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Table of Content

    25 September 1994, Volume 15 Issue 3
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    OUR UNDERSTANDING OF TRAP'S OIL AND GAS RESOURCES ASSESSMENT EXPERT SYSTEM
    Li Shusen, Wang Chuan, Fan Mingxing
    1994, 15(3):  187-192.  doi:10.11743/ogg19940301
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    Trap's oil and gas resources assessment expert system is an applying branch of expert system technology in geology field.The first important thing for this system to be successful or not is to select an appropriate knowlege domain.It is the distinguishment and assessment of oil and gas pools that is the knowledge domain on which the system can be used on. The knowledge obtained should be made up of the model of oil and gas pools and the understanding of the pools that experts have in their minds.In order to make the assessment way and assessmet results to be accepted easily by users,we should make the thinking mode of the system like that of human geological specialists.So geological anology inference is used to simulate the thinking mode of geological specialists.Like human expert,the system should have considerable depth and extent of knowlodge.The depth is come from appropriate knowledge domain and from the expert's special and experiential knowledge.The extent is come from the wide scope and vast amounts of knowledge.In order to make the expert system have both great amounts of knowledge and nimble operation,it is proposed to adopt "Assembling and producing" mode for the establishment of the system's knowledge base.Since mest of the questions in petroleum geology are uncertain,the uncertainty reasoning would be the running mode of the system's inference engine.The principle of selecting an oil and gas accumulation model is that the model can stand for a kind of mechanism of oil and gas accumulation.Through the model,one can know well the accumulation process,the producing condition and the gsometry characteristics of oil and gas pools formed under this mechanism.

    AN APPROACH TO MESOZOIC STRIKE-SLIP ACTIVE ZONE IN LOWER YANGZI REGION
    Xia Bangdong, Li Peijun, Shang Yanjun, Gu Lianxing
    1994, 15(3):  193-200.  doi:10.11743/ogg19940302
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    The depocenter of Middle-Upper Triassic,Lower-Middle Jurassic and Cretaceous sediments in Lower Yangzi Region is a sinistral echelon and has obvious sedimentary thickness gradients.The MiddleUpper Triassic Huangmaqing Group contains phengite and large amounts of apatite,which demonstrats that the area composed of Precambrian metamorphic rocks and situated at the northern side of the basin was the source area of the Huangmaqing deposits,and a significant shift from the source provenance to the despition site could be found.Both the Lujiang-Zongyang and Naming-Wuhu Mesozoic volcanic basins aness the features of pull-apart basin, and occur on strike-slip extensional fault branches of NNE striking.Two fold episodes of Middle-Late Triassic are obvious in some places but obscure in others.The above mentioned characteristics suggest that Lower Yangzi Region should belong to a Mesozoic strike-slip active zone.The main tectonics controlling the development of this zone are:1.The Yangzi fault zone;2.A wedge-like fualt system in which Tancheng-Lujiang fualt is the main body;3.A horsetail-like fualt system in which Qingyang-Guangde fualt is the main part.All of the fualts were active sinistral strike-slip during Mesozoic.

    PALEOECOLOGY OF PERMIAN REEF IN GUANGXI AND GUIZHOU
    Wu Yasheng
    1994, 15(3):  201-207.  doi:10.11743/ogg19940303
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    Permian reefs in Guangxi and Guizhou Provinces are mainly constructed by scleresponges,inozoans, shpinctozoans,hydrozoans,rugosa,bryozoans and calcareous algae.The reefs Can be divided into 7 types of fabric-factes:frame factes,baffle factes,prebaffle facies,floated facies,briccia factes,packwacked factes and grained factes.Six guilds have been recognized in the reefs.They are:(1) framing guild,(2) baffling guild,(3) prebaffling guild,(4) binding guild,(5) epibiont guild,(6) dwelling guild.Guilds(1),(4),(5) and (6) are distributed in the framed factes; guilds(2),(5),(6) and (4) are distributed in the baffled facies; guilds(3),(6) and(5) are distributed in the prebaffled factes.Community-types and communities in the reefs are as follows:(1) binder-Framer-community.It includes(a) Archaeolithoporella-sponge community,(b)Archaeolithoporella-thin sponge community,(c) Archaeolithoporella-Monostysisyrinx community,(d)Archaeolithoporella-bryozoan community.(2) epibiont-binder-Framer-community .It includes Tubiphytes-Archaeolithoporella-sponge community.(3) dweller-Framer-community.It includes (a) Tubiphytes-sponge community,(b) foraminiferarugosa community.(4) dweller-Baffler-community.It includes(a) Tubiphytes-less sponge community,(b)foraminifera-less rugosa community.(5) dweller-Prehaffler community. It includes Tubiphytes-few sponge community.The community types(1 ),(2) and (3) are distributed in framed factes; the community-type(4) is distributed in baffle factes; the community-type(5) is distributed in prebaffle facies.The community replacement in the reefs is characterized by the cyclic development of the community-types.This might reflect the fluctuation of the paleoclimate.

    SECONDARY PORE FORMATION MECHANISM OF THIRD MEMBER OF SHAIJEJIE FORMATION,RAOYANG DEPRESSION
    Zhang Yiming, Hou Fanghao, Fang Shaoxian, Zhu Lianru, Tao Hongxing
    1994, 15(3):  208-215.  doi:10.11743/ogg19940304
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    Three developmental zones of secondary pores could be recognized vertically in the 3rd member feldspathic sandstone of the Shahejie Formation.The pore spaces are primarily feldspathic dissolution pores.The acidic composition resulted from organic matter decarboxylation,balance-reactinons between mineral phrases in special diagenetic environment and favourable conservation conditions in local places are the main cause for the development and preservation of the secondary pores in study area.three favourable zones have been divided in prediction according to their depositional environment, structural feature and burial diagenetic history.

    FLUID INCLUSION IN XICHANG BASIN AND ITS APPLICATION TO HYDROCARBON EXPLORATION
    Qin Jianxiong, Zhang Changjun, Li Tianshen, Li Yungang
    1994, 15(3):  216-225.  doi:10.11743/ogg19940305
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    According to the research made on fluid inclusions in Lower Permian carbonate rocks in Xichang Basin,the fluid inclusions could form in every stage of reservoir diagenetic evolution,hydrocarbon generation,migration and accumulation.This could be the direct evidence for the formation environment and development stages of reservoir porosity,and for hydrocarbon generation, migration and accumulation.The study on diagenetic cements and pore-filling minerals of fluid inclusions in different stages shows that the evolution of Lower Permian source rocks and reservoir porosity development underwent following seven diagenetic stagesl,namely penecontemporaneous,early diagenetic,mid-late diasenetic,epidiagenetic,early,middle and late reburial stages.The epidiagenetic karst porosity, early reburial deep dissolution porosity and middle-late structural cracks constituted the main oil and gas reservoir spaces in hydrocarbon accumulation period. Hydrocarbon generation and primary migration occurred during LatePermian(i.e.early reburial stage); large amounts of hydrocarbon migrated and accumulated during the Triassic(middle reburial stage) and most of natural gas migration and accumulation took place in Jurassic(late reburial sarge) and thereafter.Hydrocarbon generation,migration and accumulation in the study area were closely related to Hereynian basalt eruption,and the tectonics and magmatic intrusion of indo-China and Yenshanian.

    SEDIMENTOLOGY OF GRAVITY FLOW DEPOSITS OF MIDDLE ORDOVICIAN PINGLIANG FORMATION IN WEST AND SOUTH MARGINS OF ORDOS
    Wu Shenghe, Feng Zengzhao, Zhang Jisheng
    1994, 15(3):  226-234.  doi:10.11743/ogg19940306
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    Pingliang Formation of Middle Ordovician developed only in west and south margins of Ordos Basin in North China Platform.Two kinds of gravity flow deposits,carbonate and elastic rocks developed in the formation.The carbonate gravity flow deposits include debris flow deposits (mainly breccialimestone),turbidites(mainly calcarenite) and grain flow deposits(echinoderm-elastic grainlimestone).Clastic gravity flow deposits are mainly turbidity flow deposits,consisting of conglomerate and sandstone.The formation and distribution of the gravity flow deposits were governed by simultaneous faulting and sedimentary framework.The latter includes four types:1.fracture-grabon; 2.fracture-slope; 3.platform-slope;4.platform-graben.The simultaneous fault is both an important factor in the formation of slopes and the source province of the gravity flow.Down along the slopes,collapse,slump,debris flow(and gravity flow), high and low density turbidity flow deposits occur sequentially.There are different complexes of simultaneous faults,and in turn differentia of gravity flow deposits and various sedimentary frameworks in the region.The gravity flow deposits are potential important hydrocarbon reservoirs.

    IDENTIFICATION OF CONTOURITES IN MIDDLE ORDOVICIAN GONGWUSHU FORMATION,ZHUOZISHAN,AND DEPOSITIONAL ENVIRONMENT
    Li Rihui
    1994, 15(3):  235-240.  doi:10.11743/ogg19940307
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    The Middle Ordovician Gongwushu Formation,distributed in the Zhuozishan area,Inner Mongolia,consists chiefly of greycoloured thin-bed limestones interbedded with shales in the lower part and thin-bed siltstones in the upper.It also yields abundant trace fossils,some planktonic organism fossils.In terms of its swhmentary characteristics,trace fossil assemblages and the related body fossils,it is suggested that the upper thin-bed siltstones should be sandy contourites,and its sedimentary characteristics are in accordance with the criteria proposed by Hollister and Heezen,Lovell and Stow.The main grain parameters are σ1:0.45-0.57;SK1:(-) 0.599;Kg,:3.089.Trace fossils which co-exist with the contourites are ichnogenus Helminthopsis and Paleodictyon.Boby fossils which occurred in the formation are graptolites,small thin-shelled brachiopds and deep-coldwater conodents.The sedimentary environment of the formation is belived to be a continental slope with water depth no less than 200-600 metrs during the deposition process.

    SEISMIC FACIES OF JURASSIC IN EASTERN JUNGGAR BASIN
    Pn Renhai, Met Zhicao, Tang Zhonghua
    1994, 15(3):  241-247.  doi:10.11743/ogg19940308
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    Extensively developed Jurassic coal-meassures in the eastern Junggar Basin have considerable influence on seismic velosity and seismic amplitudes,and this might even impose restriction to some extent on the study of laminnae through seismic factes.But the planar distribution pattern and extension tendency of complex amplitude anomaly in dense 2-dimensional seismic netwotk may be efficient in the prediction of some depositional bodies of suitable thickness.According to Jurassic reflective markers,eight seismic factes have been generalized in this paper,and they in turn could be interpreted as allavialfan,fluvial channel,delta,lake and marsh land.It is proposed by the authors that lake-marsh land facies are the main hydrocarbon-generation factes zones of the region,and the fluvial channels are themain reservoir factes.

    EFFECT OF DIAGENESIS ON PORE STRUCTURE OF THIRD OIL LAYER IN XINGOUZUI FORMATION,QIANJIANG
    Wu Guanghong, Yao Xiaoming
    1994, 15(3):  248-256.  doi:10.11743/ogg19940309
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    The effect of diagenesis on pore structure of sandstones in third oil layer of Xingouzui Formation in Tuoshi area,Qianjiang Depression is discussed in this paper.The compaction and cementation decreased the pore throat and pore radius of the sandstones in different degrees,and caused the pores to disintegrate into micropores and intercrystal pores,the throats into schistose throats and tubebundle throats in sandstones.The dissolution increased the pore throat and pore radius of sandstones,turned the pores into coarse ones and tubular throat.The compaction resulted in better pore sorting,but the cementation and dissolution made it more complicated.In sandstones of compaction type and cemetation type,the permeability contributed peak position is inconsistent with that of the pore distribution peak position,and their permeability for air is usually less than 1 thousandth of square micron and devoted by few pore spaces with radius bigger than 8 micron.In sandstones of dissolution type,the permeability devoted peak position is usually consistent with that of the pore distribution,thus the main pore spaces of the sandstones are vadose pores.

    SEISMIC STRATIGRAPHY OF UPPER JURASSIC-LOWER CRETACEOUS IN SONGLIAO BASIN
    Yang Changqing
    1994, 15(3):  257-263.  doi:10.11743/ogg19940310
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    Songliao Basin is composed mainly of Upper Jurassic-Lower Cretaceous sediments and could be divided into four seismic sequences and two supersequences.According to the texture and geometry of the basin's seismic reflectance,sedimentary bodies such as subaqueous fan,fan delta,lacustrine,fluvial,turbidite fan,volcanic rocks and volcaniclastic rocks have been recognized.