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Table of Content

    25 September 1996, Volume 17 Issue 3
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    GENETIC TYPE AND ENRICHMENT LAW OF TERRESTRIAL NATURAL GAS IN CHINA
    Qian Kai, Wang Mingming, Wei Wei
    1996, 17(3):  171-176.  doi:10.11743/ogg19960301
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    Natural gas resources are widespread in terrestrial basins of China.Large or middle size gas fields have been found in southeast sea areas.The terrestrial gas can be divided into five genetic types: biogenetic-thermal overprint gas, near-sapropelic pyrolysis gas, near-humic pyrolysis gas and biological degradation gas.Gas rich depressions include five types: continuously deep buried, pulsative deep buried, continuously mid-deep buried, early slow and late rapid mid-deep buried and continued shallow buried types.Gas richest places are faultedanticline zones within the depressions.They are mostly distributed along paleouplifts, inherited structures or neighbouring places around source-rock sags.Two most advantageous domains of terrestrial gas enrichment are high geotemperature or rich coal measure regions in mid-deep depth and favourible environment for microorganism at middle-shallow depth.

    IDENTIFICATION AND CORRELATION TECHNIQUES OF SEQUENCE STRATIGRAPHIC BASE-LEVELS AND THEIR APPLICATION
    Deng Hongwen, Wang Hongliang, Li Xizhe
    1996, 17(3):  177-184.  doi:10.11743/ogg19960302
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    The key of high resolution isochronostratigraphic correlation is to identify multi-order stratigraphic cycles that represent multi-order base-level cycles in stratigraphic record.There bound to exist certain marks recording the time that corresponding order base-level cycle experienced in each stratigraphic cycle.The sedimentary and stratigraphic characteristics of stratigraphic cycles are: 1.vertical variation in single-phase physical properties; 2.variation in factes sequences and factes assemblage; 3.changes in cyclic stacking pattern; 4.stratigraphic geometry and contact relation.These characteristics reflect the variation of the ratio between containing space and sediment alimentation.Outcrop profile and well profile have higher resolution, and could be used to identify short term base-level cycles; well log could be used to identify mid-term base-level cycles; seismic profile could only by used to identify mid to long term base-level cycles due to the limitation of its resolution.The turnround point of base-level cycle would be selected as optimum position of high resolution isochronostratigraphic correlation.Time-space diagram is very effective on time-space inversion of stratigraphic profile and on checking the reliability of stratigraphic correlation.It has been proved by practice that the techniques could also be used in nonmarine strata.

    THEORY OF CORRESPONDING DISTRIBUTION OF FIELDS AND OIL-GAS GIRDLES IN DONGYING DEPRESSION
    Liu Xingcai, Qian Kai, Wu Shixiang
    1996, 17(3):  185-190.  doi:10.11743/ogg19960303
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    The girdle distribution of hydrocarbon in Dongying Depression bears close inherent relation with the properties and strenghs of the fields of paleobiology, paleogeotherm, paleostressand paleofluid potential.The girdle distribution of oil and gas puts forward the "field-girdle corresponding theory".Paleobiology field determines the character and abundance of deposited organic matter; paleogeothermal field provides the energy with which organic matter could be transformed into hydrocarbon; paleofluid potential and paleostress fields offer power and space for hydrocarbon migration and preservation.Therefore, the ring-type distribution of the above mentioned four fields has controlled the girdle distribution of oil and gas.Seeking for oil and gas enriched zone around the high potential belts of the four fields is of guiding importance in hydrocarbon exploration.

    RELATIONSHIP BETWEEN STRESS FIELD AND NATURAL GAS ENRICHMENT IN CENTRAL HUANGHUA DEPRESSION
    Yang Yufeng, Shi Zhanzhen, Wang Mingming, Lin Jie
    1996, 17(3):  191-194.  doi:10.11743/ogg19960304
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    The stress field of the bottom of the First Member of the Shahejie Formation in the central part of Huanghua Depression in Bobai Bay Basin was analyzed by applying finite element computer simulation.According to its distribution characteristics, its property and the relation between the stress field and gas enrichment, it is suggested that the environment of weak extension and strong shearing stress is favourable for natural gas accumulation.It has been proved that bigger gas fields in the Bobai Bay Basin are almost associated with compressoshear stress environment.The main cause for this is that the environment is beneficial for natural gas generation and expulsion, and it is also favorable to form good sealing traps.

    RESEARCH INTO FORECASTING METHODS OF OIL AND GAS PRODUCTIVITY IN SHAAN-GAN-NING BASIN
    Wang Qing, Li Guoping, Wang Shuyin
    1996, 17(3):  195-200.  doi:10.11743/ogg19960305
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    Based on small holes and caves developed in Lower Paleozoic carbonate reservoirs in Shaan-Gan-Ning Basin, two methods such as synthetic index method and acoustic time difference anomaly method were established using well log data so as to forecast oil and gas productivity.The synthetic index method is the product of resistivity and acoustical ways, which could be the synthetic reflection of oil volum in the reservoirs.According to the differences of synthetic indices, the productivity of the reservoirs in the basin could be divided into five productivity areas, and the coincidence rate is more than 75%.The acoustic time difference anomaly could be fine indicator of hydrocarbon abundance of underlying reservoirs.The more the acoustic wave curve deviates from compaction curve, the higher the productivity would be.The study area thus could be divided into four productivity zones, and the coincidence rate is greater than 70%.

    APPLICATION EFFECT OF HIGH RESOLUTION SEISMIC EXPLORATION IN IH JU LEAGUE
    Ouyang Yonglin, Feng Qi, Zhang Jinghua, Yu Min
    1996, 17(3):  201-205.  doi:10.11743/ogg19960306
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    High resolution technique in seismic exploration is a systematic engineering.In high resolution seismic exploration made in Ih Ju League, spectrum shaping, high frequency promotion and compesation, high sample rate methods were adopted to preserve high frequency signals; in seismic processing, pre-stack precise static correction, noise eliminating and poststack wavelet processing were used to improve signal/noise ratio, heighten master frequency and widen spectra.This technique has been proved to be effective especially in: 1.improving lamina resolution acuity; 2.increasing profile displaying ability; 3.improving the accuracy of structure interpretation.

    THE CLASSIFICATION OF GAS POOLS
    Tian Xinyi, Wang Guoyuan, Lu Xiaoxin, Han Yongxin
    1996, 17(3):  206-212.  doi:10.11743/ogg19960307
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    According to the properties of China's natural gas pools, single-factor classification and indices including trap, reservoir, expulsion, phase state, component, pressure and economy were studied.Based on the study, ternary structural combination and 9 naming principles were proposed in this paper.The gas pools could be classified into 5 types such as normal, condensate, acidic, high-pressure, special benefit pools and 25 sub-types.

    PREDICTING THE INCREASE OF CHINA'S PROVED GAS RESERVES BY USING "WENG'S CYCLE
    Ren Hongbin, Kong Zhiping, Li Dongxu
    1996, 17(3):  213-216.  doi:10.11743/ogg19960308
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    Weng's Life Cycle" is suitable for the description and prediction of the finite system of life amount, and its curve coincides to the increase curve of China's proved natural gas reserves."Weng's Cycle"could be used to describe and predict oil and gas reserves.As oil and gas are non-regenerated resources, the results indicates that the peak period of gas reserve increase will be 2011～2024 A.D., and the fina amount of proved gas resources will be 11.5 ×1012～23.0 × 1012m3.

    ANALYSIS OF COAL-BED GAS EXPLORATION AND DEVELOPMENT PROSPECTS OF CHINA
    Zhang Jianbo, Wang Zecheng, Wu Shixiang, Liu Chenglin, Shen Juehong, Yang Yong
    1996, 17(3):  217-220.  doi:10.11743/ogg19960309
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    According to statistic data, China's coal-bed gas resources are 30×1012～35×1012m3.Excepting the loss resulted from buried depth, metamorphism, gas weathering zones and coalfield structures, the actural recoverable coal-bed gas resources are only 10 ×1012m3.Based on the process of American coal-bed gas exploration, it is predicted that China's coal-bed gas production would be 0.43 ×108～0.65 × 108m3 in 2000 A.D., it will be 20 ×108m3 in 2000～2010 A.D., 100×108m3 in 2020 and in the year of 2050 A.D.., the production will be 2050 ×108m3.

    DETACHMENT-TYPE THRUST STRUCTURES IN MAJIATAN, WEST MARGIN OF ORDOS
    Wang Zecheng, Wang Yuxin
    1996, 17(3):  221-225.  doi:10.11743/ogg19960310
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    Majiatan thrust belt in the west margin of Ordos Basin is a typical detachment thrust belt.The main detachment beds are Carboniferous coal measures and the boundary plane between basement and sedimentary cover in the area.The genetic types of the thrusts are floor thrust, branch thrust, recoil fault and cross fault.The fold types of the thrust belt include fault-extended fold and fault-slided fold.The thrust belt contains recoil, recoil-cut and branch types of frontal structures and two structural transformation forms such as thrust to thrust and thrust to fold.The south end of the thrust front is favourable for oil and gas exploration.

    CHINA'S SHALLOW GAS RESOURCES AND EXPLORATION PROSPECTS
    Ding Guosheng, Tian Xinyi
    1996, 17(3):  226-231.  doi:10.11743/ogg19960311
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    Shallow gas is specialized to various natural gas resources buried shallower than 1 500 m, including biogas, oil gas, coal-formed gas, water soluble gas and etc..China's natural gas resources are primarily distributed in south China coastal regions, small Meso-Cenozoic basins, hydrocarbon-bearing basins in East and West China and major coal basins.Gas pools could be divided into three kinds: 1.super-shallow primary micro-pools; 2.proximal shallow small pools; 3.shallow conventional pools.The exploration of shallow gas is characterized by lower pressure, small production, simple technique and less investment.

    CHARACTERISTICS OF LAND GAS RESOURCES IN CHINA
    Ma Shuopeng, Zhang Fudong, Kong Zhiping Li Dongxu, Zhang Guangwu
    1996, 17(3):  232-236.  doi:10.11743/ogg19960312
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    The distribution characteristics of China's on-land natural gas resources were analysed based on the distribution locality, stratum, origin, buried depth, geography and unproved resources of natural gas.It is considered that the on-land gas resources are mainly distributed in Central and West China (about 40% and 36% respectively).Natural gas reservoirs are primarily in Carboniferous, Ordovician, Permian, Triassic and Tertiary systems.Within the natural gas resources, oil-gas in up to 70% of the total amount, and coal-gas is 29%.Natural gas is buried mostly deeper than 2 000 m, and 80.98% of it is under thick loess domes, hills and desert areas.The gas resources could be divided into 3 types based on their geological and exploration conditions.Among them, type-Ⅰ is basically distributed in the central depressions of Songliao Basin, Tertiary sediments of hydrocarbon-rich depressions in Bobai Bay Basin, the central and east of Sichuan and Ordos Basins, Ih Ju League, Tarim, Junggar, Turpan-Hami and Qaidam Basins in West China.

    FORMATION AND DISTRIBUTION OF CONDENSATE GAS POOLS IN CHINA
    Huang Ruchang, Li Jingming, Xie Zengye, Li Jian
    1996, 17(3):  237-242.  doi:10.11743/ogg19960313
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    China's condensate gas pools are mainly distributed in Bobal Bay, Tarim, Turpan-Hami Basins, the East and South China coastal regions.The total reserve of the condensate gas is about 4 000 ×108 m3, which is one third of total natural gas reserve.The gas pools are primarily formed from terrigenous parent materials and coal, the pools formed from lacustrine or marine sapropelic hydrocarbon-forming systems are seldom.The internal factor of condensate gas pool enrichment is humic or near humic source rocks.Excepting geological conditions needed by conventional gas pools, the condensate gas pools need temperature ranging from 70℃ to 130℃ , and pressure of 30～60 MPa.According to synthetic analysis, the target areas of condensate gas exploration should be Tarim, Turpan and Hami Basins in Xinjiang, the rift systems in Northeast China and inner Mongolia, the rift basins in the East China, the South China, the East China and Bobal Bay regions.

    CONTROL OF PALEOPRESSURE OVER NATURAL GAS FORMATION IN TIGHT CLASOLITE RESERVOIRS
    Xu Guosheng, Zeng Fangang
    1996, 17(3):  243-250.  doi:10.11743/ogg19960314
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    Upper Triassic clasolite reservoirs in West Sichuan are a set of tight sand-mud rocks with low porosity-low permeability, high aqueous saturation and abnormal high pressure.According to their fluid pressures and gas reserves, the reservoirs could be divided into superhigh pressure-low reserve type (Ⅰ), high pressure-high reserve type (Ⅱ) and normal to transitional pressure-high reserve type(Ⅲ).The formation and evolution of paleopressure controlled the formation of gas reservoirs.Successive pressure increase caused by gas generation and compression resulted in superhigh pressure-low reserve type reservoirs (Ⅰ) ; long-term pressure increase resulted in long distance gas migration and trap area enlargement, and thus forming high pressure-high reserve type reservoirs (Ⅱ); the development of structural fractures and high-pressure enlarged fractures, the early-stage enrichment and late-stage reformation of the reservoirs should be the basic formation model of normal to transitional pressure-high reserve type reservoirs(Ⅲ).