Table of Content

25 June 2007, Volume 28 Issue 3

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A discussion on the unit classification in reserve estimation

Zhao Wenzhi, Bi Haibin

2007, 28(3):  309-314.  doi:10.11743/ogg20070301

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Based on the research of the application of four-order units(i.e.oil/gas field,block,development unit,and calculation unit) in reserve estimate,basic principles are proposed for establishing the corresponding relationship of the four-order unit.Upon this relationship,the paper analyses in detail the classification of calculation units,and suggests that in order to maintain the accuracy of reserve calculation,the oil-gas-water systems shall be incorporated or subdivided vertically and horizontally.Vertically,the main concerns shall be the lithologic association,fluid property,oil/gas reservoir type,reservoir distribution,etc.;while horizontally,factors such as oil/gas reservoir scale,complication,and configuration of oil,gas,and water layers,shall be taken into consideration.

A new approach to producing reserve calculation of fractured-vuggy carbonate rock reservoirs

Chen Zhihai, Chang Tielong, Liu Changhong

2007, 28(3):  315-319,328.  doi:10.11743/ogg20070302

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Owing to their severe heterogeneity,fractured-vuggy carbonate reservoirs distribute and extend in an unpredictable way,causing difficulties in the determination of single-well producing area and undermining the accuracy of single-well producing geological reserves calculation with the volumetric method.Based on the reservoir material balance principles and division of fractured-vuggy reservoir units,a new reserve calculation method is developed.It first determines single-well controlled area according to the single-well recoverable reserves,and then calculates single-well producing geologic reserves with the volumetric method.The new method is applied to the calculation of the producing reserves within the typical fractured-vuggy carbonate reservoir units in Tahe oilfield.The results are consistent with that obtained by using the dynamic method,indicating that the new method is practical in calculating the producing reserves in severely inhomogeneous fractured-vuggy carbonate reservoirs.

An improved calculation method for reserve of constant-volume sour gas reservoirs

Cen Fang, Lai Fengpeng, Jiang Hui, Huang Zhiwen, Zou Cunyou

2007, 28(3):  320-323,336.  doi:10.11743/ogg20070303

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The material balance equation for gas reservoir can be used in the calculation of the original gas in place(OGIP) of reservoirs and has been widely adopted in the calculations of gas reserves.However,the equation is not suitable in the calculation for the reserves of constant-volume sour gas reservoirs due to such facts as sulfur may precipitate and form depositions and etc.The neglect of differences caused by sulfur deposition would distort the results to some extent in the calculation of OGIP in constant volume gas reservoirs.This paper levels at such features of sour gas reservoirs and formulates a new material balance equation,which takes the diffe-rences into consideration.The application of the new equation to constant-volume sour gas reservoirs yields positive results and shows that it is more reliable.

Analysis of the Youquanzi oil-bearing structure in Qaidam basin

Mo Wuling, Zheng Yadong, Zhang Wentao, Guan Ping

2007, 28(3):  324-328,319.  doi:10.11743/ogg20070304

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On the basis of comprehensive analysis data on outcrop,seismic reflection profiles and drilling,the Youquanzi oil-bearing structure is confirmed to be an asymmetric half-box anticline retained by conjugate kink zones with a straight hinge dipping towards NNE.The northern limb is a large scale kink zone of over 800 m wide and dips towards SSW at a high angle with sub-vertical inner-bed in it.The rotation of the inner-beds indicates that the southern side shears reversely towards the north.Four small-scale kink zones are developed on the southern limb and shear reversely southward,carving the limb into the step occurrence dipping SSW at 20? as a whole.Along the boundaries of the kink zones on both limbs,there are merely a few small-scale high-angle reverse faults.Fractures,mainly bedding-separation fractures,followed by separation fractures sub-normal to the bedding(mostly occurring in competent calcareous siltstones)and occasionally small-scale low-angle thrusts,are developed in the kink zones.These fractures are commonly filled with fiber gypsum and show locally some oil traces,indicating that these fractures are the products of high-pressure fluid.Seeing that the kink zones and relevant anticlinal highs are fractured and favorable for both oil-gas migration and accumulation,they can be a new way for finding fissure-type reservoirs with the absence of enough ideal lithologic-re-servoirs.

Characteristics of the present pressure filed in the Paleogene Sha-4 Member of Zhanhua sag,Jiyang depression and their function to the distribution of oil and gas pools

Qin Runsen, Xu Guosheng, Xu Xinyou, Li Jianlin, Yuan Haifeng

2007, 28(3):  329-336,323.  doi:10.11743/ogg20070305

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The measured pressure data and pressures calculated with balanced depth method are used to reconstruct pressure profiles and classify vertical pressure variation sequences in single well in Zhanhua sag.Two different types of sub-sag,i.e. sub-sags with normal-transitional and transitional-abnormal pressure,are recognized in the Paleogene Shahejie Formation in the sag where the vertical superimposed pressure field controls the distribution of oil and gas pools.There are three modes of coupling relationships between the reservoirs in the 4th member of Shahejie Formation(Es⁴) and the pressure fields: abnormal-pressure reservoirs,transitional-pressure reservoir,and normal-pressure reservoirs,among which the mode that oil with double lithologic and pressure seal are the most favorable to the formation of high yield reservoirs.The middle-deep normal pressure zone and transitional pressure zone in sub-sag of transitional-abnormal pressure are potential plays for the disco-very of high yield oil layers in the Es⁴.

Mud volcano structure in South Caspian Basin and its impact upon hydrocarbon accumulation

Duan Haigang, Chen Kaiyuan, Shi Buqing

2007, 28(3):  337-344.  doi:10.11743/ogg20070306

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Mud volcano structures appear as discontinuous blank to chaotic reflections with weak amplitudes in seismic facies,and are in columnar uncomformable contact with adjacent rocks.Controlled by stress field and tectonic active belt of the basin,the mud structures are better developed in the piedmont thrust belt on the basin margin in the center of subsidence.In the same structural belt,mud volcanoes occur in paternoster distribution along trend of the major fault and anticlinal zone.Mud volcano structures are characterized by episodic eruption with radial normal faults and slump structures developed in shallow layers.The volcano structures can be classified into anticlinal,strike-slip fault,and thrust types,according to their origins and characteristics.Geological background,tectonic activity in compressional strike-slip stress field,rapid sedimentation and abnormal formation pressure,are the major reason behind the formation of mud volcano structures.The mud volcano structures exert influences over the hydrocarbon generation,migration,accumulation,preservation,and destruction as well as trap formation,and development of reservoirs.

Characteristics of structure transform zones in the fold-thrust belts on the southern margin of Junggar basin,Northwest China

Wang Xinwei, Wang Xinwen, Ma Yongsheng

2007, 28(3):  345-354,394.  doi:10.11743/ogg20070307

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The lateral tectonic transform zones in the fold-thrust belts at the southern margin of Junggar basin can be classified into three levels.They dominate the structural-sedimentary evolution,spreading of structural lines,structural pattern and deformation extent in the study area.While the vertical transform zones feature in echelon distribution of the main thrust faults and anticline systems. The main factors that control the formation of the la-teral and vertical tectonic transform zones are related to the basement structures,former structures,detachment faults,differences in sedimentary facies and lithology,and compression stress pattern and so on.They control the patterns of deformation in different areas and segments of the folded-thrust belt and the distribution of potential prospects in study area.

Relations between geothermal history and hydrocarbon generation in Jiyuan-Zhongmou-Huangkou depression belt

Liu Li, Ren Zhanli

2007, 28(3):  355-361.  doi:10.11743/ogg20070308

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The Upper Palaeozoic source rocks in Jiyuan-Zhongmou-Huangkou depression belt experienced complicate structural and thermal evolution.The three depressions were similar in thermal history before the Middle Triassic,but the differential subsidence during the late of the Jurassic-Cretaceous period led to their difference in thermal evolution of the Upper Paleozoic source rocks.Jiyuan depression suffered no or tiny uplifting after the Triassic and received continuously Mesozoic and Cenozoic deposits.The Jurassic-Eogene period is its main hydrocarbon generation stage.Zhongmou depression passed through extensive subsidence since the Cenozoic resulting in continuous rising of the temperature of the Palaeozoic.The Eogene is its main hydrocarbon generation period.Huangkou depression began to subside since the Jurassic and subsided again in the Late Eocene.Its thermal maturity is low and the Cretaceous-Eogene period is the main stage of hydrocarbon generation.

Diagenesis of Liaozhong sag in Liaohe depression and pore evolutionin its middle-deep strata

Jiang Shu, Cai Dongsheng, Zhu Xiaomin, Zhu Guanghui, Hu Xiaolin

2007, 28(3):  362-369.  doi:10.11743/ogg20070309

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A detailed analysis based on test data of thin rock section,X-ray diffraction,geochemistry,etc.,is carried out on the diagenesis of Liaozhong sag in Liaohe depression and pore evolution in its middle-and deep-strata.Five diagenetic stages are classified according to the analysis.They are A and B stages of early diagenesis,and A,B,and C stages of late diagenesis.A study on the evolution characteristics and forming mechanism of the secondary pores and their relationships with diagenesis reveals that two main secondary pore zones in middle-and deep-strata are formed mainly by the rapid evolution of clay minerals,hydrocarbon generation,and overpressure,and correspond respectively to the B stage of the early diagenesis and the A stage of late diagenesis.It is concluded that the secondary pore zones in middle-and deep-strata of overpressured areas in Liaozhong sag are the potential exploration targets for the future.

Characteristics of volcanic rock reservoirs in Ou-Huang area of the eastern sag in Liaohe depression and prediction of favorable reservoirs

Zhang Xinpei, Deng Hongwen, Zhang Jichang, Sun Xiaoming

2007, 28(3):  370-376.  doi:10.11743/ogg20070310

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Three types of volcanic rocks,i.e.basalt,trachyte,and tuff,are developed in the Shahejie Formation of Ou-Huang area in Liaohe depression.The trachyte that had gone through structural fracturing in la-ter stage forms high-grade reservoir in the area.To acquire accurate parameters that honestly reflect the reservoir space types and features,techniques such as SEM,cast lamella,and X-CT scanning,are integrated for fine description of the primary pores and fractures and secondary dissolution pores and fractures in the reservoir space of trachyte,and for obtaining reservoir physical properties in combination with RLT.The result indicates that the dissolved vuggy-fractured reservoir has the best poroperm properties,and the second best are the dissolved pore-micropore reservoirs.It also suggests that by adopting technologies like log response and multi-well constrained impedance inversion,together with proper choice of methods and parameters,the re-cognition and prediction of high-grade reservoirs in the study area(where conventional techniques are inefficient)is not only possible but consists well with the real drilling/well-logging data(with thickness error at 3% only).

Evolution of sandstone reservoirs in the Lower Jurassic Xiaomeigou Formation,Shiquantan area,Qaidam basin

Yao Genshun, Shou Jianfeng, Wang Shaoyi, Chen Ziliao

2007, 28(3):  377-383.  doi:10.11743/ogg20070311

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Recent oil and gas discoveries in the thick sandstone reservoirs in the Lower Jurassic Xiaomeigou Formation in Shiquantan area,Qaidam basin,attract attentions to their reservoir characteristics and genetic mechanisms.Detailed petrological study of the reservoirs of 7 wells in the area reveals that the sandstone reservoirs in the Xiaomeigou Formation are dominated by secondary pores dissolved by the leaching atmospheric water and that the intensity of leaching determine the poroperm characteristics of the reservoirs.The reservoirs went through the following stages: weak compaction during the Early Jurassic(with diagenetic compaction rate of 5.5%-6.5%),atmospheric water leaching during the Middle Jurassic and Cretaceous(with pore increase rate of 4.6%-16.5% and the generation of montmoirillonite),strong compaction during the Paleogene(with diagenetic compaction rate at 19.0%-21.5%,precipitation of small amount of calcite,and disappearance of primary pores),and uplifting and preservation during the Neogene with no significant changes in reservoir characteristics.The atmospheric water leaching during the Middle Jurassic and Cretaceous and the intensive compaction in the Paleogene are the two major stages in the evolution of the reservoirs,and determine the genetic types and characteristics of the reservoirs.

Enrichment pattern of carbonate cements in reservoirs of the Hetaoyuan Formation in Nanyang sag,Nanxiang basin

Sun Simin, Luo Jiaqun

2007, 28(3):  384-389,400.  doi:10.11743/ogg20070312

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Based on cast thin section and test data,a study is carried out on the occurrence of the carbonate cements in the reservoirs of the second member in Hetaoyuan Formation of Zhandian oilfield and the change of their contents with burial depth.The carbonate content increases on the whole with its increasing burial depth but presents different characteristics in different diagenetic stages.In the mature stage of organic material especially the semi-or low-maturity stage(the early of late diagenetic stage),the content of carbonate drops sharply and the secondary pores are well developed.After the late diagenetic substage B(the late of late diagenetic stage)when the hydrocarbon generation peak is past,the content of carbonate cements reservoirs especially those of high porosity obviously increases.The continuous enrichment of carbonate in reservoirs is related with shale compaction and dissolution of acid pore water during the mature stage of organic materials.The locations where carbonate enriches vary in different microfacies.It mainly enriches at the bottom of sandbodies in delta front distributary channels,and at the top of sandbodies in mouth bar.The enrichment of carbonate in reservoirs is one of the key factors that cause the reduction of reservoir porosities,especially the reservoirs with a burial depth larger than 2450m.

Enhancing accuracy of saturation model of low-porosity and low-permeability reservoirs by using nuclear magnetic resonance logging data

Huang Yi, Zhao Jun, Cheng Pengfei, Zhao Weixin

2007, 28(3):  390-394,354.  doi:10.11743/ogg20070313

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Nuclear magnetic resonance logging has an edge on the evaluation of porosity structures over the traditional mercury-injection capillary pressure method.For oil reservoirs with low-porosity and low-permeability,the variations in pore structures have a significant impact upon the saturation index 'n',i.e.,when big pores dominate,the 'n' is small;and when small pores dominate,the 'n' is big.The good correlativity between 'T₂',the geometric mean of lateral relaxation time of nuclear magnetic resonance,'m',the cementation index,and 'n',the saturation index,can be used to determine the values of 'm' and 'n'.The errors of value assignment caused by changes of pore structures are eliminated,thus a more accurate value for 'S₀.'(oil saturation) can be obtained from saturation model.The processing of the data in Well TZ111 yields a porosity free of influence of pore enlargement and a saturation closer to the testing results,greatly improving the accuracy of the saturation model.

New approach for pore pressure prediction

Wei Maoan, Chen Chao, Wang Yanjiang, Ma Hai

2007, 28(3):  395-400,389.  doi:10.11743/ogg20070314

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By analyzing the limitations of the traditional pore pressure prediction methods,a new pore pressure prediction approach based on the effective stress theorem and the acoustic velocity model is proposed.It first calculates clay content,porosity,and acoustic velocity with relevant log data,and then calculates vertical effective stress by using Support Vector Machines for Regression and the overburden pressure with density log data,and finally calculate formation pore pressure by the effective pressure theorem.Practical application of the approach shows that it is feasible in prediction of abnormal formation pressure of sandstone and shale caused by undercompaction.Compared with traditional pore pressure prediction methods,the approach does not require establishing normal compaction trend line and has better adaptability and higher accuracy of predictions.

Reservoir prediction of the Upper Guantao Formation in the Neogene—an example from northern Kendong area in Zhanhua sag,Jiyang depression

Jing Hui, Zhang Xiaowu, Zhao Minghai

2007, 28(3):  401-406.  doi:10.11743/ogg20070315

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Three reservoir prediction approaches are proposed based on reservoir characteristics,reservoir velocity,and forward modeling analyses in northern Kendong: 1) direct 3-D tracing of the reservoirs on amplitude data volume can be performed with visualized interpretation software since the isolated river channel sands feature in seismic reflectance signatures of high amplitude and lenticular shape;2) characteristic curve inversion can be an option in the study of spatial distribution of reservoirs due to the facts that continuous crests and troughs of high amplitude indicate a successive sedimentation of sandstone and similar velocities of sandstone and mudstone render an ineffective distinction of sandbody through impedance data;and 3) wave impedance inversion can be used in prediction of the spatial distribution of gas reservoirs because the typical gas reservoirs in the study area show low impedance and a velocity far lower than that of mudstone.An integrated application of the three approaches is of great significance in improving the accuracy of reservoir prediction and performing lateral prediction of reservoirs in the study area.

Identification of hydrocarbons in low-porosity and low-permeability reservoirs by integration of surface log data with wire log information

Yang Sitong, Sun Jianmeng, Ma Jianhai, Huan Guanghui

2007, 28(3):  407-412.  doi:10.11743/ogg20070316

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Reservoirs in the Upper Youshashan Formation(N₂²)and the Lower Youshashan Formation(N₂¹) of Wunan oilfield in Qinghai Province are low in porosity(with average porosity at 13.0% and 13.6% respectively) and permeability(with average permeability at 3.88?10³ μm² and 2.93?10³ μm²).In this type of reservoirs,logging data is greatly affected by the reservoir lithoglogy,formation water characteristics,and reservoir physical properties,causing difficulties in distinguishing the curves of oil/gas-bearing layers and differentiating oil and gas layers from water layers according to logging data only.In this paper,BP neural network technology is applied to the integrated processing of wire logging data and surface logging data from the low-porosity and low-permeability reservoirs in Wunan oilfield.The abundance and thigh resolution of wire log information are combined with the directness and accuracy of surface log data to identify hydrocarbon zones in reservoirs with low porosity and low permeability.

Genesis and physical modelling of aquifer in deep basin gas pool of He-8 Member in Sulige region,Ordos basin

Wang Shiyan, Luo Qun, Song Zixue, Ke Bin

2007, 28(3):  413-418,426.  doi:10.11743/ogg20070317

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Both exploration proactice and physical modelling indicate that deep basin gas accumulations contain aquifers of various geneses.Aquifers in deep basin gas pool of He-8(the eighth member of Shihezi Formation)in Sulige region,Ordos basin, are of two origins—one is bottom water in common lenticular sandstone gas reservoirs with mixed water and gas layer,and the other is bottom water in "lithologic" gas reservoir within the local sandbody of high-porosity and high-permeability in gas-water transition zone of deep basin gas pools.Experiments indicate that water present almost in all but the high tide stages of the evolution of deep basin gas pools.It could be pore space water existed before the accumulation of deep basin gases or bottom water in lithological gas reservoirs formed during the senescence phase of deep basin gas when formation water entered the high-porosity and high-permeability sandstones.It is suggested that the high-porosity and high-permeability sandstones on the migration paths of deep basin gases contains no or very limited amount of water and serve as the most favorable exploration targets for deep basin gas.

Genetic types and distribution pattern of natural gases in Gubei buried-hills,Jiyang depression

Lin Wu, Li Zheng, Li Juyuan, Xu Xingyou

2007, 28(3):  419-426,418.  doi:10.11743/ogg20070318

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Research on the compositions,carbon isotope,and geochemical properties of light hydrocarbons of natural gases in Gubei buried-hills of Jiyang depression suggests that gases there are of three genetic types: oil-related gas,coal-related gas,and mixed gas.Natural gases in Well Bo-601 and Boshen-6 belong to oil-related gas,that in Well Yi-155 and Gubeigu-1 are coal-related gas,and that from Well Gubeigu-2,Bogu-4,and Yi-32 belong to mixed type.Study in combination with the geologic characteristics reveal that the carbon isotope and light hydrocarbon show certain regularities in the study area.From the first row to the fourth row of buried-hills(from west to east),the carbon isotope become progressively heavier,the values of indexes of methylcyclohexane and benzene gradually increase,and the genetic types of natural gases shift from oil-related gas to coal formed gas.It is suggested that the distribution of natural gases in the area are obviously controlled by the gas source rocks and faults in the study area.Oil-related gas is mainly concentrated in the first row of buried-hills,mixed gas is predominantly distributed in the region near the Gubei fault in southern part of the second and the third row of buried-hills,while coal-related gas is preserved in the northern part(regions far away from the Gubei fault)of the second and the third rows of buried-hills,and the fourth row of buried hills.

Genetic characteristics of associated gases from crude oil biodegradation in Gudao oilfield,Jiyang depression

Wang Wanchun, Li Juyuan, Tang Hongsan, Cui Junhan, Kang Yan

2007, 28(3):  427-432.  doi:10.11743/ogg20070319

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Associated gases from crude biodegradation possibly contain remnants from microbial degradation as well as products from the anaerobic biodegradation of crude.Studying this kind of associated gas and restoring its original properties are helpful to gas source correlation and exploration of natural gas.The components and isotopic compositions of associated gases from crude biodegradation in Gudao oilfield of Jiyang depression indicate that the natural gas in this field is generated by the sapropelic organic materials mainly in the third member of the Shahejie Formation.The interfusion of secondary biogenic methane with relatively lighter carbon and heavier hydrogen isotopic compositions that are generated from the biodegradation of oils results in the drier components and abnormal negative correlation between the carbon and hydrogen isotopic compositions of methane for the associated gases of crude biodegradation.The attack of micro organisms on propane and n-butane of the na-tural gas causes evident heavier δ¹³C values of propane and n-butane in some samples.

Geochemical behaviors of crude oil in the southern margin of Junggar basin

Wei Dongtao, Jia Dong, Zhao Yingcheng, Yang Haibo, Chen Tao, Wu Liangyu, Shao Hongshun

2007, 28(3):  433-440.  doi:10.11743/ogg20070320

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A comprehensive geochemical analysis of the crude oil samples frorn the southem margin of Junggar basin helps to classify them into six basic types of three categories.They are oil from the Jurassic coal measure(type (一七)),and from lacustrine source rocks of the Permian(type (一四)),Cretaceous(type (一五)),and Eogene(type (九)),and mixed oils from the Jurassic and the Eogene(type V),and from the Jurassic and the Eogene(type V).It is showed that different tectonic units from the east to the west have different types of oils.The type iv,type (一七),and type V,are found in Fukang fault zones.The Qigu faulted-fold belts have similar oil types to those of the Fukang fault zones but with the additional type (一五).While the Huoerguosi-Manasi-Tugulu anticline and Sikeshu sag are relatively simple with the former contains mainly type (一四) and later harbors type (九) and type iv.According to the above oil-source analyses,it is suggested that the (一四)-type oil from the Cretaceous should be the source of oil in the study area.