Oil & Gas Geology-1999, Volume 20 Issue 2

I/S RATIO INCREASE WAYS AND ITS COMPOSITION CONTROL OF ILLITE SMECTITE MIXED LAYER CLAY:AN EXAMPLE OF TWO WELLS IN ZHUJIANGKOU BASIN

Wu Jinhua, Yu Shuyu, Xu Shice, Liu Lihua

1999, 20(2): 99-103,119. doi:10.11743/ogg19990201

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Based on the sectioned quantitative study of XRD data of clay minerals in argillites from two wells in Zhujiangkou Basin,it is proved that the increase of the ratio of illite and smectite layer contents in illite-smectite mixed layer clay(I/S)is related mainly to the dissolution of potassium feldspar.When deposited organic substances and potassium feldspar are abundant enough,the ratio increase would proceed by the net increase of illite layers at the temperature roughly corresponding to or slightly higher than that of the oil generation threshold;when the temperature is lower than that of threshold,smectite layers would be converted to illite according to dissolution precipitation mechanism;if no supply of K⁺,the ratio would increase by net dissolution of smectite layers.In general,the increase ways are independent of the permeability because it could usually allow the ions to transport smoothly.Only when it as low as to filter merely the big organic complex aluminium ions,the illitization reaction would substitute for the net addition of illite layers.Permeability even lower than that or the system being closed would stop the trend of the increase in all ways.

CONDITIONS OF SEALING AND ACCUMULATION IN COAL BED GAS

Sang Shuxun, Fan Bingheng, Qin Yong, Tang Shuheng, Ye Jianping, Jia Shetun

1999, 20(2): 104-107. doi:10.11743/ogg19990202

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In places with simple hydrogeological conditions,the sealing of coal bed gas is mainly determined by geological structures and cap rock lithologic propertices.In general,compressional fault could increase the content of coal-bed methane while tensional fault would decrease the content of coal bed methane.Symmetric high stress zones in parallel stripped shape would usually form in two sides far off the fault,thus causing the increase of coal bed methane content,and forming a natural curtain to block methane migration to the fault.Coal bed methane accumulation would occure above the balancing surface of anticlines and below the balancing surface of syncline.According to their expulsive pressure and permeability,the cap rocks of coal-bed methane could be divided into shielding bed,semi-shielding bed and permeable bed,which in turn could be subdivided into 9 types of lithologic assemblages.Examples of Pingdingshan coal dristrict show that,tpye-Ⅰ assemblage is more favourable for coal-bed gas;type-Ⅱ,type-Ⅳ and tpye-Ⅴ assemblages are secondany;the rest are poor.

SEQUENCE STRATIGRAPHY AND RESERVOIR DISTRIBUTION IN CHINA'S TERRIGENOUS CLASTIC BASINS

Deng Hongwen, Wang Hongliang, Zhai Aijun, Xu Changgui

1999, 20(2): 108-114. doi:10.11743/ogg19990203

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Sequences of different basins differ considerably in depositional pattern,distribution characteristics.The sequences of foreland basins are mainly dominated by alternation of thrus flexure deformation and unloading,and their distribution is very asymmetric;the sequences in cratonic basins are mainly controlled by eustasy,and coincident in broad extent;the sequeces of inland rift basins are controlled by different scales and different orders of episodic fracture movements,thus resulting in multicycle sequences;sequences of large depressions are similar to those of passive continental margins;those of intermontane basins are related to episodic movement,paleoclimate and source materials;those of piedment fault-depressed basins are related to strike-slip and pull-apart movements.The above mentioned differences are bound to cause considerable differences in types and collocation of source-reservoir-cap rock association.In general,the turning positions between rising and downing processes of the cycles are favourable places for source rooks;the sand bodies formed in semi rising and semi downing cycles are the main reservoirs.

APPLICATION OF HIGH RESOLUTION SEQUENCE STRATIGRAPHY IN RESERVOIR NUMERICAL SIMULATION

Xu Cuangming, Xu Huaida, Kong Xiangyan

1999, 20(2): 115-119. doi:10.11743/ogg19990204

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According to recognized stratigraphic base level cycles and the results of time depth tansformation,log sequences were marked on seismic profiles and were contrasted with each other so as to obtain reservoir high-resolution sequence stratigraphic framework.Take intermediatie-term cycle as the stratification of reservoir physical model,the distribution of the cycle's sedimentary microfacies could be use to divide nonhomogenous subregions of the model.A reservoir physical model established by application of above mentioned methods must be more practical;the reservoir numerical simulation will be more easier to match with actural production history.

THE DISCOVERY OF TAHE OILFIELD AND ITS GEOLOGIC IMPLICATION

Zhang Kang

1999, 20(2): 120-124,132. doi:10.11743/ogg19990205

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Tahe Oilfields is composed of different ages of reservoirs such as Triassic,Carboniferous and Ordovician reservoirs.The main part is the network consisting of karst cracks and holes in Ordovician limestone reservoir.Its controlling factors are karst holes,cracks and pores which formed quite different in size,time and extending direction and connected into nets in very complicated ways.The reservoirs vary in reserve,productoin capacity and oil quality due to the different levels of net developing and history of reservoir forming.

CHARACTERISTICS AND ORIGIN OF FIRST ORDER TRANSFER ZONES IN HUANGHUA BASIN

Wu Guanghui, Qi Jiafu

1999, 20(2): 125-128. doi:10.11743/ogg19990206

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Regional structure transfer zone in Huanghua Basin is characterized by complicated fault zone that the main extension structures intersected each other with high angles.The transfer zone is situated in the extensional variation section of the basin,possessed twisting property,and resulted in the variation of the basin's texture and sedimentary characters.It is suggested by analysis that the differences in basement textures are the premise of the occurrence of regional structure transfer zone;non uniform oblique extension is the leading role;the variation of transformation and intensity of the basin's rift-subsidence is the motive mechanism.

APPLICATION OF NEURAL NETWORK EXPERT SYSTEM TO PREDICTING THE PRODUCIBLE OIL RESERVES—An example of Fanjia Oil district in Shengli Oilfields

Peng Dunlu, Xu Shijin, Wang Rucheng, Guo Yanjun

1999, 20(2): 129-132. doi:10.11743/ogg19990207

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There are various kinds of factors that effect producible oil reserves.It is difficult to describe the relationship between the producible oil reserves and the effecting factors by an expression simply.Neural network expert system provides a new approach to solve the problem.Particular process is like that:1. select five reservoir parameters (cumulative thickness,temperature,effective porosity and permeability,pressure) and three crude oil parameters (saturation,viscosity and density)as characteristic parameters;2.the parameters should be standardized and normalized;3.take 8 known oil recovery areas in Fanjia sub oil field as learning samples to train the network system;4.use the trained system to predict the producible oil reserves of unkown oil areas.The prediction results fitted well with actural circumstances and the errors are exceptable.

ORDOVICIAN PALAEOKARST LANDFORM IN ORDOS BASIN AND GAS ENRICHMENT CHARACTERISTICS

Xia Riyuan, Tang Jiansheng, Guan Bizhu, Luo Weiquan, Ma Zhenfang, Zhou Shuxun, Yu Zhongping, Pan Linghong

1999, 20(2): 133-136. doi:10.11743/ogg19990208

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Palaeokarst landform developed in the top of Ordovician weathering crust in mideast Ordos Basin controls the reservoiring of natural gas and could be divided into 3 types such as karst highland,karst platform,karst basin and 9 sub types. The karst platform that underwent intense karstification is most favourable for gas enrichment;the terrace in the highland,the gentle hill in the platform and the remnant hill in karst basin are favorable areas of gas accumulation.High yield gas wells are located at the upper part of the slopes in both sides of the eroded karst flute.

RESERVOIR DESCRIPTION AND EVALUATION OF EOGENE SYSTEM IN GAOYANG REGION

Chen Gang, Qu Zhihao, Zhao ShengLiang

1999, 20(2): 137-139,151. doi:10.11743/ogg19990209

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Thin layer sandstone prediction is the key problem in reservior description.In this paper,the structure,physical parameters,lateral variation of a reservoir could be accurately predicted by the technology of comprehensive constrained seismic inversion.This method improved the resolution of the impedance profile and the reservoir prediction.This method was used in the reservoir description and assessment of Eogene thin layer sandstone reservoirs in Gaoyang Region and was proved to be effective.The reservoir trap types,accumulation regularities as well as exploration targets in the area were predicted.

EXPLORATION ORIENTATION ANE ROCK, PALAEOGEOGRAPHIC TYPES OF CHINA'S GAS RESERVOIRS

Du Yunhua, Qian Kai, Zhang Shoupeng

1999, 20(2): 140-143. doi:10.11743/ogg19990210

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The number of China's medium and big gasfields is only 20.8% of the country's total mumber of gasfields,but their reserves are 83.44% of the total reserve;the number of big gasfields is 4.3% of the total number of gasfields,but their reserves are 50.35% of the total reserve.The reservoir rocks of the medium and big gasfields are predominantly sandstone and carbonate rock,their reserves are 99.65% of the total reserve.This coincides with the tendency of world's gasfields.It thus indicates that China's gas exploration should always aim at big and medium sizes of sanstone and carbonate rock gasfields.According to the distribution of structural palaeogeography,gas exploration provinces could be divided into 4 type:1.inner cratonic basins in Central China;2.composite basins in West China;3.epicotinental basins in Southeast China;4.rift basins in East China.These basins correspond to gas,oil,rich gas and gas-bearing provinces respectively.On this basis,the furture strategy is enhancing Central China gas exploration, developing West China gas explaration,paying more attention to marine exploration and improving exploration in East China.

STABLE ISOTOPIC CHARACTERISTICS OF DIAGENESISIN DEEP WATER CARBONATE ROCKS

Guo Chengxian, Wang Zhengyun, Wang Fangping

1999, 20(2): 144-147. doi:10.11743/ogg19990211

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Stable isotopic method can be used effectively in the diagenetic research of deep water carbonate rocks.According to the oxygen and carbon isotopic compositions of the Early Palaeozoic deep water carbonate rocks developed along the southeastern marginal slop of the Middle Yangtze carbonate platform,some diagenetic environments and diagenetic mechanisms are as fallowe:1)the δ¹⁸O values of nodules of Lower Ordovician nodular limestone are always more positive than those of matrix,suggesting that the prototype of the modular limestone was the product of solution and cementation occurred repeatedly on the sea floor;2)the Lower Cambrian massive dolomite with relatively concentric values of δ¹⁸O and δ¹³C was the product of high density brine replaced dolomitizatin,whereas the lower Ordovician massive dolomite with high negative δ¹⁸O value was formed by the deep burial dolomitization;3)Burial recrystallization altered strongly the Lower Ordovician carbonate rocks,and made them to have the same high negative δ¹⁸O values.

RESERVOIRING AND SEALING CONDITIONS OF NON STURCTURE POOLS

Wu Jincai, Liu Lanlan, Zhou Zhuoming, Qing Chongwen, Yang Changqing

1999, 20(2): 148-151. doi:10.11743/ogg19990212

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Reservoir rocks of no-sturcture traps in southern part of Songliao Basin consist of different types of sandbodies in LST,EST and HST such as basin floor fans and progressive wedges in Lower Stand System Tracts(LST),transgressive sands and river channel sandbodies in Expanding System Tracts(EST),delta front,fan delta and fan-toe turbidite in High Stand System Tracts(HST).Most of the sands are not large in size and their destribution is limited.These sandbodies can form oil and gas traps without the matching of structural condition,but require high sealing condilion.According to the relatiorship between sealing positions and sequence boundaries,seeling conditions of non structrure formed reservoirs can be classified into 7 types:E-S-H-H,E-E-S-H,E-L-S-H,E-S-B,E-L-L,E-E-E and H-H-H.Among them,E-E-E,H-H-H and E-L-S-H are the most favourite sealling conditions.

RESERVOIR CHARACTERIZATION TECHNIQUE WITH MULTI WELL LOG USED IN BAMIANHE OILFIELD

Ma Xiaochang, Cui Yong, Zhao Chenglin

1999, 20(2): 152-154,163. doi:10.11743/ogg19990213

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Multi well log reservoir characterization technique is a new technique which combines reservoir geology with well log.The technique is characterized by plenty of information and complete characterization of the reservoir's 3-D geological property.On the basis of the reservoir interpretation model which was established by log data standardization of different well types and core analysis in GB8-X2 block reservoir of Bamianhe Oilfield,the plane variation characters of lithology and petrophysics were studied and high resolution structural map was made,and then low-resistivity pays was identified.According to these,the dynamic prediction of reservoir flow was made by subdividing reservoir units and resedual oil enrichment could be found. This technique is used to search for residual oil enrichment zones,the result is successful.The totalized newly proved reserves are 248?10⁴t and available reserves are 51?10⁴t.

APPLICATION OF SEISMIC INTERVAL-VELOCITY AND ACOUSTICTIME TO PREDICTING SEALING CAPABILITY OF CAP ROCKS

She Xiaoyu, Wu Yajun, Luo Kaiping, Chen Deqing, Zeng Tao, Gao Shanghai

1999, 20(2): 155-159. doi:10.11743/ogg19990214

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The sealing capability of cap rocks is closely related to the porosity,permeability,the ratio of sand to mud contents and fluid pressure of the rocks.The sealing capability could be predicted by using seismic interval velotity and acoustic time.At first,fitted experiment formula is used to calculate some physical parameters such as porosity and residual fluid pressure,then calculate formation pressure,and finally predict and evaluate the sealing capabilities both laterally and vertically according to the calculated results.As compared with actual measured results,the absolute errors of the predicted porosity of seal rocks are -1.32%～-1.39%,their proportional errors are 3.07%～15.4%;and that the absolute errors of break out pressure are -0.23～0.63 MPa,their proportional error are 1.81%～12.27%.The results show that the abnormal formation pressune system resulted from uncompaction has obviously controlled the migration,accummulation,preservation and distribution of hydrocarbon.

SEQUENCE STRATIGRAPHY AND RESERVOIR PREDICTIONOF CHANGTU DEPRESSION

Wang Hongliang, Deng Hongwen

1999, 20(2): 160-163. doi:10.11743/ogg19990215

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The Jiufutang Fuxin Formations could be divided into MSC1, MSC2 and MSC3 medium term base level cycles, among them MSC2 and MSC3 are elevated semi-cycles.These three cycles correspond well to S_A,S_B and S_C recorded in seismic sections.Accordimg to well drilling and seismic data,the marsh coal-bed in fan-delta front and shallow lake mudstone of MSC1 and the flood dark mudstone of MSC3 are most favourable source rocks;fan-delta front subfacies and subaqueous medium fan subfacies of every cycle are good reservoir facies.It is suggested that the middle and upper parts of MSC3 and MSC1 elevated semi-cycles should be taken as the main exploration sequences.

RELATIONSHIP BETWEEN SOURCE ROCK MACERALS AND OIL FORMING THRESHOLD OF NANPU DEPRESSION

Zhou Haimin, Zheng Hongju, Zhang Chunmei, Yin Wenqing

1999, 20(2): 164-166. doi:10.11743/ogg19990216

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As the thermal evolution degree of hydrogen rich macerals in source rocks of Dongying and Shahejie Formations in Nanpu Sag increases,the wave peak λ_max of its fluorescence spectrum will increase,the relative intensity of red light and green light will increase and fluorescence intensity will decrease and periodic changes would occur in 3400 m depth.It thus suggests that the oil-forming threshold of Nanpu Sag is±3400 m.

FRACTURE CHARACTERISTICS OF EOGENE LOW PERMEABLE RESERVOIRS IN LEIJIA OILFIELD

Zeng Lianbo

1999, 20(2): 167-169. doi:10.11743/ogg19990217

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The fractures in Eogene low-permeable reservoirs of Leijia Oilfield could be divided into joint-type and fault-type fractures,within which the fault-type fractures could be subdivided into cross bed and bedding fractures.The joint-type fractures are distributed vertically with no displacement on the two sides of the fractnres,while those of fault-tyre have evident displacement.The cross-bed fractures cut rock layers at high angles and are similar in distribution and association pattern to that of normal faults in the study area; the bedding fractures are distributed in mud interlayers parallel to bedding plane.The development and distribution of the fractures are controlled by lithologic characteristics,rock thickness and faults.Well developed fractures in mud interlayers usually connect with each other and form 3-D fracture network.This is important for oil and gas reservoiring.The average space between fractures bear linear relation.Fractures developed near extentional fault show evident zonation,and the fractures developed well in the upper wall of the fault than that on the lower well.

A NEW METHOD FOR FOUNDING THE MODEL OF FLOW UNIT RESERVOIRS

Yin Taiju, Zhang Changmin, Chen Cheng, Lu Guopu, Jiang Jianwei, Li Qingming, Liu Lina

1999, 20(2): 170-175. doi:10.11743/ogg19990218

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Flow unit model is the premise of reservoir numerical simulation.According to the reservoir properties,the model can be founded through five steps as following:①divide and determine cored-well flow units;②divide and determine the uncored-well flow units;③found reservoir architectural model;④found parameter model;⑤found flow unit models.According to the study made in Shuanghe Oilfield,Henan Province,four types of flow units as E,G,F,P were recognized,within which type E has perfect reservoir property and is distributed in distributary channels and river mouth bars;type P has the poorest property and is distributed in sheet sandbodies.It is proposed that formation factor is the main factor in determining the flow units,and could be used in dividing the flow units of uncored wells.

PREDICTION METHOD FOR PRODUCING PRESSURE DIFFERENCES OF INTERWELL FLOW UNITS

Sun Laixi, Sun Jianping, Yang Fengbo, Yao Guoping

1999, 20(2): 176-178. doi:10.11743/ogg19990219

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In oil and water phases,fluid percolation obeys Darcy's law.According to this,the formula for calculating producing pressure differences of the interwell fluid units could be established.The fluid units could be classified according to the pore radius,permeability and petrophysical property of a reservoir.The fluid units in Shuanghe Oilfields could be divided in to 4 different types.Calculated results suggest that the theoretical pressure differences of different flow units in Shuanghe Oiffields fitted well to the measured pressure differences.

FORECASTING SANDBODIES BETWEEN WELLS USING STOCHASTICSIMULATION METHOD

Li Longyan, Chen Gongyang, Zhong Baorong, Zhang Zhenshun, Han Musen

1999, 20(2): 179-181. doi:10.11743/ogg19990220

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A new method of forecasting the sandbodies between wells by application of geostatistics and fractal geometry is proposed in this paper.This method could be used to estimate reservoir variation tendency in large scale by Kriging interpolation field,to describe reservoir variation property in small scale by stochastic fractal field.Then 2-D Kriging interpolation and stochastic fractal fields were stacked so as to obtain the forecast result.The study of an example shows that this method could be used in sandbody distribution simulation,the result is reliable.

FLUID DYNAMIC FIELDS IN POOL-FORMING DYNAMICS OF OIL AND GAS

Ye Jiaren, Wang Lianjin, Shao Rong

1999, 20(2): 182-185. doi:10.11743/ogg19990221

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Temperature field,pressure field,energy field and stress field are the main contents in the study of fluid dynamic field.The present temperature field is determined by observed temperature in well drilling and the value of geothermal heat flow;palaeo-temperature field is principally determined by the uniform temperature of inclusions.The methods for studying pressure field are mainly acoustic log,observed formation pressure and seismic interval velocity.The first two methods are usually used in drilled areas,the last one is particularly used in undrilled areas.The energy field study should be stressed on the restoration of Palaeo-fluid potential in 3-D hydrocarbon source rock masses and fluid passage systems.In general,the places with higher stress usually have higher pressure.As for particular region,it is of the first importance to divide vertical compaction pressure belt of single well ,then divide pressure system,and finally make forword modeling so as to probe pressure forming mechanism.Underground fluid fields are connected and coupled with each other,one must consider the fluid dynamic fields as a whole.

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