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Table of Content

    25 June 1996, Volume 17 Issue 2
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    PETROLEUM GEOLOGICAL CONDITION AND EXPLORATION DIRECTION OF QINGZANG PLATEAU
    He Zhiliang, Liu Jishun
    1996, 17(2):  87-95.  doi:10.11743/ogg19960201
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    Qingzang Plateau is an important part of Tethys domain between paleo-Eurasia and Gandwana. The petroleum geological condition there is complicated due to the regional framework of nearly E-W trending arc faults alternated with faulted terrains, the complex crust-mantle architecture and intensive neotectonic movements within the plateau. Since Cambrian, the plateau has undergone multi-cyclic geological evolution of four major stages: Proterozoic ocean, palaeo-Tethys, new Tethys and indian Ocean. The composition and overlapping of the prototype basins in different places and different periods within the plateau formed potential oil-bearing regions. Among them, Northern Himalaya is composed of overlapped cratonic depression-intercontinental rift-passive continental margin-peripherral foreland basin: the Northern Gangdise is composed of superposed cratonic rift depression-back arc basin-remnant back are basin-strike slip pull apart basin : Northern and Southern Qiangtang consist of superimposed cratonic rift depression-quasipassive continental margin-strike slip and compressional basin, and cratonic depression-passive continental margin-peripheral foreland basin and strike slip basin respectively. On the setting of intensive compressional deformation and uplifting,the basins show unique stratigraphic distribution,tectonic framework and structural patterns,and complex oil-gas-water system. Various blocks in the plateau have multiset of source rocks and reservoirs, but the organic matter of the source rocks is a little overmatured. As the plateau uplifted, the period of high geothermal environment was little later than that of tectonic deformation. This might probably result in secondary oil generation and late stage pooling in some places within the plateau. Mudstones and shales that widely developed there, gypsolyte distributed in local places and permafrost formed multi-type of source-reservoir-cap rock assemblages. Different types of structural, lithologic and sedimentary traps are targets for oil and gas exploration. Strategic break-through in oil and gas exploration could be achieved by selecting stable blocks with fine oil-gas-water system and overlapped basins with favourable matching within the plateau.

    COVER TYPES AND THEIR CONTROL OVER HYDROCARBON MIGRATION AND ACCUMULATION
    Zheng Chaoyang, Zhang Wenda, Zhu Panliang
    1996, 17(2):  96-101.  doi:10.11743/ogg19960202
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    Based on the relationship between sealing mechanism and rock pore texture, the covering strata can be diyided into micro-pore type and micro-fracture type. The former has monopeak saturation-pressure ratio curve and the peak saturation-pressure ratio is greater than 3. 0?10-2MPa-1: the later has multi-peak curves of saturation-pressure ratio, the peak saturation-pressure ratio is less than 3. 0?10-2MPa-1. The micro-fracture cover beds are the evolution result of micro-pore cover beds, and are mainly buried in mid-deep depth (below oilwindow) : the micro-pore cover beds are mainly distributed shallower (above oil-window). The micro-pore type could not only be the direct cover bed of hydrocarbon, but also could form high quality regional covering strata in association with high energy fluid surface: the micro-fracture type could only be the direct cover bed.

    ESTABLISHMENT OF ACCUMULATION MODEL EVALUATION SYSTEM IN GAS RESOURCES
    Wang Chuan, Huang Zheng, Fan Mingxing, Li Shusen
    1996, 17(2):  102-109.  doi:10.11743/ogg19960203
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    The establishment of accumulation model evaluation system is a subsystem of natural gas resources assessment export system(GRAES). It has integrated complicated quantitative calculation model with the qualitative evaluation model,therefore the system could reach a higher stage of processing sophisticated logical inference. One of the key technique of the system is to establish mathematical and physical calculation models according to gas accumulation mechanism. The other key technique is to found some new knowledge logical relations that could combine quantitative calculation model with qualitative inference model properly. On this base,the gas accumulation model is established with elastic rocks as the example,and the concepts and inference calculating models of six knowledge logical relations are discussed in this paper.

    HYDROCARBON POOL-FORMING CONDITION OF FAULT-DEPRESSED BASIN IN SOUTH SONGLIAO REGION
    Chen Kongquan, Zhu Luzhong, Xu Yangang
    1996, 17(2):  110-116.  doi:10.11743/ogg19960204
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    Songliao Basin is a superposed basin composed of fault-subsidence and depression. The pool forming system of the fault-subsidence was controlled by faulting and subsiding intensity. The source rocks of the basin are mainly type-Ⅲ and type-ⅡB of high thermal evolution. Hydrocarbon generation took place quite early and most of the hydrocarbon is natural gas. Hydrocarbon migrated vertically through faults and fractures associating with lateral migration along T3, T4 interfaces. Traps such as contemporaneous, early stage structural and multistage composite traps are favourable for trapping oil and gas. Since the traps are small,source rock are dispersive and posttectonic reworking was intensive, the pool-forming efficiency is quite low. As for the depressed basin, its source rock distribution is stable and extensive, the kerogens are primarily type-Ⅰand type-ⅡA,and on the whole,the evolution degree of organic matter is lower. Hydrocarbon, mainly oil associated with gas, generated late in the depressed basin. Oil and gas in the basin migrated laterally along T1, T2 interfaces and reservoirs. Verious kinds of traps superposed on paleo-uplifts and paleo-slopes are more favourable to form oil and gas pools.

    ADVANCES IN SIMULATED TEST OF BIOGAS
    Li Mingzhai, Zhang Hongnian, Liu Hua, Zhang Hu, Deng Yu, Lian Liwen, Yin Xiaobo
    1996, 17(2):  117-122.  doi:10.11743/ogg19960205
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    Three primary advaces in biogas simulation test of "eight five-year plan" key tasks are: (1)The method of suspended inocula was used in the simulation. That is to say,by discarding most of the inactive organic matter of the first time cultured micro-organisms, propagated the active ones and cultured them for the second time so as to improve their density and activity. This method could reduce the biogas produced by inocula themselves and shorten test period: (2) When test temperature increased to 75℃, the bacteria could still be alive and produce methane: (3) The simulation test made on coal and crude oil show that, under anaerobic condition, they can be degraded and can produce methane, and this is also one of the reasons of forming dense oil. What's more, dource produced methane bacteria were obtained from crude oil in this simulation test.

    CARRYING AND SEALING PROPERTIES OF FAULTS IN TARIM BASIN
    Yang Keming, Gong Ming, Duan Tiejun, Wu Hong
    1996, 17(2):  123-127.  doi:10.11743/ogg19960206
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    Faults developed very well in Tarim Basin. The control of the faults over oil and gas would principally be realized by carrying and sealing. The carrying could be seen by following: (1) abundant hydrocarbon seepages occurred along faults: (2) alternation presented in carrying oil and gas: (3) connecting underlying source rocks with overlying reservoir : (4) faults cut numerous source beds of different kerogens, thus resulting in the mixing of source rocks of various attributes. The sealing may be distinct from each other due to the differences betweene geometric and kinematic properties of faults and fault systems. The sealing of normal faults is closely related to intra-fault material flowage and the butt joint of the lower wall reservoir with the upper wall argillite: the sealing of abnormal faults is related to the gouge, mylonite within the faults, and the butt joint of reservoir on one side of a fault with the impermeable rock on the other side. Larger faults usually have carrying function on hydrocarbon, and smaller faults generally have sealing function.

    HYDROCARBON GENERATION POTENTIAL OF CARBONATE ROCKS IN SHALLOW PLATFORM
    Gao Jianjun, Li Mingzhai, Hu Tilin, Ge Baoxiong
    1996, 17(2):  128-133.  doi:10.11743/ogg19960207
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    The carbonate rocks of shallow platform factes is the primary sedimentation type in China's marine carbonate rocks. Its sedimental environment favoured the propagation of organisms but did not favour for the preservation of organic matter. Since sedimental boundary surface was near oxidizing milieu, large amount of organic matter was resolved during deposition and shallow burying process. This resulted in lower abundance and poor types of organic matter. Though the organic matter come from lower grade aquatic lives, hydrocarbon generation potential, especially liquid hydrocarbon generation potential is quite low. So it is suggested that, shallow platform carbonate rocks could not be considered as important oil source rocks but could be taken as gas source rocks.

    GAS EXPLORATION TARGETS OF PERMO-TRIASSIC IN NORTHEASTERN SICHUAN
    Long Shengxiang, Zeng Tao, Li Jianlong
    1996, 17(2):  134-139.  doi:10.11743/ogg19960208
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    Northeastern Sichuan Basin has fevourable geological condition to form gas pools in Permian and Triassic. A number of gas fields or gas-bearing structures have been discovered. This region is one of the important gas exploration area. This paper discribes how to use the gas resource assessment expert system and fuzzy set analysis method to appraise the gasbearing probability of 88 traps in Lower Permian, Upper Permian and Lower-Middle Triassic in the study area. The traps were analysed and divided into four levels of gas-bearing traps. Finally, exploration decision analysis system was adopted to analyse the 21 structures of Ⅰ and Ⅱ level traps, and tow exploration plans are put forward.

    LOG FACIES ANALYSIS OF THIRD MEMBER OF SHAHEJIE FORMATION IN GAOSHANGPU OIL FIELD
    Liu Cuirong, Ran Qiyou, You Xiuling
    1996, 17(2):  140-145. 
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    Based on the plate of lithofacies, log factes and sedimentary factes, the fan-delta of the third member of the Shahejie Formation in Gaoshangpu oil field could be divided into 9 natural gamma curve shapes and assemblages (M), 8 rock types (N). This constitutes M/N type of log factes so as to demonstrate different kinds of sand bodies. The dipmeter data from two wells were used to distinguish channel sand body represented by large red mode, sand bar represented by large blue mode and distal sheet sand body of small blue or green mode through arrow plot of short correlation. The results sho that the stretch directions of sand bodies are coincident with that of paleocurrent,the water depth was less than 15 m during deposition.
    TECTONIC EVOLUTION AND HYDROCARBON POOL FORMING HISTORY OF PESO-PALEOZOIC IN LOWER YANGTZE REGION
    Zhang Jianqiu
    1996, 17(2):  146-149.  doi:10.11743/ogg19960210
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    Lower Yangtze Region is a composite hydrocarL,on-bearing area cmoposed of superposed multicyclic depositional body. The depositional body includes: marine sediments deposited on the stable Paleozoic and Middle-Lower Triassic: intermontane basin formed in Upper Triassic-Lower Cretaceous compressive environment: fault-depression formed in post-Late Cretaceous tensive environment. Two peak stages of oil generation could be determined in the evolution history of marine source rock. The first one was the Caledonian, and the source rock was Lower Paleozoic: the second one happened post-Late Cretaceous in Upper Paleozoic, Middle-Lower Triassic Systems. Three main pool-forming stages were Caledonian, Indosinian-Yenshan and Late Yenshan-Himalayan Periods. The pools formed in late Yenshan-Himalayan are most favourable targets for hydrocarbon exploration.

    GAS EXPLORATION DECISION OF NORTH AREA IN YISHAAN SLOPE
    Zhao Ru, Jin Yanjun, Long Shengxiang, Zeng Tao
    1996, 17(2):  150-155.  doi:10.11743/ogg19960211
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    The decision analysis of the traps of the upmost Ordovician weathering crust in the north area of Yishaan slope, Ordos Basin indicates that among the 10 traps represented by relict tables, unakas, the traps of No.11, No. 8, No. 6-7 and No. 4 have relatively large cumulative areas,richer gas resources, higher economic benefit, lower critical probability, higher probability for the first well to be the discovery well, and these traps are more prospective in gas exploration. The traps of No. 15 - 13 are secondary: traps No. 14 and No. 9 are the last.

    RELATIONS BETWEEN METAMORPHISM AND COAL-BED GAS RESERVOIRING OF CARBONIC-PERMIAN IN NORTH CHINA
    Ning Zhengwei, Chen Xia
    1996, 17(2):  156-160.  doi:10.11743/ogg19960212
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    Reservoiring property bears close relation to metamorphic grade. According to the metamorphic grade, the Carboniferous and Permian Systems in North China could be divided into three kinds. In lower metamorphic coal beds, micropores developed well, but middle to big pores and fractures are not so well: though permeability and desorption are high enough, sorption capacity and methane content are both low. This kind of coal formations are not favourable for the diffusion and migration of coal-bed gas. High metamorphic coal suffered high pressure and high temperatiure, contains rich micropores, less fractures and less big to mid size pores. This kind of coal is not good in reservoiring property even if its sorption capacity and methane content are high. Mid metamorphic grade coal contains large amounts of internal fractures, big and mid pores developed well due to proper temperature and pressure. Most of the gas could be sorbed and preserved after generation, and the gas could be degraded, desorbed and migrated easily. This kind of coal is most favourable for coal-bed gas exploration. So it is proposed that the coal-bearing areas of the outer and inner flanks, the arc inside Taiyuan-Changzhi-Zhengzhou high metamorphic zone and the esat foot of Taihang Mountains should be taken as target areas for coal-bed gas explortion.

    DISTRIBUTION AND EXPLORATION PROSPECTS OF MESO-CENOZOIC OIL-GAS POOLS IN NORTHERN TARIM
    Zhang Ximing, Liu Qingfang, Wang Guiquan, Ye Desheng
    1996, 17(2):  161-163.  doi:10.11743/ogg19960213
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    The distribution of Meso-Cenozoic oil (gas) pools in Northern Tarim is primarily related to paleo-uplifts, paleo-slopes and the associated faults and overthrust-fold zones. Vertically the reservoirs are composed of Meso-Cenozoic double-layer texture: horizentally they could be divided into Tianshan piedmont overthrust-fold zone, depressed zone and uplift (including slope) zone. Geological data analysis indicates that Kuqa Depression is the only place to discover large oil fields in the study area: Yakela faulted uplift-northwest Shaya uplift, west Shaya uplift, Akqule uplift and the slope areas are favourable for seeking mid to small size of oil and gas fields.

    INTERPRETATION AND EVALUATION THINKING OF OIL GEOCHEMICAL EXPLORATION
    Chen Li
    1996, 17(2):  164-166.  doi:10.11743/ogg19960214
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    Hydrocarbon geochemical exploration, started from ground surface geochemical exploration,has entered into the realm of down-hole geochemical exploration and 3-D geochemical exploration,and it has been playing more and more important role in regional assessment and regional exploration, 3-D detailed survey and reservoir evaluation. The development of computer technique largely improved the interpretation and evaluation technique of hydrocarbon geochemical exploration. The optimization of index, the determination and screening of anomaly,the fitting of geology-geochemistry,the tapping of information and synthetic evaluation have become the brand-new thinking of hydrocarbon geochemical exploration in present-day.