Table of Content

25 December 1981, Volume 2 Issue 4

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ON THE BIOLITHITE AND ITS OIL POTENTIAL FROM QIXIA FORMATION IN CHANGXING,ZHEJIANG

Yang Wanrong, Jiang Nayan, Qu Yonglong, Feng Zhiyao

1981, 2(4):  299-313.  doi:10.11743/ogg19810401

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The Qixia Formation,outcroping on the flanks of the Meishan synclinein Changxing,Zhejiang Province,has a total thickness of 236.94meters.It Consists mainly of bioclastic limestone intercalated with two beds of siliceou srocks which were formed by chemical precipitation.This Formation may bedivided into five lithologic members from top to bottom:the Top Limestone Member(18.11m);the Upper Siliceous Rock Member(24.48m);the Chert-bearing Limestone Member(114.11m);the Lower Siliceous Rock Member(24.04m)and the Stink Limestone Member(56.20m).The limestone contains abundant fossils of many species,but is lack ofcarbonate grains,terrigenous debris and sparry calcite cement.No rocks andsedimentary structures of supra-intertidal or evaporite facies are found.These features show a slightly restricted,subtidal,reducing and shallow-seaenvironment with low energy.The biolithite contains plenty of organic matter with more than 3 per-cert of organic carbon.This limestone,especially that of the Stink Limes-tone Member,is a good oil-source rock.Generally,the oil-storing conditionsof the biolithite are poor,but the suite of sparite and granular biolithite inthe upper part of the Chert-bearing Limestone Member in Meishan-Dushanarea can be considered as a favourable reservoir.According to the infrare dspectrum,the oil and gas are in high degree of thermal evolution and oxidization.

A DISCUSSION ON SOME QUESTIONS IN THE STUDY OF MESO-CENOZOIC CONTINENTAL HYDROCARBONBEARING BASINS OF CHINA

Guan Shicong

1981, 2(4):  314-320.  doi:10.11743/ogg19810402

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The continental hydrocarbon-bearing basins of China,formed in different periods during the Meso-Cenozoic times,have their own peculiarities ingeological and tectonic framework,type of sedimentary formation and hydro-carbon potential.Tectonic phase plays the most important role in controllingand distinguishing them.In time and space,the stress patterns of tectonic phases are converted each other due to the change of limiting conditions ofstress fields,thus determining the generation,distribution and type of basinsof various ages and regions,and their characters of sedimentation and miner-alization,etc.According to the relation between time and space of evolution of basins,they can be initially subdivided into two fundamental types:trough-basin andopen-basin.Their origin,sedimentary formation and hydrocarbon potentialshow different characteristics,which just reflects genetic relationship between basin evolution and tectonic phase A concept of“petroleum stratigraphy”is advanced for studying the rela-tion of stratigraphic combination and hydrocarbon potential Although a de-finite meaning is not given to the term“petroleum stratigraphy”,its study in-cludes the relationship of various sedimentary formations in all types of basinsto hydrocarbon generation,migration,accumulation and redistribution;whilethe source-reservoir-cap rock combinations are also its important component.Only when the relation of tectonic trace in present basin to hydrocar bonaccumulation is further analysed on the basis of the recognition of how tec-tonic phase correlates with generation and sedimentation of different types ofbasins,can it be able to indicate the basin-forming and oil-generating peri-ods of China in Meso-Conozoic times,to evaluate hydrocarbon potential,and to guide prospecting and exploration for oil and gas.

DIAGENESIS OF RECENT HOLOCENE REEF ROCKS OF XIAODONGHAI,HAINAN ISLAND

Sha Qingan, Pan Zhengpu

1981, 2(4):  321-327.  doi:10.11743/ogg19810403

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Xiaodonghai coral reef situated in the south part of Hainan Island isa fringe reef.δC¹⁴-dating shows that it developed about 8000 years ago.The texture constituents in reef rocks include reef-building organic frame-work which consists mainly corals,reef-philic organic skeleton fragments,boulders of organic framework,and bioskeleton mud and silt.They areregularily distributed in the certain part of reef flat.Diagenesis of reef rocks has its specific features which is dominated bythe process of organism in which adhesion and encrust acted a principlerole.These diagenetic process reflected different sedimentary environmen tsand their changes. In this paper the authors intend to discribe and discuss the adhesion andencrust of coral,coralline algae and foraminifera,and the fill of bioske-leton mud and silt,etc.These process usually were occurred together,andthey are controlled by sedimention-diagenesis environments.The similar diagenetic process are quite common in ancient reef or reefrocks.They are good keys to recognize ancient sedimentary facies and envi-ronments.

GEOLOGICAL CHARACTERISTICS OF PETROLEUM IN TARIM BASIN

Kang Yuzhu

1981, 2(4):  329-340.  doi:10.11743/ogg19810405

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The Tarim basin is the largest inland basin in China,covering an areaof about 0.56 m.sq.km.Considerable work was done in the past of petro-leum prospecting and exploration but was mainly confined to the Kuqa and the Southwestern depressions.Generally speaking,the basin has not been studiedfully.The writer has made an evaluation of the basin in three aspects.Firstly,based on data of stratigraphy,the sedimentary and tectonic evolution of the basin has been described;the structural systems and divisions,as well asthe features in the development of local structures has been expounded fromthe viewpoint of geomechanics and traditional geology;an explanation of main oil source beds,reservoirs and types of potential oil and gas traps hasbeen presented thereafter.Finally,the writer suggested that the Tarim basin would be a verypromising area for oil and gas.According to the available data,it is pointedout that the oil and gas potential varies in following descending order:the Southwestern depression,the Eastern depression and the Kuqa depression,the Central uplift,and the Southeast fault-step area.

THE PROSPECT OF PERMO-CARBONIFEROUS COAL-FORMED GAS IN NORTH CHINA

Chang Xiaozhe, Zhen Yichuen, Xie Chenkan, Yang Fuxin

1981, 2(4):  341-350.  doi:10.11743/ogg19810406

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The Middle Carboniferous-Late Permian strata in North China are char-acterized by complete development,widespread distribution,common exist-ence of coal,and more stable petrography and thinkness.Coal rank rangesfrom gas coal to anthracite,predominantly the medium-high level metamorphiccoal.The predicted reserves,above 1,000m,is estimated at 1,300 billionton.Based on a genetic rate of coal-formed gas of 250 M³/T,the predictedgenetic potential of coal-formed gas amounts to 325,000 billion cu.m.Becauseof the intense tectonic activity in this area,an accumulation factor of 1percent is used for calculating.As a result,coal-formed gas can be stillaccumulated at 3,250 billion cu.m.The traps,formed during the lndosinian and the Early Yenshanian movements in North China,are favorable to the accumulation and preservationof coal-formed gas.So far the following preservative forms of coal-formedgas have been recongnized in this area.1)the accumulation in the Permian and Triassic red beds overlying coalmeasures.2)the accumulation in coal measures.3)the accumulation in ancient weathering crust.4)the accumulation in the Meso-Cenozoic sandstone.5)the accumulation in the solution in water layer.The prospecting and exploration for coal-formed gas,first of all,shouldbe in areas where Triassic system developes better and structural traps ex-ists and where the burial depths of the top of coal measures are at 1,000-4,000 m,for example,Qinshui Basin,Jiyuan Depression and Baodin-Shijia-zhuang-Xingtai-Handang-Anyang areas,etc.coal-formed gas means the gas associated with a coal source.

A PRELIMINARY APPLICATION OF GEOMATHEMATICAL METHODS TO OIL PROSPECTING IN WEST JIUQUAN BASIN

Cheng Liguan, Cheng Guangying, Li Hongzhi, Zhang Yinzhai

1981, 2(4):  351-358.  doi:10.11743/ogg19810407

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After years of exploration,three oil fields,including Baiyang River oilfield,were discovered in the monocline zone in the northern part of the west Jiuquan basin.It is an urgent task for us to find out new oil fields.There-fore,we have,combining with geological studies and using trend surface anddiscriminant analyses,comprehensively studied the relations of known oil fields with geological variables,such as reservoir's structural residual value,thickness and its residual value,mean value of self-potential curve,frequen-cy of sand bed,ratio of thickness of less permeable intercalation to totalthickness of reservoir,and with the marginal slopes of these variables.It isdemonstrated quantitatively that the oil pool in the middle and upper parts of Huoshaogou Group(Eh₂₊₃) is mainly controlled by lithological and structural factors.The characteristics summarized here of the distribution of oil fieldsare as follows All known oil pools occupy the favorable structure positions in areas with positive residual values and with less permeable zones along updip formations.They may also be alined as strings of beads in a northwestern direction.Based on this,it was suggested that drilling should be carried out in eight promising blocks of four areas.Consequently,oil sand or commercial oil was found in blocks A,B and C by test-weels（Fig.8）,which shows that initial success has been achieved in the prediction.

ON THE ORGANIC GEOCHEMICAL CHARACTERISTICS AND OIL-SOURCE CORRELATIONS IN TARIM BASIN

Hu Boliang

1981, 2(4):  359-368.  doi:10.11743/ogg19810408

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In this paper,by using of some advanced techniques,the organic geoche-mical characteristics of the crude oil and its possible source rocks in Tarimbasin and their oil-source correlations have been studied and presented here.It is pointed out that,in Tarim,the marine beds of Upper Cretaceous-Low-er Tertiary is a moderate source rock only;the Jurassic lacustrine formationis rich in organic matter and may be the best source bed in this basin,but itis distributed only in some local areas,such as Kuqa and Kashi depressions;the Permo-Carboniferous system has a relatively low content of organic mat-ter,but it is widespread and very thick,therefore,it may be the most poten-tial source bed for oil and gas among the three possible source beds in the basin.The high-yield crude oil and gas in the continental Miocene of the Keke-ya oil field are highly maturated and characterized by terrigenous origin,therefore,the author believes that they may migrate from Permo-Carboni-ferous source beds.Some crude oil in the Kuqa depression is marked by marine origin,whichshows that the Meso-Cenozaic in this area may contain some marine sourcebeds.

AN OUTLINE OF SPORO-POLLEN ASSEMBLAGES IN CRUDE OIL IN THE SECOND MEMBER OF SHAHEJIE FORMATION AND OF THE OIL AND GAS MIGRATION,SHENGLI OIL FIELD

Wang Kaifa, Zhang Yulan, Yin Mo

1981, 2(4):  369-372.  doi:10.11743/ogg19810409

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The fossil sporo-pollen assemblages found in the crude oil of the Second Member of Shahejie Formation in Shengli Oil Field have the same characte-ristics as those in the underlying Third Member,which indicates that theycame,in company with the migrating oil and gas,from oil source rocks ofthe Third Member.It follows that the study of characteristics of fossil sporo-pollens may behelpful to tracing the migration history of oil and gas,and is useful to theoil-to-source rock correlation.

EARLY CRETACEOUS SPORO-POLLEN ASSEMBLAGES FROM EJINUOR BASIN,EASTERN INNER MONGOLIA

Wang Congfeng, Qian Shaohua

1981, 2(4):  373-381.  doi:10.11743/ogg19810410

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This paper deals with the systematic analyses and determinations of spore and pollen fossils from the Early Cretaceous Bayanhua Formation of Ejinuor Basin in eastern Inner Mongolia.A total of 48 genera were studied,among which 1 genus and 8 species are newly discovered.The Bayanhua Formation contains two sporo-pollen assemblages:1)in the Upper Member,the“Cicatricosis porites-Concavissimis porites-Pinaceae”assemblage;and 2)in the Middle Member,the“Lygodiaceae-Pinaceae”as-semblage.No sporo-pollen is discovered in the Lower Member of this For-mation.Should the Rehe Group be designated as the Late Jurassic or the Early Cretaceous? This question has been strongly controversial in recent years.Weconsider that,after study and comparison,the Bayanhua Formation in theupper part of this group should be designated as the Early Cretaceous.

A DISCUSSION ON THE TOP BRECCIA OF QINGLONG GROUP AND JINZI MOVEMENT IN NANJING AREA

Sun Wanquan, Huo Xiufeng

1981, 2(4):  382-387.  doi:10.11743/ogg19810411

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A paper entitled“The Jinzi Orogenic Movement and the Carbonate breccia at the base of the Huangmaqing Group in Nanjing area”was published in“Oil& Gas Geology”(1981,Vol.2,No.1),the views presented in this paper arequite different from ours.Since 1970's,we have made a systematic study of the Triassic System,particularly of its breccia in Nanjing area.We consider that this breccia isactually a altered product of gypsum and salt-bearing formation at the top of Qinglong Group.When it was exposed on,or occurred near the surface,the formation was leached by water.As a result,its wall rocks,the intercalationsof sediments themselves,or even the overlying strata were collapsed into frag-ments.Subsequently,it was recemented to become this breccia called a dissol-ved-salt breccia or collapse breccia.Therefore,it is not the product of the“Jinzi Movement”and can not be considered as a“basal conglomerate”ofthe Huangmaqing Group.It is known that gypsum and salt deposits of the Qinglong Group of theTriassic period in the lower reaches of the Yangtze River are distributed with in an area of several ten thousand square kilometers.Based on the occur-rence of surface dissolved-salt breccia,a prediction can be made for the pre-sence of subsurface gypsum and salt deposits.Indeed,this predicion is proved successfuly by nearly one hundred drill holes in this region.

THE PRESENT SITUATION AND DEVELOPMENTS OF PETROLEUM GEOCHEMISTRY IN OUR COUNTRY AS VIEWED FROM THE SECOND ANNUAL MEETING OF CHINESE PETROLEUM SOCIETY

Huang Difan

1981, 2(4):  388-390.  doi:10.11743/ogg19810412

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The Second Annual Meeting of Chinese Petroleum Society recieved more than 100 papers concerning petroleum geochemistry and selected 13 papers from these to read out at the special conferece about oil generation.References tocon stitution of source materials,methods and criteria of classification of or-ganic matter types,evolutionary mechanims and model of organic matter,andits thermo-reactive kinetics,biological markers(such as porphyrin,perylene,sterane and terpane et al.)oil and gas source rock correlation,evaluationindex of source rock and quantitative evaluation of oil generated,time-temper-ature index,the application of laser-pyrolysis gas chromatograph and othernew techniques and methods to the study of petroleum genesis are made.In comparasion with the First Annual Meeting,these results,both in their tech-nical level and their research depth and width,have obviously increased.Inthe field of organic geochemistry,Chinese geochemists have brought forth somenew ideas and begun doing their own contributions anew.The distinction bet-ween our research level and that of the world has been reduced.However,there are still some weak links and some new items which remainto be developed,we still have a long way to go in laberatorial techniques.For exampl,carbonate rock is widespread in China,but its amount of organicmatter is lower,maturation level is higher,and regional structures are morecomplex.Therefor,it is one of pressing items how to evaluate its hydrocar-bon potential and predict its favorable exploration targets.Other items,such as quantitative evaluation of source rock,composition and structuremodel of kerogen,analytical techniques,biological markers and simulatingtests have yet to be stutied deeply.