Table of Content

08 December 2013, Volume 34 Issue 6

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Progress of research on hydrocarbon accumulation of tight sand gas and several issues for concerns

Guo Yingchun, Pang Xiongqi, Chen Dongxia, Jiang Fujie, Tang Guomin

2013, 34(6):  717-724.  doi:10.11743/ogg20130601

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Continuous tight sand gas is a significant unconventional resource for natural gas.To understand the progress of geological research on this kind of gas reservoir,this paper summarized the criteria for identification of tight sand reservoirs,their classification,geological characteristics,elements of hydrocarbon accumulation,and trapping mechanisms.The current criteria for identivation of continuous tight sand gas reservoirs does not take accumulation conditions into conside-ration.The real critical conditions of tight sand gas change along with hydrocarbon accumulation conditions.The key elements of hydrocarbon accumulation in tight gas reservoir involve hydrocarbon source rock,tight sandstone close to source rock and stable tectonic environment.It should be noted that the nature of tight sandstone is nano-micro scale pore throat and the percentage of pore throats is about the same as that of pores,and that abnormal pressure is not an essential difference between tight sand gas reservoir and conventional gas reservoir.Several key issues concerning continuous tight sand gas accumulation are presented.The first is study on dynamic trapping mechanism for tight sand gas reservoir,i.e.the force balance between driving force(gas pressure)and resistance(capillary force,viscous force and formation water pressure)at the interface of gas water inversion.The quantitative description and simulation of evolution of these forces are particularly important.The second is the research on the mechanism and process of adjustment of tight sand gas reservoir as well as restoration of the original tight sand gas reservoir.The restoration of the original reservoir can be realized by means of force balance relation at the interface of gas water inversion.All of the late adjustment and modification were realized through changing the critical conditions of gas water inversion.The third is study of the control of sandbodies with relatively high porosity and permeability on gas accumulation in tight sandstone.The existence of these sandbodies changes the accumulation conditions and complicates the accumulation process.

Migration mechanism of the Permian hydrocarbon and shale oil accumulation in Malang Sag, the Santanghu Basin

Liu Bo, Chi Yaao, Huang Zhilong, Luo Quansheng, Wu Hongzhu, Chen Xuan, Shen Ying

2013, 34(6):  725-730.  doi:10.11743/ogg20130602

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The shale oil potential is high in the Permian Lucaogou Formation in Malang Sag,Santanghu Basin.Its genetic mechanism and accumulation patterns are greatly different from those of conventional reservoirs.Migration is a major component of genetic mechanism of shale oil.Based on core and thin section observation,and in combination with geochemical data and geological condition analysis,this paper studied the migration mechanism of shale oil,including dynamic force,pathway,direction,distance,efficiency and so on.Migration effect of shale oil within source rocks is insignificant,thus shale oil reservoirs are not the result of oil migration and accumulation within source rocks.In contrast,vertical migration effect of shale oil out of source rocks is significant.The existence of large active faults may lower the abundance of shale oil in source rock.High formation pressure caused by hydrocarbon generation is the main dynamic force of primary migration.After small scale migration through kerogen network,interlamination and microfractures,most of the oil generated retain in place,and the migration efficiency is very low.On the contrary,in areas where carrier faults are well developed,the oil can migrate vertically along the faults and accumulate in the overlying reservoirs of the Lucaogou Formation.This migration mechanism of shale oil determines the characteristics of shale oil play such as continuous distribution,no obvious oil-water contact,no influence of structure on oil accumulation,and low abundance of oil in areas with active faults.

TOC logging interpretation method and its application to Yanchang Formation shales, the Ordos Basin

Xie Haochen, Yu Bingsong, Zeng Qiunan, Feng Ziqi

2013, 34(6):  731-736.  doi:10.11743/ogg20130603

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Total organic content(TOC)of organic rich shale is an important parameter in resource assessment.In order to predict the TOC of shales in the non-cored wells in the study area,this paper established a mathematical model of TOC for the target layer through logging interpretation.Based on an analysis of the relationship between the measured TOC of cores sampled from the Yanchang Fm in 20 wells and the corresponding logging parameters,we found that the measured TOC values are positively correlated with the logarithm of Rt and GR,but not insignificantly correlated with AC.Multivariate analysis method was used to establishe a mathematical model for predicting TOC of the Yanchang organic-rich shale with the logarithm of Rt and GR.Its application in the cored Liuping-177 well gave a mean error of 5.35% between the logging interpreted TOC and the measured TOC.The mathematical model was used in calculation of TOC of the Yanchang organic-rich shale in 46 non-cored wells.The spatial distribution of TOC of the Yanchang organic-rich shale in the study area was mapped based on these calculation results and the measured TOC of additional 20 cored wells.The TOC distribution is consistent with the distribution of sedimentary microfacies,verifying the reliability and effectiveness of this method.

Quantitative characterization of superimposition relationship and distribution of reservoir sandbodies in the Upper Palaeozoic of Gaoqiao region, the Ordos Basin

Tian Jingchun, Zhang Xingliang, Wang Feng, Chen Rong, Lin Xiaobing

2013, 34(6):  737-742,815.  doi:10.11743/ogg20130604

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In order to quantitatively characterize the spatial and temporal distribution characteristic of superimposed reservoir sandbodies,drilling core data,logging data,and test data are integrated to analyze the superimposeition relationship and sandbodiesbody size of the Upper Palaeozoic in Gaoqiao region of Ordos Basin.The superimposition styles of sandbodies in the Shanxi-Xiashihezi formations in the study area include scouring-cutting type(truncated channel sandbodies),scouring-contact type(complete channel sandbodies)and continuous transitional contact type(isolated channel sandbodies).Distributions of sandbodies formed in different periods are different.Sandbodies in the Shanxi Formation are relatively narrow,showing a banding distribution.In contrast,the very thick sandbodies consisting of superimposed distributary channels of multi-stages in the 8^th member of the Shihezi Formation feature in laterally continuous and large scale distribution.Based on core measurement,we calculated the channel water depth range of bankfull stage,single sandbody thickness,single channel width and river width in the 2^nd member of Shanxi Fm,the 1^st member of Shanxi Fm and the 8^th member of Shihezi Fm.The rivers in meandering river delta in the 2^nd member of Shanxi Fm has a width of 700-1 500 m,the rivers in meandering river delta in the 2^nd member of Shanxi Fm has a width of 600-1 200 m,and the braided rivers in the upper and lower 8^th member of Shihezi Fm have a wide of 1 000-2 000 m and 750-1 600 m respectively.

Depositional system characteristics of the first member of the Nantun Formation in Tanan sag, the Hai-Ta Basin

Liu Zongbao, Zhao Rongsheng, Yan Li, Yu Yinghua

2013, 34(6):  743-750.  doi:10.11743/ogg20130605

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Tanan Depression is one of the most important oil and gas exploration areas in Hailaer-Talmud Zagat Basin.Various data including cores,logs and 3D seismic data were integrated to study in detail the sequence stratigraphic framework and sedimentary system characteristics of K₁n¹(the 1st member of Nantun Fm)in Tanan Sag,Haita Basin.Three unconformites and two lake flooding surfaces were identified in K₁n¹,according to which K₁n¹ was divided into three third-order sequences.The types of sedimentary facies and distribution characteristics of sedimentary system were analyzed on the basis of isochronous stratigraphic framework.Three sedimentary systems namely fan delta,sublacustrine fan and lake were identified in the K₁n¹.Fan delta sedimentary system under the control of provenance on the western gentle slope dominated in the study area during the deposition of the middle-lower part of K₁n¹ due to the influences of oscillatory subsidence of "flood basin" during passive rifting.In contrast,lake deposition system was predominant in the study area during the deposition of the upper part of K₁n¹ due to the rapid subsidence in the process of active rifting.At the same time,the secondary depression-controlling faults experienced NW-SE extension and tilted,forming large-scale reverse normal faults.Efficient hydrocarbon expulsion characteristics of interbeded source rock and reservoir combination,high porosity and permeability of distributary channel sands of fan delta front facies and structural high in the upthrown block of fault jointly determined the footwall of antithetic fault in the western subsag to be the main location of oil accumulation.

Microfacies characteristics and sedimentary models of the third member of Funing Formation in Zhangjiaduo oilfield

Chen Qianqian, Ding Xiaoqi, Wan Youli, Zhang Shaonan

2013, 34(6):  751-757.  doi:10.11743/ogg20130606

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Four types of lithofacies are identified in the 3rd member of Funing Formation in Zhangjiaduo oilfield,the Su-bei Basin,including dark mudstone,bioturbated siltstone,siltstone-fine sandstone lithofacies with argillaceous laminates and burrow as well as fine sandstone with parallel bedding.Upward-coarsening reverse rhythm is the main section structure,followed by first upward-coarsening and then upward-thinning composite rhythm,while positive rhythm is very rare.All the features of lithofacies,section structure,logging facies and cumulative grading curve show that the 3rd member of Funing Fm is typical shallow lake beach-bar facies.According to the sedimentary characteristics and spatial distributions,the reservoirs are further divided into sandstone of bar microfacies and sandstone of beach microfacies.A beach-bar sedimentary model is proposed.The sandstone reservoirs of bar microfacies are high in hydrocarbon fullness,due to its low shale content and high porosity.In contrast,the sandstone reservoirs of beach microfacies show great variance in hydrocarbon fullness as argillaceous laminations are well developed,heterogeneity is week,and hydrocarbons mainly fill in the fine sandstone lithofacies with parallel bedding and argillaceous laminates+burrow fine sandstone lithofacies.

Physical simulation of deltaic deposits

Wang Junhui, Jiang Zaixing, Zhang Yuanfu, Gao Liming, Wei Xiaojie, Zhang Wenzhao

2013, 34(6):  758-764.  doi:10.11743/ogg20130607

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In order to fully understand the sedimentary characteristics of deltaic deposits and the development patterns of associated sand bodies,this paper presents a physical simulation of delta development through flume experiment and introduces the experiment results in respects of sedimentary process and characteristics of distributary channels,mouth bars,and slide-slump deposits.The experiment reveals that the development of delta is an alternating process of deposition and erosion.Deposition is dominant in flood season when distributary channels carry a heavy sediment load,while erosion is dominant in non-flood season.The growth of mouth bars initiates from an underwater shoal in an order of forward,upward,backward and transverse.In addition,there are two modes of bifurcation,i.e.multi-stage bifurcation by one mouth bar and simultaneous bifurcation by multiple mouth bars.The channels on a deltaic plain may evolve in two modes,i.e.redirection and diversion,which are related with flood and mouth bar respectively.Flood events could be the trigger of delta front slide-slump deposits.Deltas are formed in the process of sediment transportation and sedimentation determined by the interaction of alluvial and basinal dynamics.In this process,sedimentary slope break is formed,which is favorable for the development of high quality reservoirs.

Impact of feldspar dissolution on reservoir physical properties：a case from Dongying Sag, the Bohai Bay Basin

Yu Chuanqi, Song Xiaojiao, Li Jingjing, Jiang Shuangze, Zhang Lianliang

2013, 34(6):  765-770.  doi:10.11743/ogg20130608

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Sandstone reservoirs in Dongying Sag,the Bohai Bay Basin are rich in feldspar,dissolution of which is very common and has an important influence on reservoir physical properties.Polarizing microscope,SEM and X-ray powder diffraction technologies were used to study the distribution characteristics of feldspar and its dissolution products in the sandstone reservoirs in Dongying sag.The content of feldspar varies in different areas.The highest content of feldspar occurs in the north,followed by the south,and the lowest is in the central area.Vertically,Es¹ is the richest in content of feldspar,followed by Es² and Es⁴ f,and Es³ is lowest.The main dissolution products of feldspar in the sandstone reservoirs in Dongying sag include kaolinite,illite and chlorite.The transformation kaolinite to illite and chlorite causes the decrease of content of kaolinite.The illite and chlorite in the shallow layer are mainly transformed from I/S,while they come from kaolinitic alteration in the deep layer.The content of I/S is high in shallow layer,and reduces with the increasing depth.

Cenozoic tectonic evolution in the north-central Jizhong Depression

Dong Dawei, Li Li, Liu Jian, Li Jiyan

2013, 34(6):  771-780.  doi:10.11743/ogg20130609

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On the basis of fine seismic interpretation,various methods including fault throw method,fault activity intensity method,balanced cross-section technique and physical simulation are adopted in this paper to analyze the Cenozoic tectonic characteristics and evolution process as well as the forming mechanism of structures.The results show that the north-central part of Jizhong Depression was dominated by extensional structures in the Cenozoic,with strike-slip structure style also occurring.In Baxian Sag,tilting and sliding fault terrace structural styles were predominant.While Raoyang Sag was dominated by anticline structural style except for its northernmost part where strike-slip structure style was common.The extensional intensity shows large diversity in different periods in both Baxian Sag and Raoyang Sag,strictly controlled by the activity of boundary faults.Raoyang Sag was controlled by Liulu,Hejian,and Maxi faults from south to north.The extension of sag as characterized by transition from "south being larger than central-north" in Ek-Es⁴ to "central-north being larger than south" in Es³-Ed.Baxian Sag was controlled by the diversity of Niudong fault activity along strike,featuring in the tectonic evolution of "strong early stage but weak middle and late stages" in south,"weak early stage strong middle stage and weak late stage"in the central,and "weak early stage but strong middle and late stages" in north.The physics simulation experiment validates the fault development process of research area.The experiment result has strong similarity with the development characteristics of the faults,demonstrating the correctness of tectonic geometry and kinematics characteristic analysis.On the basis of above research,the tectonic evolution process of Raoyang Sag and Baxian Sag is divided into three stages,namely weak early stage,strong middle stage,and fair late stage.Finally,the mechanism and deep background of tectonic formation and evolution are discussed.

Structure features and dynamic mechanism of basin formation in Kongdian-Shahejie periods in western Bohai Sea

Li Minggang, Wu Jingfu, Wu Keqiang, Liu Pengbo, Yang Haifeng

2013, 34(6):  781-789.  doi:10.11743/ogg20130610

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Based on the overall study and comparative analysis,the theory of oilfield structural analysis was used to understand the structure features and dynamic mechanism of basin formation during the deposition of the Kongdian and Shahejie formations in Western Bohai Sea,so as to reveal the distribution of source rocks in the Kongdian and Shahejie formations and guide play evaluation and exploration target selection.Basin architecture was controlled by basement structure,and tectonic deformation was different in the east and west due to the difference of crystalline basement types.In addition,the tectonic deformation was influenced by two pre-existing NE-NNE-trending and NW-NWW-trending conjugate basement faults,resulting in the E-W zonation and N-S segmentation in the west part while E-W segmentation and N-S zonation in the east part.Structure features in different deposition periods of Kongdian formation and Shahejie formation vary largely,showing an evolutionary sequence of downwarp-fault depression-fault depression and fault-downwarp depression(depression).And the structural deformation during despotism the Kongdian and Shahejie formations in western Bohai Sea was controlled by vertical extensional stress field induced by mantle diapir and uplift.Tectonic deformation in the east part was mainly controlled by the near SN extensional stress field,while that in the west part was controlled by the superimposed NW-SE and near SN extensional stress fields.

Quantitative evaluation of control of faults on hydrocarbon accumulation and play fairway prediction：a case from Es³⁽¹⁾ in Qijia-Yuanyanggou area, the Liaohe Depression

Sun Tongwen, Lv Yanfan, Liu Zhe, Fu Guang, Sun Yonghe, Zhang Dongwei

2013, 34(6):  790-796.  doi:10.11743/ogg20130611

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In order to understand the control of faults on hydrocarbon accumulation in the Paleogene Shahejie Fm(Es³⁽¹⁾)in Qijia-Yuanyanggou area,the Liaohe Depression,source rock-rooted faults were identified on the basis of fault system division.In addition,the SGR method and fault growth rate were applied respectively to quantitatively evaluate the lateral sealing capacity of fault traps and the fault activity intensity after hydrocarbon accumulation period.The results show that the control of faults on hydrocarbon accumulation is depicted mainly in the following three aspects.Firstly,the oil source-rooted faults control the locations of hydrocarbon accumulation;secondly,the lateral sealing capacity of faults controls fullness of the fault traps;and thirdly,the fault activity intensity after hydrocarbon accumulation period controls the preservation of pre-existing oil and gas.Based on the above studies,criteria for selection of favorable targets were established.When oil sources are sufficient and reservoir physical properties are good,class-Ⅰ trap is defined as fault traps under the control of two or more source rock-rooted faults,having a hydrocarbon fullness greater than 50% and fault activity intensity(after hydrocarbon accumulation period)less than 2m/Ma.Drilling risk of class-Ⅰ is minimum,followed by class-Ⅱ and class-Ⅲ traps.Finally,two class-Ⅰ traps and one class-Ⅱ trap were mapped,and the oil-bearing area of Es³⁽¹⁾ in these traps is 5.8 km²

Characteristics of the NE-trending strike-slip fault system and its control on oil accumulation in north peri-cline area of the Tazhong paleouplift

Yang Shengbin, Liu Jun, Li Huili, Zhang Zhongpei, Li Jingjing

2013, 34(6):  797-802.  doi:10.11743/ogg20130612

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A series of strike-slip faults occurr in north peri-cline area of the Tazhong Uplift in the Tarim Basin.The structural styles include flower structure,parallel high-steep fault,en-echelon structure etc.In the Middle Caledonian, the Tazhong-Ⅰ fault and the southern boundary fault were most active,and the NE-trending tear faults were formed because of the differential movement of NW-trending overthrust nappe or sliding block.In the Late Caledonian,the Tazhong uplift experienced strong oblique compression from the SE direction,which was the dynamic mechanism for the formation of strike-slip faults.This resulted in right-lateral strike-slip on the basis of basement weak zone.NE-trending strike-slip faults were formed in the tectonic setting of intraplate transpressional nature,and were connected with the NW-trending thrust fault.In the Late Caledonian to Early Hercynian,faults were developed in inheritance along the Middle Caledonian tear faults,and were characterized by multistage activities.The strike-slip faults not only greatly modified carbonate reservoirs,but also controlled the development of structural trap in the Paleozoic clasitc rocks.In addition,they also acted as important pathways of hydrocarbon migration.

Salt-related fault characteristics and their petroleum geological significance in Zarzhu terrace and its adjacent areas, the Amu Darya Basin

Nie Minglong, Wu lei, Sun lin, Gao Anhu

2013, 34(6):  803-808.  doi:10.11743/ogg20130613

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A set of salt-gypsum rocks occur in the Upper Jurassic in Zarzhu terrace and its adjacent areas in the Amu Darya Basin,making fault and their combination types complicated,thus being of great significance for petroleum exploration.Through the analysis of the drilling data and seismic data,we studied the development characteristics of salt-related faults and their control on hydrocarbon accumulation.The results show that there are two fault systems in the pre-salt layer and above-salt layer in the study area respectively.They appear in 3 combination styles,i.e.thrust fault in above-salt layer-thrust fault in pre-salt layer,strike-slip in above-salt layer-thrust fault in pre-salt layer,and strike-slip-basement involvement in above-salt layer.The salt-related faults are controlled by tectonic stress field,pre-existing basement faults and thickness of salt-gypsum rocks.In the east part of the study area,where the salt-gypsum rock is thick,there develops two fault combination styles,i.e.strike-slip in above-salt layer-thrust fault in pre-salt layer,and thrust fault in above-salt layer-thrust fault in pre-salt layer.The faults provide trap conditions for hydrocarbon accumulation and do not destroy the sealing integrity of the salt-gypsum rock.While in the west part of the study area,where the salt-gypsum rock is thin and the compress is weak,there develops strike-slip-basement involvement in above-salt layer.The development of faults were controlled by the basement fault,and is destructive to the accumulation of oil and gas in pre-salt layers.

Fracture parameter optimization of large hydraulic fracturing based on the fine geological model

Gou Bo, Guo Jianchun

2013, 34(6):  809-815.  doi:10.11743/ogg20130614

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The key geological factors determining fracturing effect in north Z23 ultra-low permeability reservoir are analyzed based on the fine geological model of reservoir established by using the Petrel software.According to the key geolo-gical factors(reservoir thickness,permeability),the target layers of sand unit 1,2 and 3 are classified into four types.Fracturing parameters of eight reservoir types are optimized by using numerical simulation and ENPV methods based on the fine geological model.The results show that the fracturing parameters vary greatly for reservoirs with intense heterogeneity.To obtain ideal productivity,long fractures are needed for the low permeability reservoir,while fractures with high flow conductivity is needed in reservoirs with relative high permeability.Field test shows that the hydraulic fracturing with fracture parameters optimized by using this method is effective.

Coupled conduit flow-throttled flow-seepage flow separate-layer injection rate allocation method for polymer injection wells：a case study from Daqing oilfield

Li Haicheng, Li Xiaofeng, Gao Guanglei, Xu Dekui, Hu Junqing, Liang Fumin

2013, 34(6):  816-820.  doi:10.11743/ogg20130615

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In the process of polymer flooding,polymer solution flows first through tubes in wellbore after injected from wellhead. A vertical conduit flow frictional pressure loss equation is set up according to the theory of non-Newtonian fluid mechanics.Usually,a part of pressure and viscosity will be lost when the polymer solution flows through a nozzle.The relationships of nozzle length to diameter ratio(L/D₁)with friction coefficient(λ)and Reynolds number (Re)can be established through experiment modeling the process of polymer solution flowing through nozzle.The basic equations of pressure lossΔp and viscosity loss Δη are developed by using dimension analysis method.In combination with the experimental data,an incidence formula of pressure drawdown and dynamic viscosity loss can be built through regression analysis with SAS software. After polymer solution enters strata,it will squeeze the skeleton of rock under pressure of polymer solution and the injection rate will also decrease with time.Partial differential equations of single phase radial flow of non-Newtonian fluid is established according to the seepage characteristics of non-Newtonian flow.The equations are discrete by using the finite difference and solved by software with the boundary conditions of the equations constrained by the real data,pressure drawdown and dynamic viscosity loss caused by conduit flow and throttled flow.The relationships between injection pressure,injection rate and time are established,providing a theoretical basis for separate-layer polymer injection rate allocation.

Analysis and evaluation on horizontal well seepage models and their developing trends

Lian Liming, Qin Jishun, Yang Siyu, Yang Yongzhi, Li Yansong

2013, 34(6):  821-826.  doi:10.11743/ogg20130616

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As productivity of mature oilfields lowers and the proportion of reserves in low-permeability reservoirs increases,horizontal-well theory needs to be improved to innovate horizontal well technologies. Beginning with the basic see-page flow theory,this paper reviews different seepage models of horizontal wells at home and abroad.These models are divided into 4 types,including steady state model,pseudo steady state model,unsteady state model and wellbore-reservoir coupled flow models.The applicable conditions as well as advantages and disadvantages of every model are analyzed and evaluated.The results show that the steady state model is of pioneering significance,but their assumptions are too ideal to be in accordance with the actual situations;the pseudo steady state model is simple in forms,but can only describe see-page flow in a short-period;the unsteady state model is universal,but does not take the influences of wellbore flow in near wellbore areas into consideration; the wellbore-reservoir coupled flow model is high in accuracy,but also high in complexity of computation.Based on the study above,the paper presents the trend of seepage model development.Actual parameters will be introduced based on the wellbore-reservoir coupled flow model and will be fitted according the actural conditions.Some of the parameters will be determined to simplify the calculation procedure.Moreover,methods such as tracking streamline and vector well pattern will be incorporated to enrich research tools.

Statistical method series for the resource assessment of petroleum accumulation system

Sheng Xiujie, Jing Zhijun, Yan Qi, Xiao Ye, Xie Guojun, Xu Jingxin

2013, 34(6):  827-833,854.  doi:10.11743/ogg20130617

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Based on the principles of petroleum accumulation system,this paper systematically summarizes and perfects the traditional techniques of petroleum resource assessment,and expounds the connotation of resource evaluation under a petroleum accumulation system.On the basis of a deep understanding of the controlling factors of petroleum accumulation and the principles of statistical models,we defined the key objectives of resource assessment at various exploration stages,categorized and standardized the most popular mainstream approaches used in the industry and academia,as well as me-thods evolved during the development of PetroV(a petroleum resource evaluation system of Sinopec),and proposed a methodology framework for resource assessment of a petroleum accumulation system.The categorized five methodology series include 1)probabilistic inference or analogue approaches for frontier targets,2)Monte Carlo approaches for conceptual plays,3)statistical methods for established plays in early exploration stage,4)probabilistic reasoning models for targets in mature plays and 5)discovery process and spatial statistical models in well explored regions. We elaborate the objectives of assessment and the suitability of statistical methods under a variety of exploration scenarios through real examples.In practice,the proposed assessment framework can effectively reduce the sensitivity on parameter selections and the impact due to differences in the geological models on output,thus enhancing applicability of the statistical methods.In addition,the proposed framework may also provide useful information for direction on future methodology development.

Application of pre-stack geo-statistics inversion technology in quantitative prediction of complex reservoirs

Qian Yugui, Ye Tairan, Zhang Shihua, Wang Yan, Zhan Xin, Yin Yingzi

2013, 34(6):  834-840.  doi:10.11743/ogg20130618

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The deterministic inversion technology and the post-stack geo-statistics inversion technology have been widely adopted in prediction of tight clastic reservoirs.However,they are not very effective in prediction of thin reservoirs with complex lithologic structure and wave impedance.The combination of the simultaneous inversion technology and the pre-stack geo-statistics inversion technology is effectively applied in the quantitative prediction of such reservoirs.The application of these technologies can not only improve the vertical and horizontal resolution but also can recognize effective re-servoirs even when the impedances of surrounding rocks and reservoirs are overlapped.Although the pre-stack simulta-neous inversion technology can extract P-wave impedance,S-wave impedance,v_P/v_S and density,and can recognize reservoirs with complex impedance,it has limited vertical resolution due to the limitation of frequency band.Stochastic mode-ling-based pre-stack geo-statistics inversion technology can effectively integrate geological,logging and 3D seismic data,greatly improve both vertical and lateral resolutions,thus can realize fine description of reservoirs.Based on deterministic pre-stack inversion,this technology can effectively identify thin reservoirs and thin interbedded reservoirs.It has been successfully applied to the prediction of reservoirs in the 4^th Member of Xujiahe Fm in Xinchang gas field of western Sichuan Basin, a continental tight clastic gas field.

Numerical simulation of palaeotectonic stress field in Yakela faulted salient, the Tarim Basin

Luo Xiaolong, Tang Liangjie

2013, 34(6):  841-846.  doi:10.11743/ogg20130619

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Thrust faults are widely developed in Yakela faulted salient due to long-term compression regime.However,some normal faults were also formed during the Early Himalayanian.In order to decode the mechanism of formation and evolution of these faults,we conducted 3D finite element numerical simulation for the Late Hercynian and Early Himala-yan stress field in the Yakela faulted salient.During the Late Hercynian,the compressive stress resulted in the low stress areas in the central and eastern parts of the Yakela faulted salient and the low to moderate stress in the west and north part.This stress field caused the development of some small-scale thrust faults in the Yakela faulted salient.During the Early Himalayan,the compressive stress induced uplifting of the study area,with the amplitude of uplifting increasing from west to east.As a result,the strata bended in the study area,with the strongest tensile stress occurring on top of the boundary fault,and normal faults were also developed in these locations and extended inwards.Meanwhile,compression stress was weak in the lower part of the whole study area,thus did not induce the further development of thrust faults in the inner parts of the study area.

Hydrocarbon detection methods for the Paleogene ultra-deep gas reservoirs in the Qikou Sag

Hong Zhong, Zhang Menggang, Liu Huaqing, Su Mingjun, Yuan Shuqin

2013, 34(6):  847-854.  doi:10.11743/ogg20130620

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In recent years,exploration of the Paleogene ultra-deep gas reservoirs in the Qikou Sag has been fruitful.Yet no researches have been performed on the seismic response features of these gas reservoirs and relevant gas detection techniques,impeading exploration to some degree.In an attempt to solve these problems,a comparative study on various spectral decomposition methods was performed according to the typical frequency domain responses of the ultra-deep gas re-servoirs,i.e.high-frequency attenuation and low-frequency resonation.In addition,according to the features of the ultra-deep gas reservoirs,instantaneous wavelet absorption and amplitude to frequency ratio attribute were employed to detect gas-bearing intervals and their boundaries.The result shows that the spectral decomposition method is the basis of abnormal gas-bearing reservoir detection.The Short Time Fourier Transformation through Hanning time function with a time window length being two times of average distance between two through of seismic wavelets is suitable for detecting low-frequency abnormaly of gas reservoir with high resolution both in time and frequency domains.The results of gas detection with these techniques match the drilling results of the new exploratory wells,verifying the effectiveness of these methods in ultra-deep gas reservoir detection in the Qikou Sag.