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Table of Content

    25 March 1999, Volume 20 Issue 1
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    MATHEMATICAL MODELING OF TEMPERATUREPRESSUREZTRANSIENT VARIATION IN OPENING FRACTURES AND SEDIMENTARY FORMATIONS
    Luo Xiaorong
    1999, 20(1):  1-6.  doi:10.11743/ogg19990101
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    Based on the geothermal anornaly and pore pressure distribution in Yinggehai Basin,South China Sea,a 2D mathematical model is established and applied to analyze the transient variation process of fluid flow and fluid pressure within paralle opening fractures and in the connected permeable formations.A characteristic time constent was obtained to illustrate the influences of stratigraphic and hydrodynamic factors on the process.The fluid transmisson coefficient of the fracture surfaces and the hydraulic conductivity of the fracture surfaces control the peak flow and the time duration keeping this flow through the fracture respectively.The vertical flow of underground thermal fluid resulted from the opening fracture is the important cause of geothermal anomaly.However,the existences of high abnormal thermal indexes,such as the smectite lillite transformation and vitrinite reflectivity observed in Yinggehai Basin,should be the results of a large flow of hot fluid along the vertical fractures during a long period.

    MULTIPLE ROOTS IN WELLRESTRICTED IMPEDANCE INVERSION
    Ma Jinfeng, Wang Xuejun, Zhong Jun, Xu Yajun
    1999, 20(1):  7-10.  doi:10.11743/ogg19990102
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    Log datarestricted wave impedance inversion technique is based on convolutional model.Because of misunderstanding its theory foundation,this method was misused to obtain high-resolution impedance profile or to improve seismic profile resolotuion.The theoretic modeling results of log data-restricted wave impedance inversion indicate that seismic inversion result has multiple roots.The similarity between seismic tracs does not mean the similarity between impedance series or reflection coefficient series.Coherent coefficient obtained from comparing synthetic seismic profile with original seismic profile can not be used as restricted condition to invert highresolution impedance profile or to improve seismic profile resolution in practical seismic data processing.

    REVIEWINGTHE RESERVOIR MODEL OF LOWER PERMIANGAS POOLS IN SICHUAN BASIN
    Lu Zhengyuan, Chen Liguan, Wang Honghui
    1999, 20(1):  11-14,29.  doi:10.11743/ogg19990103
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    The tubular cave system resulted from erosion in Dongwu stage are the main reservoir space of Lower Permian limestone reservoirs in Sichuan Basin.The cave system were burried first,then filled up and eroded and finally reformed by Himalayan tectonic fractures.The geological model of the reservoirs could be described as a combination of tubular caves system of Dongwu stage and Himalaya tectonic fracture network.It is proposed that the place where Dongwua stage cave system developed and the place where unicline and syncling developed should be taken as furthur exploration areas.

    HYDROCHEMICAL CONDITION OF NATURAL GAS ENRICHMENT IN EAST SICHUAN CARBONIFEROUS SYSTEM
    Xu Guosheng, Liu Shugen, Zhang Yingjun, Zhang Longteng
    1999, 20(1):  15-19.  doi:10.11743/ogg19990104
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    According to the analysis of water quality of more than 100 wells,the formation water of the Carboniferous in east Sichuan possesses high density and high direct metamorphic degree.The formation water in most parts of the study region is CaCl2 type,and the water in local places is NaHCO3 and Na2SO4-types.The formation water underwent the process of contemporary sea water→erosion leaching water→condensed metamorphic water with high mineralization in buried stage→associated water in gasfield.The places containing high mineralized formation water are favourable for gas accumulation;the places containing CaCl2-type water are favourable for gas accumulation and preservation.When Nal/Cl ratio of formation water is ≤0.65,natural gas could be found;when desulphuration index is less(except gypsum and rock salt distributed area)than one,gas preservation condition is favourable.

    STUDY ON PALAEOSALINITY OF CHANG 26 OIL RESERVOIR SET IN ORDOS BASIN
    Zheng Rongcai, Liu Meiqing
    1999, 20(1):  20-25.  doi:10.11743/ogg19990105
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    Take the geochemical indicators of boron,equivalent boron,adsorptive K++Na+,Sr and the ratio of Sr/Br etc.as palaeosalinity indicators,the palaeosalinity of Chang6 oil reservoir set in Ordos Basin is analysed and calculated by using the formula advanced by T.D.Adams and E.L.Couch.The results indicate that the Late Triassic Ordos Basin is not an inland fresh water lake as recognized for a long time,but a brackish water to semisalt water marginal lake caused by intermittent seawater ingression.The paleosalinity of water body of the reservoir set was 0.940%～01.016% during its deposition.The contents of K++Na+ and the ratio of K/Na in the above mentioned paleosalinity do not correspond with that of Chang 26 reservoir set;the contents of boron,equivalent borom, adsorptive K++Na+,Sr and Sr/Ba ratio are reliable identifying indicators of the paleosalinity.After the regression analysis of the identifying results of various indicators,it is suggested that the results calculated by E. L. Couch formula are more reliable.The identificatin of paleosalinity could not only distinguish the water type of paleolake,but also could know the evolution of source rock.

    DISPLACING EFFICIENCY AND AFFECTING FACTORS OF RESERVOIRS IN YAN'AN FORMATION, JIYUAN REGION
    Sun Wei, He Juan
    1999, 20(1):  26-29.  doi:10.11743/ogg19990106
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    Based on the true micromodels of sandstone,the twophase displacing process of oil by water of the Jurassic Y-9 and Y-10 oil reservoirs in Fanjiachuan-Yuancheng oilfields was observed.The results show that the displacing efficiency was in inverse proportion to the entering pressure and direct proportion to permeability.The displacing efficiency of Fanzhong area and Y-9～Y-2 substratum were the best among the three zones and the three substratums of Y-9 reservoirs respectively.The main factors that affecting the displacing efficiency are drive pressure,permeability,the microheterogeneity of pore structure and apparent porethroat volume ratio.

    SEQUENCE STRATIGRAPHY OF PERMIAN SYSTEM IN SICHUAN-GUIZHOU-GUANGXI REGION AND ITS OIL-GAS EXPLORATION
    Qin Jianxiong, Chen Hongde, Tian Jingchun, Yang Zousheng
    1999, 20(1):  30-33.  doi:10.11743/ogg19990107
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    Five different kinds of basins in Permian System in SichuanGuizhouGuangxi region contain different stratigraphic sequences,so their hydrocarbon prospects are different.In general,transgressive system tracts(TST),condensed section(CS),highstand system tracts (HST)and lowstand system tracts (LST) of platform basin, deepwater basin and coalbearing carbonate formations of highstand system tract in cratonic basin and isolated carbonate platform are generally important source rocks and significant cap rocks .They include all kinds of favourable sandbodies in different system tracts:1.basin-floor and slope fans,delta front,alluvial fan,channel sandbodies,progradation complex,shoal-bioherm-reef complex,calcareous and mixed clastic turbidites within lowstand system tract;2.sandbodies of barrier beach,shoal,estuary,tide-controlled delta,fandelta,turbidity fan,lag sediment,bioherm-reef complex,pyroclast turbidite within transgressive system tract;3.river and wave dominated deltaic sandbodies,alluvial fan-channel sandbodies,fan-delta,turbidity fan,terrigeneous and carbonate shoals,bioherm-reef complex,calcareous-clastic beach-bioherm-reef complex,calcareous clastic turbidite and dolostone within highstand system tract;4.paleo-karst reservoir dominated by sequence boundary.

    FORMATION MODELS OF DEVONIAN AND CARBONIFEROUS DOLOMITES IN GUIZHOUGUANGXI REGION
    Fang Shaoxian, Hou Fanghao, Dong Zhaoxiong, Zhu Xiaohui
    1999, 20(1):  34-38,45.  doi:10.11743/ogg19990108
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    The Devonian and Carboniferous laminated dolomites in GuizhouGuangxi Region are mainly distributed on the edge of continentlinked(shelf)carbonate platform and the isolated carbonate platform near deep trough.The dolomitization mechanism includes active tidal pumping dolomitization ,normal seawater dolomitization,mixed near surface dolomitization,buried squeezecompaction flow dolomitization, tectonic hydrothermal dolomitization.It is suggested that different dolomitization models possess different mechanisms and characters.

    EVENT SEDIMENTS OF CAMBRIAN IN YANGJIAPING, NORNORTHWEST HUNAN
    Guo Chengxian, Zhu Zhongde, Jin Tao, Xie Hong
    1999, 20(1):  39-45.  doi:10.11743/ogg19990109
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    Yangjiaping,Northwestern Hunan,is situated in the west margin of Central Hubei carbonate platform.In the Cambrian,there occurred successively a series of catastrophic events in the study area,including oceanic anoxic event,turbidity event and tempest event.According to the petrological characterisitics of the black rock series and the facts that they occur on the bases of the rapid transgressional sequences and are distributed widely in South China and the whole world,the formation of the black rock series should be related to the meteorite impact,the break up of pancontinent and the eustatic sealevel abrupt rising between the Sinian and Cambrian.The turbidity events and tempest events were all strong local catastrophic events.The former resulted in phosphorous turbidites and calcareous turbidites,their induced factors were related to tempest activities;the latter resulted in near source tempestites and scoured basement autochthonous tempestites.

    TECTONIC THERMAL EVENTS OF LATE MESOZOIC IN QINSHUI BASIN
    Ren Zhanli, Zhao Zhongyuan, Chen Gang, Wang Shicheng
    1999, 20(1):  46-48.  doi:10.11743/ogg19990110
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    Through the analysis of vitrinite reflectance,inclusion and apatite fission track,paleogeotemperature and paleogeothermal gradient obtained in Late Mesozoic of Qinshui Basin show well coincidence with each other.The paleogeothermal gradient of Qincan-1 well is between 4.73℃/100 m～6.10℃/100 m,its paleoheat flow is 82 mW/m2～106 mW/m2.This is evidently related to tectonic thermal event.In horizental,the distribution of Ro value coincides with the configuration of the basin in Late Mesozoic,and the high Ro value distribution region was related to magmatic activity.The isotopic age of the rock bodies is between 95.34 Ma～166.45 Ma, and the highest abundent of that in the peripheral magmatic active zones is 124 Ma～153 Ma.It suggests that the tectonic thermal event happened in Late Jurassic-Early Cretaceous,and that the event was the reflection of mid Yenshan movement.

    CONTROLING THE TECTONIC ACTIVITY TO SEQUENCES LOWER TERTIARY OF IN TANGYUAN FAULTED DEPRESSION
    Yang Yufeng, Wang Kongwei, Wang Shibo, Sun Dejun
    1999, 20(1):  49-54.  doi:10.11743/ogg19990111
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    According to sequence stratigraphic analysis,4 sequences of thirdorder could be identified from the Low Tertiary in Tangyuan faulted depression.These sequences are different from each other in scale and composition since they underwent different tectonics.In extension rifting background,fault depressed sequences are mainly composed of thick coarse fragments of lowstand system tract(LST);in rapid extension subsiding background,the sequences are characterzed by finegrain in lower part and coarsegrain in upper part;in the compression uplift background,sequence scale is small and lacustrine facies is poorly development.The most favorable sequence types are quickly depressed faulted sequences and quickly faulted depressed sequences,for they both contain best source,reservoir and seal rocks.

    CHARACTERISTICS OF MEDIUM-DEEP RESERVOIR AND SEDIMENTARY HISTORY IN YINGGEHAI BASIN
    Wang Hua, Zhu Weilin, Wang Yan
    1999, 20(1):  55-57,61.  doi:10.11743/ogg19990112
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    Yinggehai Basin is a fault-depressed basin developed on the basement of PreTertiary System.In vertical,the basin shows generally transgressive filling sequences.The basin underwent three deposition processes since Eocene.Tg～T70(before 28 Ma)was rapid subsidence period,the total rate of descent was 600 m/Ma;the total descent rate of T70～T30(28 Ma～5.2 Ma)period was 500 m/Ma;that of T30～ present day (5.2 Ma～ present) is 600 m/Ma.The amount of subsidence caused by tectonics is about 1/2～1/4 of the total amount;the rest is mainly related to isostatic subsidence.It is proposed that deltaic,beach and turbidite sandbodies are the main mediumdeep reservoirs in the basin;the distributary channel sandbodies deposited during Huangliu Formation may be favourable reservoirs.

    DIAGENESIS OF RESERVOIRS IN BAZHOU DEPRESSION, MINHE BASIN
    Liu Linyu, Di Shixiang, Xue Xiangxi
    1999, 20(1):  58-61.  doi:10.11743/ogg19990113
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    The reservoir diagenesis of Bazhou Depression,Minhe Basin was intense.The major diagenesis of clastic rocks in the Hekou Formation and the upper section of the Datonghe Formation was mechanical compaction and calcite cementation.The major diagenesis of the lower section of the Datonghe Formation and the Yiaojie Formtion was authigenic clay and quartz mineral cementation and fracturing.The primary pore texture of the reservoirs was destroied by diagensis.The fracturing transformed the reservoirs of the lower section of Datonghe Formgtion and the Yiaojie Formation into dense fracture reserviors.

    SEDIMENTARY MICROFACIES OF ALLUVIAL FAN IN XIAZIJIE FORMATION, XIAOGUAI OILFIELD
    Cao Hong, Yao Fengchang, Song Xinmin, Chen Jun
    1999, 20(1):  62-65,77.  doi:10.11743/ogg19990114
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    Xiazijie alluvial fan in Xiaoguai Oilfields could be divided into three subfacies and ten microfacies.Fanhead subfacies is composed of coarse sediments with high resistivity,and could be subdivided into main trough,side trough,trough beach,flood land and mudrock flow microfacies;the intrafan subfacies is composed mainly of fine grained sediments of high maturaty and could be subdivided into braided stream,sand island and difusion microfacies;the fan margin subfacies is composed of the finest grained sediments among the three subfacies with the lowest fluid energy,and could be further subdivided into radial water channel and laminar flow microfacies.The sedimentary model of the alluvial fan has been established based on its multisource,its evident volcanic activity and vitric tuff sediments.

    FORMATION AND CHARACTERISTICS OF LIGHT HYDROCARBON GEOCHEMICAL FIELDS
    Li Guangzhi
    1999, 20(1):  66-69.  doi:10.11743/ogg19990115
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    Light hydrocarbon geochemical field is one of the manifestations of hydrocarbon.Geochemical field is composed of field source and field effect.The field source is the material base of light hydrocarbon remigration;the field effect, which is effected by the solubility of formation water and country rock property,is the interaction of light hydrocarbons and soil substrate.During migration,light hydrocarbors possess the behaviour of dynamical equilibrium and divergence,the migration direction is determined by the contrast between passages and resistance.It is suggested that,in geochemical exploration,one should not only consider the property of field source,but also the preservation state,the composition and contents of light hydrocarbons,and carry out comprehensive analysis in time-space.

    FISCHER DIAGRAM AND ITS COMPUTER SIMULATION OF SEDIMENTARY RESPONSE A CASE STUDY ON THE UPPER MEMBER OF Eh3 IN BIYANG FAULTDEPRESSION
    Hu Shouquan, Chen Guoneng, Wang Yingmin, Tong Chongguang
    1999, 20(1):  70-75.  doi:10.11743/ogg19990116
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    The upper member of Eh3 in Biyang fault-depression includes 3 terrigenous sequences with the span ages of 1.08 Ma,1.40 Ma and 1.02 Ma respectively.A depositional system of fluvial fanfan delta-lacustrine facies was developed in ShuangheZhao'ao region of the depression.The 3 terrigenous sequences consist of 13 parasequence sets,more than 50 recognizable parasequences and 10 microfacies.The accommodation change curves of the terrigenous sequences were obtained by using Fischer diagram.The accommodation variation process and the terrigenous sequence response characters of the uper member of Eh3 in ShuongheZhao'ao area during deposition were simulated by the application of quantitative sequence stratigraphic simulation system.The results indicate that the terrigenous sequences of the study area formed under the condition of high and uniform velocity of material source supply,and that S4 sequence of TST should be taken as important target for hydrocarbon exploration.

    DIFFERENTIAL ANALYSIS OF ΔC IN DIFFERENT PARTS OF OIL-GAS POOLS
    Tang Yuping, Jiang Tao, Liu Yunli
    1999, 20(1):  76-77.  doi:10.11743/ogg19990117
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    The distribution of ΔC in different parts of oil and gas pools are different.The ΔC in wells on the margins of the reservoirs is higher than that in oil wells,and the ΔC in oil wells is higher than that in dry well.The variation of ΔC is not related to the variation of buried depth.It is suggested that,in geochemical exploration,ΔC could be used as the index of environmental correlation in horizental,but could not be used as vertical migration index.

    RESERVOIR CHARACTERS OF PONGLAIZHEN FORMATION IN LUODAI GASFIELD, CHENGDU
    Cao Wei, Liu Jichang, Chen Weiming
    1999, 20(1):  78-80.  doi:10.11743/ogg19990118
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    Experiments were made on the porosity,permeability and the compaction regularity of the reservoirs of Ponglaizhen shallow gas pools in Luodai Gasfields.The results indicate that the porosity and permeability decreased with the increasing of confining pressure.When the confining pressure increases to 10 MPa,the porosity and permeability would decrease maximally to 7.39% and 80% respectively as compared with those measured at normal temperature and pressure.The variation of reservoir porosity is closely related to the contents of calcium and anhydrite.A mathematical relational expression is established according to core data.The description of textural parameters suggest that,the main peak of throat radiuses of Ⅰ～Ⅲ type reservoirs of the gas pools are distributed between 0.4～4.0 μm;more than 90% of the cumulated permeability are distributed in those the throat radiuses greater than 1.0 μm.This shows that large throat radius dominats gas mgration.

    METHOD OF LITHOLOGIC RECOGNIZING BASED ON FEEDFORWARD NEURAL NETWORK
    Lu Xinwei, Jin Zhangdong
    1999, 20(1):  81-84,93.  doi:10.11743/ogg19990119
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    Geological explanation of logging data is an important link of logging work.When there are scanty core data and more log data,feedforward neural network is a very effective method to recognize the logging lithology.This paper introduces an identifying method of logging lithology by the pattern recognition approach using feedbach nueral network.The approach firstly regards the relationship between drilling cores and logging parameters as an identifying pattern so as to obtain intelligent knowledge from the identifying pattern,and finally applies the knowledge to identify the logging lithology of well.The method was used in lithologic recognition of the 4th member of Shahejie Formation in Shengli Oilfields,the result is satisfactory and shows good application prospects.

    LOG RESERVOIR EVALUATION IN FAULT BLOCK POOLS
    Yang Shaochun, Xin Quanlin
    1999, 20(1):  85-89.  doi:10.11743/ogg19990120
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    The influence of geological factors should always be taken into account in establishing well log interpretation model,log data processing and reservoir evaluation.The log responce,the lithologic,petrophysic,rhythmic and electric characters and water contents of different types of reservoirs,different sedimental facies and different exploitation periods are different.According to these differences,the models of interpretation and calculation for porosity,permeability and oil saturation degree are establoshed and the interpretation accuracy thus inproved.Besides,the complexity of the fault blocks and the connection between the fault blocks should also be considered in log data processing during oil exploration and development.Based on the reservoir parameters obtained through data processing and the characters of fault block reservoirs,the methods of log reservoir quantitative and qualitalive evaluation are summerized by applying grey theory and fuzzy mathematical methods.The practical application results of the methods coincide well with well drilling.

    RECOVERING PLATE ON INITIAL THICKNESS OF CLASTIC ROCKS IN SEDIMENTARY BASINS: A quick and practical method
    Wei Yongpei, Chen Huixin
    1999, 20(1):  90-93.  doi:10.11743/ogg19990121
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    There are several methods of recoverying initial strata thickness such as compaction,coefficient of compaction,dehydrata compaction,vitrinite reflectance and geological statistics.Most of these methods have evident shortcomings and are irrational.So the plate of recoverying initial strata thickness has established by means of the computation of the initial strata in certain artificial well.The initial strata thickness can be obtained by this method through knowing present strata thickness and lithology in wells.This method is proved to be covenient and practical.

    SIMILAR ANALOGY IN GEOLOGIC RESEARCHES
    He Zi'ai, Yang Jianchao
    1999, 20(1):  94-98.  doi:10.11743/ogg19990122
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    Similar analogy is an approach of discovery,creation,prediction in scientific researches.A basic principle of geological research is that the present is the key to the past and this is closely related to similar analogy.The analogy is a logic method but dominated by thinking in images which is the foundation of analogy and the start point of association and summary.The principles of analogy are that:1.dynamic state is higher than static state,that is to say,static textural analogy must be improved to systematical and coherent dynamic analogy;2. resemblance in spirit is louder than that in appearance,the function of that is creation and this is reconstruction;3.entirty is greater than sum in the accumulation of knowledge and the key must be adopted derivative method which is constantly assembled for similar information and sought for principles through phenomenon.