Table of Content

24 October 2008, Volume 29 Issue 5

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Theories,techniques and practices of petroleum exploration in marine sequences in China

Mou Shuling

2008, 29(5):  543-547.  doi:10.11743/ogg20080501

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Practices of petroleum exploration in marine carbonates in China,marked by the exploration and development of Tahe oilfield and Puguang gas field,reveal a prospective exploration field worthy of research.Since there are no practicable exploration theories and mature engineering techniques,petroleum exploration in marine carbonate sequences of China is characterized by large difficulty and high risk,challenging management of exploration and development in marine sequences.An integrated management philosophy,which incorporates theoretical innovation,technical research and advantageous team,is proposed based on a summarization of previous experiences and lessens.In the context of theories,marine petroleum theories are quite different with continental petroleum theories and the marine petroleum theories in China also have large differences with oversea marine petroleum theories.While in the context of engineering techniques,marine carbonates in China are characterized by highly variable topographic and geomorphologic conditions,complexity of subsurface structures due to muhiphase deformation and superimposition and deep burial of targets,challenging oil and gas exploration.Therefore, both theoretical innovation and technical research should be emphasized in exploration of marine sequences. However,attentions should be paid to both general techniques and specific techniques,and equal stress should be laid on both fundamental and applied researches,so as to speed up transferring of science and technology to productivity.Four combinations including production with scientific research,geology with engineering,theory with technique,and research with management,should be realized.It is necessary to summarize the theories and practices of exploration in marine carbonate sequences in China,so as to further promote the advancement of marine petroleum technologies and achieve larger breakthrough in exploration of marine sequences in China.

Building-up process of carbonate platform and high-resolution sequence stratigraphy of reservoirs of reef and oolitic shoal facies in Puguang gas field

Ma Yongsheng, Chu Zhaohong

2008, 29(5):  548-556.  doi:10.11743/ogg20080502

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Puguang gas field and other major discoveries in northeastern Sichuan Basin obtained in recent years prove the correctness of the strategy searching for large gas pools in reservoirs of reef and oolitic shoal facies according to the exploration idea of structural-lithologic combination gas pools and lithologic gas pools occurring in deep marine sequences.Theories and methodologies of sedimentology,sequence stratigraphy and seismic sedimentology are applied to systematically study the building-up process of carbonate platforms and the formation and distribution of super-thick complexes of reef and oolitic shoal facies in sequences from the Upper Permian Changxing Formation to the Lower Triassic Feixianguan Formation.It is discovered that the vertical superimposition of platform-margin reef and open platform bioclastic shoal of the Changxing Formation and the platform-margin and open platform oolitic shoal in the first and second members of Feixianguan Formation resulted in the largest and thickest carbonate platform in Sichuan Basin and China.The Changxing Formation reef was formed on continental shelf during marine transgression of second-order sequence and is represented by moundy blank reflections on seismic profile.The Feixianguan Formation platform-margin and intra-platform oolitic shoal was formed at the early HST of second-order sequence and is represented by moundy chaotic-discrete strong reflections.The Changxing Formation reef and post-reef deposits provided a high energy shallow water environment for the formation of the successive Feixianguan Formation oolitic shoal.Carbonate sequence stratigraphic research shows that the Changxing Formation and the Feixianguan Formation can be divided into 5 third-order sequences, each of which can be subdivided into 2 to 3 fourth-order sequences.Integrated study of carbonate sedimentology and sequence stratigraphy reveals the evolution of Puguang carbonate platform.High-resolution sequence stratigraphic research of the carbonates based on drilling data reveals the symmetrical high-frequency cyclic features of the dolomite reservoirs of reef and shoal facies.Reservoir porosity increases along with the decreasing of gamma ray and resistivity and the coarsening of dolomite crystalline in each cycle.The building-up process of the platform and the characteristics of reservoir porosity distribution in the high-frequency sequences provide not only the necessary theoretical bases for further exploration of carbonate sequences of reef and shoal facies,but also a guide to gas development.They constitute an important part of the integrated research of exploration and development of carbonate oil/gas pools.

Essential Feature and potential of hydrocarbon accumulation in China marine sequences

Cai Liguo, Jin Zhijun, Chen Kongquan, Li Tiejun

2008, 29(5):  557-564,573.  doi:10.11743/ogg20080503

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Paleozoic and Mesozoic sediments of continental margins and platform covers are mostly folded into mountains in China,and the unique marine superimposed-residual basins become a significant feature of China petroleum geology.During the geological evolution,the ancestors of these basins once had excellent source,reservoir and seal rocks,with their conditions of hydrocarbon resources and accumulation as good as those of other basins in world petroleum provinces.However,the marine carbonate sequences in China are older in age,deeper in exploration targets,and complex in hydrocarbon accumulation due to multiple events of tectonic superimposition and reworking,resulting in the peculiarity of petroleum exploration in these marine carbonate sequences.Recent exploration results have shown that large hydrocarbon accumulations are still likely to be formed under suitable conditions in these marine sequences because of their foundations of organic matter.Differential tectonic evolution has make the marine basins be significantly different in hydrocarbon potential and production capacity. Thus,Sichuan and Ordos basins are predominated by gas production,and Tarim basin is able to produce both oil and gas.Therefore,looking for giant and large fields should be focused on Tarim,Sichuan and its periphery and Ordos basins with developed marine sequences.

Geology of giant Tahe oilfield and a review of exploration thinking in the Tarim Basin

Zhai Xiaoxian, Yun Lu

2008, 29(5):  565-573.  doi:10.11743/ogg20080504

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As the first marine Paleozoic giant oilfield in China and an oilfield dominated by palaeokarstic reservoir of Ordovician carbonate rock,Tahe is located on the southern Akekule Salient of Shaya Uplift,the northem Tarim Basin,with its reserves over 1 billion tons.The obtained results and knowledge about the oilfield are summarized by us in tectonic evolution,sedimentary patterns,reservoir features and hydrocarbon accumulation models.It has been practically demonstrated that continuous enrichment and improvement of petroleum geology theories on Paleozoie marine carbonate in Tarim Basin is a foundation for discovering Tahe oilfield and extending towards its periphery and deeper intervals,and that the mature,whole and effective exploration technology is a tool to make major discoveries.

Tectonic and sedimentary conditions of pre-Mesozoic marine reservoirs in China

Zheng Herong, Hu Zongquan, Zhou Xiaojin, Zhang Haiqing, You Weifeng, Yang Fan

2008, 29(5):  574-581.  doi:10.11743/ogg20080505

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Tectonic and sedimentary factors are of importance in controlling the formation and distribution of marine reservoirs.Confronted with the spreading of ocean basins and dispersing of plates from Sinian to the early period of Early Paleozoic(Z-O₂),sedimentary systems of stable platform-passive margin slope developed around the main plates of China such as Huabei,Tarim and Yangtze.Carbonate rocks of platform facies bloomed during that long period,and were mainly composed of limestone,grainstone and dolomite.The high-stand Ordovician is one of the main marine strata for hydrocarbon discoveries in China.Subduction of ocean basins and con-vergence of Paleo-China continent occurred during the late period of the Early Paleozoic(O₃-S).Along with retrogression,the central part of the plates uplifted and became erosion areas,around which marine elastic reservoirs were developed,such as the Silurian in the northern Tarim Basin and areas from west Hubei to east Chongqing.The Caledonian karstifieation imposed an important influence on the early diagenetic evolution of the Lower-Paleozoic carbonate reservoirs.From the Late Paleozoic to the Early Mesozoic(D-T),convergence dominated in northern China,where marine elastic reservoirs were mainly developed,such as the Carboniferous and the Permian in North China and Junggar basins and the Devonian in the Tarim Basin.The Lower Palaeozoic carbonate rocks underwent the major karstification during the Hercynian period.While divergence dominated in southern China,where the South China platform underwent tectonic dispersion and broke down into several smaller platforms surrounded by deep basins,with reservoirs of shoal and reef facies deposited on the edge of platforms.Under long and multistage tectonization,marine reservoirs lost primary porosity progressively;meanwhile, conjunction of karstification,hydatothermal erosion,dolomitization and fracture formed secondary porosity and improved marine reservoirs remarkably.

Main deformation phases of the Paleozoic marine hydrocarbon source rocks in South China

Wang Qingchen, Lin Wei

2008, 29(5):  582-588,622.  doi:10.11743/ogg20080506

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There are multiple sets of hydrocarbon source rocks developed in South China,which experienced several tectonic events.By analyzing deformation succession,four deformation phases are recognized for Paleozoic marine hydrocarbon source rocks in South China,on a basis of field observation and seismic section interpretation,i.e.,late Early Paleozoic(421-441 Ma),Late Triassic(215-230 Ma),Late Jurassic-Early Cretaceous and Early Cretaceous-Tertiary.It is suggested that the main deformation phases occur in the Middle-Late Mesozoic,forming superimposed structures with different sizes.

Hydrocarbon accumulation features and exploration direction in the Silurian of the Middle-Upper Yangtze Platform

Xiao Kaihua, Li Shuangjian, Wang Xinwei, Zhang Rongqiang, Long Shengxiang

2008, 29(5):  589-596.  doi:10.11743/ogg20080507

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High quality source rocks in the Upper Ordovician and the Lower Silurian in southern China are mainly developed in the Wufeng Formation of the Upper Ordovician and at the bottom of the Lower Silurian.Both the Silurian elastic reservoirs and carbonate reservoirs feature in low-and ultra-low porosity and permeability and the former is the predominant reservoir type.The Lower Silurian Longrnaxi Formation is a set of quality regional seal and is in the B to late stage of diagenesis as a whole.Although being at high level of evolution,they serve as good sealing for petroleum accumulations.The eastern Sichuan basin of the Upper Yangtze Platform had witnessed large-scale hydrocarbon generation in a relatively early time with most of the Silurian source rocks reaching hydrocarbon generation peak during the middle Jurassic;while most of the Silurian source rocks in the Middle Yangtze Platform entered hydrocarbon generation peak late in the Late Triassic.The hydrocarbon migration and accumulation during the Silurian were controlled by Paleo-tectonic evolution.Therefore,it is suggested that the southwestern Sichuan provinces,western Hubei Province,and eastern Chongqing municipality are the most favorable areas for exploration of Silurian gas,while the thrust-fold area in the southern Jianghan plain is the favorable area.

Transformation and deformation of the Meso-Paleozoic basins in the Yangtze Plate

Ding Daogui, Pan Wenlei, Peng Jinning, Lu Yongde

2008, 29(5):  597-606.  doi:10.11743/ogg20080508

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The Meso-Paleozoic basins in the Yangtze Plate experienced three episodes of transformation and deformation of different tectonic actions since the end of the Middle Triassic.The first episode occurred in the IndoChinese epoch from the end of the Middle Triassic to the early Middle Jurassic,when the SE-NW overthrusting of the Jiangnan-Xuefeng basement detachment body(with the induced S-N and E-W overthrusting)and the transformation of faulted depression with resilient relaxant trailing edge caused the progressively decreasing thrustingfolding deformation of the Meso-Paleozoic marine basins.The second episode occurred in the Yanshan epoch from the Later Jurassic to Early Cretaceous,when the basins were overprinted with simple shear caused by the NNE-trending horizontal strike-slip structures(represented by the Tan-Lu fracture zone)and deformation induced by pull-apart and faulting tectonic mechanisms.The last episode occurred in the Himalayan epoch from the Later Cretaceous to the Paleogene.when the Lower Yangtze area experienced transformation and deformation caused by S-N extension and detachment as well as domino type pulling-apart and faulting structures.These three episodes of transformation and deformation facilitated the early accumulation,later thermal evolution and re-distribution of marine oil and gas in the Yangtze Plate.

Method system of thermal reconstruction for marine basins

Hu Shengbiao, He Lijuan, Zhu Chuanqing, Wang Jiyang

2008, 29(5):  607-613.  doi:10.11743/ogg20080509

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Unfolding itself first with record and reconstruction of multiple-episode thermal evolution,the paper introduces the basic principles and methods adopted in conventional thermal history reconstruction,summarizes the latest advancement in the research of palaeotemperature scale and basin models,and proposes a possible system of thermal reconstruction for paleo-marine basins as well as related working methods,which puts emphasis on both basin scale and lithosphere scale and integrates multiple palaeotemperature scales with basin models.Hopefully,they may lead to comprehensive discussion and thinking over the issue and promote the advancement of thermal reconstruction for paleo-marine basins.

Structure-controlled hydrothermal dolomitization and hydrothermal dolomite reservoirs

Chen Daizhao

2008, 29(5):  614-622.  doi:10.11743/ogg20080510

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Sharing similar lithologic characteristics with dolomite seam hosting MVT Pb-Zn sulfide ores,hydrothermal dolomite reservoirs contains mainly massive-matrix-replacement dolomites and void-or fracture-filling saddle dolomite dotted with small amount of other hydrothermal ores,such as sphalerite,galena,quartz,pyrite, barite,and fluorite.Saddle dolomite-filling microfractures and zebra textures formed by shear stress and dolomite breccias are also common in these reservoirs.Unfilled vugs,fractures,and pores from differential dissolution of the original carbonates(mainly limestone)provide the necessary spaces for later hydrocarbon charges.The hydrothermal fluids preferentially flow upwards along the extensional and transtensional fault systems,where dolomitization preferentially occurs on the hanging walls and extends laterally in the course of fault propagation.The hydrothermal dolomite reservoir can be well characterized and predicted through high-resolution seismic attribute analysis and imaging.

Diversity of buried-hills and comparison of their hydrocarbon-pooling factors in the Bohai Bay Basin

Yang Minghui

2008, 29(5):  623-631,638.  doi:10.11743/ogg20080511

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An analysis of geological and geophysical data and hydrocarbon-pooling factors shows that the buriedhills of the Bohai Bay Basin are characterized by diversities in lithology,structure and genesis.The lithology includes metamorphic,sedimentary(carbonates and/or clastics)and volcanic rocks;the structure can be divided into single structure and composite structure;and the genesis includes thrusting,extension and strike-slip.The metamorphic and volcanic buried-hills occur mainly in the Liaohe,Bozhong and Jiyang depressions;the tilting fault-block carbonate buried-hills occur in the Jizhong depression;while the inner carbonate buried-hills occur in the Huanghua and Jiyang depressions.Reservoir space is the main controlling factor for hydrocarbon-pooling in buried-hills.The reservoir spaces in the metamorphic and volcanic buried hills are dominated by fractures; while that of carbonate buried hills have both fractures and disollution pore-vug-fractures.The development of fractures in the metamorphic buried hills is affected by lithology,geomorphology and structural stress;while the development of the pore-vug-fractures in carbonate buried hills are related to lithology,horizon and other factors.

Conditions of hydrocarbon pooling in the Silurian Kepingtage Formation in the southern Tahe region of the Tarim Basin

Wang Yi, Chen Yuanzhuang

2008, 29(5):  632-638.  doi:10.11743/ogg20080512

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Based on an integrated analysis of the conditions of hydrocarbon pooling,types and distribution of the reservoirs in the Lower Silurian Kepingtage Formation in the southern Tahe region of the Tarim basin,this paper focuses on the distribution patterns of the Silurian hydrocarbon reservoirs in the southern Tahe region and estimates the hydrocarbon potential in this area.The Kepingtage sandstones are reservoir rocks with low porosity and low permeability,but some of them are quality reservoirs,such as thick shoreside facies,distributary channels in delta,mouth bars and tidal channel.Several reservoir-seal combinations were developed in the Silurian.Hydrocarbons generated from the Cambro-Ordovician source rocks in the southern Tahe region migrated to and accumulated in the Kepingtage sandstones through Upper Ordovician Sangtamu mudstone via faults,fractures,sandstone layers and unconformities.Five types of reservoirs,including anticline,unconformity barrier,onlap,lithological and structural-lithological combination reservoirs,are recognized in the Kepingtage Formation and were mainly developed in the Himalayan period.The unconformity barrier reservoirs are mainly distributed around the denudation pinch-out line of the Silurian in the high of the northern Tahe area,while the anticline,onlap,lithological and structural-lithological combination reservoirs are mainly distributed in the southern Tahe area.The Silurian sandstone in the study area has the characteristics of deep burial,large area of distribution,low abundance,thin hydrocarbon-bearing layers,linkage via faults and overlapping of oil-bearing areas.The estimated oil reserves in the Silurian are about 160 million tons.Moreover,tight sands gas reservoirs may also occur in the study area.

Application of comprehensive geophysical methods in the research of the pre-Cenozoic residual basins in circum-Bohai Bay region

Hao Tianyao, Wu Jiansheng, Xu Ya, Wang Jialin, Song Haibin, Huang Song, Wang Zhenli

2008, 29(5):  639-647.  doi:10.11743/ogg20080513

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Macro spatial distributioin of residual basins in the circum-Bohai Bay area and the characteristics of their residual thickness distribution are defined through peeling off the influences of the Cenozoic and deep basement and by adopting an integrated geophysical method.The method is mainly based on gravity and magnetic data,and it takes data of high accuracy such as MT and shallow seismic data as the constraints and is realized through forward modeling and inversion.The residual basins in the area shows an‘E-W zonation',with the superimposed area of the Cenozoic and Upper Paleozoic as the favorable target for the Pre-Cenozoic oil and gas exploration.Ten favorable areas of the Pre-Cenozoic are also defined through combining the residual thicknesses of the basins and geological conditions for oil and gas accumulations.

Review on geophysical methodology of oil reservoirs in the second round of hydrocarbon exploration

Liu Hong, Li Youming

2008, 29(5):  648-653.  doi:10.11743/ogg20080514

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The eighteen years of research on oil reservoir geophysics during the second round of hydrocarbon exploration provided a sound basis for the proposition of an effective expression of wave field based on structure preserved algorithm and pseudo-differential operator technique.The expression transfers operator calculation into function calculation and multiplication into summation and promotes the development of rapid and effective methods of seismic wave field calculation and data processing.Various techniques such as high-precision depthvelocity estimation,asymmetric travel-time migration,multiple prediction through pre-stack spectrum decomposi-tion,elastic inversion,and dealias reconstruction,are continuously sharpening in the process of practical applications with real data.

Pre-stack seismic prediction of fractured-vuggy carbonate reservoirs in the south of Tahe oilfield

Guan Luping

2008, 29(5):  654-667,675.  doi:10.11743/ogg20080515

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The carbonate reservoirs of the Middle and Lower Ordovician in southern Tahe oilfield are mainly of fractured-vuggy type featured in effective fractures and rugs formed by dissolution.The distribution of fractures in these reservoirs is controlled by faults,the oil layers are thin,and water bodies are active.The fracture-rug combinations are of different scales,irregular spatial distributions,and various filling properties.In view of the characteristics of the fractured-vuggy carbonate reservoirs in the study area,two techniques are presented,namely the pre-staek anisotropy analysis technology for detecting the intensity and azimuth of fractures and the pre-stack elastic parameter inversion method for predicting,in combination with log data,the growth of the fractured-vuggy zones and fluid-bearing indicators.The application of the techniques in southern Tahe oilfield reveals that the prediction results are basically consistent with data gathered from the known fractured-vuggy reservoirs and drilling data.The application of these two techniques has improved the prediction of spatial distribution of smallscale fractured-vuggy reservoirs and also shows that there are several favorable fraetured-vuggy zones distributed in the southern Tahe oilfield.

Seismic detection and prediction of tight gas reservoirs in the Ordos Basin

Dong Ning, Liu Zhenfeng, Zhou Xiaoying, Wang Jianbo, Liu Junzhou, Xia Hongmin, She Gang

2008, 29(5):  668-675.  doi:10.11743/ogg20080516

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Several tight lithologic gas fields with low permeability have been found in the north of Ordos Basin. From bottom to top,their main gas-bearing strata are the Taiyuan Formation of the Upper Carboniferous,the Shanxi Formation and lower Shihezi Formation of the Lower Permian.In view of the characteristics of lithologic traps and tight clastic reservoirs with low-permeability,studies are performed on integrated seismic reservoir prediction and characterization techniques for exploration and production of these gas fields.Corresponding techniques,including rock physics analysis,seismic attribute optimization,frequency decomposition and stochastic simulation inversion,are developed and applied.They form a complete series of reservoir prediction techniques that are suitable for tight clastic reservoirs with low porosity and low permeability,and can enhance the accuracy of reservoir prediction and promote the development process of tight gas fields in Ordos Basin.

A Study on seismic imaging techniques in complex surface and subsurface areas

Yang Qinyong, Fang Wubao

2008, 29(5):  676-682,689.  doi:10.11743/ogg20080517

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Aiming at seismic survey difficulties in complex surface and subsurface areas of South China,seismic migration and imaging techniques are studied.First,migration algorithms are discussed and the methods to calculate travel-time and weighting factor are derived for pre-stack time migration,presenting an idea of calculating asymmetrical travel-time,which can allow Kirchhoff pre-stack time migration directly from rugged topography to match higher lateral changes of velocity.Second,a technique to build an overall velocity model(a technique to integrate shallow,middle and deep velocity into a model)is discussed,resulting in a workflow to build a comprehensive velocity model under a condition of rugged topography.Finally,the continuation operator of Fourier finite difference has been developed for the pre-stack depth migration directly from rugged topography.All the proposed methods have been verified with synthetic and real seismic data.

Application of 3D-3C seismic technique to the prediction of fractures in tight sandstone—an example from Xinchang gas field in the Western Sichuan Depression

Yang Keming, Zhang Hong

2008, 29(5):  683-689.  doi:10.11743/ogg20080518

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The reservoirs in the Xujiahe Formation in Western Sichuan Depression are characterized by ultradeep burial,ultra-tightness,ultra-low porosity,ultra-low permeability,ultra-late structures,ultra-high pressure, complex GWC,and complex anisotropy.Therefore,conventional seismic techniques are faced with great challenges when predicting and identifying such complex reservoirs and fracture systems,especially the fractures in Xujiahe Formation in the Western Sichuan Depression.Both conventional P-wave data,which could reflect the characteristics of matrix and fluid,and C-wave data,which could reflect matrix and anisotropy,could be achieved by using 3D-3C converted wave technique.This technique is of more advantages than simple P-wave technique in respect of identifying lithology and fluid property by using combined P-and S-wave data as well as predicting fractures by using azimuthal anisotropy of converted wave and split S-wave data.In view of the characteristics of the Xujiahe Formation gas reservoirs in Xinchang gas field,P-waves and converted waves 3D-3C data are fully utilized to perform fracture prediction with P-wave attributes,fracture detection with azimuthal anisotropy and fracture detection with split S-wave based on integrated interpretation of converted waves of 3D-3C data.Based on prediction of large-scale faults and fractured zones by only using P-wave attributes,small-scale fracture network is predicted by using azimuthal anisotropy and split S-waves.The problem of fracture prediction for the tight reservoirs in the Xujiahe Formation in Xinchang gas field is solved and the prediction accuracy is improved.

Prediction and evaluation of reservoirs in Heba area, the Northeastern Sichuan Basin

Liu Bin, Fu Xiaoyue, Liu Guoping, Feng Qiong, You Yuchun

2008, 29(5):  690-696,702.  doi:10.11743/ogg20080519

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Reservoirs in Heba area are characterized by large burial depth,strong diagenesis,extreme heterogeneity,and complicated gas accumulation conditions.Based on stratigraphic division and correlation,study of sedimentary facies,analysis of basic features of reservoirs,logging interpretation,and reservoir prediction and quantitative evaluation in Heba area,depositional patterns of these reservoirs are established,the types of reservoir space are defined,the spatical distribution of the reservoirs are predicted,and the favorable areas for development of quality reservoirs are evaluated.A set of methods that are suitable for prediction and comprehensive evaluation of the reservoirs in Heba area is presented.

Research on the selection and evaluation of development blocks in lithologic gas reservoirs with low-permeability

Liu Chuanxi, Yao Hefa, Yan Jin

2008, 29(5):  697-702.  doi:10.11743/ogg20080520

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Lithologic gas reservoirs with low-permeability feature in higher heterogeneity and lower abundance and production.Through fully utilizing geologic,logging,seismic and test data and integrating geology and gas reservoir engineering with economic evaluation,this paper establishes 3-D geologic models,open-flow capacity forecast models,technical and economic limits of development,and criteria for selection and evaluation of development blocks on the basis of research on multi-information constrained stochastic modeling,the relationship between productivity and static geologic parameters,and technical and economic limit.Based on the above-mentioned research,a set of dynamic-static integrated quantitative methods are presented for the evaluation and selection of development blocks in low permeability lithologic gas reservoirs to offer a scientific strategy basis for selection of gas field development targets and construction of production capacity.The field application of the methods reveals that they are suitable for selection and evaluation of low-permeability lithologic gas reservoirs and may serve as guidance for developing reservoirs with similar nature.

Efficient development of vuggy carbonate reservoirs:an example from the Block 11 of Tahe oilfieid

Wang Guangfu

2008, 29(5):  703-708.  doi:10.11743/ogg20080521

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Four kinds of typical wells,namely paying,stripped,deficient,and barren wells are recognized in the Block 11 of Tahe oilfield through integrated research of geology,geophysics,and reservoir dynamics.A development plan,which gives first priority to paying wells followed by stripped wells,minimizes deficient wells and eliminates completely barren wells,was proposed based on an analysis of the specific geophysical features and performances of the reservoirs encountered by these wells.The practice shows that the plan is quite effective in improving drilling success ratio and economic returns.