Table of Content

28 February 2017, Volume 38 Issue 1

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Petroleum Geology

New advances of the “Source-to-Sink” system research in sedimentary basin

Xu Changgui, Du Xiaofeng, Xu Wei, Zhao Meng

2017, 38(1):  1-11.  doi:10.11743/ogg20170101

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The "Source-to-Sink" system has been the focus of sedimentology research in recent years.In this paper,new research advances of "Source-to-Sink" at home and abroad are systematically reviewed,research methods and multi-methods integrated analysis technologies of the "Source-to-Sink" system are summarized and research trends are predicted.The "Source-to-Sink" system in continental margin basins focuses on the drivers of sedimentary event and transportation process,while in complex continental rift basins,principle of temporal-spatial coupled "Source-to-Sink" sandstone control and corresponding sandstone distribution models have been innovatively established.The "Source-to-Sink" research also focuses on application of multiple methods in sediment tracing to reveal paleo-provenance and reconstruct paleo-drainage.For the "Source-to-Sink" system in a provenance of continental rift basins,detailed analysis of sequence stratigraphy in potential eroded zone recovers the initial features of disappeared provenance in geological history.Quantitative characterization of the elements in the "Source-to-Sink" system and quantitative reservoir prediction has been under study,and establishment of quantitative relationship from source to sink is the final purpose.Sedimentary process simulation under the quantitative constraint provides significant support to reservoir prediction in sparse wells conditions.The research trends of "Source-to-Sink" include the following aspects:to improve provenance system research,to experiment on quantitative reservoir prediction,to combine multiple subjects and methods,to emphasize on process and mechanism analysis,and to form industrial application standard.

Theory progress and key issues of deep water marine clastic sequence stratigraphy

Qin Yanqun, Ji Zhifeng, Wan Lunkun, Li Zhi, Gao Xia, Ma Feng, Liang Yingbo

2017, 38(1):  12-21.  doi:10.11743/ogg20170102

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Due to the complexity of geological characteristics and lack of available data,there is still no commonly accep-ted view of theoretical cognition on deep water marine clastic sequence stratigraphy.This article overviews recently well-known sequence stratigraphic models worldwide,including classic sequence stratigraphic model,sequence stratigraphic model built based on deep-water system classification,that built on deep water sediment architectural superimposition style,that built based on quartered system tracts and that built based on physical sedimentary interfaces.It emphasizes on analyzing approaches and ideas of different models,advantages and disadvantages as well as the application condition in the deep water sedimentary research.We also summarize the key issues such as source-to-sink process of deep water sedimentation and allogenic factors of sequence stratigraphy,base level changes of deep water,order division of deep water sequence stratigraphy and auto-cycle of deep water.A high resolution sequence stratigraphic analysis based on available data and limited by physical interfaces is proposed for deep reservoir research.

Analysis on the different sealing conditions required by mudstone caprock at different fault evolution stages: A case study on the 1st member of Qingshankou Formation in the Sanzhao Depression and 2nd member of Dongying Formation in the structure No.5 of the Nanpu Sag

Zhang Bowei, Fu Guang, Zhang Juhe, Chen Xueqing, Lan Jingjing, Hu Xinlei

2017, 38(1):  22-28.  doi:10.11743/ogg20170103

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To decipher the hydrocarbon distribution pattern of oil bearing basins with hydrocarbon generating in the deeper formations and then migrating along faults upwards to the shallower reservoirs,we have studied hydrocarbon migration characteristics along faults and mudstone caprock sealing conditions required for accumulating hydrocarbon.Fault characteristics at different evolution stages were studied and corresponding pressure conditions were depicted.The results showed that to seal hydrocarbons migrating along faults,different conditions were required at various stages.The hydrocarbon migration along active faults was driven by both buoyancy and formation overpressure.While the carrier system is associated cracks and induced fractures,the corresponding porosity and permeability were relatively good.In this case,the hydrocarbon migration resistance crossing through the mudstone caprock was lower.Therefore,only when faults above the caprock are disconnected with those below,can the caprock seal the migrating hydrocarbon.In contrast,the hydrocarbon migration along static faults was driven only by buoyancy,while the carrier system was of fault rock pores.In this case,the corresponding porosity is relatively poor with higher migration resistance for the hydrocarbon to break through the mudstone caprock.Therefore,to seal hydrocarbon migrating along faults,the displacement pressure of fault rock should be equal to or greater than the reservoir overpressure.

Extension direction and tectonism in rift basins and their control on structural style: A case study on the south fault terrace in the Gaoyou Sag, Subei Basin

Wu Lin, Chen Qinghua, Liu Yin, Wang Xi, Zhang Xiaodan, Sun Ke, Chen Chuanhao

2017, 38(1):  29-38.  doi:10.11743/ogg20170104

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As the tectonic boundary belt,the south fault terrace,which consists of Wubao fault terrace and Zhenwu fault terrace,has complicated tectonic history and style.Based on the geometrical characteristics of the south fault terrace,guided by the stress-strain theory and extensional rate from the balanced section,we figured out the dominate extensional direction in different periods and analyzed the amount of extension and strike-slip of the south fault terrace,and their control on structural style.The evolution of the dominate extension direction of the Gaoyou sag can be divided into three stages since the late Cretaceous,including NW(K₂t²-E₂d),NS(E₂s),and NW(Ny-Qd).Detailed understanding of the direction of stress field in the Gaoyou sag was obtained since the late Cretaceous in a quantitative way for the first time.Because the dominate extensional direction is not always parallel with the axis of fault terrace,Wubao fault terrace experie-nced 3 periods of tectonism,extension,right-lateral slip-extension,and extension.This resulted in the simple faults style with skew traces in plane view and horse tail-like in profiles.Similarly,Zhenwu fault terrace also experienced 3 periods of tectonism,left-lateral slip-extension,right-lateral slip-extension and left-lateral slip-extension,which resulted in the complicated faults style of grid fault trace in plane view and duplex horse tail-like in profiles.The study on the history of extension rate and strike-slip shows that E₁f,E₂d and E₂s were the main periods of extension and strike-slip,which played a key role in the formation of structural style.

Water redox conditions and environment for source rock deposition in lacustrine during the Initial Eocene Thermal Maximum(IETM): A case study on the Paleogene Kongdian Formation in the Dongying Sag

Liu Ping, Tan Xianfeng, Chen Qing, Wang Jia, Liang Mai, Wang Ping, Wang Weiqing

2017, 38(1):  39-48,143.  doi:10.11743/ogg20170105

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The Initial Eocene Thermal Maximum(IETM) has seriously affected the water quality and biological activities of sea and lake.Based on the experimental results of drilling cores,elemental analysis,organic carbon isotope and TOC,the lakewater oxidation-reduction conditions and paleoproductivity of Dongying terrestrial fault basin during early Eocene has been studied in this paper.It turned out that the lacustrine was strongly reductive but resumed oxidation environment afterward.The fluctuations of redox interface caused by the extreme climate events changed the lacustrine redox pattern,which resulted in the "disharmony" of the oxidation-reduction variation along the water depth.The productivity of the lacustrine was high in the early time,followed by a rapid decrease but increased progressively again.The lowest productivity period is basically consistent with the IETM.It has confirmed that the Initial Eocene Thermal Maximum (IETM) has affected the spatial and temporal fluctuation of the lacustrine.This event has obvious sedimentary record and biogeochemical response,which determines water oxidation-reduction and the bio-mass activities of the original basin.The hypoxia of lacustrine caused by thermal maximum resulted in the temporary decrease in productivity.However,productivity has been greatly restored with the sufficient oxygen supply after the event.This is especially demonstrated in the No.four section of Shahejie Formation with the higher TOC content and the productivity,and thus becomes the main reservoir of tight oil and gas production.

Micro-petrology, pore throat characteristics and genetic mechanism of tight oil reservoirs-A case from the 6^th and 7^th members of Triassic Yanchang Formation in the Ordos Basin

Zhong Dakang

2017, 38(1):  49-61.  doi:10.11743/ogg20170106

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The 6^th and 7^th members of Yanchang Formation (Chang 6 and Chang 7) contain a large number of tight oil in the Longdong area of Ordos Basin. However,poor understanding of their microscopic characteristics and genesis has hindered the exploitation of tight oil. The current study attempts to investigate the pore throat characteristics and genesis of tight oil reservoirs of Chang 6 and Chang 7 members of Yanchang Formation on the basis of pore cast thin section,field emission electron microscopy (FE-SEM) and so on. The results show that the tight oil reservoirs were deposited in distal bar and sheet sand of delta front and gravity flow of semi-deep to deep lake,and the tight oil reservoir rocks with fine grain size and high matrix content (8%-10%) consist of very fine sandstones,siltstones,pelitic siltstones and silty mudstones. These reservoir rocks have very poorly developed pores,low thin section porosity averaging at 1.8%,small pore radius averaging at 30 μm,fine throat radius averaging at 0.08μm,low porosity averaging at 9% and low permeabi-lity of less than 0.3×10^-3 μm². The main pore types of the tight oil reservoirs are micropore of intergranular matrix,dissolution pore of feldspars and rock fragments and intercrystalline pore of cements. The microscopic characteristics of different oil reservoir rocks are different. The low-energy sedimentary environment is decisive in determining the fine grain size and high matrix content of the reservoir sandstones,which have weak resistance to compaction in early burial stage,hence,significant amount of original pore volume is lost,and the pore throat sizes become smaller. In the reservoir rocks with tiny pore throats,the strong carbonate and clay mineral cementation (especially the bridging and network-like cementation of illite),caused by semi-permeable membrane effects of ions,further reduce the porosity and permeability of the reservoir rocks,preventing the later acidic fluid dissolution and formation of secondary porosity. In addition,the strong replacement of quartz by detrital micas grain,hydromuscovite matrix and carbonate cement lowers the resistance of the reservoir rocks and increases the solid volume,finally leading to the tightening of the reservoir rocks.

Characterization of fault system and its control on reservoirs in the Bozhong Sag, Bohai Bay Basin

Wang Guanmin, Xiong Zhouhai, Zhang Jian, Guo Yonghua, Lin Guosong, Fu Yao

2017, 38(1):  62-70.  doi:10.11743/ogg20170107

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The Bozhong Sag is not only the depocenter of the Bohai Bay Basin,but also an important oil/gas-bearing sag in the Bohai Bay Basin.The reservoirs surrounding the Bozhong Sag are mostly fault-controlled structural or structural-lithological reservoirs.The patterns and degrees that these faults control on petroleum reservoirs directly determine the evaluation of structural traps and exploration strategy.By detailed structural characterization of 237 petroleum reservoirs with shallow to medium depth in the Bozhong Sag,this paper statistically analyzed multiple parameters,e.g.,faulting classification,faulting mechanism,fault throw,faulting activity,fault strike/dip,combination styles,plain view geometry,screening types,SGR,etc.Our study suggested that,with proper assemblage of primary faults and minor faults,faulting characteristics contributing to petroleum accumulation includes:striking NNE or EW/NE,dip angle of 66°-80°,fault throw of 20-150 m,faulting rate of 10-30 m/Ma,SGR > 0.3,R_m > 0.35,multiple assemblage styles (e.g.,oblique crossing,en echelon,Y-shape,semi-flower and stepwise faults) and antithetic screening.In plain view,it is more favorable for hydrocarbon accumulation in positions where faults are intersecting and convex section.In general,fault sealing property is the key factor controlling hydrocarbon accumulation in structural traps.The fault sealing property is determined by faulting rate,scale and fault types.

Characteristics and controlling factors of fan delta facies low permeability reservoirs in Bohai A oilfield, the Bohai Bay Basin

Zhou Junliang, Hu Yong, Li Chao, Fu Rong, Lai Youchun

2017, 38(1):  71-78.  doi:10.11743/ogg20170108

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In order to understand reservoir characteristics and controlling factors of the lower 3^rd Member of Shahejie Formation(E₂s^3L) in Bohai A oilfield,we studied the lithological composition,pore types and structure,porosity and permeability distribution and discussed the controlling factors of petrophysical properties of the reservoirs from sedimentary,diagenetic and tectonic perspectives based on thin section,scanning electron microscopy (SEM),mercury injection and other conventional lab test data.The results show that the reservoirs of fan delta facies in E₂s^3L have low to ultra-low poro-sity and ultra-low permeability.They are composed of lithic arkosic sandstone with low compositional maturity,their main pore throat types are primary intergranular pore,dissolution pore and residual pore,and the pore throat structure is fine to micro.The reservoir properties were controlled by various factors,including sedimentation,dissolution and tectonic movements etc.Sedimentary environment of distributary channel and mouth bar at fan delta front controlled the grain size and sorting of the reservoir,resulting in relatively good reservoir properties.Compaction and cementation were the main factors causing the low permeability,however,dissolution of feldspar and detritus components by organic acids formed secondary pores,and the abnormal high pressure in the reservoir weakened compaction and helped the preservation of primary intergranular pores.Fractures are well developed near the faults formed by various tectonic movements,which also helped to improve the physical properity of the reservoirs.Through comprehensive analysis of all available data,we can conclude that strong hydrodynamic depositional environment,later dissolution and well-developed fracture network are the main factors that control the formation of the reservoirs with relatively high porosity and permeability.

Quality distribution and origin of super heavy crude in LX Structure of the Liaoxi Sag, Bohai Sea

Wang Bingjie, Xu Changgui, Wu Kui, Peng Jingsong, Liu Feng

2017, 38(1):  79-89.  doi:10.11743/ogg20170109

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A correct understanding of the quality distribution and origin of super heavy crudes is critical to their exploration assessment and development planning.A quality assessment model for characterizing heavy crude samples from the Neogene Minghuazhen and Guantao Formations in the steep slope zone of LX structure in Liaoxi sag of Bohai Sea was established based on a method combining rock pyrolysis with seismic multi-attribute analysis.The quality distribution and origin of the samples was also studied through analyses of paleo fluid activities and physical properties of relevant reservoirs.The result shows that,vertically speaking,the quality of samples from the top is worse than that from the bottom of the Minghuazhen Formation while the Guantao Formation is the opposite with samples from the top better than that from the bottom.Horizontally,the quality of samples from areas near structural highs is less favorable while those near faults and reservoir boundaries yield better-quality samples.As a whole,sample quality shows a zonal distribution,which is considered to be closely linked to the "two-stage reservoiring and densification" of the crude.It is suggested that the crude of the Dongying Formation experienced a reservoiring and densification process in the early stage,and later the reservoirs that had experienced the first densification in the Dongying Fm were destroyed,leading to the re-reservoiring of the crude in the Minghuazhen and Guantao formations.It is also suggested that crude quality is poorer in intervals with better physical properties as a result of more extensive densification.The second stage of reservoiring is proposed to be accompanied by charges of newly-generated better-quality crude along faults and reservoir boundaries that helped improving the quality of existing crude in these areas and resulting in the current spatial distribution of crude quality.

Temporal-spatial evolution of diagenetic environment and diagenesis pore evolutionary process of red beds in the eastern Dongying Sag, Bohai Bay Basin

Li Jiyan

2017, 38(1):  90-97.  doi:10.11743/ogg20170110

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Diagenetic environment is one of the vital factors to control pore types and evolutionary process of the red beds.On the basis of a great amount of microscopic thin section combining with ‘elemental geochemical index quantifiable forward modeling’ and ‘diagenetic product type and quantifiable inversion’,Temporal-spatial evolution of diagenetic environments are qualitatively analyzed in red beds of the eastern Dongying Sag,and diagenetically reformed pore volumes are quantitatively described.Additionally,pore evolution models under the control of multiple diagenetic environments are established in red beds.The results show that diagenetic environments in red beds can be divided into original alkaline environment and burial acidic environment owing to primary depositional environment,organic acid and hydrocarbon injection period at temporal dimension.On the plane view,with alkaline water released by saline lake areas and changes of organic acid concentration along with the migration distance,diagenetic environment can be divided into four parts from lake area to sag margin:moderate strong alkalinity-weak acidity,moderate-strong alkalinity-weak acidity,weak alkalinity-moderate-strong acidity,weak alkalinity-weak acidity.Due to the spatial variation of diagenetic environment,the degree of original pore reduction and secondary pore generation are obviously different in different tectonic positions,which in turn leads to diversified reservoir space types and significant porosity difference red beds in the eastern Dongying Sag.

Characteristics and controlling factors of fine-grained mixed sedimentary rocks from the 2^nd Member of Kongdian Formation in the Cangdong Sag, Bohai Bay Basin

Yan Jihua, Deng Yuan, Pu Xiugang, Zhou Lihong, Chen Shiyue, Jiao Yuxi

2017, 38(1):  98-109.  doi:10.11743/ogg20170111

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Mixed clastic-carbonate deposits are widely distributed in the fine-grained sedimentary rocks from the 2^nd Member of the Kongdian Formation in Cangdong Sag.The mixing styles of the fine-grained sedimentary rocks can be divided into componential mixtures(CM) and structural mixtures(SM).The componential mixtures are characterized by mixing of different minerals within one lamina.The structural mixtures feature in vertical overlying of different single-mineral laminae and componential mixture laminae.Through detailed core description,thin section observation and X-ray diffraction analysis,it was considered that there develop two types of componential mixtures in the 2^nd Member of Kongdian Formation in Cangdong Sag,namely clay-carbonate(CM1) and felsic-carbonate-clay(CM2) componential mixtures.And there also develop four types of structural mixtures,namely felsic/clay-carbonate(SM1),felsic/clay/carbonate(SM2),clay/carbonate(SM3) and clay-carbonate/clay-organism(SM4) structural mixtures.There are two kinds of vertical combinations both with a bottom-up order change from massive structure to bedded structure and lamina structure.The vertical combination dominated by dolomitic(limy) fine-grained mixed sedimentary rocks is formed due to climate changes.And the vertical combination dominated by felsic fine-grained mixed sedimentary rocks is due to the changes in supply intensity of terrigenous materials.

Characteristics and evolution of sedimentary sequences of the 3rd member of Shahejie Formation in Shuangtaizi tectonic belt, the Liaohe Depression

Man Xinxin, Wang Hongliang, Shan Junfeng

2017, 38(1):  110-120.  doi:10.11743/ogg20170112

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The Shuangatizi area in Liaohe Depression with multi-typed provenances and complicated sedimentary conditions has not been well explored.Armed with terrestrial rift basin sequence stratigraphy and sedimentology theories,the authors studied the sedimentary facies in the sequence stratigraphic framework of the third member of Shahejie Formation (Sha-3 member) through comprehensive analysis of core facies marks,drilling/logging and seismic data.Three sedimentary facies were identified,including the fan delta,the sublacustrine fan and the lacustrine facies.A sequence stratigraphic framework with 3 third-order sequences (namely the lower Sha-3 sequence,the middle Sha-3 sequence,the upper Sha-3 sequence) was also established by using relevant theories and technologies for the third member.It shows that sublacustrine fans were developed extensively during the full sycle of the lower and the ascending half cycle of the middle Sha-3 sequences,fan deltas were developed in the north part of the area and sublacustrine fans were developed in the south part of the area during the descending half cycle of the middle Sha-3 and the full cycle of the upper Sha-3.In general,the sublacustrine fans show features of migration towards the central depression with scales changing from small to large and then to small again.

Numerical simulation research on a regional outpost well and its hint on the future hydrocarbon exploration direction of the Maichen Sag, Beibuwan Basin

Zhang Wei, He Jiaxiong, Hu Yang, Liu Ju, Li Xiaotang

2017, 38(1):  121-131.  doi:10.11743/ogg20170113

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Based on the petroleum-geological data of the Y1 well that is located in the southwestern margin of Maichen Sag of the Beibuwan Basin,in this study,the petroleum-geological and geochemical numerical simulation has been conducted using the PetroMod software.The results show that only the dark mudstones in the second section of Eocene Liushagang Group meet the standard of sufficient organic matter abundance to be defined as hydrocarbon source rock,but they have not reached the hydrocarbon generation threshold because of their low maturity.In addition,the geothermal field of the Maichen depression is generally low,and the mature hydrocarbon generation threshold depth,by comprehensive judgment,has been determined as 2 600 m,which is obviously deeper than that of Eocene hydrocarbon source rocks of the Weixinan and Wushi Sags.As Y1 well is out of drainage range of effective hydrocarbon generation,its structure may not have received sufficient hydrocarbon charge,to become a hydrocarbon accumulation in local structures and trap.Thus,this should result in an empty trap where the Y1 well is targeted.Therefore,favorable zones and traps within the effective hydrocarbon drainage zone of Eocene hydrocarbon source rocks should be focused on,in order to achieve a breakthrough of the commercial hydrocarbon exploration.

Shale gas reservoir characteristics of the Wufeng-Longmaxi Formations in Huangjinba construction block of the Luochang Syncline, the Sichuan Basin

Xu Zhengyu, Liang Xing, Wang Xiyou, Wang Gaocheng, Zhang Jiehui, Xiong Shaoyun, Lu Huili, Xu He

2017, 38(1):  132-143.  doi:10.11743/ogg20170114

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Luochang Syncline is located in the southern Sichuan Basin.The main target layer of Wufeng-Longmaxi Formations shale has been deformed during Indosinian,Yanshanian and Himalayan.The shale deformation was relatively weak with moderate burial,promising good condition for shale gas accumulation and preservation.Thus the syncline has become an important part of the core shale gas area in the upper Yangtze region.According to characteristics of lithology,electrical,mineral composition,organic matter and gas bearing property,Wufeng-Longmaxi Formations shale of the Syncline can be divided into three third-order sequences,three lithologic sections,three types of facies and four types of sub-facies and various of micro-facies.Deep water shelf depositional stage is the best stage (layerⅠ) for possible organic rich shale deposition and could be subdivided into five layers,namely Ⅰ₁,Ⅰ₂ and Ⅰ₃,Ⅰ₄,Ⅰ₅.Integrated analysis of physical property and pressure coefficient of the shale in the Huangjinba development block,shale gas is mainly preserved in the residual syncline which was the main part of deep shelf.The gas reservoirs are divided into two sets,the bottom of the Longmaxi Formation and the Wufeng Formation,separated by the Guanyinqiao Member limestone.Based on fracturing evaluation and production test results,the bottom of Longmaxi Formation Ⅰ₃ and Ⅰ₄ are the best production layers after fracture transformation.

Pore types and characteristics of volcanic reservoirs of the Jiamuhe Formation in Jinlong oilfield, Junggar Basin

Wang Xiaojun, Zhao Fei, Zhang Qin, Wang Dongxue, Xia Jinjie, Wu Xingzhou, Li Chenxi, MeiXiaohan, Lyu Dehong

2017, 38(1):  144-151.  doi:10.11743/ogg20170115

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Volcanic rocks in the Jiamuhe Formation are favorable reservoirs in Jinlong oilfield.It is a key step for exploration and development of volcanic reservoirs to analyze the characteristics of volcanic reservoir and define the distribution of favorable reservoir facies belts.Based on core,thin section,high pressure mercury injection and reservoir property data,this paper defined the characteristics of lithology and property of the volcanic rocks,and predicted the distribution of favorable volcanic reservoirs.The results show that the volcanic reservoirs consist of volcanic lavas,volcaniclastic lavas,volcaniclastic rocks and depositional volcaniclastic rocks.The volcanic reservoirs in Jinlong Oilfield are characterized by medium to low porosity and low to extra low permeability.The reservoir spaces are divided into pore vs. fracture classes according to their shapes in the rock,and primary vs. secondary categories on the basis of genesis,of which the contraction pores and fractures are the main reservoir spaces of the volcanic reservoirs in Jiamuhe Formation.Volcanic rocks with different lithologies and petrofacies have different types of mercury-injection curves.There are 3 curve types featuring respectively in fine pore throat with bimodal positive skew distribution,fine-micro pore throat with unimodal positive skew distribution,and micro pore throat with unimodal negative skew distribution.Overall, the micro-fine pore throats are predominant and the sorting is poor to moderate.Lithologically,the volcanic breccias,basalt and andesite are the most favorable reservoirs in the study area,while as to petrofacies,the best reservoirs occur in the explosive facies and the upper part of the effusive eruption facies.The best favorable reservoir facies belt is located at the middle part of the study area and is in NW-SE-trending banded distribution.

Sequence division and platform sedimentary evolution model of the Lower Cambrian Xiaoerbulak Formation in the NW Tarim Basin

Bai Ying, Luo Ping, Zhou Chuanmin, Zhai Xiufen, Wang Shi, Yang Zongyu, Wang Shan

2017, 38(1):  152-164.  doi:10.11743/ogg20170116

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Based on the outcrop observation and thin section identification,the distribution of microbial carbonate is described and sequence stratigraphy framework is established in the Lower Cambrian Xiaoerbulak Formation in the Aksu area,Tarim Basin.Finally the carbonate platform evolution during the deposition period of the Xiaoerblak Formation is summarized and rebuilt.The results show that the Xiaoerblak Formation can be subdivided into two third-order sequences.The lower part,SQ1,corresponds to a set of microbial mats which are middle-inner ramp deposition corresponding to the stage of ramp carbonate platform.The upper part is SQ2,which is a TST,and represents a transition from ramp carbonate platform to slightly rimmed shelf carbonate platform.On the slope the tempestite deposited without microbial carbonate,while on the paleokarst highland,the large-scale transgressive mircobial reef was built through the microbial skeleton growth and correlatively bonding effect.The HST represents the stage of slightly rimmed shelf carbonate platform,where the margin and inner-platform are sharply different.On the platform margin,the EHST is characterized with chambered Epiphyton bioherm,while the LHST features some small-scale transgressive microbial bonding reefs.The inner-platform developed microbial shoal facies during the high stand,and its EHST is absent.The inner-platform LHST is characterized by laminites,spongiostromata stromatolites and stromatolites.Their formation is related to the sticky microbial mats.

High resolution sequence stratigraphy of the Ross Sandstone deepwater turbidite outcrops in the Clare Basin, Ireland

Zhang Leifu, Wu Chenjun, Su Yang, Guo Yanjun, Wang Hongliang

2017, 38(1):  165-174.  doi:10.11743/ogg20170117

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Using the principles and methods of high-resolution sequence stratigraphy,the Ross Sandstone deepwaterturbidite lobe outcrops in the coast of western Irelandare studiedbased on four factors:laterally extensive mudstones,sedimentary structures and lithofacies associations,degree of sand amalgamation and sedimentary pattern and thickness.The high-resolution sequence stratigraphic framework has been established,the depositional model of deepwaterturbidite lobe is proposed,and the controlling factors for base level cycles at different hierarchies are discussed.The results show that,the organic-rich pelagic mudstone with abundant goniatites represents the transition of two adjacent long-term base level hemi-cycles.Within the long-term base level cycle,each mid-term base level cycle is bounded by the thin mudstones with subordinate siltstones which can extend laterally several kilometers to tens of kilometers.Each mid-term cycle is composed of several thickening-upward cycles which are 0.5-7 m thick and several hundred meters to several kilometers across,suggesting continuous lobe progradation.

An optimization method to measure rock threshold pressure gradient of oil and gas reservoirs

Zhu Weiyao, Tian Wei, Zhu Huayin, Song Zhiyong, Sun Yan

2017, 38(1):  175-180,196.  doi:10.11743/ogg20170118

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Instantaneous threshold method and dual-ends pressure balance method are commonly used to test minimum threshold pressure gradient,but they are time-consuming and hard to ensure the accuracy of measurement data.The test results of pseudo threshold pressure may be slightly higher by using method of "differential pressure-flow" under constant confining pressure.Based on the above considerations,a set of integrated experiment process is designed,and the method of unsteady threshold-pressure balance is formulated.Also the way to implement the method of "differential pressure-flow" is optimized.The accuracy of the test results is ensured by using precise equipments in the experiment process,and the process is suitable for a wide range of core permeability test of threshold pressure gradient.Test results meet the expectation when this method is applied to well cores in Tuha oilfields,and this method can become a common measurement in the lab.

An independent development method of low permeability oil thin layers with extreme high water cut in Changyuan Structure, Daqing oilfield

Gao Dapeng, Ye Jigen, Li Qi, Shi Chengfang, Hu Yunpeng, Hou Shaoji, Ji Shuhong, Huang Lei

2017, 38(1):  181-188.  doi:10.11743/ogg20170119

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Low permeability thin oil layers have become the main object for waterflooding production in extreme high water cut stage in Changyuan area,Daqing oil field.However,conventional methods,such as well pattern infilling and layer-specific water injection,could get no satisfying effect.Therefore,a method of independent development of low permeability thin oil layers is put forward by taking into account features of these low permeability thin oil layers and technologies of layered hydraulic fracturing.Two kinds of development models are suggested,and one of the models designs how water wells perforate reservoir zones depending on the number and pattern of oil wells that perforate low permeability thin oil layers only,the other one designs how oil wells perforate zones depending upon the number and patterns of water wells that perforate low permeability thin oil layers only.Then,the recovery of these two modes are compared by waterflooding physical simulation experiments with multi-layer artificial casting cores.The productivity model of layered fractured vertical well is deduced considering the threshold pressure gradient and horizontal fractures in shallow reservoirs,and the technology limits are calculated and analyzed for the independent development of low permeability thin oil layers.The results show that the first model will get more recovery than the second one,and the technical limit of spacing is about 228 m,the economic limit of thickness is 2 m.With the increasing of low permeability thin oil layers thickness to total perforated thickness ratio,recovery declines firstly and then remained stable,and rises rapidly finally.Field application shows that the average well production is 3.7 tons/day under the independent development of low permeability thin oil layers,its development effect is better than tertiary well pattern infilling.

Quantitative characterization of complex fractures after volume fracturing in shale

Shang Xiaosen, Ding Yunhong, Lu Yongjun, Wang Yonghui, Yang Lifeng

2017, 38(1):  189-196.  doi:10.11743/ogg20170120

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According to the typical geometry of complex hydraulic fractures of shale,a new method which takes the fracture complexity,the fracture distribution and the attribution of fracture to production into consideration was proposed to describe complex fractures.Moreover,the concept of fracture potential index was put forward,and it can be used as one of the parameters for quantitative evaluation of the complex fractures.The density of fractures with different distances from the stimulation location was estimated with the method for determining the effectiveness of the fracture network.Compared with the fracture network with the characteristics of being dense inside but sparse outside,the fracture network being sparse outside but dense inside is more effective in enhancing production according to the description results.Hydraulic fracturing experiments were conducted and the geometries of hydraulic fractures in the shale were described with the application of the method.Results show that the potential index of fracture network formed under low horizontal geostress difference is greater than that of fractures formed under high horizontal geostress difference.It reflects that the fracture network formed under low horizontal geostress difference has higher potential for enhancing production.The above results indicate that the method established for describing complex fractures can comprehensively reflect the fracture complexity,fracture distribution and attribution to production.It provides a mean for evaluating the effectiveness of complex hydraulic fracture network.

Application of improved fuzzy-grey comprehensive evaluation method to quantitative reservoir evaluation: A case study of the low-permeability gas reservoirs of the lower part of 8th member of the Shihezi Formation in Su X block of Sulige Gasfield

Zhu Zhaoqun, Lin Chengyan, Zhang Sujie, Ren Lihua, Zhao Jianxuan, Chen Shizhen, Jia Xiaopeng, Chen Li, Zhang Ji

2017, 38(1):  197-208.  doi:10.11743/ogg20170121

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For the lower section of 8th member of the Shihezi Formation (Middle Permain) in the Su X block of the Sulige gasfield,significant degree of uncertainty was involved in early-stage evaluation of low-permeability gas reservoir due to immature understanding and incomplete information,which causes difficulty to a fine reservoir description.It is vital for a better reservoir evaluation to fully account for uncertainty and effectively magnify the differences of different reservoirs in evaluation results.In this paper,based on the idea of multi-information superposition,the methods of fuzzy mathematical evaluation and grey correlation analysis are linked by membership degree and are integrated to establish a more effective fuzzy-grey comprehensive evaluation model,along with differentiated and improved internal algorithm.The application of the model to reservoir evaluation in this study suggests that this method enhances the differences and precision for the low-permeability reservoir classification and characterization,with consideration of the fuzzy and grey properties of reservoir.In this case study,four types of reservoir are classified and the type Ⅰ and Ⅱ are deemed to be the favorable targets.The different reservoir categories are better separated in plane view than before.The comparison of evaluation results with the real production data and geological principles of fluvial deposition also displays good coincidence.This method may be effective and efficient for guiding the exploration and development of the gas field,and provide a new thought for similar low-permeability reservoir evaluation as well.