and multi phase gas reservoiring theory; 3.put forward the “basin geotherm hydrocarbon”theory based on the thermal system and geodynamics; 4.put forward various reservoir models composed mainly of late and ultra late hydrocarbon generation and pool forming; 5.summarized main controlling factors of large and medium gas fields in China and the strategy of natural gas exploration in the early years of the 21th century.

    NEW DEVELOPMENTS ON GEOCHEMICAL TECHNIQUE OF OIL EXPLOIT:GEOCHEMISTRY OF OIL PRODUCTION
    Hou Dujie
    2002, 23(1):  8-11.  doi:10.11743/ogg20020102
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    The physical and chemical properties of oil will change as oil production increases.Water flooding is a technique used most for oil production,the miscosity of oil increases because a lots of water enter into strata which contact with oil and bring some light crude oil components.At the same time,the water flooding will also cause emulsification of oil. As the water flooding increases,formation pressure will go up and lead to the enrichment of light components.As a result,the yield of oil also increases.The oil can also dissolve wax and cause the increase of wax content.Some asphaltene components in the pore which loosely contact with rock can be expulsed during water flooding process.This increases the asphaltene content of oil production.Combustion is another important techmique for heavy oil production.The combustion behavior is closely related to the SARA fraction of oil.Saturated hydrocarbon begin to burn first,release some energy in low temperature stage and affect the combustion front.In high temperature stage,asphaltene begin to react and release large amounts of heat,affect the succession of combustion bed.The third technique is CO2 flood used in some oil fields.These processes will increase in oil API gravty with precipitation of heavy components from oil phase due to CO2 injection.

    RESTUDIES ON PERMIAN REEFS IN EASTERN SICHUAN, CHINA
    Fan Jiasong, Wu Yasheng
    2002, 23(1):  12-18.  doi:10.11743/ogg20020103
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    Through the study of eight well cores from the Upper Permian reefs of Changxing stage in Eastern Sichuan,rocks from Tieshan 5 Well and Tiandong 10 well represent typical sponge reefs;rocks from Bandong 4 Well and Shuanglongchang 15 Well have not only the deposits of reef facies,but also crinoidal or echinoderm banks;rocks from Wolonghe 117 Well,Huanglongchang 1 Well and Yun'anchang 14 Well are mainly composed of carbonate platform deposits;rocks from Dachigan 24 Well consist of two types of reef facies:sponge framework reefs and sponge baffling reefs.Dolomites in the Permian reefs were formed of saline water mixed with fresh water during subaerial exposure of reefs above the sea level,then suffered late dolomitization during deeper burial stage,so they have evident geochemical characteristics of late dolomitization.The original deposits of these dolomites are of framework;not only they could be transformed by reef rocks,but also by those deposits of echinoderm banks,even common carbonate platform depostis.So in finding dolomite reservoirs of reef types,one should pay attention to find dolomite reservoirs formed of bank deposits as well as carbonate platform deposits.

    CONTROL AFFECT OF TECTONIC DEFORMATION TO OIL-GAS POOLS IN SOUTHERN CHINA
    Zhao Zongju, Zhu Yan, Li Dacheng, Yu Guang, Yang Shufeng, Chen Hanlin
    2002, 23(1):  19-25.  doi:10.11743/ogg20020104
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    Caledonian,Hercynian and Indosinian tectonic deformation resulted in the tectonic framework of huge uplifts and huge depressions in Southern China,and chiefly played the construction role to oil gas pools;Yanshan tectonic deformation resulted in intense thrusting,folding and denudation in the area to the south of Sichuan Basin and mainly played destroying role to oil gas pools;Himalayan tectonic deformation affected the whole South China,and controlled the final formation and distribution of nowadays'primary,secondary and regenerated oil gas pools.The primary oil pools should be explored in the Cenozoic,and Paleogene Subei and Jianghan Basins,etc.still have big exploration potential;the exploration of secondary and regenerated oil gas pools should mainly target the Mesozoic and Paleozoic Systems and that of secondary gas pools should mainly target the Upper Yangtze Region;the exploration of regenerated oil gas pools should mainly target the middle lower Yangtze Region.

    CHARACTERISTICSOFORGANIC COMPOSITIONS IN FORMATION WATERS FROM CENTRAL ORDOS BASIN
    Li Xianqing, Hou Dujie, Hu Guoyi, Liu Changqing, Li Jian
    2002, 23(1):  26-29.  doi:10.11743/ogg20020105
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    Isotachophoresis result indicates that the total organic acids concentration of Ordovician formation waters range from 9.17mg/l to 94.49mg/l and are obviously higher than those of Permo Carboniferous formation waters.But both of them have the same composition characteristics of acetic acidformic acid>propanoic acid>butanoic acid.The total alkyl phenol contents of Ordovician formation water range from 0.57mg/l to 4.73mg/l,and the average concentration is 1.77mg/l.Among the samples of phenol detection,47.06% samples are less than 1.0mg/l,and 35.29% samples are 1.0~3.0mg/l,and only 17.65% samples are more than 3.0mg/l.The concentration distribution of organic acids and phenols in the Majiagou formation waters occurs obvious heterogeneity.There are several higher organic acids and phenols concentration areas in the central part of Ordos Basin.High organic acid and phenol concentration areas of formation water(organic acids>45mg/l and phenols>2.0mg/l) are consistent with natureal gas reservoir enrichment areas in the central part of Ordos Basin.

    SIMULATION TESTS ON MIGRATION AND ACCUMULATION OF MIDDLE-SHALLOW BURIED GASES IN JIYANG DEPRESSION
    Song Guoqi
    2002, 23(1):  30-34.  doi:10.11743/ogg20020106
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    The middle and lower submembers of Sha-3 member and the upper submember of Sha-4 member in Jiyang Depression are the main gas source rocks.The burial depth is generally less than 3000 m.A german developed oil gas water phase simulation software(IES Petroflow)was used to simulate the gas migration and accummlation regularites of the depression.The result suggests that the gas could migrate in different phases.The primary migration was in solution phase;the second migration was in free phase and resulted in shallow secondary gas pools.The gas in Pingfangwang buried hill and its neighbouring areas as well as Dongxing Yonganzhen migrated in Minghuazhen Formation and Quaternary depostitional stages.The migration types could be divided into double faulted uplift zone type,single fault uplift zone type,fracture zone and slope zone types.

    METHOD AND TECHNIQUE FOR PREDICTION OF SUPER-DEEP CARBONATE RESERVOIRS IN NORTH TARIM BASIN
    Li ZongJie, Wang Qinchong
    2002, 23(1):  35-40.  doi:10.11743/ogg20020107
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    The Carbonate reservoirs of Tahe Oilfield in North Tarim are characterized by large buried depth,week seismic reflection signal and high heterogineity.Three methods could be used to predict this kind of reservoirs:1.use seismic horizon flattening technique to restore fossil landform;use seismic attribute parameters to restor fossil water system.Then predict the karst reservoir developed position;2.use the parameters of coherence,amplitude,wave impedance inversion and constrained logging to analyze the validity of the reservoir;3.use pattern recognition technique to predict reservoir's oil and gas potential,including hystogram,2-D cross plot and 3-D cross plot.The practice has proved that the predicted distribution areas of available carbonate reservoirs fit well with the actural ones,and the coincidence is 70%~80%.

    ANALYTIC TECHNIQUE OF FREQUENCY DIFFERENCE FOR DISCRIMINATION OF CAVITY FILLERS
    Tang Wenbang, Liu Laixiang, Fan Jiafang, Han Gehua, Ma Xuejun
    2002, 23(1):  41-44.  doi:10.11743/ogg20020108
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    The key of searching for carbonate reservoirs is to find large solution cavities full of fluids. Using frequency difference analysis can identify the nature of the cavity fillers.When the cavity filler is fluid,it has intense amplitude,low velocity and tuning property;when the filler is quasi viscous fluid,its tuning reflection is 90% of absolute reflection;when the filler is loose deposit,its tuning reflection is 77% of the absolute reflection.These media are most possibly oil preserving bodies.When the master frequency focuses 20~30Hz,and the cavity height is higher than 2~3 m,the natnre of the filler could be easily identified.This technique was used in Tahe Oilfield,four horizons of underground fossil river channels were discovered under the weathered surface in S-48 Well.

    APPLICATION OF IMAGING AND NUCLEAR MAGNETIC RESONANCE TO ASSESSMENT OF FRACTURED RESERVOIRS IN CHENGBEI
    Wu Haiyan, Zhu Liufang
    2002, 23(1):  45-48.  doi:10.11743/ogg20020109
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    It is difficult to understand the internal structure, the reservoir space distribution,pore types,the relation between reservoir development zones and the localities of structures of fractured reservoirs only using seismic and well log data.But imaging and nuclear magnetic resonancelog can help us to get good results.Based on the data of drilling,log,well log,well test and core,core calibration and graduation log data were used to set up log response and make rock discrimination, then use acoustic image to identify fractures,pores and cavities as well as their efficiency, finally use nuclear magnetic resonancelog data to set up well log interpretation model, quantify reservoir parameters and identify the fluids in reservoirs. This method was used in the assessment of carbonate resevoirs of Chengbei 30 buried hill,the results are satisfactory.

    LOG INTERPRETATION OF ORDOVICIAN CARBONATE RESERVOIRS IN TAHE OILFIELD
    Li Ling, Wei Bin, He Duohua
    2002, 23(1):  49-54.  doi:10.11743/ogg20020110
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    Ordovician carbonate reservoirs in Tahe Oilfield could be divided into three types.Type I is fracture pore and fracture solution cavity resavoirs with low laterolog resistivity of both shallow and deep formations,high gamm ray value,increased acoustic time and neutron log valuse;type Ⅱ is fracture reservoirs with mid higher laterolog resistivity of both shallow and deep formations,gamma ray value similar to that of limestone;type Ⅲ is poor in fractures and pores, but the highest resistivity,low gamma ray value,and overlapped shallow and deep laterolog resistivities.Then reservoir parameters could be calculated through well log normalixation and core reposition.Accordineg to the calculated parametres and log data,the lower limits of rock mass porosity and fracture porosity are 2% and 0.05% respectively.The fracture porosity of the reservoirs are determined to be≥0.05%,≥0.05% and <0.05%,and their pore porosity≥2%,<2% and <2% respectively.It has been proved that well log interpreltation results fit in with the actural porosity and fractural distribution of the reservoirs studied.

    APPLICATION OF WAVELET DECONVOLUTION TO SEISMIC INTERPRETATION IN TAHE OILFIELD
    Jiang Jinyong, Fan Huaiyang, Liu Li
    2002, 23(1):  55-57.  doi:10.11743/ogg20020111
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    During the processing of seismic data interpretation of Tahe Oilfield,pseudomorphism of adjoint phase caused by non zero phase wavelet was easily interpreted as effective reflection.It was necessary to extract impedance reflectivity based on environmental correction of sonic and density data, to extract actual non zero phase wavelet from seismic trace by comparing synthetic seismographic record with seismic trace near wells, and process seismic data with wavelet deconvolution. The processed seismic data had clear reflection character, high resolution and eliminated the pseudomorphism caused by non zero phase wavelet. The variance of coherency on the basis of processed seismic data showed clearly the characteristics of karst phenomenon on the top of Ordovician.

    CHARACTERISTICS AND RESERVOIR PROPERTY OF BIOCLASTIC LIMESTONE BANKS IN CENTRAL TARIM BASIN
    Wang Xingzhi, Wang Zhenyu, Ma Qing, Yang Manping, Tian Jun, Liu Sheng
    2002, 23(1):  58-62.  doi:10.11743/ogg20020112
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    Various kinds of banks developed in bioclastic limestone in Central Tarin Basin.Among them,the micro lithofacies of bioclastic and calcarenite bank bodies and their combination are mainly bioclastic limestone and bioclastic calcarenitic limestone with low porosity and low permeability.After tectonic reformation and burial dissolution,some reserviors with certain accumulative potential could form in local places such as Luonan 1 and luonan 2 Wells;the micro lithofacies of oncolite and oolitic banks and the related associations are mainly oncolite limestone,oolitic limestone and dolomite with well developed intercrystal pores and intercrystal solution pores.They are the most favourable reservoirs in the study area.These reservoirs are primarily distributed along Tazhong 22-Tazhong 14-Tazhong 4 and Tazhong 103 Wells.

    LOGGING IDENTIFICATION OF UNCOMPACTED AND SUPERPRESSURE BELTS
    Zhao Xinmin, Li Guoping, Wang Shuyin, Wang Qing
    2002, 23(1):  63-65.  doi:10.11743/ogg20020113
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    Uncompacted belts were formed by abnormal high formation pressure.But this does not mean that all the present uncompacted belts are now still high pressure or superpressure belts.It has to be decided by the log of the sandstone and mudstone of the same section.If the log of the sandstone and mudstone indicates the existence of uncompaction in the same interval,it is certain that the uncompacted belt is still a high or superpressure belt;otherwise,the uncompacted belt is not high or superpressure belt.This method was used in Tarim and Qinshui Basins,the results are satisfactory.

    ORIGIN AND CHARACTERISTICS OF UNDER PRESSURE SYSTEMS IN DONGYING DEPRESSION
    Liu Xiaofeng, Xie Xilong
    2002, 23(1):  66-69.  doi:10.11743/ogg20020114
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    Data derived from DST(Drill Strata Test)suggest that low pressure systems developed in Dongying Depression.The low pressure oil and gas reservoirs are usually located in the marginal uplift zone,marginal fault zone and central uplift zone.The low pressure system in the marginal uplift zone is shallower than 2000 m;in the central uplift zone,it is distributed in the strata deeper than 2000 m;and near the marginal fault zone,it developed in both shallow and deep strata.The distribution of low pressure was determined by the origin mechanesms.The main causes of the low pressure origins were diffusion of light hydrocarbons,pressure release resulting from quick fluid and hydrocarbon escape along faults and surfaces of unconformities,and osmosis due to salinity differences.The low pressure anomaly does not only exist in gas pools in the depression,but also in heavy oil pools and normal oil pools.

    CORRELATION TECHNIQUE AND HIERARCHY DIVISION OF OIL-GAS RESERVOIRS
    Wang Zhenqi, Zhang Changmin, Zhang Shangfeng, Hou Guowei
    2002, 23(1):  70-75.  doi:10.11743/ogg20020115
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    There are several methods of stratigraphic division and correlation,but they have their own systems,virtues and shortages.Through the research of chronostratigraphy,sequence stratigraphy,high-resolution straigraphy and architectural element analysis,combined with the character of hierarchy of stratigraphy,this paper expected to establish the rule and method of oil and gas reservoir hierarchy division,hierarchy description,hierarchy interpretation and hierarchy correlation from global scale to reservoir scale.

    IDENTIFICATION OF OIL HORIZONS BY ARTIFICIAL NEURAL NETWORKS IN XIEFENGQIAO STRUCTURE
    Yang Jiuxi
    2002, 23(1):  76-80.  doi:10.11743/ogg20020116
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    Xiefengqiao anticlinal structure in southwestern margin of Jianghan Basin is a litho structural complex oil reservoir.Its oil accumulation was controlled by vertical and lateral distribution and heterogeneity of the reservoir.Two kinds of neural networks—forward network(BP) and self organizing feature mapping network(SOM)—were used in reservoir parameter simulated calculation and horizon type prediction respectively.Then chose the data of Esheng 4 and Esheng 8 Wells as training samples,used drilling and log data such as RXO,RT,GR,SP,AC,CNL and CAL as input variables to set up input/ouput mapping relation between log data and POR,So and K parameters of the reservoir,used BP network to make function approximation,used SOM network to make pattern sorting.Then two parameters RT and AC of the reservoirs were reinputted,the parameters,together with POR,So and oil saturation K outputted from BP networks were taken as characteristic parameters of the reservoir identification.The characteristic parameters were standared and trained by SOM networks so as to get model sample,then inputted the data of oil horizon that needed to be predicted,the result of oil horizon identification could be outputted from SOM networks.The validity is proved to be more than 90%.

    OIL-GAS PREDICTION AND CHARACTERISTICS OF RESERVOIR BODIES FOR DA'ANZAI-1 SUBMEMBER IN BAIYA OF NORTH SICHUAN
    Li Congjun
    2002, 23(1):  81-83.  doi:10.11743/ogg20020117
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    Da'anzai-1 submember reservoir body developed in high energy shelly limestone of shallow lake carbonate facies.Recrystallization and dissolution made the shelly limestone loose and easy to be break.Solution pores,cavities and fissures developed well in it.Two compressional movements resulted in two sets of conjugate shear fractures,and also formed retensional fissures and extensional fissures on the higher part and mutation part of the structure along the shear fractures.This thus considerably improved reservoir's physical property.It has been proved that intense amplitude and high wave impedance are important evidences for the identification of thick limestone;high mutation factor is an important parameter for distingushing porous reservoirs.This method was used to predict the distribution of porous reservoir in Da'anzai 1 submember in Baiya region of North Sichuan,the result has been proved by well drilling.

    DIAGENESIS AND PORE EVOLUTION OF DEEP SANDSTONES IN JIYANG DEPRESSION
    Cai Jingong, Xie Zhonghuai, Tian Fang, Wang Wenlin
    2002, 23(1):  84-88.  doi:10.11743/ogg20020118
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    The deep sandstone of delta,fan delta and fluvial fan facies are low porosity low permeability or mid porosity low permeability reservoirs with filling micropores and intragranular pores.In general,the intragranular porosity decreased with the increasing of sandstone burial depth;the secondary enlargement of quartz,the filling of chlorite and kaolinite,the cementation of iron calcite and iron dolomite reduced the porstiy;solution in deep strata resulted in large amount of eroded pores.Late diagenesis could be divided into A,B and C diagenetic substages.Considerable organic acids in A substage caused solution pores in feldspar and debris;in the B substage,CH4 and CO2 existed,chlorite filled the pores,thus preserved micropores and solution pores;in the C substage,organic acids decreased and CH4,CO2 increased,thus forming fractures and improving reservoir property.

    APPLICATION OF STOCHASTIC SIMULATION TO INTERLAYER MODELING
    Chong Renjie, Song Chunhua, Cheng Lizhi
    2002, 23(1):  89-91.  doi:10.11743/ogg20020119
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    Pinghu oil gas field in East China Sea is a massive,bottom water drive light crude oil pool.The reservoir heterogeneity is relatively serious,and the distribution of muddy interlayers is a big variety.It is difficult to describe the size of muddy interlayers by traditional geologic model building method.It takes about 15 days and more than 10 times modifying the parameters of history fitting and reservoir simulation on H2 resevoir,because the geological model by traditional method can not describe clearly the reservoir heterogeneity,and the result of history fitting is not good.Use stochastic simulation to built prediction model,then,3-D reservoir attribute model is revised by the prediction model.It only takes 3~4 days and 5~6 times modifying the parameters of the history fitting and reservoir simulation.The result is very good and exact.

    CONTROL OF FAULTING OVER OIL-GAS POOLS OF BURIED HILLS IN BEIDAGANG STRUCTURAL BELT
    Chen Zhaonian, Chen Fajing, Su Junqing, Sun Xiaoming
    2002, 23(1):  92-95.  doi:10.11743/ogg20020120
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    Beidagang structural belt was experienced multi stang tectonic movements.It has both the thrust faulting system formed in Indosinian early and mid Yenshan epoch and extensional fault system formed in late Yenshan Himalayan epoch.The thrust fault and extensional fault had appearent control over the development of fracture cave reservoir,oil and gas potential,trap sealing conditions of Lower Paleozoic buried hill reservoir in this belt.The researches indicate that the fractures formed by thrusting and the related folding promoted the karstification and formation of the fracture cave resrevoir;source,maturity and afflux of buried hill reservoir were related to extensional faulting in Cenozoic;the sealing of buried hill traps were determined by both the lateral sealing of hasement involved normal fault and the contribution of mormal fault in the cover rock to top sealing.

    CHARACTERISTICS OF BURIED HILL OIL POOLS IN CAOQIAO-GUANGRAO
    Ma Lijuan, He Xinzhen, Chen Haiyun
    2002, 23(1):  96-98.  doi:10.11743/ogg20020121
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    Caoqiao-Guangrao Buried hill is situated in the south section of the south slope of Dongying Depression and developed in late Indosinian stage.The buried hill is in structural culmination,faults and unconformities developed well in the buried hill,so it has favourable migration pathways.Ordovician sediments are the main reservoir rocks,fractures,solution cavities and pores are the major preserving spaces;Sha 4 submember-Kongdian Formation mudston is regional cap rock.Solution,buried hill structural pattern and cap rock distribution were the controlling factors of oil pool forming.Now top and inside oil pools have been discovered in the buried hill.

    DEPOSITIONAL CHARACTERISTICS OF CARBONIFEROUS IN TAHE REGION
    Guo Qijun, Zhao Xingmin
    2002, 23(1):  99-102.  doi:10.11743/ogg20020122
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    The Lower Carboniferous Bachu Formation and Karashayi Formation developed in Tahe Region could be divided into massive sandy conglomerate facies,platy cross-bedded conglomeratic sandstone facies,trough cross-bedded conglomeratic sandstone facies,platy cross-bedded sandstone facies and 4 depositional systems such as braided river delta system,delta system,lagoon-flat system and carbonate platform system.The braided river delta system developed well in the region,and plays the main part of the Carboniferous System;carbonate platform could only be found on the bottom of the Bachu Formation.

    PETROLEUM SYSTEMS IN NORTH TARIM
    Jia Qingsu, Zhou Qingfan
    2002, 23(1):  103-106.  doi:10.11743/ogg20020123
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    Hydrocarbon source rocks in North Tarim Basin can be divided into three petroleum systems such as Cambrian Ordovician system,Tertiary Jurassic system and Carboniferous Permian system.The last one is an inferred system.The first system is a reformed residual one,and also the most important one.The early subsystem(∈-P)was an unified system with Manjar Depression as its oil generation centre;the late subsystem(∈-K)had multiple hydrocarbon generation centres and formed separate branch systems.The second system is the main gas producing realm with Kuqa Depression as its hydrocarbon generation centre.The flat gypsolith and mudrock formed in Late Cretaceous Early Tertiary are regional cap rocks.So it is considered that Cambrian Ordovician petroleum system with good preservation condition is favourable for oil exploration;Tertiary Jurassic petroleum system is an important gas exploration realm for its late hydrocarbon generation,weak reformation and good gas preservation and accumclation conditions.