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Table of Content

    25 March 1993, Volume 14 Issue 1
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    GRAVITY FLOW DEPOSITS AND ASSOCIATED SEDIMENTS FROM MIDDLE ORDOVICIAN,FINCASTLE,VIRGINIA
    Gao Zhengzhong, K.A.Eriksson, Zhou Jiarao
    1993, 14(1):  1-9.  doi:10.11743/ogg19930101
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    Fincastle Conglomerate which was considered as deposits in shallow water in the pastis mainly gravity flow deposits and associated sediments ia deep water submarine chan-nels.Five gravity flow facies have been recognized:1.pebbly mudstone facies;2.matrix-rich conglomerate facies;3.matrix-poor conglomerate facies;4.massive sandstone facies;5.graded sandstone facies.Among them 1 and 2 are debris flow deposits;3 and 4 belongto grain flow deposits;and 5 is turbidite including high density and low density currentdeposits.The associated facies comprise:6.dark shale and mudrock facies:suspension de-posit;7.contorted bed facies:slumping deposit;8.bidirectional cross-laminated sandstonefacies:internal-tide deposit;9.unidirectional cross-bedded and cross-laminated sandstonefacies:deposit of internal tide with superposing internal wave.The nine facies mentionedabove constitute five facies assemblages that show regular patterns.To sum up,the Fin-castle Conglomerate shows a clear upward-fining sequence,reflecting a process of that thesea level continued to rise and the source area was farther and farther to the sedimentarysite.

    ON THEORETICAL BASIS OF QUANTITATIVE EVALUATION OF OIL AND GAS RESERVOIR AND PARAMETERS CONCERNED
    Zhu Zhongqi
    1993, 14(1):  10-13.  doi:10.11743/ogg19930102
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    This paper discusses the theoretical basis of the quantitative evaluation of an oil andgas reservoir in detail,and proposes the potential resources of oil and gas,the expulsivepressure of the reservoir and cap rocks,the density contract of fluid,and the structureclosure as the parameters of evaluation,and also analyzes their complementarity and itssignificance.

    ORIGIN OF LOWER PERMEABILITY TIGHT-SANDSTONFS AND GAS EXPLORATION IN DEEP BEDS OF DONGPU DEPRESSION
    Yuan Zhengwen
    1993, 14(1):  14-22.  doi:10.11743/ogg19930103
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    The gas reservoirs of deep beds in Dongpu Depression are considered to be sublacus-trine fan which underwent diagenetic changes under abnormal high pressure condition.Because of the shielding of the overlying sealed beds,the separated materials includingS4+,Fe2+,Ca2+ and Mg2+ etc.ions contained in mudstone clay minerals were not easyto move out,thus causing intensely ferrian carbonate-precipitation,replacement,quartzsecondary enlargement nearby.The permeability of sandstone dropped rapidly,so inter-granular pores, intragranular pores and micropores became the main preserving spaces ofthe reservoirs,and hence the reservoirs characterized by 1.high capillary-pressure;2.highaquifer-satuation;3.high pressure-sensitivity and 4.high heterogeneity.It is suggestedthat a systematic study including geological and geophysical researches,the techniques ofwell-drilling and well-completion should be carried out to improve the success of gas exploration.

    DISCOVERY OF RHIZOCORALLIUM IN WANGHUCUN FORMATION IN XUANCHENG,SOUTHERN ANHUI AND ITS ENVIRONMENT SIGNIFICANCE
    Xia Bangdong, Zhong Lirong, Fang Zhong, Liu Honglei, Dou Shouchu
    1993, 14(1):  61-63.  doi:10.11743/ogg19930108
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    A new species of trace fossils Rhizocorallium wanghucunensis Xia,Zhong,Fang et(sp.nov)was discovered in the Wanghucun Formation of Lower Carboniferous in Xu-ancheng,Anhui Province.The fossils are distributed in siltstone and formed in tidal flat environment,suggesting that horizontal Rhizocorallium does not only indicate the deep water-low energy environment,it can also appear in tidal flat environment.

    PETROLEUM GEOLOGICAL CHARACTERISTICS AND OIL PROSPECTS IN CENTRAL JUNGGAR BASIN
    Li Xibing, Mai Guangrong, Kuang Jun, Jia Xiyu
    1993, 14(1):  23-33.  doi:10.11743/ogg19930104
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    The basement of the hinderland of Junggar Basin consists of two layers,the Pre-cambrian crystalline and the Devonian-Carboniferous slightly metamorphic basement.From Permian to Quaternary,the hinderland experienced six structural-sedimental stages:1.platform marine basin;2.foreland marine basin;3.taphrogenic remnant marine basin;4.depressed continental basin;5.oscillation continental basin and 6.constriction continen-tal basin.Nine secondary structural units can be divided and Zhongguai-Dabasong,San-nan,Baijiahai,Muosuowan uplifts are favourable for hydrocarbon accumulation.The Permian Fengcheng(P1∫),lower Wuerhe(P2ω)Formations and the Jurassiccoal measures(J1+2)are source beds in the area.Triassic-Permian traps formed in lateHercynian—Indo-China epoch received mainly oil and gas from Permian source rocksand belong to allogenic type;Jurassic traps formed in early Yenshan epoch received oiland gas from Permian and Jurassic source rocks,and belong to autogenetic and combinedtypes.

    A TEST ON MIXED SOURCES OF CRUDE OIIS AND ITS GEOLOGICAL SIGNIFICANCE
    Wang Yutao
    1993, 14(1):  34-42.  doi:10.11743/ogg19930105
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    A geochemical test on mixed sources of crude oils was made.Oil samples used werePermian oil from Bei-4 well in Bei Santai area,East Junggar Basin and Jurassic oilcollected from Mu-3 well in Fukang Depression.The result shows that the crude oil fromBei-27 well on the southwest slope of Bei Santai area is similar to the mixed crude oils of20:80(20 parts of crude oil from Bei-4 well:80 parts of crude oil from Mu-3 well),andJurassic oil sources were the major contributor;the crude oil from Tai-22 well on twosides of Santai Uplift is similar to the crude oils of 50:50,and Permian and Jurassic oilsources were both the contributors.

    ARCHITECTURE AND PROCESS INTERPRETATION OF LACUSTRINE CLASTIC SHORELINE DEPOSITIONAL PACKAGE
    Xia Wenchen, Fang Yanjun
    1993, 14(1):  43-52.  doi:10.11743/ogg19930106
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    Lacustrine clastic shoreline depositional package is common in the lacustrine system.Not only it has some particular lithofacies and genetic units which present relative deposi-tional processes,but also has special features on the shape of sand-dispersal system and internal architecture.A complete sequence of lacustrine clastic shoreline depositional package consists of deep lake and subaqueous gravity flow facies,transitional zone facies,low energy shallow lake and beach facies,high energy shoreline facies.Because the sand-dispersal system of lacustrine clastic shoreline depositional package is usually interfingering with deep lake mudstone,and the sandstone has good porosity and permeability,it is a excellent reservoir for oil and gas.

    TECTONIC CHARACTERISTICS AND EVOLUTION OF LIUSHAN AND MASHIPING BASINS
    Wang Dingyi, Wang Libao
    1993, 14(1):  53-60.  doi:10.11743/ogg19930107
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    Liushan and Mashiping Basins are located in Western Henan Frovince,North Qinling Belt.Their basements are Precambrian-Lower Paleozoie rocks,and the covering series are Upper Triassic,Upper Jurassic-Lower Cretaceous respectively.Liushan Basin is a complex syncline composed of two syncline and an anticline belts.The major faults are NWW-strike thrusts which do not control the distribution of strata.A complex syncline was also identified in Mashiping Basin.Its axis trend varied from NWW to NE-NNE direction,and was cut by boundary fault of the basin;its eastern section was almost completely destroyed by a southward thrust.The Meso-Cenozoic tec-tonic evolution can be divided into seven stages:regional uplift period(ANT3);depression period after regional uplift(T3);compresso-uplift period(J1+2);fault-subsidence period in tenso-shear condition(J3+K11);overthrust-nappe period(K12);extensional fault-subsidence period(K2+E?)and regional compresso-uplift period(N+Q).The prototype of Liushan Basin was a compressional basin,and that of Mashiping was an extensional one.Both of them were reformed by large scale southward overthrust-wrenching during late Yenshanian movement and became compresso-shear basins during the continent-continental collision between Yangtze and North China Plates.

    THE CENTRAL UPLIFT OF ORDOS BASIN AND ITS GAS ACCUMULATION
    Tang Xianming, Hui Binyao
    1993, 14(1):  64-71.  doi:10.11743/ogg19930109
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    The central uplift of Ordos Basin is located in Wuqi-Qingyang-Fuxian region and could be divided into steep slope area in the west flank,eroded area in central uplift,gen-tle slope area in the east flank,gentle slope in the north flank and steep-gentle changing area in the south flank.The uplift underwent Pre-Caledonian,Caledonian,Hercynian,Yenshan and etc.evolution periods.The uplift is close to two gas generation centers of Or-dovician,Permo-Carboniferous Systems,which provide rich gas-sources for the east flank slope area,thus the uplift is favourable in seeking for weathered-crust and other subtle traps.The bauxite of Middle Carboniferous Benxi Formation can be direct seal,and Per-mian argillaceous rocks may act as regional seals.Hence Jingbian-Zhidan-Fuxian area in the east flank of the uplift is most favorable for gas exploration,then Dingbian-Tianchi,the west steep slope is the reserve area.

    MESOZOIC HYDROCARBON PROSPECTS IN TARIM BASIN
    Tang Kaijiang
    1993, 14(1):  72-79.  doi:10.11743/ogg19930110
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    Tarim Basin,covering a range of 56×104 km2,is a Meso-Cenozoic inland basin of composite-superposed type formed on a stable landmass.The Meso-Cenozoic sediments are mainly coal-bearing clastic rocks that are distributed within an area of 38×104 km2 with the thickness of 1600m-5000m.Triassic-Jurassic source rocks are dark argillaceous rocksand coal measures intercalated with gray carbonate rocks and oil shales of 700-1200mthick.Organic matter is primarily ⅠB-Ⅲ type and partly Ⅰ-ⅡA type,vitrinite re-flectance Ro is generally 0.6%—1.2%,suggesting good hydrocarbon generating potential.As for hydrocarbon preservation condition,sandbodies of fluvial,deltiac and lacustrine facies are well developed in Mesozoic,which might form favourable preservation sedimen-tary facies in time and space;many drape structures,compression anticlines,lithologic and stratigraphic traps developed there,which prepared fine conditions for the formation of hydrocarbon pools.Thus the Mesozoic stratum in Tarim Basin has shown bright prospects in hydrocarbon exploration.This has been proved by the discovery of a number of high-productive wells such as Sha-5(K1),Sha-4(J)and Lunnan-2(T)wells.

    GEOTHERMAL GRADIENT AND HEAT FLOW VALUES OF SOME DEEP WELLS IN SICHUAN BASIN
    Han Yonghui, Wu Chunsheng
    1993, 14(1):  80-84.  doi:10.11743/ogg19930111
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    The geothermal gradient contour chart of Sichuan Basia shows that geothermal gra-dient of Central Sichuan is 25 -30℃/kin±,and it decreases to 20℃/km in the western,northern and eastern parts of the basin.A profile showing the basin’s heat conductivity was made based on 58 data of heat conductivity measured from some deep well cores and the heat flow values of 6 deep wells were calculated as follows:D-87 well in Central Sichuan is 68.83mW/m2;D-100 well and D-96 well in Western Sichuan are 48.51mW/m2 and 52.27mW/m2;D-55 well and D-69 well in Northern Sichuan Basin is 48.03mW/m2 and 42.49mW/m2;D-82 well in Northeastern Sichuan Basin is 45.49mW/m2.The average value(50.83mW/m2)is lower than North Jiangsu,South Jiangsu and NorthChina Basin.