Table of Content

28 December 2011, Volume 32 Issue 6

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Depositional patterns of oil sand layer in Northern Lights block, Alberta Basin,Canada

Yin Pengfei, Liu Guangdi, Liu Chenglin, Li Haohan, Liu Wenping, Liu Yingqi

2011, 32(6):  807-814.  doi:10.11743/ogg20110601

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Based on a lot of well and core data,McMurray Formation sequences and sedimentary environments were identified and correlated in Northern Lights oil sand block.With integrated logging data,this study analyzed the sedimentary facies and rock assemblages of the McMurray Formation.In this block,the McMurray Formation,the most important oil sand layer,consists of continuous fluvial,delta plain and tidal estuary bay deposits.The McMurray Formation was divided into three members.The lower member is longshore and shallow water deposits,the middle member is estuary bay and intertidal zone deposits and the upper member is continental fluvial deposits.The geologic characteristics,geologic time,sequence framework and depositional patterns of each sequence were confirmed.These sedimentary facies were subdivided into 9 subfacies,some of which were further subdivided into microfacies according to the logging data.Their depositional patterns were also established.The channel sands in the lower member and the estuarine and tidal channel deposits in the middle member are the main oil reservoirs of the McMurrary Formation.The study not only can provide the basis for the feasibility research of the Northern Lights Project,but also can guide exploration and development of oil sands in Alberta Basin.

Petroleum exploration prospect of the Jurassic tight reservoirs in central Sichuan Basin

Liao Qunshan, Hu Hua, Lin Jianping, Liu Zhongliang, Mu Xianzhong

2011, 32(6):  815-822,838.  doi:10.11743/ogg20110602

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From viewpoint of continuous petroleum accumulation and comparison with Bakken Formation in Willsiton Basin(USA),the paper discussed petroleum exploration prospect of the Jurassic tight reservoirs in central Sichuan Basin.The Jurassic reservoirs in Sichuan Basin are typical tight ones with an average porosity of 1-3.7%,average permeability of 0.35×10^-3-0.53×10^-3 μm and median pore throat radius of 0.05-0.24 mm.The Jurassic reservoirs contacte closely with source rocks both laterally and vertically in central Sichuan Basin.The hydrocarbons accumulates within source rocks or in reservoirs close to the source rocks.The major reservoirs are continuously distributed in the slope area and sags,have no distinct trap boundaries,and are not controlled by local structures.Multiple reservoirs superimposed vertically and connected laterally,forming a large hydrocarbon-bearing areal extent.Most oil-bearing blocks have an abnormal overpressure system,no water in the reservoir and no uniform oil/water contact.The Jurassic oil accumulation in central Sichuan Basin is a typical continuous one basically similar to the Bakken Formation.In recent years,the Bakken tight oil have been deve- loped in large scale with horizontal well and multi-stage fracturing techniques thanks to the relatively high oil price.In contrast,exploration and development of the Jurassic tight reservoirs in central Sichuan Basin have no breakthrough due to the constraints of understanding,investment and technology.Improving geological understanding,strengthening research of key technologies such as horizontal drilling and multi-stage fracturing and increasing single well production are critical to the successful exploration and development of the Jurassic tight re- servoir in central part of Sichuan Basin.

Sedimentary characteristics of the middle and lower 3rd member of Shahejie Formation in Gunan Sag,Bohai Bay Basin

Zheng Ning, Jiang Zaixing, Zhang Le, Yan Liyan, Peng Xingpeng, Li Ying, Li Chunlei

2011, 32(6):  823-831.  doi:10.11743/ogg20110603

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Based on the regional geological data and the theory of petrology,sedimentology and lithofacies paleogeography,this paper analyzed sedimentary facies markers of cores from 10 wells including color,composition,granularity,sedimentary structure and etc.The facies makers were integrated with logs of 45 wells to study the division of sedimentary microfacies and sedimentary environment evolution of the middle and lower 3rd member of Shahejie Formation in Gunan Sag,and analyzed their relation to reservoirs.Three main sedimentary facies are identified in the middle and lower 3rd member of Shahejie Formation in Gunan Sag,namely fan delta,delta and lacustrine,which are further divided into nine sub-facies and sixteen microfacies.Tempestite sediments is found for the first time in this sag,which is considered as a positive factor for improving the quality of reservoir.During the depositing of the lower 3rd member of the Shahejie Formation,small-scale delta and fan delta were developed in the north of the sag,whereas delta were developed in the south.These deltas gradually withered along with the expansion of the lake,being favorable for the development of source rock.And during the deposition of the middle 3rd member of the Shahejie Formation,the deposits supply increased and the net-to-gross ratio of the sandbody in the sag enlarged,which were favorable for the quality of reservoir.

Reservoir characteristics and controlling factors of the Paleogene Sha-2 member in 36-3 structure,Eastern Shijiutuo uplift,Bohai Sea

Liu Zhigang, Zhou Xinhuai, Li Jianping, Lai Weicheng, Du Xiaofeng, Cheng Jianchun, Wang Qingbin

2011, 32(6):  832-838.  doi:10.11743/ogg20110604

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Various data including core description,conventional thin sections,casting thin sections and SEM,in combination with conventional physical properties of reservoirs and exploration results,were used to systemically analyze reservoir poroperm characteristics,reservoir space types and influencing factors of reservoir properties of the 2^nd member of Shahejie Formation.The study indicates that Shahejie Formation reservoirs are mixed carbonate/siliciclastic rocks dominated by bioclastic dolostone with thin sandy conglomerate interbeds.The poroperm characteristics are very good,with average porosity of 27.6% and permeability of 442×10^-3μm².The reservoir spaces are dominated by primary pores(mostly intergranular pores and skeletal pores)and secondary pores.Sed- imentation and diagenesis are the two key factors controlling the physical properties of reservoirs.Dissolution and dolomitization contribute to high quality reservoir spaces.In addition,the distribution of high quality reservoirs is also delineated.It is believed that dolostone reservoirs are favorable for hydrocarbon accumulation,thus are potential exploration targets in the future.

Sequence stratigraphy of the Paleogene Shahejie Formation in Dongpu Sag,Bohai Bay Basin

Gao Hongcan, Zheng Rongcai, Chen Faliang, Han Fumin, Liu Yun

2011, 32(6):  839-850.  doi:10.11743/ogg20110605

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Based on stratigraphical correlation of over 300 wells,detailed core description of more than 3 000 m,and analysis of regional tectonic-sedimentary evolution,we divided the Paleogene in Dongpu Sag into three super long-term sequences according to various data such as tectonic geology,paleontology,lithology,geochronology,logging and seismic reflection,etc.The three sequences corresponds to the lower 4^th member of Shahejie Formation,the upper 4^th member to the 3^rd member of the Shahejie Formation,the 2^nd member of Shahejie Formation to the Dongying Formation respectively.Furthermore,strata from the upper 4^th member to the 1^st member of Sh- ahejie Formation is divided into four long-term sequences,corresponding to the upper 4^th member to the 4^th sub-member of the 3^rd member,the 3^rd sub-member of the 3^rd member, the 1^st to the 2^nd sub-member of the 3^rd member and the 1^st to the 2^nd member of Shahejie Formation respectively.This paper indicates that a set of continuous salt deposits is undividable when dividing the super long-term and long-term sequence.Taking the Dongpu Sag and Bohai Bay Basin as examples,we pointed that the common practice of making sequence stratigraphic class- ification scheme consistent with lithostratigraphic classification scheme is possibly incorrect.

Lithologic characteristics and petroleum exploration potential of the Permian volcanic rocks in northern Tarim Basin

Li Bin, He Kai, Lü Haitao, Gao Shanlin, Yang Suju

2011, 32(6):  851-858.  doi:10.11743/ogg20110606

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Permian volcanic rocks are widely distributed in northern part of Tarim Basin,and well test results of the volcanic reservoirs in well HT1 confirm their oil bearing in this area.The author mainly discussed the electrical characteristics of the volcanic rocks,horizontal and vertical distribution of the lithology-facies and pore types of the volcanic rocks.The study showed the thick and massive dacite and basalt of effusive facies were dominated in Aiding-Tuoputai-Hadexun area,which are relatively homogeneous in lithogy and stable in lateral distribution.Well data indicate that the Permian volcanic rocks in Tahe oilfield are of well-developed secondary pores and fractures.Core test results show that the volcanic reservoirs have low porosity and low permeability.The reservoir properties mainly depend on the combination of fractures,vugs and pores.Combined with hydrocarbon accumulation model of volcanic reservoirs in this area,it is believed that anticlines and stratigraphic traps exist in the volcanic rocks.The volcanic rocks and directly overlapping thick mudstone of Triassic Ketuer Formation form better reservoir-seal system.The volcanic rocks have favorable conditions for hydrocarbon accumulation and good potential for petroleum exploration.Based on re-evaluation of the drilled wells,the re-testing work of two wells is presented in order to promote exploration development of Permian volcanic rocks in Northern Tarim Basin.

Pyroclastic deposits:an important reservoir for hydrocarbon accumulation

Liu Xiang, Lang Jianjun, Yang Qingfu

2011, 32(6):  859-866,889.  doi:10.11743/ogg20110607

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Pyroclastic deposits are important reservoirs and can be divided into fallout tephradeposits,pyroclastic flow deposits,lahar deposits and base surge deposits by their genesis.The four kinds of pyroclastic deposits have different reservoir characteristics and potential.The identification and interpretation of the pyroclastic deposits can significantly influence the exploration methods of volcaniclastic sequences and the prediction of reservoir geometry and quality.The Lower Jurassic Wrightson Formation in Arizona is a multi-crater complex.Its pyroclastic deposits and lavas with various genesis can be divided into crater,proximal,middle and distal facies.The influences of these facies on reservoir quality are discussed.Volcanic clasts are mostly composed of chemically active and unstable minerals that can change rapidly and extensively during burial diagenesis.The occurrence of volcanic clasts may contribute to the development of dissolution porosity which can enhance reservoir quality.

Characteristics and origin of natural gas in large- and medium-sized gas reservoirs in northeast Sichuan Basin

Wang Qiang, Xu Liheng, Chen Jianfa

2011, 32(6):  867-872,881.  doi:10.11743/ogg20110608

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Abundant natural gas resources have been discovered in the Lower Triassic Feixianguan Formation and Upper Permian Changxing Formation in northeast Sichuan Basin,revealing good potential for natural gas exploration.Based on an analysis of the characteristics of hydrocarbon source rocks in northeast Sichuan Basin,we identify the major hydrocarbon source rocks by the comparision of the natural gas composition and isotope features of the Changxing and Feixianguan formations with that of the Carboniferous reservoirs.The Changxing and Feixianguan formations were densely sampled to measure their organic carbon contents and to quantitatively calculate bitumen contents of the reservoirs.Meanwhile,the total gas volume from oil-cracking in Puguang ancient oil reservoirs were calculated based on the principle of conservation of matter.The study shows that the Longtan Formation source rocks are the major source rocks for Changxing and Feixianguan formation gas reservoirs.The kerogen-cracking contributed more gas than secondary cracking of crude oil,thus gas from kerogen-cracking is the primary gas source.The total gas generated from oil cracking is 361 BCM in the Puguang gas pool,which is not large enough for the forming of the huge Puguang gas pool.This further proves the conclusion that the major gas for the Changxing and Feixianguan formation gas reservoirs comes from kerogen-cracking gas.

Charging time sequence of mantle CO₂ and hydrocarbon in southern Songliao Basin: an evidence from dawsonite-bearing sandstones

Liu Li, Hou Qijun, Liu Na, Yang Huidong, Li Fulai, Yu Zhichao

2011, 32(6):  873-881.  doi:10.11743/ogg20110609

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Charging time of mantle CO₂ in sedimentary basins is a basis for studying interaction of CO₂-sandstone and CO₂-crude oil.Generally,eruption age of volcanic rocks near CO₂ reservoirs is supposed to be the charging time of mantle CO₂,but this approach is obviously not suitable to hydrocarbon basins with multi-stage volcanic eruption.Two hydrocarbon charging phases and one CO₂ charging phase have been identified in the dawsonite-bearing sandstone by the systematic observation and determination of diagenetic sequence and fluid inclusions in Southern Songliao Basin.The first and second hydrocarbon charging were recorded by the liquid hydrocarbon inclusion and gas-liquid hydrocarbon inclusion within fractures of authigenic minerals and detrital minerals,while the mantle CO₂ charging by the dawsonite and CO₂-bearing inclusion within fractures of detrital minerals.The charging time of mantle CO₂ is slightly latter than or approximately the same as the second phase of hydrocarbon charging.According to the analysis of diagenetic sequence and liquid inclusions in dawsonite-bearing sandstone,and in combination with the timing of hydrocarbon accumulation and structural fractures development,the charging time of mantle CO₂ leading to dawsonite formation in Songliao Basin might be from the end of Cretaceous (the end of Mingshui period) to Paleogene.

Influences of caprock sealing capacity on natural gas accumulation: an example from D-12 wellblock of Daniudi gas field in Ordos Basin

Zhang Wenqi, Wang Zhizhang, Hou Xiulin, Xu Fang, Liu Lang, Li Chunlei

2011, 32(6):  882-889.  doi:10.11743/ogg20110610

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In view of the large variations of production capacity both vertically and laterally in Daniudi gas field,this paper analyzed the influences of the caprock sealing mechanism and capability on natural gas accumulation by cores,laboratory test and logging data.The result indicates that the caprocks are overpressure sealing caprocks consisting of interbedded tight mudstone and undercompacted mudstone.The sealing capability is jointly controlled by the normal compacted mudstone and uncompacted mudstone.Thickness,total porosity,gross-to-net ratio and abnormal pore fluid pressure are selected as parameters to assess the sealing capacity of caprocks.The sealing capability is in positive correlation with the tested average open flow capacity and the maximum open flow capacity.The 3rd member of Xiashihezi Formation is the main gas pay zone thanks to the regional caprocks,and the high yield area is located on the western edge of the study area.The other pay zones are controlled by the sealing ability of direct caprocks,their gas are too scattered with low abundance to form large-scale contig- uous gas-bearing areas which is a key factor limiting productivity in the D-12 wellblock.

Characteristics of tight carbonate cap rock and its control on hydrocarbon accumulation in the north slope of Tazhong uplift

Zhao Yue, Yang Haijun, Liu Dandan, Han Jianfa, Zhang Yanping, Zhang Yangchun, Wang Haijiang

2011, 32(6):  890-896,908.  doi:10.11743/ogg20110611

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Large marine carbonate condensate gas reservoirs occur in the Yingshan Formation in the north slope of Tazhong uplift and their cap rock is tight carbonates in the 3^rd-5^th member of Lianglitage Formation.The carbonates are distributed widely in the whole north slope of Tazhong uplift,which is massive and is superimposed vertically and connected laterally,sealing the hydrocarbons in the underlying Yingshan Formaiton.Based on analyses of lithology,thickness and clay content of the tight carbonates,we summarized their distribution patterns and relationships with hydrocarbon accumulation and discussed the control of their thickness and clay content on oil/gas distribution.The study shows that the tight carbonate cap rock in the north slope of Tazhong uplift may be efficient seals when its thickness is equal to or more than 80 m and its clay content GR value is over 20 API,Thickness and clay content can complement each other for sealing capacity.

Development mode optimization for small fault-block reservoirs with edge and bottom water

Tang Jiandong, Jin Yong

2011, 32(6):  897-902.  doi:10.11743/ogg20110612

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Small complex fault-block reservoirs with edge and bottom water usually feature in narrow oil-bearing belts,multiple oil layers and large stratigraphic dip and so on.Controlled by structural shape,reservoirs and interbed barrier,the driving mechanisms of edge and bottom water are complicated and have big influences on development effect,making it difficult to determine development mode.We established mathematic and numerical models based on quantification of sealing capacity of interbed barriers.Using numerical simulation,we defined development modes under different conditions of interbed barriers and oil-bearing belt width.For oil reservoirs with strong vertical sealing capacity of interbed barriers and wide oil-bearing belts,layer-by-layer or layer-subdivision production can improve oil recovery.While for oil reservoirs with narrow oil-bearing belts,cross-layer production should be avoided.Oil recovery of layer-by-layer or layer-subdivision production is higher than that of other development modes.However,layer-by-layer production may reduce production rate and separate layer production may increase investment,so commingled production would be more profitable when the oil-bearing belts are narrow.In narrow oil reservoirs,the nearer the producer is to edge water,the lower oil recovery is,so producers should be placed from edge water as far as possible.

Comparison and evaluation of hydrocarbon accumulation conditions between the southern and northern Tien Shan thrust-fold belts

Zhao Guiping

2011, 32(6):  903-908.  doi:10.11743/ogg20110613

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The fold-thrust belts on the southern and northern sides of Tien Shan are among the most important target areas for oil and gas exploration.According to the preserve condition analyses for oil and gas,there are some similarities between these two side fold-thrust belts like in the aspects of source rock features,reservoir characters,structures and traps.However,the petroleum geology on the southern side of Tien Shan is better than that on the northern side of Tien Shan,such as the content of organic of source rocks,the characteristics and thickness of reservoirs,structure styles and trap characters.The main factors for these differences are various basin attributions/evolution history,basin-mountain contact relationships,sediment burial history,the lithology of the detachment zone and preserve conditions.

Tectonic evolution and its petroleum geological significances of the Maigaiti Slop,Tarim Basin

Zhang Zhongpei, Liu Shilin, Yang Ziyu, Li Jianjiao

2011, 32(6):  909-919.  doi:10.11743/ogg20110614

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In order to analyze the favorable conditions of hydrocarbon accumulation and identify favorable plays of Maigaiti slop in Tarim basin,we used the tectonic analytical method of superimposed basins to study the cha- racteristics and genesis of the eastern and western segments of the slope and discussed their hydrocarbon exploration significances based on integration of seismic and well data and analysis of the dynamic evolution of Maigaiti Slope.Multi-stage evolution and differential evolution are the key factors causing the obvious differences between the eastern and western segment in respects of hydrocarbon,migration and accumulation conditions and main exploration targets.The western segment in the Late Hercynian tectonic belts has good preservation conditions,and the up-dip upper Paleozoic lithologic body near the faults are key factor controlling hydrocarbon accumulation and enrichment.The eastern segment is located in the Hetian paleo-uplift,where Yubei-1 wellblock is placed in an area with the Middle and Late Caledonian tectonic stress superimposing with the Late Hercynian tectonic stress,providing more favorable conditions for the Ordovician fractured-vuggy reservoir development.The Lower Ordovician exposure in the buried hill zone to the east of Yubei-1 wellblock is covered by a seal of certain thickness which is favorable for the effective preservation of solution pores,vugs and fractures,thus is also a potential exploration target.

Tectonic transport characteristics and their influences on hydrocarbon accumulation in Beibuwan Basin

Hu Wangshui, Wu Chan, Liang Jianshe, Hu Fang, Cai Feng, Chai Haodong, Zou Qiyang

2011, 32(6):  920-927.  doi:10.11743/ogg20110615

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Geological data and various logging data were integrated to perform geologic interpretation of 3D seismic data of 4 sags in Beibuwan Basin.Characteristics of tectonic transport in this basin were discussed based on analyses of spatial distribution of the major boundary faults of each sag,fault throw at different stages and the transport of depocenter and subsidence center in the basin at different stages.The influences of tectonic transport on hydrocarbon accumulation was also discussed.The tectonic transport of Beibuwan Basin is characterized by wave-like directivity and convergent bias-symmetry.Tectonic transport resulted in present tectonic framework of the basin,controled the source-reservoir-caprock assemblages within the basin,changed temperature and pressure fields,accelerated source rock maturation and evolution,and hydrocarbon migration and accumulation.Because of the influence of tectonic transport,the source rock richness are different from sag to sag in the basin,the Weixinan sag has the richest source rock followed by the Wushi sag,Haizhong sag and Maichen sag.

Quantitative evaluation of fractures with fractal geometry in Kela-2 gas field

Feng Zhendong, Dai Junsheng, Deng Hang, Xiao Xiangjiao, Zhao Libin, Zheng Guangquan, Wang Ke

2011, 32(6):  928-933,939.  doi:10.11743/ogg20110616

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According to the relationship between faults and structural fractures,this paper processed fault system with fractal geometry,and set up the relationship of dimension value with fracture density in combination with log interpretation,performed fractal statistics of faults on top of the dolomite interval in the Kumugeliemu Group (Paleogene),and the second and third lithologic intervals of the Bashijiqike Formation (Lower Cretaceous),built relationship between fractural dimension values of faults at well point and the fracture density,and predicted interwell fracture distribution.The fractal dimension value of faults increases with fault density and length increase.Statistical values of fractal dimension of faults at well point show positive correlation with the linear density of fractures obtained by well logging interpretation.Fracture growth is significantly influenced by the geom- etry of anticlines.Fractures are commonly well developed in areas close to the axis of anticline and having a fractal dimension value over 1.25.The fracture density of three reservoir intervals near the A3 well is relatively large.Furthermore,some of the fractures may penetrate through the barriers,causing the watering of gas well.The study indicates that quantitative evaluation of fractures by using fractal geometry can guide exploration and development planning,and can be used to evaluate fractured reservoirs in oil/gas fields.

Approach and application of proration and injection allocation at the middle-late production stages in channel sandstone reservoirs

Feng Bin, Lü Aimin, Wang Wei, Zhao Fenghua

2011, 32(6):  934-939.  doi:10.11743/ogg20110617

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Channel sandstone reservoirs are generally poor in continuity and small in area.These features,in combination with the scarcity of basic data,make reservoir simulation difficult to work effectively.According to the dynamic regular patterns of the reservoirs,this paper puts forward statistic relationships between the injection and production index of channel sandstone reservoirs,including double logarithmic linear relationship between cumulative liquid production and time,semi-logarithmic linear relationship between cumulative water injection and the cumulative oil production.Based on the statistic relationships,we derive the relationship of the cumulative liquid production,monthly oil production,monthly water injection,monthly injection-production ratio with production time.Furthermore we set up a series of formulas for proration and injection allocation that can reveal the increasing of cumulative liquid production,monthly water injection and monthly injection-production ratio with time,and the decreasing of monthly oil production with time during stable waterflooding stage.The formula application in Zhuang 106-54 sandstone,Laohekou oilfield,indicates that the monthly oil production decrease obviously,whereas the daily water injection and monthly injection-production ratio increase monthly,a trend in accordance with the regular pattern of water flooding sandstone reservoirs.The proration and injection allocation approach has been successfully applied in Zhuang 106-54 sandbody of Laohekou oilfield and has contributed significantly to the stabilization oil production.

Geological factors influencing water shutoff effects of fractured-vuggy carbonate reservoirs in Tahe oilfield

Rong Yuanshuai, Gao Yanxia, Li Xinhua

2011, 32(6):  940-945.  doi:10.11743/ogg20110618

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The major reservoirs of Tahe oilfield consist of fractured-vuggy carbonates which underwent multiple stages of karstification and hydrocarbon charging.These reservoirs are of strong heterogeneity,complex oil-water contact and poor water shutoff effect.This study indicates that reservoir types and oil-water distribution patterns are the two key geological factors affecting water shutoff.The remaining oil distribution of the carbonate reservoirs of fractured-vuggy type is quite complicated due to the existence of big solution cavities,especially the high-angle fractures.The big solution cavities can make plugging water diffcult,while the high-angle fractures can easily result in complete shutoff,leading to poor shutoff effects.The fracture-vuggy reservoirs show quasi-homogeneity similar to sandstone reservoirs,thus their water shutoff effects are fair.Oil-water relationship pattern of quasi-homogeneous type corresponding to the reservoir types and wells with slowly-increasing or step-wise increasing water cuts have better water shutoff effects.Moreover,the existence of tight sections also can improve the water shutoff effects.

Water production pattern of Daniudi low-permeability gas field, Ordos Basin

Zhou Junjie, Li Yingchuan, Song Dongbin, Zhong Haiquan, Liu Tong

2011, 32(6):  946-951.  doi:10.11743/ogg20110619

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Calculation method of saturated water content of natural gas was adopted to qualitatively and quantitatively analyze produced water sources based on the production data and water sample test results of Daniudi low-permeability gas field in Ordos Basin.Moreover,gas wells were classified according to average gas yield and cumulative water and gas ratio (WGR),and water production patterns of different pay zones and single well of various types were analyzed.It is concluded that both water production and gas yield of single well are low in Daniudi low permeability gasfield in Ordos basin.The produced water consists of condensate water,formation water and operating fluid,of which the formation water is predominant.Different pay zones show different production behaviors.The third pay zone in the Permian Xiashihezi Formation and the first pay zone in the Permian Shanxi Formation feature in low water production but high gas production.The first and second pay zones in the Permian Xiashihezi Formation show both low water production and low gas production.The second pay zone in the Shanxi and Taiyuan formations are characterized by high water but low gas production.The gas production of single wells of different types is almost same,but horizontal wells produce more water with a higher WGR.These results can be used to guide selection of water discharging technologies and analysis of production performance.

Reservoir pore structure and micro-flow characteristics of waterflooding: a case study from Chang-6 reservoir of Wangyao block in Ansai oilfield

Quan Honghui, Zhu Yushuang, Zhang Hongjun, Li Li, Shao Fei, Zhang Zhang

2011, 32(6):  952-960.  doi:10.11743/ogg20110620

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The real sandstone micromodel was used to perform an experiment of microscopic waterflooding in Chang-6 reservoir with low permeability in Ansai oilfield, Ordos Basin. Based on the experiment and the in-depth analysis of thin section observation, physical property,SEM,relative permeability and mercury injection data,we studied the relationship between pore structure and micro-flow characteristics of waterflooding, which provide a scientific basis for effective oil exploitation in the future. The study shows that the lithology of reservoir is mainly fine-grained arkose with low compositional maturity; there are three major pore types including resid- ual intergranular pore, dissolved pore and dual pore+fracture, of which the residual intergranular pore is dom- inant; Dissolved pore and fracture are the key factors influencing the micro-heterogeneity. The experiment results indicate that there are homogeneous, reticular and finger-like micro-flows. Pore structure is closely related with micro-flow features. Reservoirs with different pore types show different micro-flow features. Flow paths of injected water depend on the relative permeability of pores and fractures in zones with well-developed fractures. Pore structure heterogeneity and wettability are the two main factors influencing displacement efficiency.