Table of Content

24 June 2008, Volume 29 Issue 3

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Deformation characteristics and finalizing age of the folds in the Qiangtang Basin and their relations to oil and gas accumulation

Li Yalin, Wang Chengshan, Huang Jijun

2008, 29(3):  283-289,296.  doi:10.11743/ogg20080301

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Qiangtang basin is the largest and most prospective petroliferous basin in Qianghai-Tibet plateau.Its surface fold buildings mostly occur in zonal distribution within the Jurassic structural layer,and are dominated by EW-NWW trending upright horizontal folds in pseudo-ejective assemblages.The deformation mechanisms of folds were controlled by compression,strike-slip,and basal structures.Nevertheless,the orogeny along the NS-trending suture zone was the dominant dynamics factors that controlled the geometry,styles and spatial distribution of the folds in the basin.The large folds in the Jurassic structural layer were formed during the Late Jurassic-Early Cretaceous and their temporal and spatial relationships with the generation,migration and accumulation of hydrocarbons from the major source rocks were favorable for hydrocarbon pooling.Therefore,they are favorable trap structures.

Evolutionary characteristics of the Palaeogene basin-controlling boundary faults and types of basin architectures in the Dongying Sag

Sheng Wenbo, Cao Yingchang, Liu Hui, Zhang Yu

2008, 29(3):  290-296,289.  doi:10.11743/ogg20080302

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The shape of the Palaeogene basin-controlling faults of Dongying sag had evolved from planar in the early period(basically corresponding to the deposition of the Kongdian Formation),to listric in the middle period(deposition of the fourth member to the Lower third member of Shahejie Formation),and finally to slope-flat in the late period(deposition of the second member of Shahejie Formation to Dongying Formation).The intensity of basin-controlling fault activity in Dongying sag shows a left-lateral feature.The spatial distribution of deposits is basically consistent with the strike of main faults in different evolutionary stages of the Palaeogene rifted basin.The fault activities controlled the sedimentary process.Corresponding with the evolution of boundary faults,the Palaeogene basin in Dongying sag had gone through the early rotation half-graben,middle rolling half-graben,and late compound half-graben.

Topographic relief and fluid modification:the important content of petroliferous basin analysis and evaluation

Fang Jianjun, Liu Chiyang, Wang Jianqiang, Qiu Xinwei, Ma Yanping, Zhao Junfeng

2008, 29(3):  297-302,311.  doi:10.11743/ogg20080303

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The Well Yuncan-1 is the first stratigraphic well in Yunlong depression,Chuxiong Basin.A severe lost circulation happened during the drilling of the well.Comprehensive analysis of the conditions and adjacent environment of the accident reveals that it may be caused by non-sealed extensive fluid motion and exchange in the study area and genetically related to the relatively large topographic relief in a short distance caused by strong and inhomogeneous reformation during the later stage of the basin formation.This indicates that modification of fluid flow is one of the most important effects during the later stage of basin formation and topographic relief is one of the basic conditions for modifications of fluid flow.Both of them contributed to the formation of fluid modification basins.Therefore,this article suggests that both topographic relief and modification of fluid flow are indispensable to analysis and evaluation of petroliferous basins.As to basins or areas featuring in large topographic relief,large amount of atmospheric precipitation,well-developed drainage system,deep fluvial incision(e.g.,basins in western and southern China),the influence of fluid modification on accumulation and dissipation,reservoiring,adjustment and distribution oil and gas shall be strengthened during oil and gas evaluation and exploration deployment.

Sedimentary characteristics of the Lower Cretaceous and reconstruction of the prototype basin in the Jiuxi Basin

Wang Xiaofeng, Zhang Zhicheng, Guo Zhaojie, Zhang Cheng, Gong Jianye

2008, 29(3):  303-311,302.  doi:10.11743/ogg20080304

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An integrated analysis of depositional characteristics such as paleocurrents and gravel composition of the Lower Cretaceous strata in the Jiuxi Basin,combined with the seismic,logging,and drilling data of Yumen oilfield,proves that Chijinxia mountain and Hei mountain didn't exist in the Early Cretaceous,and the Kuantanshan low uplift(with Kuantan mountain as a part of it) did not separate Jiuxi Basin from Huahai sag due to its small scale and NE-SW-trending long axis.The researches shows that Jiuxi Basin was a rifted basin controlled mainly by NW-SE extension in the early Cretaceous.The basin experienced three stages during its evolution: initiation,growth and die-out,which correspond to the deposition periods of Chijinbao,Xiagou,and Zhonggou formations respectively.

Hydrocarbon generating history and exploration prospects of the Upper Paleozoic in the central and south Bohai Bay Basin

Hu Zongquan, Zhu Jianhui, Zhou Xinke, Wang Chuangang, Zhang Yulan

2008, 29(3):  312-319.  doi:10.11743/ogg20080305

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The Upper Paleozoic coal-bearing formation in Bohai Bay Basin is the major source rock in the Paleozoic strata.It had experienced complicated history of bury,thermal maturation and hydrocarbon generation of multiple episodes.The petroleum system in the Upper Paleozoic of the areas features in late reservoiring and it is only meaningful when it happened in effective reservoiring period with later hydrocarbon generation.Three types of hydrocarbon generating history are classified by establishing the geologic model of hydrocarbon generation in the Upper Paleozoic.The areas such as Dongpu sag with a burial history of uplifting in Yanshanian period and deep burial in Yanshanian period are the most potential for secondary hydrocarbon generation,the areas such as Dongying sag with a burial history of shallow burial in Yanshanian period but deep burial in Himalayanian period have relatively large potential of secondary hydrocarbon generation,while the areas such as Shenxian sag expe-rienced relatively deep burial in Yanshanian period and relatively shallow burial in Yanshanian period have limi-ted potential of secondary hydrocarbon generation.Numerical simulation is carried out to evaluate the hydrocarbon generating intensity at different stages.It reveals that the quantity of hydrocarbons generated in Cenozoic accounts for 60% of the total in Jiyang depression,14% in Linqing depression,as high as 90% in Dongpu sag is.Simulation of hydrocarbon generation history indicates the plane distribution of hydrocarbon generating intensity in Jurassic-Cretaceous and Cenozoic,and the resource potential and exploration targets of the Upper Paleozoic natural gas in Bohai Bay Basin.

Study of sequence stratigraphy and exploration of lithologic reservoirs in the Paleogene Middle Sha-1 Member,the Banqiao Sag of the Huanghua Depression

Shi Shige

2008, 29(3):  320-325.  doi:10.11743/ogg20080306

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The sublacustrine fan sandbodies developed in the deep lacustrine mudstones are the most favorable reservoirs and the main target of the lithologic reservoir exploration in Banqiao sag.The distribution of the sublacustrine fan sandbodies is so subtle and complicated due to their nature of sudden flood events that it's difficult to predict.Based on the sedimentary study on the sublacustrine fan,the author suggests that the sublacustrine fan sandbodies slump deposits of gravity flow on a fan delta front.The sublacustrine fan sandbodies occur in lenticularity vertical to the direction of the gravity flow and in imbricate arrangement parallel to the direction of the gravity flow.According to the responses of sublacustrine fan,the author predicted the distribution of the sublacustrine through seismic facies analysis and seismic attributes Abstraction,revealed that the distribution of the sublacustrine fan was controlled by the geomorphologic low and pointed out the favorable targets for lithologic reservoir exploration in Banqiao sag.

Risk assessment for oil and gas exploration with new approaches in the Shenxian Sag of the Jizhong Depression

Wuna, Guo Qiulin, Liangkun, Kong Fanzhi, Wang Shaochun

2008, 29(3):  326-333,341.  doi:10.11743/ogg20080307

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A parameter system for exploration risk assessment and a spatial attribute property set of oil & gas wells and dry holes was created based on study of oil accumulation patterns as well as their main controlling factors in the third member of Shahejie Formation in Shenxian sag of Bohai Bay Basin.In combination with the drilling data,templates for exploration risk assessment were established by using data integration methods,such as Mahalannobis distance method and Fuzzy mathematics method,and Bayes probability model.They were used to predict and visualize the risk probability of exploration for every point in the whole sag.The results revealed several low risk targets: Shenxian low amplitude structure,Shenxi,Hengshui and Shennan fault terrace.This work offered important information for further exploration in this area.However,disparity exists in the prediction results because of the limitations of these methods.The accuracy of the above former two methods is 73.7% and 79% respectively,and that of the integrated method is 86%.Since the Fuzzy assessment method employs all the information that represents favorable geological conditions,the low risk areas predicted with it is relatively large,hence increasing the exploration risk.On the contrary,Mahalannobis distance method only selects effective geological factors that can distinguish the oil & gas wells from dry holes,the favorable exploration area it predict is relatively small and the targets are more accurate.However,it may miss some potential exploration areas.

Sedimentary facies of the fourth member of the Quantou Formation in Fuyu oilfield,the South Songliao Basin

Hu Xuezhi, Bao Zhidong, Na Weihong, Zhang Qingguo, Zhou Xinmao

2008, 29(3):  334-341,333.  doi:10.11743/ogg20080308

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Based on the core and logging datum,and through the research of mudstone's colors,granularity distribution,sedimentary structures,fossils,rock types and their association in the fourth Member of the Quantou Formation in Fuyu oilfield in south part of Songliao basin,it confirmed that the sedimentary environment here was shallow delta facies.Furthermore,it was classified two subfacies of delta plain and delta front.The plan distribution map of sedimentary microfacies of Fuyu oilfield was draw,and based on it,the sedimentary model of Fuyu oilfield was established and the evolutionary characters were also studied.All of those offer basis for increasing reservoir in old oilfields.

Study on the oil-source correlation and charging history of the Dongying Formation reservoirs in the Wenliu Structure of the Dongpu Sag,the Bohai Bay Basin

Chen Yicai, Lou Xiaoping, Shen Zhongming, Chang Zhenheng, Hu Yujie

2008, 29(3):  342-347,354.  doi:10.11743/ogg20080309

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The Dongying Formation in Wenliu structure of Dongpu sag,Bohai Bay Basin,consists mainly of light brown sand-shale of alluvial fan depositional system.Saturated hydrocarbon chromatograms and Terpanes & Ste-ranes mass chromatagrams reveal that the oil-bearing sandstone in the Dongying formation features in high gammacerane,low pristane/phytane ratio,and relatively low ratio of C₂₉aaa20S/(20S+20R) steranes and other mature indexes.Oil-source correlation indicates that oil from the Formation has a relatively close parentage relationship with the Es³ source rock.A comprehensive analysis of the homogenization temperature of organic inclusions,burial history and palaeogeothermal reconstruction,and geochemical characteristics of oil-bearing sands suggests that continuous oil charging lasted about 5.6Ma.During the middle and late periods of tectonic uplifting,about 1000 meters of the upper part of the Dongying Formation was denuded,causing the crude in the Formation biodegraded to different degrees,but leaving the normal alkanes distribution of inclusions basically intact.Since the Neogene,the burial depth of Dongying Formation has been increasing continuously,and the reservoirs has stepped into the stage of adjustment and preservation.

Characteristics of the Mesozoic marine source rocks in the Qiangtang Basin,Tibet

Wu Xinhe, Zhang Li, Wang Chengshan, Yi Haisheng

2008, 29(3):  348-354,347.  doi:10.11743/ogg20080310

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Qiangtang Basin has well-developed thick marine deposits with the Jurassic as the thickest(ten thousand meters).Four sets of high quality source rocks,namely the Triassic Xiaochaka Formation,the Jurassic Buqu,Xiali,and Suowa formations,are extensively distributed in the Mesozoic Qiangtang basin.These source rocks are mainly composed of limestone and mudstone with a maximum thickness over 3000 m.The source rocks in the Upper Triassic Xiaochaka Formation and the Middle Jurassic Buqu Formation have larger thickness and their organic matters are mainly of type Ⅱ with maturity varying from mature to over-mature,and average TOC is over 1.5%.They have favorable burial conditions and are the main hydrocarbon source in the basin.The Jurassic Suowa Formation is also rather thick and its organic matters are of mostly type Ⅰ and Ⅱ,however,the formation was over exposed and not favorable for hydrocarbon generation.There were two peaks of hydrocarbon generation:late Jurassic-early Cretaceous and Neogene.

Distribution of high molecular weight hydrocarbons and genesis of high wax content oil from the south slope zone of the Dongying Sag,the Jiyang Depression

L? Hui, Chen Zhilin, Wang Zhong, Tang Hongsan

2008, 29(3):  355-360.  doi:10.11743/ogg20080311

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A study of the components,distribution and unconventional biomarkers of high molecular hydrocarbons in high wax content oils from the south slope zone of Dongying sag was carried out by using high temperature gas chromatography and dual mass spectrometry.The results suggest that the high wax content oil in the Ordovician well Wanggu-1 share the same source with that in the Kongidan Formation,yet its maturity is higher than that of the latter.GC-MS-MS analysis indicates that the high wax content oils in the study area are rich in C₂₆,24-norcholeatane,which distinguishes them from the normal oils originated from the Upper Es⁴ and proves that the high wax content oils might come from alginite.Apart from terrestrial organic matters,hydrobionts of lower rank are also important original source materials of high wax content oils.Other important factors for the generation of the high wax content oils include microbial action.The relatively high maturity has certain influences on wax content within certain maturation ranges.

Identification of subtle reservoirs in highly-mature development area of the Biyang Depression,the Nanxiang Basin

Jiang Jianwei

2008, 29(3):  361-364,390.  doi:10.11743/ogg20080312

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After more than 30 years of exploration and development,the Biyang depression has been highly mature in exploration and development,with most of the fields entering the late stage of development with high water cut.Analysis of the geological conditions for the formation of subtle reservoirs indicates that they share the same source and happened in the same period with larger-scale reservoirs.Three methods for identifying subtle reservoirs are presented here based on the abundant dynamic and static data available.They are fine correlation of subzone,trap assessment,and micro-structure analysis.Proper use of these methods can effectively identify subtle light oil reservoirs in the matured areas in Nanxiang basin.The results show a success rate of identification over 90% and increamental geologic reserves of more than 5 million tons and annual crude production growth of more than 10000 tons.

Reservoir sensitivity in low-permeability Qiaokou gasfield,the Dongpu Sag and the solutions to it

Xie Aihua, Liu Sheqin

2008, 29(3):  365-368.  doi:10.11743/ogg20080313

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Low-permeability reservoirs in Qiaokou gas field,Dongpu sag,features in large reserves and complica-ted geological conditions.By dint of SEM,X-ray diffraction,sensitivity testing,and other means,the author sums up factors of reservoir damages,specifies that the reservoirs in the study area mainly suffer from stress sensitivity,velocity sensitivity,water sensitivity,salt sensitivity,alkali sensitivity and acid sensitivity.Based on research and evaluation of all kinds of sensitivities,this paper presents approaches and solutions for maintaining the original reservoir permeability or enhancing reservoir permeability,and proposes practical measures for protecting low-permeability reservoirs and improving production performance.

Genetic mechanism and prevention of heavy hydrocarbon stemming in the Ordovician reservoirs of Tahe oilfield

Li Jianglong, Kang Zhijiang, Huang Yongmei, Yi Bin, Wu Yongchao, Cao Jianbao, Hu Chengxian

2008, 29(3):  369-375.  doi:10.11743/ogg20080314

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Normal production of 24 oil wells had been interrupted in fractured-vuggy carbonate reservoirs in Tahe oilfield due to blockage of wellbores by bitumen.Lab experiments of bitumen precipitation in mixture of condensate oil and heavy oil show that bitumen stemming is mainly caused by blending of condensate oil and heavy oil.This conclusion with the play characteristics in Tahe oilfield leads to the discovery that blocked wells are all located in the transitional zone from condensate oil to heavy oil.Based on the analysis of production performance,the article sums up the changing pattern of production performance before and after bitumen precipitation and proposes comprehensive prevention methods including blockage removing with addition of modified heavy oil as the core and prevention of bitument precipitation through injecting active water or formation water through annular space.The application of the methods had successfully cured 6 wells and resumed normal production.

Deliverability characteristics of gas pools with abnormal pressure——an example from well Heba-1 in the third member of the Feixianguan Formation of Hebachang block,the Sichuan Basin

Zhang Shuqiu, Liu Chuanxi, Liu Zhengzhong

2008, 29(3):  376-382.  doi:10.11743/ogg20080315

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Aiming at the geological features of gas pools in the third member of Feixiangua Formation,Heba block,northern and eastern Sichuan Basin,the article studies and analyzes the formation test and production test data and summarizes the types of abnormal pressure gas pools and their production performance.The results show that production proration according to a value less than 1/5 of AOF(calculated with production testing data) can bring the formation energy into full play,longer production plateau period,and higher recovery ratio.The research also confirms the reliability of predicting bottom hole pressure with well head pressure and points out production characteristics of abnormal pressure gas pools as well as problems that need to be addressed during the production,providing references for the development of similar gas pools.

Application of EMI in evaluation of fractured sandstone reservoirs in the Dongpu Sag

Zhao Junfeng, Ji Youliang, Chen Hanlin, Wang Qian

2008, 29(3):  383-390,364.  doi:10.11743/ogg20080316

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In order to effectively identify and accurately evaluate the Triassic fractured tight-sandstone reservoirs featured in'double porosity medium',the author strengthened geological application research of the electro-imaging logging data and improved its applications to qualitative identification and quantitative evaluation of fractures,formation occurrence description,analysis around wells,earth stress analysis and lithologic discrimination,and etc.Core data were used to calibrate electro-imaging logging(EMI),which was used in turn to calibrate conventional general well-logging.The log responses of the Triassic fractured sandstone reservoirs are summarized under the constraints of geologic conditions and test data.And based on all these,the author proposed a set of effective method for classifying fractured reservoirs.The testing results of ten wells indicate that the coincidence rate of log interpretation with the method is up to 84.3%.The application of the log interpretation of fractured reservoir improves the fractured reservoir identification through well-logging.

Study on the coupling of seepage and stress fields in low-permeability reservoirs

Zhou Zhijun, Li Jing, Liu Yongjian, Song Kaoping, Liu Weiwei, Li Xiaofeng

2008, 29(3):  391-396,404.  doi:10.11743/ogg20080317

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Mathematical and numerical coupling models of seepage and stress fields of low-permeability reservoirs are developed based on the basic theories of rock mechanics,fluid mechanics in porous medium,geologic mechanics,computational mechanics and fluid-solid coupling seepage,and etc,and by taking into consideration of their start-up pressure gradient of seepage flow and characters of fluid-solid coupling.A program is designed by using numerical computing method of coupling with finite difference and finite element integrated,and the coupling law of seepage and stress fields in low-permeability reservoirs is studied.The varying law of stress-strain with time and space,dynamic changing law of rock physical properties,changing pattern of development index in the process of natural depletion of single well are studied through numerical simulation and correlated with the calculation of rigidity model.It is revealed that the fluid-solid coupling effect in low permeability reservoirs is rather obvious.

Review and enlightenment of seismic acquisition technology development in Shengli exploration area

Liu Chengzhai

2008, 29(3):  397-404,396.  doi:10.11743/ogg20080318

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Seismic acquisition technologies in Shengli Oilfield have evolved from 2D,conventional 3D,and 3D of high resolution since its application in 1958.According to exploration targets,seismic apparatus and acquisition methods,the history of 2D acquisition technology development can be divided into three stages:the single-fold stage(1958-1972),the multifold stage(1973-1984) and the high resolution acquisition stage(after 1985);while the 3D acquisition technology development went through exploring(1966-1984),developing(1985-1992),large-scale application(1993-1999),and high resolution acquisition(after 2000).Each technical progress results in a rapid growth of reserves in the oilfield and deeper understandings of the subsurface from simple structures,to complex fault block structures,and to subtle reservoirs.

Prediction of sandbody distribution in the Upper Triassic Xujiahe Formation,the West Sichuan Depression

Zheng Rongcai, Ye Tairan, Zhai Wenliang, Dai Chaocheng, Gao Hongcan

2008, 29(3):  405-411,417.  doi:10.11743/ogg20080319

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Guided by the high-resolution sequence stratigraphy theories and methods,the authors divided the Upper Triassic Xujiahe Formation into 4 long-term sequences and 14 medium-term sequences through sedimentary dynamics analysis of the structures of base level cycle and superimposition patterns and combining comprehensive study of outcrops,coring,logging and seismic data.A sequence stratigraphy framework of the long-term and medium-term cyclic sequences in Sichuan Basin and West Sichuan depression was also constructed under constrain of seismic reflection.Directed by the method of lithofacies paleogeographical mapping,they compiled lithofacies-paleogeographical maps for Sichuan Basin and West Sichuan depression with the elevating and falling fa-cies tracts of long-term and middle-term base level cycle as the mapping units,established high-resolution stratigraphic framework with short-term cycle as unit in 3D seismic survey area.Taking the sequence interface and lake flooding interface of long-term and middle-term cycle as the unit,they also set up low-frequency model and then used it to perform seismic lothological inversion and map sandbodies thickness and sedimentary microfacies of short-term cyclic sequences.Finally,they discussed the relationship between the sandstone distribution and base-level cycle variation and lacustrine ingression and regression,and predicted the vertical and horizontal distributions of potential sand reservoirs.

Discussion on the changing patterns of base-levels in faulted lacustrine basins

Xiong Wei, Qiu Guiqiang, Min Wei, Shang Bing, Xing Huanqing, Shi Hongxia

2008, 29(3):  412-417,411.  doi:10.11743/ogg20080320

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Based on previous study,this article discussed factors and patterns that influence the base-level and accommodation.It concluded that both Absolute and relative accommodation changes exist and that the sediment supply isn't a factor influencing the change of base-level.It also studied the vertical superimposing patterns and lateral variations of short term base-level cycles and advanced the approach of predicting favorable reservoirs according to change of paleotopography based on the analysis of base-level cycles.