Table of Content

25 September 1981, Volume 2 Issue 3

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A PRELIMINARY STUDY OF HYDROCARBON PRODUCTION FROM VARIOUS TYPES OF KEROGEN AT DIFFERENT MATURE STAGES

Li Wenguo

1981, 2(3):  199-211.  doi:10.11743/ogg19810301

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After reviewing a few main available methods of calculation for hydrocar-bon production,the writer,based on the mechanism of hydrocarbon forma-tion through the evolution of kerogen,suggests a new method of calculatinghydrocarbon production according to the variation in elemental proportionduring the evolution of kerogen,and using this method,calculates theamount of hydrocarbon produced by individual types of kerogen at differentmature stages.The results are shown in the following table(primary kero-gen considered as 100%).

ON THE PORE GEOMETRY OF THE MIDDLE CARBONIFEROUS CARBONATE RESERVOIR IN EASTERN SICHUAN

Luo Zhetan, Wang Yuncheng, Deng Xunkang

1981, 2(3):  213-226.  doi:10.11743/ogg19810303

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This paper applied the mercury capillary-pressure test,pore casts and dynamic test to study the pore geometry of the Middle Carboniferous car-bonate reservoir in eastern Sichuan and attempted to explain its pore geo-metry chracteristics and porosity parameter.On the basis of the observation of core-cast-sections of Xiang-16,Wo-49 and Zhang-2 wells,the pores of the reservoir may be classified into threetypes,i.e.intercrystal pore,fracture and irregular corrosion pore.In orderto precisely evaluate the role of every basic pore type in capacity and per-meability,the relationship of pore combination have been further studied and divided into eight combination forms.The optimum pore combination isthe“coarse intercrystal pore-corrosion pore-corrosion fracture”,the sec-ond,will be“coarse intercrystal pore-fine intercrystal pore”and“inter-granular pore-intergranular intercrystal pore”,the others,belong to lowcapacity-permeability.In short,the goodness of the capacity-permeability of the reservoir depends on the development of corrosion pore and coarseintercrystal pores.The authors propose that the lower limit of width of effective(hydro-carbon bearing)porosity in reservoir may be defined as 0.1μ.This value,according to the characteristics of flaky throats of acrbonate rocks,corre-sponds to the pore-throat width of mercury injection at 75 atm.Applyingthe mercury capillary-press ure method,the effective porosity of more than 0.1μ of each sample may be determined.With respect to the Middle Car-boniferous,the effective porosity is one of the main parameters in evalua-ting reservoirs.The pore-size distribution of corroded dolomite is caused by various origins during the diagenetic and deuterogenic processes.In statistics,they wouldbe characterized by the numeral characteristic parameter of the geologicalmixed experimental distribution.By using the matrix operation method,wecan calculate four important characteristic parameters expressing the poredistri bution of reservoir rocks,i.e.mean value(X),standard deviation(σ)variable coefficient(C)and skewness(Sk).In order to describe completelythe capacity of carbonate reservoir,the authors suggest a synthetical param-eter of eflective porosity(M_g)and pore geometry,i.e.M_g×C or M_g/X.Consequently,on the basis of main pore combination,effective porosity(>0.1μ)and the syntheitcal parameter of porosity and pore geometry,we can classify and evaluate the Middle Carboniferous rersevior.On thesegrounds,the reservoir of Xiang-16 well may be divided into seven members,the thicksess of effective reservoir of each member and its effective meanporosity have been listed in table 2.For the sake of studying fracture porosity,the data of dynamic test hasbeen used to analyse the combination relationship of pore-fracture in reser-voir.The main characteristics of actual build-up pressure curve of shut-ingas wells in Middle Carboniferous apper to be multistep-shaped.This is be-cause of that the matrixes of reservoir rocks are not homogeneous,there-fore,their original pores are multigrade,and inevitably there exist multi-grade pore throats.They indicat that the reservoir must be a medium comp-osed of multipore systems-a multiporous medium.In this paper,we have sug-gested a reservoir model of multiporous medium,and deals with the methodwhich applied multistep build-up curve to calculate the total porosity.Finally,some actual calculations of porosity in various parts of Xing-guosi gas field have been made,they reflect that the fracture porosity pred-ominates over this gas field,especially in the structural high.

A MODEL OF CRETACEOUS SEDIMENTARY FACIES IN SONGLIAO BASIN

Wang Hengjian, Chao Wenfu

1981, 2(3):  227-242.  doi:10.11743/ogg19810304

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The Cretaceous system in Songliao Basin is composed of fluviolacus-trine deposits.Based on hydrodynamic conditions and characteristics offrame work sand body,it is appropriate to divide the sediments of the lakebasin into several major facies,i.e.diluvial,flood plain,distributary plain,delta front,near-shore shallow lake,moderately deep-deep lake and alluvialplain facies.Major target formations for oil and gas exploration are locatedin the distributary plain,delta front and near-shore shallow lake facies.The distributary plain facies may be subdivided into distributary river bed,crevasse fan,natural levee,and interdistributary depression subfacies.Their lithologic assemblage,oryctocoenose,stratification and the shape of sand body are different.The delta front facies is composed of river mouth bar,front sheet and subfluvial channel sands as a framework.According to therelation between the delta extension and the basin axis,the delta facies maybe classified into lobate delta complex and fan delta complex.The former hasa wide zone of fluviatile facies,and the latter has diluvial material flowe ddirectly into the lake.Individual deltas in the lobate delta complex havethe following three types:the lobate,the bird-foot and the sheet.They represent respectively the moderate lake regression,maximum lake regre-ssion and lake transgression periods.They developed in succession on profileand formed a complete delta cycle.After a systematic study of the delta in Songliao Basin,we have pointed out the difference between the sea-warddelta and the lake-ward delta.A near-shore shallow water facies among deltasmay be subdivided into underwater sand bar,shallow lake sand sheet,ostr-acoda or oolitic beach and mudflat subfacies.This is the facies zone wherebiogenic and chemical deposits are most developed in the lake basin,aparticular authigenic mineral—glauconite—is formed.

ON THE DEVONIAN LONGTOU MOUNTAIN ATOLL,NANDAN,KUANGSI

Zhou Dikang

1981, 2(3):  243-253.  doi:10.11743/ogg19810305

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Longtou Mountain atoll is developed in a open sea of early Middle Devo-nian.The explored reef is a dome-like carbonate body stricking NNW,4.8km long,3km wide and more than 900m high.The reef-building organisms are mainly composed of Stromatopora,Ta-bulata,HelioIites,Chaetetes and a few of Tetracoral.Some reefphilic organi-sms such as Echinodermata,Brachiopoda are also abundant.In reef coreand forereef subfacies,the organism contents in situ are usually 30-40%,locally above 80%.The atoll may be divided into forereef subfacies(including forereef flatbioclastic limestone microfacies):reef core subfacies(including reef base orinterreef sand-size intraclasts-Echinodermata limestone microfacies,irre-gular and coarse arborescent Tabulata-Stromatopora lime bafflestone micro-facies,tabular and dome-like Tabulata-Stromatopora lime framestone micro-facies);reef flat subfacies(including back-reef flat bioclastic limestonemicrofacies,sand-size intraclasts-pellet or lump limestone microfacies);back-reef lagoon subfacies(including Amphipora micrite microfacies,birds-eye micrite microfacies).Nearly all above mentioned subfacies and micro-facies appear to be hemi-circular zones bulging southwest wards.In the reef body,there are rich in nonferrous metals such as cassiter-ire,lead,zinc and a large amount of bitumen.The bitumen,produced between the grains of rock and in the organisms,are controlled by the pri-mary porosity and are mainly distributed in forereef and reef core;and yet,thebitumin,produced in structural fractures,vugs and stylolite,may be relateded to the fissures which are formed by the reef diagentic and epigenetic changes.The presence of large amount of bitumen indicates that there existed an oilpool which has been destroyed now.The writer believes that the openseablack mudstone and argillaceous limestone surrounding and covering the reefwere good source rock and cap-rock.

DINOFLAGELLATES AND ACRITARCHS FROM DALANSHAN FORMATION AND THEIR SIGNIFICANCE IN EXPLAIN THE DEPOSITIONAL ENVIRONMENT

Yu Jingxian, Sun Mongrong, Sun Suying, Mao Shaozhi

1981, 2(3):  254-264.  doi:10.11743/ogg19810306

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Plenty of dinoflagellates and acritarchs are firstly discovered in theLate Cretaceous Dalanshan formation of Sanshui Basin,Guangdong Province.Two assemblages recognized in the Formation,from bottom to top,areas follows:1.The Palaeostomocystis-Compenia assemblage,in which pollen,spores and Pediastrum are predominat but with sparse plank tonic algaeindicating a near-shore transitional environment;2.The Parastrocysta-Api-culadinium assemblage.The content of phytoplankton in this assemblageis equal to,or much greater than,that of pollen and spores,and rich ingenera and species,whereas Pediastrum degenerated.Most of dinoflagellatesin the Formation are small in size.with thin outer membranes and sparseornaments,clear girdle and apex,obscure tabulates,archaeopyle is unseen,“nucleus”is present near the ventral surface.These features may indi-cate that the sediments were deposited in brackish water and the Late Cre-taceous transgression had some influence on this area.The depositionalenvironment of this assemblage might be favorable for the oil genesis.Five new genera are described in this paper,they are Parastrocysta,Apiculadinium,Belatudinium,Sanshuia,and Pseudoslephodinium,all together14 new species.

NORMAL DRAG STRUCTURE AND ITS SIGNIFICANCE IN OIL PROSPECTING

Wang Ningguo

1981, 2(3):  265-275.  doi:10.11743/ogg19810307

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The occurrence of anticlinal structures in coincidence with synsedimentary thrusts have been usually seen in Qaidam basin.The author thus proposeda new type of contemporaneous structure—normal drag structure.The normal drag structures appear to be similar to the reverse dragstructures(rolling anticlines)in shape,but the scale of the former is muchbigger than the latter,the character of faults and their dynamical mechanismare also completely different to reverse drag structures.The faults,distributing in bands,may usually reach to and is controlled by the basement rock,therefore,the fault plane is smooth,its dip-angle usually exceeds 45°.In comparison with the downthrown sides,the strata on the upthrown sides is thinner and itsgrain-size is coarser,and besides the fault displacement increases with depth.The normal drag anticlines,in general,are developed on upthrownsides,being confined in between two thrusts in a shape of reverse chinese character “丷”.The anticlines are characterized by thinner strata and coar-ser grain-size on thier tops,steep dip angle in the deeper part and gentledip angle in the shallower,as well as the vertical congruence of antictinal heightsat v arious depths with the basement rises.There are some post-depositional anticlines,with thicker strata on itstop and steeper dip-angle in upper beds,superim posing on the earlier con-tamporaneous normal drag anticlines.This fact shows that in different stages of the anticlinal development,we must analyse and distinguish themthroughly.Normal drag structure is a contemporaneous anticline controlled by thesynsedimentary fault in basement rock under continuous horizontal compres-sion of block-fault,crust-wave and folding movements during deposition in Meso-Cenozoic periods.According to the data of Qaidam basin,the normaldrag structure may be mainly divided into two types:normal drag anticlineand wedge-like anticline.Experience has demonstrated that normal drag structures are favour able to oil and gas accumulation and usually constitute some oil and gas accu-mulation zones.There are various types of oil and gas pools in normal dragstructures.Exploring for normal drag structure along synsedimentary thrustsis always a effective approach for oil and gas exploration.The author believes that more and more normal drag structures wouldbe continually discovered in the oil and gas-bearing basins which formedin the compressive zones in western China.

ON THE SEISMIC STRATIGRAPHIC SEQUENCE,LAKE LEVEL FLUCTUATION AND OIL PROSPECTING IN QIANJIANG DEPRESSION

Hu Bingxuan Liu Yizheng

1981, 2(3):  276-283.  doi:10.11743/ogg19810308

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This paper applies the method of seismic stratigraphy to divide the stra-tigraphic sequence of Qianjiang depression and to map the periodic fluctua-ting curves of the old lake level.The following results have been obtained:1.Two erosional surfaces has been discovered recently,one at the top ofthe Jingsha formation of Lower Tertiary,and the other at the top of the Yuyang formation of Cretaceous.The authors suggest that the explorationof oil and gas pools should be associated with these uncomformity planes.2.Among the horizons of Lower Tertiary—the lower and the upper partsof the 4th Member,the 3rd,2nd,and 1st Members in the Qianjiang forma-tion;the 4th,1st-3rd Members in the Jinghezheng formation—we have found the relation ship of onlap contacts.A new point has been suggested thatsome overlap unconformable stratigraphic oil and gas pools should be foundin the northern part of the Qianjiang depression.3.With correlation of periodic fluctuating curves of the lake level and the global Tertiary sea level,the Lower Tertiary in Qianjiang depression has been further divided in age.

THE MATURITY OF ORGANIC MATTER AND OIL AND GAS POTENTIAL OF TAIYUAN FORMATION IN NORTHERN ORDOS BASIN ACCORDING TO THEIR VITRITE REFLECTIVITY

Zhu Zongqi, Lee Biqi, Xie Qiuyuan

1981, 2(3):  284-291.  doi:10.11743/ogg19810309

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This paper briefly clarifies the basic geological theories of vitrite refle-ctivity（R^o max）and gives a preliminary discussion with R^omax on the con-ditions of oil and gas origin in Taiyuan formation of Carboniferous Sys-tem in northern Ordos Basin.It is suggested that R^omax ranging from 0.5to 1.3% is confirmed as the main stage of oil formation;<0.5%,as im-mature stage;>1.3%,as overmature stage,that is,gas formation stage.The result shows that the organic matter of Otoc County and its south ernregion have reached overmature stage;in its northern region,the Taiyuan formation is just at the main mature stage,but the conditions of conser-vation on both sides of east and west are rather defective,the availableregion is only restricted in a narrow zone in the southern part of the west.Finally,in combination with the geotectonic evolution,sedimentary cha-racteristics and lithofacies of the basin,the districts of oil and gas pot-ential of Taiyuan formation has been divided.

GEOGRAPHICAL DISTRIBUTION OF OIL AND GAS DISCOVERED IN ANCIENT CHINA

Dai Jinxing

1981, 2(3):  292-298.  doi:10.11743/ogg19810310

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China is one of the pioneering countries in discovering and using oil andgas.The first gas field(Ziliujing gas field)in the world,for example,was developed in China.In the Western Zhou Dynasty of our country(from the 11th century B.C.to the 771 B.C.),oil and gas seepage——“firein swamp”was discovered.In ancient China,oil was called“oil in firewell”,“well-oil”,“fire oil”,“surphur oil”,“realgar oil”,“fierce-fire oil”,“naphtha”,“mud oil”,“crude oil”,“earth wax”,“stone lacquer”,“oil-water”,“paraffin”etc.;and gas was called“fire in well”,“well-fire”,“coal gas”,“fire dragon”,“fire spring”etc.Historic literature indicates that a lot of oil and gas shows weredistributed in 23 provinces,municipalities and autonomous regions of thepresent administrative division:1.Beijing,2.Shanghai,3.Tianjin,4.Sha-anxi,5.Sichuan,6.Hebei,7.Shanxi,8.Shandong,9.Anhui,10.Zhejiang,11.Jiangxi,12.Fujian,13.Taiwan,14.Guangdong,15.Guangxi,16.Hunan,17.Hubei,18.Henan,19.Yunnan,20.Xinjiang,21.Gansu,22.Liaoning,and 23.Heilongjiang.