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    25 December 1996, Volume 17 Issue 4
    STRONG LATE-REFORMATION:ONE OF THE IMPORTANT CHARACTERISTICS OF SEDIMENTARY BASINS IN CHINA
    Liu Chiyang
    1996, 17(4):  255-261.  doi:10.11743/ogg19960401
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    Sedimentary basins of China are characterized by plenty of types and appearances,complex geological features. This is seldom found in the world. A further research on the basinswill enrich and develop the theory of basin geology. One of the most important characteristicsof the basins is strong late-reformations. This is caused by the configuration, evolution ofChina continent and its special tectonic location. The features of the late-reformation are asfollows: 1. The reformation almost occurred in all basins and differed spatially; 2. The reformation was violent. The earlier the basin was formed,the more reformation times the basinwould suffer; 3. The later the reformation took place,the stronger it would be; 4. The reformation occurred for many times. Each time of it differed differently. As for sedimental basinscontaining hydrocarbon resources,the main ge6logical functions resulted in the reformationinclude tectonic movement,denudation (transportation),deep burying and thermodynamics.According to the characters,the strength of the reformation,and the possible reconstruction degree of original basin,the reformation could be divided into five types: 1. The originalface of a basin has changed due to late-stage denudation. This resulted in the decreease of the basin range; 2. New geological phenomena, as the formation of NW trending structures inQ8idam Basin, took place; 3. Structural property has transformed. That is, Mesozoic shearcompression structures in the east part of North China Craton has transformed into transtensional structures in Triassic; 4. The relative positions of basins have changed. This can beseen from the reformation of original basins by Huanghua detachment structure in Bobal BayBasin and Shigouyi gliding nappe structure in the west margin of Ordos Basin;5. The originalshape of a basin has changed entirely.It is suggested that to understand and study the strong late-reformation of China’s sedimentary basins is very important for geology and for sedimental resources exploration.

    FRACTURE STRUCTURES AND HYDROCARBON THIRD MIGRATION IN NANPU DEPRESSION
    Zhang Shulin, Tian Shicheng, Zhu Shuian, Zhang Qingyun, Zhou Haiming
    1996, 17(4):  262-267.  doi:10.11743/ogg19960402
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    Hydrocarbon third migratgion is a periodic flow process. When faults are in dormantstage,large faults are sealed and hydrocarbons could accumulate to the fault traps within abnormal high pressure source sets to form primary pools lwhen faults are active,large faultsare open,hydrocarbons in the primary pools would migrate upward along the large faults toform secondary hydrocarbon pools in shallow traps. As the third migration is quick and concentrated,it did not result in evident chromatographic effect but did result in obvious differentiae between the primary and secondary pools since most of the hydrocarbons overflowedfrom the primary pools are light components. The hydrocarbons overflowed continuouslyfrom the primary pools, and were flushed by water-flow, then entered different reservoirswith water-flow,thus resulting in random distribution of secondary pools vertically.

    DIAGENESIS AND PORE ZONATION OF SANDSTONE RESERVOIRS IN HUANGHUA DEPRESSION
    Zheng Junmao, Wu Renlong
    1996, 17(4):  268-275.  doi:10.11743/ogg19960403
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    The diagenesis of Tertiary sandstone reservoirs in Huanghua Depression varied obviously with the increase of buried depth and it should belong to normal buried diagenesis. Thecharacteristics and evolution degrees of the reservoir porosity differ differently with theburied depth of the reservoirs,and based on this,the reservoir porosity could be classified into three zones: 1. shallow zone with the buried depth less than 2 200 m and primary porosityplaying the main part; 2. transitional zone with buried depth between 2 200-3 000 m and secondary porosity occupying 30%-50% ; 3. deep zone with buried depth greater than 3 000 mand secondary porosity occupying the main part. It is suggested that the boundary betweeneogenetic A and B stages should be in 2 200-2 500 m depth;the boundary between early andlate diagenetic stages should be at 3 000 m depth. The study results show that the diagenesisis controlled by buried depth,the pore evolution is controlled by diagenesis. Sedimentary environment has less influence on reservoirs beyond certain depth.

    SICHUAN MOVEMENT IN WEST SICHUAN FORELAND BASIN AND ITS RELATON TO OIL AND GAS
    Liu Shugen, Luo Zhili, Dai Sulan, Dennis Arne
    1996, 17(4):  276-281.  doi:10.11743/ogg19960404
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    The measurement and computer modelling of apatite fission tracks in Western Sichuanforeland basin and Longmenshan Region offer new information for the recognition of "Sichuan Movement". The "Sichuan Movement" has four episodes. The first one took place in60 Ma (Early Paleocene-Late Paleocene),the second one took place in 35-36 Ma (EoceneOligocene),the third episode happened in 10 Ma (Middle-Late Miocene),and the fourth onein Early-Late Pleistocene. It could be seen from the above mentioned that the so-called"Sichuan Movement"is acturally the Himalayan movement. This movement provided available condition for hydrocarbon migration and accumulation,and it is also the main cause resulting in effective fractures in the basin. Most of the gas pools in the basin were formed during this period.

    AWATI INTRACONTINENTAL FORELAND BASIN IN XINJIANG
    Tian Zuoji, Luo Zhili, Luo Zhetan, Peng Dajun, Yu Huijijn, Song Jianguo
    1996, 17(4):  282-286.  doi:10.11743/ogg19960405
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    Await foreland basin is located in the northwestern Tarim Basin. In Cenozoic,Kalpintagthrusted voilently towards southeast with NE trend Shajingzi fault being its major slip plane.Great thickness of Cenozoic sediments deposited on the southeastern side of the Shajingzifault. The thickness reduced rapidly southeastward,thus forming asymmetrical fie-cure sedi.mentary basin. According to its geotectonic location,its developing time and genesis,Awati foreland basin should neither belong to peripheral foreland basin,nor belong to retroarc foreland basin. It is a new kind of foreland basin-intracontinental foreland basin.

    OIL-GAS SYSTEMS IN THE EAST PART OF PEARL RIVER MOUTH BASIN
    Zhang Qunying, Den Hannan
    1996, 17(4):  287-292.  doi:10.11743/ogg19960406
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    The east part of Pear Rive Mouth Basin contains Huilu-Dongsha, Xijiang,Enping andBaiyun petroleum systems. Among them, Huilu-Dongsha is the richest one. The primarysource rocks of the systems are in the bottom of fracture horizon. This results in intrahorizonand allochthony types of oil migration-accumulation assemblages. The traps of the system arecomplete and contemporanous. In the system,the peak period of oil generation matched withtrap forming period,especially weak faulting period. This provides favourable conditions forthe long distance lateral migration of oil and gas. The system's oil pools are distributed inzonary type paralleling with water current direction. Accoring to the differentiae of hydrocarbon generation of the basin,and the migration and accumulation model,it is suggested thatthe deep water regions in the south part of Huilu-Dongsha system,the eastern and southernparts of Xijiang system as well as the eastern,central and south parts of Baiyun oil systemare favourible regions for oil exploration.

    DEEP HYDROTHERMAL DISSOLUTION OF DA'ANZHAI RESERVOIRS IN NORTH SICHUAN
    Zheng Rongcai, Chen Hongde, Liu Wenjun, Li Anren, Zhang Xiaopeng, Liu Meiqing
    1996, 17(4):  293-301.  doi:10.11743/ogg19960407
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    The formation of Da'anzhai limestone reserviors are closely related to multi-stage deephydrothermal dissolution. Lake beach and lakeside factes are most favourable for the development of the dissolution;the fluid that exuded by argillaceous source rocks of semi-deep lacustrine factes during different evolution stage6 is the primary solution source;Late YenshanEarly Himalayan period is the main formation stage of the reservoirs due to frequent dissolution. The deep hydrothermal dissolution could be divided into diagenetic, tectonic and postdiagenetic stages and five secondary mineral filling substages. It is pointed out that the occurrences of the pores,caves and fractures, the cathodoluminescence of the filling minerals, thegeochemical properlies,the inclosions,lithologic and fluid characters of different stages differdifferently. Based on the above mentioned, a model of deep hydrothermal dissolution inDa,anzhai abnormal limestone reservoirs is proposed in this paper.

    APPLICATION OF FLUID-SEDIMENT SIMULATING TECHNIQUE IN OIL-GAS RESERVOIR PREDICTION OF X REGION
    Zhang Guijia, Li Congxian, Lu Jiuhua, Liang Shulan, Gu Yunfei, Zhou Faping
    1996, 17(4):  302-307.  doi:10.11743/ogg19960408
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    Fluid-sediment simulation technique is a kind of dynamic simulation model in which hydrodynamic and kinetic formulars and equations are used to control and describe the transportation and deposition processes of sediments with the help of computer. This technique isused in the simulation of the lower part of the upper member of the Jiufutang Formation in Xregion. The results suggest that the provenance of the sediments is in the margin of the basinsoutheast to the region;the sediments shaped as a fan spreading northwestward. The paleocurrents there are between 29°~34°,which basically coincide with the spreading direction ofthe sediments,80% of the predicted thicknesses of the sand bodied coincide with that provedby drilling.

    CHARACTERISTICS AND ORIGIN OF TAR MATS IN YAHA OIL-GAS FIELDS,TARIM BASIN:OCCURRENCE AND MARCROSCOPIC COMPOSITIONAL FEATURES
    Zhang Min, Zhang Jun, Mei Bowen
    1996, 17(4):  308-312.  doi:10.11743/ogg19960409
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    Two tar mats were firstly discovered and determined accurately in Paleogene nonmarineoil-gas pools in Yaha Oilfields,Tarim Basin, by thin layer chromatography-flame ionizationdetector (TLC-FID) and Rock Eval. The relative content of asphaltene in gross compositionof tar mat extracts is more than 30%,but the content in corresponding oil leg is less than20%. In the profile geochemical description of oil reservoirs, sudden changes in asphaltenecontents between the tar mats and oil layers could be seen. This is an important marker todetermine tar mats.

    TYPES AND EVOLUTION CHARACTERISTICS OF PETROLEUM SYSTEMS IN TURPAN-HAMI BASIN
    Li Wei, Niu Jiayu, Zhao Wenzhi
    1996, 17(4):  313-320.  doi:10.11743/ogg19960410
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    Turpan-Hami Basin contains two types of source rocks and four petroleum systems suchas coal measure-noncoal formation combined type, noncoal formation type and Toksun,Taibei, Hami, Nanhu petroleum systems. Within the first type, oil traps that were mainlyformed in Late Cretaceous matched well with the peak period of hydrocarbon generation ofPermian-Triassic source rocks, thus forming Toksun petroleum system; the oil traps ofTaibei system were formed in Middle-Late Jurassic and matched well with the peak period ofhydrocarbon generatioll of Early-Middle Jurassic coal measures and that of Permian-Triassicsource rocks, thus forming Taibei petroleum system; Hami oil traps were formed in LateJurassic,matched with the peak period of Triassic lacustrine mudstone hydrocarbon generation, and formed Hami petroleum system.As for the noncoal formation system, since itscaprocks were formed so late and underwent three serious damages,large amounts of oil andgas were lost,it is not favourable to form large oil and gas pools.

    HYDRODYNAMIC FIELDS AND LOW-PRESSURE GAS POOLS IN SHIWU FAULT-DEPRESSION,SONGLIAO BASIN
    Lou Zhanghua, Lu Qingmei, Zhao Qingji, Xiao Haiyan, Tang Liming
    1996, 17(4):  321-325.  doi:10.11743/ogg19960411
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    In Shiwu fault depression of Songliao Basin, sediments buried shallower than 1 250 mbelong to normal pressure zone;that deeper than 1 500 m belong to low-pressure zone sediments between above mentioned zones are in tranzitional zone. Hydrodynamic fields corresponding to these zones are respectively free replacing zone,obstructive replacing zone and irreplacing zone. The amounts of gas losses in the obstructive replacing and irreplacing zonesare greater than that of subsurface water leakage recharge,and the deeper the gas buried,theless the subsurface water recharge amount would be. This resulted in the decrease of , essurecoefficient with the Increasing of buried depth,and the formation of low-pressure gas pools. Itis considered that gas reservoirs in the obstructive replacing zone and irreplacing zone are themain productive beds of the region.

    PATCH REEF OF LATE ORDOVICIAN STROMATOPOROIDS AND CORALS IN YUSHAN,JIANGXI
    Chen Xueshi
    1996, 17(4):  326-332.  doi:10.11743/ogg19960412
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    Stromatoporolds-coral patch reefof Lateordovlcaln Sanjushan Formation In Dashanjlaoof Yushan,Jlangxl Province,developed on an isolated carbonateplsteform In Sanshan region.It is a complex and multlcycle superimposed reefcomposed vertlcallyby two patch reefs.Themain reef-building organisms are Tabulato,stromatoporolds andalge.Basedon the paleoecology of reef-building organisms,they could be divided into four communities.It is consideredthat the rock types of the reef complex are dominantly baffflestone,bind-bafflestone,bafflebindstone and algal binded framestone.Reef fades may be divided into five subfacles such asreef base,reef core,interreef deposit,reef talus and reef cap.The reef core underwent clearlythree evolution cycles.The evolution of the reef was controlled by structures and the fillingof argillaceous debris.

    STRUCTURAL TRAP SERIES IN SOUTH SONGLIAO BASIN
    Huang Fulin, Luo Chuancai, He Xinghua, Zhao Qingji
    1996, 17(4):  333-336.  doi:10.11743/ogg19960413
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    Different structural trap series developed in different evolution stages of the faultdepression process in the south of Songliao Basin. During fault-depressing period,extensionalstructures mainly developed in cracking stage under the influence of extension fracturing,andtraps formed in this period are primarily syngenetic drape structures and growth anticlineslreversal structures that resulted from the compressional tectonics of Dengluku stage developed well,the structural traps formed in that time are mostly reversed anticlines. During depressing period,gentle structures occurred in subsiding stage, and the traps formed in thisstage are basically inherent syndepositional anticlines, syndepositional anticlines; compressional and strike-slip structures developed in fold-uplifting stage due to the influence of LateNenjiang-Late Mingshui tectonics and structural traps formed then are reversal anticlines,fault-block anticlines and flower shape structures. It is suggested that the syngenetic drapestructures, syndepositional anticlines, reversal anticlines, especially multi-stage inherentstructural traps are the most favourable targets for deep-seated hydrocarbon exploration.

    THE SKELETON STRUCTURE OF CALATHIIDS AND ITS BIOLOGICAL ATTRIBUTE
    Liu Bingli, Zhu Zhongde, Jiang Yanwen
    1996, 17(4):  337-342.  doi:10.11743/ogg19960414
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    A large number of Calathium specimens were collected from west Hubei. They are characterized by: 1. The organism is in the shapes of inverted cone, born or cup with the opensides upward and the closed tips anchored on the sea bed; 2. Porous double-wall and ring-likeintervallum of the organism constitutes a water circulatory system similar to that of Archaeocyathids and sponge; 3. The organism has no axis but has a broad central cavity which actsprobably as a cloacal 4. Most specimens possess foot-like or tumour-like outgrowth structures with anchoring,twining or balanching function. All these features indicate that the organism should be a kind of lower class animal of filter feeder with certain affinity to Archaeocyathids but should not be classified into algae.

    DEFINITION OF LOWER LIMIT OF CARBONIFEROUS NET PAY RESERVOIRS IN EAST SICHUAN
    Zhou Wen, Wang Yuncheng, Zhang Gaoxing, Ran Hong, Pu Jiaqi
    1996, 17(4):  343-346.  doi:10.11743/ogg19960415
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    Carboniferous dolomite reservoirs in East Sichuan could be divided into four grade: 1.middle porsity-middle permeability(grade-I); 2. middle porosity-lower permeability (gradeⅡ); 3. lower porosity-lower permeability (grade-Ⅲ); 4. ultra low porosity-ultra low permeability (grade-Ⅳ).Reservoirs and nonreservoirs could be distinguished by 20% of porosityand 50% of water saturation. Based on the reservoir grades and their position above watergas boundary, the contrast of injected buoyance and different capillary pressures, a newmethod-bouyance-capillary pressure contrast method is proposed in this paper so as to determine a reservoir to be net pay one or not. The result suggests that the reservoirs ofgraded I above water-gas boundary 5 m,of grade-Ⅱ above the boundary 25 m, of grade-ⅢA above the boundary 60 m and of grade-ⅢB above the boundary 100 m are all net pay reservolrs.

    FACIES AND ENVIRONMENT OF EARLY ORDOVICIAN AT HUANGHUACHANG,YICHANG,HUBEI
    Hu Mingyi, Gong Wenpin Xiao Chuantao, Zhu Zhongde
    1996, 17(4):  347-352.  doi:10.11743/ogg19960416
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    The Early Ordovician at Huanghuachang,Yichang can be classified into four group lithofacies: water current genetic grainstone ; biogenic reef limestone; biochemical genetic stromatolithic limestone;polygenetic micrltic dolostone;marl and shale. These lithofacies consist offive kinds of lithofacies asso(ations: restricted platform,open platform, platform shoal,platform reef, neritic shelf factes associations. They constitute two lithofacies sequences in ascending order:carbonate rock platform lithofacies sequence and subsided platform lithofaciessequence.

    THERMOLYSIS ASSESSMENT METHOD FOR RESERVOIR OIL POTENTIAL
    Pan Zhiqing, Mei Bowen, Su XiufangFang Xiaolin, Yang Shaofang, Hou Dujie
    1996, 17(4):  353-355.  doi:10.11743/ogg19960417
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    According to the thermolysis assessment standard of reservoir oil potential which isbased on the thermolysis data of a certain basin,a reservoir could be qualitively classified intooil bed,oil-water bed,water-bearing bed and dry bed (or water bed). Except well correspondence with oil showings,thermolysis parameters could also be used to describe oil heterogeneity through variation coefficent and oil thickness coefficient.