Table of Content

08 December 2016, Volume 37 Issue 6

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Main controlling factors on shale fractures and their influences on production capacity in Jiaoshiba area,the Sichuan Basin

Guo Xusheng, Hu Dongfeng, Wei Xiangfeng, Li Yuping

2016, 37(6):  799-808.  doi:10.11743/ogg20160601

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Shale samples were taken from the Wufeng-Longmaxi Formations in Jiaoshiba Block of Fuling shale gas field to study the key controlling factors of shale fractures and their influences upon gas production capacity through analysis methods including core observation,FMI logging interpretation,Ar-ion Milling SEM images and etc.The results show two main types of fractures:micro-fractures (cleavage fractures,intergranular fractures and grain-around fractures) and macro-fractures (high angle fractures-oblique fractures and vertical fractures,horizontal fractures-foliation fractures,interlayer slipping fractures).Their growth is clearly under the joint control of mechanical properties,abnormal high pressure,distance from the main decollement surface,and bentonite and tectonism.The micro-fractures and horizontal fractures are best developed at the bottom of both Formations,while high angle fractures are mainly developed in the Wufeng Formation in structurally stable regions far from fault belts and occur in all the shale gas formations in areas near the fault belts.The differential development of natural fractures in horizontal and vertical directions is found to control the productivity of single shale gas wells through the following ways.First,it controlled shale gas enrichment as the micro-fractures and horizontal fractures far from faults around Jiaoshiba Tectonic contributed greatly to the accumulation of shale gas in the stable structural zones.In contrast,the open fractures with high angles possibly acted as channels for shale gas to escape,thus leading to a low gas abundance and a low formation pressure.Secondly,it may lower the effectiveness of volume fracturing as the high-angle open fractures not only can cause severe drilling mud leakage,but also deter the formation of fracture networks through fracturing.

Structural deformation and its influences on gas storage in Fuling shale gas play, the Sichuan Basin

Sun Jian, Luo Bing

2016, 37(6):  809-818.  doi:10.11743/ogg20160602

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The shale gas reservoirs of the Wufeng-Longmaxi Formations in the Fuling shale gas play,the eastern Sichuan Basin have been put into commercial production.In the first-phase development block,the single well productivities show a great difference and the gas storage varies laterally,but the causes are still poorly understood.The previous geological evaluation indicated that the lateral distributions of the primary reservoir qualities like shale thickness,mineral composition,and organic carbon content are stable,thus could not be the key factors affecting gas storage.Instead,the variation of gas storage may be closely related to structural deformation.Starting with the characterization of regional structural deformation,this paper presents a systematical research on the structural features,tectonic framework and structural styles in the study area.The study area experienced multi-stage tectonic movements,resulting in multi-level decollement structures,which can be vertically divided into 3 structural deformation layers and 7 structural styles,with an obvious difference in structural deformation intensity.A preliminary quantitative characterization of the structural deformation intensity shows that the fault throw,formation thickening ratio,curvature and fault density are the key parameters for characterizing the structural deformation intensity of the study area.Based on the quantitative characterization,four structural deformation areas are recognized in the study area,and they have significantly different gas storage,indicating that the structural deformation intensity is the key factor causing the variation of gas storage in the study area.

Formation and evolution of normal pressure shale gas reservoir in Wulong Syncline,Southeast Chongqing,China

Fang Zhixiong, He Xipeng

2016, 37(6):  819-827.  doi:10.11743/ogg20160603

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In order to understand the formation and evolution of the normal pressure shale gas reservoirs in Wulong Syncline in Southwest Chonqing,China the major controlling factors of shale gas accumulation were studied through drilling data analysis,thin section observation,Ar-SEM,tectonic balanced section and burial history analyses,in combination with analysis of four dynamic preservation factors (sedimentation,burial evolution,hydrocarbon generation,and tectonic uplifting).Results show that there are 3 key elements controlling the formation and evolution of the typical normal pressure shale gas reservoirs in Wulong syncline.The first one is the favorable lithological association of the Wufeng and Longmaxi Formations.The quality shales of deep shelf facies are stable in lateral distribution and have high potential of hydrocarbon generation,while the overlying thick shale has good sealing capacity,thus is favorable for the preservation of shale gas.The second one is the favorable reservoir conditions.The organic nanopores provide high porosity for gas storage and the complex pore geometries improve the permeability of the shale reservoirs.In addition,the brittle minerals associated with the organic maters acted as skeleton and protected to some extent the organic nanopores from compaction during diagenesis.The third one is tectonic evolution which determines the reservoir scale.After the continuous deep burial and main period of hydrocarbon generation,the target reservoirs experienced reformation during tectonic uplift,which led to the partial gas migration and dispersion,and the formation of normal-pressure shale gas reservoir with a pressure coefficient in the range from 0.8 to 1.2.

Tectonic characteristics and their shale gas geological significance of the Mesozoic-Paleozoic in Jiaoshiba area,the Sichuan Basin

She Xiaoyu, Chen Jie, Zhang Shiwan, Shu Zhiguo, Yu Fei, Li Dongdong, Gong Xiaoxing

2016, 37(6):  828-837.  doi:10.11743/ogg20160604

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Through 2D and 3D seismic interpretation and application of balanced cross section technique,basement structure,and tectonic characteristics and its evolution of the Mesozoic-Paleozoic of Jiaoshiba area,the Sichuan Basin are analyzed in this study.The results show that there are two types of structures in the study area.The first type is basement-involved structure,which is characterized by five structural patterns and assemblages,including back thrust anticlines,ramp syncline,imbricate thrusting,positive flower wrench and "多"-shaped wrench.The other type is cap detachment structure,which is characterized by five structural patterns and assemblages,including fault-propagation or fault-bend,fault-slipping,imbricate thrusting,imbricate ramp and thrust wedge.Additionally,the Early and Middle Yanshanian period are two major tectonic deformation periods.During the Early Yanshanian period,the nearly horizontal westwards detachment and decollement-nappe structures occurred along the interface between the Mesozoic-Paleozoic and the basement and the interfaces within the basement,resulting in the anticline-syncline alternating Zhuluoshan fold.The Jiaoshiba area between Fangdoushan fault and Datianchi anticline is within a broad compressional synclinorium structural background.During the Middle Yanshanian period,the detachment of the middle-deep burial basement in the eastern trough-like fold belt caused intensive westward thrusting,and then led to the formation of the tectonic framework of obduction-thrust-overthrust in the Jiaoshiba area.The double-layer back-thrusting anticline and faulted fold belt in the flanks were formed in Jiaoshiba area after three deformation episodes,including basement-involved imbricate thrusting-cap rock decollement-left-lateral transpression.Furthermore,Shimen faulted fold belt is characterized by multi-layer detachment folding structure and Wujiang fault-fold belt is characterized by detachment and left-lateral transpression structure.The tectonic deformation properties and types,decollement degree of the Longmaxi and Wufeng Formations,and layer-slipping structural fractures are the major tectonic factors controlling the shale gas play.

Vertical heterogeneity and its controlling factors of the gas shale in the Wufeng-Longmaxi Fms in Fuling area,the Sichuan Basin

Meng Zhiyong

2016, 37(6):  838-846.  doi:10.11743/ogg20160605

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The organic shales in the Lower Silurian Longmaxi Fm in Fuling area,the Sichuan Basin are proved to be shale gas reservoirs of high quality.Nevertheless,they have relatively strong vertical heterogeneity,directly influencing its gas content and reservoir fracability.An isochronal sequence stratigraphic framework is first established.Then,the heterogeneities of the shale are analyzed in respects of petrological and mineralogical compositions,the content of pyrite,sedimentary structures and organic matter abundance within this framework.The shales deposited during TST are characterized by authigenic siliceous minerals and pyrites of sedimentary origin,obvious lamellation,high TOC and special positive relationship between TOC and siliceous mineral content.The shales deposited in the early HST feature in the occurrence of terrigenous silts,small wavy lamination and lenticular bedding,higher clay content than that of TST,moderate TOC,and the existence of both authigenic and secondary pyrites.The shales deposited during the late HST feature in even higher clay content but lower silt content,low TOC and the existence of both authigenic and secondary pyrites.The factors influencing shale heterogeneity are discussed in respects of sedimentology,paleo-marine productivity and redox conditions and they mainly include the influx rate of terrestrial deposits,paleo-marine productivity,redox conditions and paleo-current.

A preliminary study on prospects for shale gas industry in China and relevant issues

Long Shengxiang, Cao Yan, Zhu Jie, Zhu Tong, Wang Feng

2016, 37(6):  847-853.  doi:10.11743/ogg20160606

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Shale gas exploration and development in China has been pushing forward in a rapid pace with breakthroughs achieved in several domains.A macro analysis of the state quo,basis,opportunities and challenges of shale gas industry in China also confirmed the breakthroughs and indicated a potential development of commercial scale.Compared with the history of shale gas industry in the US,we believe that the industry in China is now in an initial stage of rapid development.The distribution and quality of shale gas resources in the country infers that Sichuan Basin and its periphery areas with their resource potential for a gas productivity of tens of billion cubic meters are the near- and mid-term exploration targets.Shale gas exploration activities in the country show that technologies for an efficient and environmental-friendly development of shale gas buried in depth less than 3 500 meters are maturing.However,for gas buried deeper or in complex structures with low pressure and low abundance or in continental or transitional facies,the country still lacks of suitable technologies.We suggest that China adopt active strategies to develop core technologies during the 13th-Five-Year-Plan period so as to attain the goal of extracting 20 to 30 bcm of shale gas annually.To do this,we think it is necessary to further perform shale gas resources assessment and exploration target evaluation as well as shale gas engineering technology development.Meanwhile,environment issues shall also be addressed base on a scale benefit of the resource.

Features of paleogeomorphological evolution and its control on reef flat composite in Changxing-Feixianguan Formation in Jiange-Jiulongshan region,the Sichuan Basin

Chen Hui, Guo Haiyang, Xu Xiangkai, Zhang Benjian, Liang Hong, Wu Yulin

2016, 37(6):  854-861.  doi:10.11743/ogg20160607

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Utilizing core,well logging and 3D seismic data,technologies such as horizon flattening,section and attribute analysis were used to reconstruct the paleogeomorphology environments in Changxing and Feixianguan Formations' main sequence boundaries in Jiange and Jiulongshan districts,the Sichuan Basin.The features of paleogeomorphological evolution were investigated and their control on the reef flat were discussed.Results show that paleo topography of the area is featured by higher southwestern parts and dipping down to the Northeastern parts.The carbonate platform's constant progredation from southwest to northeast during the paleo-geomorphological evolution in the area leds to features such as marine regression,sediment filling into deep water during the periods of Changxing and Feixianguan deposition.The reef flat's favorable depo-center areas were also transferred in tune with the migration of paleo-landform's high belt and platform margin.The area around wells Lg68,Lg63 and Lg62 is an inherited paleogeomorphological high grounds,representing the most favorable place for the reef flat's vertical aggredation of Changxing and Feixianguan carbonates in the Jiange district.The major positive structure in Jiulongshan area is composed of Feixianguan formation's second section,which are a set of platform margin oolitic beaches superimposed one on another in transverse and overlaying fashion.It is also the most favorable area for development of oolitic beach in Feixianguan formation.

Hydrogeological-hydrogeochemical characteristics and hydrocarbon preservation conditions of the Qianbei Depression and its periphery,Upper Yangtze Block

Zhu Zhenhong, Lou Zhanghua, Jin Aimin, Zhang Runhe, Si Chunsong, Yao Genshun

2016, 37(6):  862-873.  doi:10.11743/ogg20160608

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The petroleum preservation conditions in the Qianbei depression and its periphery were studied based upon the analysis of groundwater hydrochemical and hydrodynamic characteristics.The results show that the Qianbei depression and its periphery experienced three hydrogeological cycles as follows:Caledonian epoch,Hercynian-Indosinian epoch,and Yanshan-Himalayan epoch.Caledonian epoch and Hercynian-Indosinian epoch are the two main periods of oil-gas reservoirs deposition,although these reservoirs were eroded almost completely during the period of Caledonian and Yanshan-Himalayan movements.The hydrocarbon preservation conditions of strata less than 2 500 meter depth below surface in the Qianzhong uplift and 3 000 meter depth below surface in the Qianbei depression are generally poor due to the multiple tectonic movements and meteoric water infiltrations.This zone with low mineralization formation water is named as free exchanging zone and its lower boundaries are still unclear.The strata deeper than 800 meter are regarded as an exchanging-inactive zone in the Chuannan depression and hydrocarbon preservation conditions thereby are relatively good.

Accumulation conditions and models of tight oil reservoirs in Chang-7 of Huaqing area,the Ordos Basin

Wu Weitao, Deng Jing, Zhao Jingzhou, Sun Bo, Guo Hanqin, Deng Xiuqin, Er Chuang, Bai Yubin

2016, 37(6):  874-881.  doi:10.11743/ogg20160609

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Based on drilling,mud logging,wireline logging,production test results,thin section observation and laboratory data,this paper focuses on a study on accumulation conditions,source rock qualities,migration-accumulation conditions of the Chang-7 tight oil reservoirs in Huaqing area,Erdos Basin.A tight oil pooling model is also established.The result shows that the reservoirs are mainly feldspar lithic sandstones with an average porosity of 7.4%,and an average permeability of 0.134×10^-3 μm².The reservoirs are also found to contain largely secondary dissolved nanopores (accounting for 70.6% of the total surface porosity) with radius mostly less than 1 μm.The best source rock of Chang-7 occurs in the third interval of Chang-7.It has an average TOC of 8.99%,obviously greater than that of its second (2.17%) and the first (1.12%) intervals.Its thickness ranges between 28 m and 36 m,while the total thickness of the first and the second intervals is between 35 m and 55 m.It has Ro values between 1.02% and 1.2%,clearly a type I kerogen and within the peak stage of hydrocarbon generation (the hydrocarbon generation capacity is up to 600×10⁴ t/km²).The migration pathway in Chang-7 is a three dimensional network carrier system consisting of horizontal fractures,oblique crossing fractures and sandbodies.The oblique crossing fractures on the source-reservoir interface are considered to be the primary pathways for the initially expulsed hydrocarbons.The migration is driven by an overpressure in the range from 15 MPa to 22 MPa caused by hydrocarbon generation.The tight oil reservoirs in Chang-7 include lithologic thinning-out type,lenticular type and diagenetic trap type and they are large in number and are laterally connected and vertically superposed,thus being quasi-continuous reservoirs.The source rock in the third interval of Chang-7 and the reservoirs in its first and second intervals constitute a lower-generation and upper-storage assemblage,and the source rocks and reservoirs within the first and second intervals of the Chang-7 form inner-source alternating assemblages.The two types of assemblages constitute a quasi-continuous type of reservoir-forming model with two-source hydrocarbon supply.

Burial,diagenesis, hydrocarbon charging evolution process and quantitative analysis of porosity evolution: A case study from He 8 tight sand gas reservoir of the Upper Paleozoic in Eastern Ordos Basin

Li Miao, Hou Yundong, Luo Jinglan, Chen Juanping, Luo Xiaorong, Jia Yani

2016, 37(6):  882-892.  doi:10.11743/ogg20160610

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Current researches about the evolution process of diagenesis-porosity,the burial-thermal history,and the hydrocarbon charging history of tight sandstone reservoirs are still in a static stage in China.Apparently,less attention has been paid to the relevance between hydrocarbon charging and tightening process caused by the petrological components of sandstones and its differential diagenetic evolution process.In order to better understanding the dynamic evolution history of burial-diagenesis-hydrocarbon charging-porosity of tight sandstone,samples from the 8^th Member of Xiashihezi Formation (He8) of the Upper Paleozoic in eastern Ordos Basin were studied in detail through the identification and quantitative statistics of cast sections,together with various analysis methods such as SEM,CL,homogenization temperature and chemical composition of fluid inclusions etc.Furthermore,the differences of the timing of densification process and hydrocarbon charging among different sandstone layers were discussed.The results indicate that the diagenesis-hydrocarbon charging evolution processes of both the calcium-cemented sandstone and high plastic lithic sandstone are relatively simple.The former became tightened after carbonate cementation in the stage A of middle diagenesis phase,which confirms that hydrocarbon charging was early than tightening; while the latter became tightened after compaction in the early diagenetic stage,which confirms that tightening occurred before hydrocarbon charging.In contrast,the quartz sandstone and lithic quartz sandstone are complicated in diagenetic-charging evolution process and their tighenging and hydrocarbon charging synchronous.

Characteristics of the Lower Cretaceous source rocks and shale gas exploration potential of eastern basin group,NE China

Meng Yuanlin, Shen Wanqi, Zhou Xingui, Li Shizhen, Wang Dandan, Zhang Wenhao, Qu Guohui, Cui Cunxiao

2016, 37(6):  893-902.  doi:10.11743/ogg20160611

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In order to study the characteristics of Lower Cretaceous source rocks and shale gas exploration potential of the eastern basin group in Northeast China,field sampling,geochemical analysis and rock-mineral tests of source rocks were performed and geochemical parameters were measured in the Sanjiang Basin,Jixi Basin,Tonghua Basin,Liuhe Basin and Hongmiaozi Basin.The results indicate that the abundance and type of organic matter in the Lower Cretaceous source rocks are mainly controlled by sedimentary facies,while the maturity of source rocks is influenced by the depth of Moho surface.The Lower Cretaceous source rocks in the north of the study area were deposited in shallow water environment that results in large cumulative thickness of mudstones and higher silt content.These source rocks contain type Ⅱ₂ kerogen and Ⅲ kerogen and are graded as poor-moderate source rocks at mature to over-mature stages.The Lower Cretaceous source rocks in the south of the study area were deposited in deeper water environment that results in thick mudstone deposition (with thickness of 233 m to 446 m) and high organic content.These source rocks mainly contain type Ⅰ-Ⅱ₂ kerogen at low-mature to mature stages.Moreover,the Lower Cretaceous hydrocarbon source rocks are characterized by high content of brittle minerals,important content for development of pores and fractures between clay minerals,intergranular pores as well as organic pores with pore throat structure of micro- and meso-pore.Therefore,there exists favorable exploration prospects for both conventional hydrocarbon and shale gas in Lower Cretaceous of eastern basin group in Northeast China.

Sedimentary evolution and distribution of sand bodies of retrogradational shallow-water delta: A case study from 4^th member of the Cretaceous Quantou Formation in the Lingjiang area,Songliao Basin

Cai Quansheng, Hu Mingyi, Hu Zhonggui, Yang Jingjing, Yue Xin, Qiu Xiaosong

2016, 37(6):  903-914.  doi:10.11743/ogg20160612

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Sedimentary sand bodies of shallow-water delta has become one of the main target areas of the current exploration.Thus a further study on sedimentary evolution and distribution of sand bodies of shallow-water delta should be of great importance for exploration.The 4^th member of Cretaceous Quantou Formation in Linjiang area provides an interesting example to study sedimentary evolution and distribution of sand bodies of shallow-water delta during the stage of lake transgression in detail.The work is based both on previous research and on a combination of cores,well logging and seismic data.The results show that delta plain and delta front are still the main component of retrogradational shallow-water delta,whose sediment grain size becomes gradually finer upwards,and the color of mudstone component shifts from aubergine to celadon controlled by short-term fluctuation of sedimentary water.With rise of lake water level,sedimentary facies boundaries moved quickly towards land.However,this movement is superimposed by multiple shorter-term fluctuations of lake level and bi-directional migration of facies boundary,and the channel sandstones can form quite some distance away from lake shore.As the main type of sand bodies of retrogradational shallow-water delta,the size of channel sandstone reduced gradually during lake transgression,showing increasing thinning of sand thickness upwards.The channels terminate as distributary sheet sands,reformed by infra-littoral wave.On the plane view,the cycles of channel development become fewer from proximal to distal.Channel sandstone of delta plain and nearshore delta front,which mainly developed before large-scale lake transgression,is favorable targets for oil-gas exploration.

Characterization of the pore space in tight sandstone reservoirs from macroscopic and microscopic perspectives: A case study of Gaotaizi reservoir in Qijia area,the Songliao Basin

Li Yilin, Zhang Yunfeng, Yin Shuli, Cong Lin, Yan Ming, Tian Xiaoxiong

2016, 37(6):  915-922.  doi:10.11743/ogg20160613

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Comprehensive analyses are conducted to characterize the Gaotaizi tight reservoir in Qijia area from macroscopic and microscopic perspectives,through Nano Micron CT,automatic mineral identification system (QEMSCAN),MAPS image mosaic technology,and environmental scanning electron microscopy (ESEM).From the macroscopic perspective,lithologies are mainly siltstone and argillaceous siltstone.The sedimentary bedding structures are diversified-massive bedding are the majority but cross-bedding,wedge bedding and lenticular bedding are also present.The obvious sand-shale interlayer and complicated sedimentary beddings commonly contribute to the heterogeneity of the tight reservoirs,even though the massive bedding is the most favorable for the enrichment of tight oil.The microscopic perspective reveals more interesting characteristics.Pores are continuously distributed in the micro to nano meter level,with the peak of micro pore sizes concentrated in the range of 2-3 μm,and that of nano pores around 200-300 nm.Microscopic heterogeneity can be obviously displayed in the pore-throat spatial distribution and connectivity features of different 3D modeling areas.The main pore spaces are intergranular dissolved pore,intragranular dissolved pore and micro cracks.Moreover,high porosity generally corresponds to high concentration of organic acids,indicating the controlling of porosity by dissolution.

Controlling effect of fine-grained sedimentary microfacies upon the microstructure of shale oil reservoirs in the Dongying Sag,Bohai Bay Basin

Zhang Shun, Wang Yongshi, Liu Huimin, Chen Shiyue, Tan Mingyou, Zhang Yunyin, Hao Xuefeng, Xie Zhonghuai

2016, 37(6):  923-934.  doi:10.11743/ogg20160614

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Shale samples from the lower third member of the Shahejie Formation of the Palaeogene in Dongying Sag were taken for a sedimentation characterization,a classification of lithologic facies and microfacies and an analysis of planar and vertical distributions of the shales of semi-deep and deep lacustrine facies through a centimeter-scale core description,thin section identification and X-ray diffraction analyses of the samples.Such means as observations of SEM images and laser confocal microscope and experiments of low-temperature nitrogen adsorption were also resorted to study the genesis,types,morphology,size and distribution of pores and fissures in the samples.The results show various types of minerals and the fine-grained sediments being regarded previously as high-quality source rocks are largely carbonates.It also indicates that there are various pore and fissure types and the pores are of multi-scales and have complicated structures.The shale reservoirs with different types of microfacies differ in micro-structures.The controlling effect of sedimentary microfacies upon the micro-structure of reservoirs is mainly displayed in compositions and fabric of minerals,and deposition and preservation of organic matters,which further affect the types and structures of pores.The shale reservoirs developed in flat and semi-deep lacustrine facies are found to contain high content of organic matters,various types of rocks and brittle minerals dominated by calcite.They also harbor pores and fissures of various types.With fairly connected open pores,the reservoirs are considered to be potential exploration targets in the sag.

Influences of hydrocarbon charging and overpressure on reservoir porosity in Kela-2 gas field of the Kuqa Depression,Tarim Basin

Guo Xiaowen, Liu Keyu, Song Yan, Zhao Mengjun, Liu Shaobo, Zhuo Qinggong, Lu Xuesong

2016, 37(6):  935-943.  doi:10.11743/ogg20160615

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In order to investigate the factors controlling reservoir porosity in the Kela-2 gas field of the Kuqa Depression,Tarim Basin,the sandstone reservoir characteristics,the origin of overpressure,as well as the evolution of the reservoir charging history were studied by using quantitative grain fluorescence and fluid inclusion data.The research results indicate that horizontal tectonic compression played an important role in the overpressure generation in the Kela-2 gas field.The overpressured presalt sandstone reservoirs with the maximum paleoburial depth over 6 000 m have anomalously high primary porosities.The reason is that the cementation of the sandstone was influenced and even undercompaction occurred as the oil charged into the sandstone reservoirs was not expelled under the efective sealing of salt and gypsum cap rocks in the Kela-2 gas field.This is evidenced by that sandstone reservoirs with high intensities of Quantitative Grain Fluorescence (QGF) and QGF on extract (QGF-E) are associated with high porosity and permeability intervals,and sandstone units below the ancient oil-water contact have low porosity and permeability.Late oil charging occurred at the early period of the Kuqa Formation deposition and the corresponding sandstone reservoirs in the Kela-2 gas field had shallower burial depth and high primary porosities.This research suggests that the oil charging and overpressure played important roles in the development of reservoirs porosity.

Influence of tectonic movement on Cretaceous carbonate reservoirs in the Zagros Foreland Basin: A case study of Y oilfield

Tang Ying, Fan Tailiang, Zhang Tao, Wang Zhe, Zheng Yuanchao

2016, 37(6):  944-951.  doi:10.11743/ogg20160616

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On the basis of drilling cores,thin sections,imaging logging and 3D seismic data,the study discusses the effects of tectonic movement on diagenesis,fractures development and hydrothermal fluid activities of carbonate reservoirs in Y oilfield of the northeastern Zagros Foreland Basin.Tectonic movements from the late Cretaceous to the Holocene have most significant effect on the Cretaceous carbonate reservoirs in Y oilfield.During this period,because of compressional uplift,target strata were heavily eroded and weathered,which leads to development of an unconformity surface.Reservoirs below the surface suffered from severe dissolution.With the collision between Arabian plate and the Eurasian plate,and resultant folding and thrusting induced formation of fractures within reservoirs.Density and location of fractures were influenced by the intensity of folding and faulting,but also related to lithology.Fractures were mainly developed in the area around faults,and along fold axis or the lower end of fold limbs.In terms of lithology,fracture density in dolomite is obviously higher than that in limestone.Tectonic movements also controlled the hydrothermal fluid activities in Y oilfield.The faults are the main pathways of hydrothermal fluid into Y oilfield.Hydrothermal dolomitization occurred in grabens close to faults or fracture zones.Discussing the influence of tectonic movements on carbonate reservoir is beneficial for predicting and locating high-quality reservoirs in the study area,and optimizing production deployment of the oilfield.

Characteristics of different types of glauconite and their classification systems

Zhang Qin, Mei Xiaohan, Xie Yinfu, Wang Quanxin, Li Chenxi, Yang Xiaofa, Du Huiyao, Lu Jiajing

2016, 37(6):  952-963.  doi:10.11743/ogg20160617

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Origin and classification of glauconite,a typical kind of sedimentary facies indicator,have long been the hot topics of mineralogy and sedimentology.This paper investigates the characteristics of autochthonous,parautochthonous and allochthonous glauconite,and documents its classification systems and genesis based on previous researches on the genesis of glauconite and a large number of case studies of glauconite worldwide.Several hypotheses have been proposed to interpret the genesis of autochthonous glauconite.The results suggest that the grain verdissement and pseudomorphic replacement hypotheses are applicable for the interpretation of the genesis of granular and autochthonous glauconite in the microscopic pores of shale,but are inapplicable for the interpretation of the formation of glauconite cement in intergranular pores in sandstones.Different types of glauconite show significant differences in elemental composition,maturity,morpho-logy and hosting environment.Autochthonous glauconite tends to accumulate in a thin layer of condensed section,and shows high maturity.Its element-composition features,thus,are symptomatic of depositional environment.Parautoch-thonous glauconite is characterized by multi-stage involucrums.Detrital glauconite generally accumulates in sandstones with large-scale bedding structure,and is commonly oval or granular.Its element-composition features cannot be used as the indicators of sedimentary environments.New classification systems are proposed to replace the current confused classification systems of glauconite.The glauconites are divided into "primary" vs."secondary" classes and "autochthonous" vs."allochthonous" categories,according to two main criteria (i.e.,genesis and whether removing from the initial formation place).An authigenic precipitation and cementation theory is proposed to interpret the genesis of glauconite that shows shapes of cement,halo edge and involucrum.Moreover,the existence of the authigenic glauconite cement is proved by a large number of case studies.Glauconite,therefore,plays a significant role in diagnosis sedimentary environment,rock dating and improving reservoir physical properties.

Calibration method of shale petrological facies and its application in Fuling area,the Sichuan Basin

Peng Yongmin, Long Shengxiang, Hu Zongquan, Du Wei, Gu Zhixiang, Fang Yu

2016, 37(6):  964-970.  doi:10.11743/ogg20160618

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Petrological facies calibrations were performed on shale of horizontal wells in Fuling,Sichuan Basin,based on geological and well-logging characteristic marks,and specialized petrological facies.In accordance with the three key marks (lithological combination,calcareous content and siliceous content),the whole set of 89-meter-thick shale interval in the typical pilot wells of the Lower Silurian Longmaxi Formation in Fuling were divided into nine different types of petrological facies.The No 1,3 and 6 petrological facies were identified as specialized petrological facies based on geological marks like marker beds,carbon dyes and silty laminae as well as logging marks such as logging response anomaly,the types of logging curve shape,excavation effect and pseudo excavation effect.We compared the results of projected well-logging information through horizontal section-based vertical projection with characteristic marks and specialized petrological facies in typical pilot wells to determine the top and bottom boundaries of the petrological facies and accomplished the calibrations.The relationship between petrological facies and the post-fracturing tested productivity was used to identify the petrological facies in prolific horizontal wells.It was found that the petrological facies with high calcareous and silica contents (No.1 and 3 facies with) have the greatest productivity potential,thus were determined to be the best petrological facies.Based on the principle of the best petrological facies,we suggest the best trajectory of horizontal well or landing point of target window be between the No.1 and 3 facies.Application of the calibration method to Fuling shale gas field were positive,with the coincidence rate between the predicted and tested productivities being more than 80%,proving it a potential method for optimizing well trajectory design and increasing single-well production.

Shale brittleness prediction based on elastic parameters of VTI media

Xu Tianji, Cheng Bingjie, Hu Bin, Jiang Yingying, Tiang Jianming

2016, 37(6):  971-978.  doi:10.11743/ogg20160619

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Numerous studies show that shale brittleness has great influences on the anisotropy,pooling capacity,permeability and fracability of oil and gas reservoirs,thus making the prediction of shale brittleness one of the hot spots in shale gas reservoirs evaluation.Lab analyses also confirmed a close relationship between shale brittleness and several factors like the mineral content and the pore structure that affect mechanical properties of shale rocks.Rickman et al (2008) proposed a method for brittleness coefficient calculation based on elastic parameters.The method combined Young's modulus and the Poisson ratio-two mechanical parameters that can only be calculated with an assumption that the reservoirs in concern are isotropous.Therefore,the method can not accurately describe the brittleness of complex media.To deal with the problem,we introduced the elastic parameter calculation method of VTI media proposed by Thomsen (2013),and developed a brittleness calculation formula comprised of anisotropic parameters ε,γ and δ.Theoretically,the formulat links shale brittleness to anisotropy and offered a better way for anisotropic characterization of shale rocks.Application of the method to the study of the 5^th member of the Xujiahe Formation in Xinchang-Xiaoquan gas field of Sichuan Basin indicated that shale reservoirs in areas with abnormally high brittleness coefficients have strong brittleness,thus it can be used to better identify "brittle sweet spots" within "geologic sweet spots".The brittleness prediction results coincide well with the drilling results of the only two shale gas wells.

An quantitative evaluation method of probability for diversion flow oil and gas laterally from faults to sand bodies: A case study from Leave Chu Structure in the Raoyang Sag,Bohai Bay Basin

Wang Wei, Sun Tongwen, Cao Lanzhu, Lyu Yanfan, Fu Guang, Lu Xiuqin, Deng Wei, Zhang Huan

2016, 37(6):  979-989.  doi:10.11743/ogg20160620

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In hydrocarbon exploration,it is very important to identify the dominant strata for oil and gas lateral charge after vertical migration,but there is few effective evaluation method.This paper took Leave Chu area of the Raoyang Sag in the Bohai Bay Basin as an example.On the basis of comprehensive analysis on factors influencing oil and gas lateral diversion probability,such as caprock thickness and contact area between faults and sand bodies,evaluation methods of influence factors were established by using reservoir seismic inversion.Correlation between percentage of trap-filling and various selected factors was systematically analyzed to build quantitative evaluation equation for fault-sand lateral diversion probability.The results show that when fault-sand lateral diversion factor R>0.3,oil and gas lateral diversion initiates.A positive correlation between the R and percentage of trap-filling is observed.Moreover,when R>0.9,reservoirs are fully charged net pay zone.The factor R is applied to the faults f038 and f008,and the results are in good agreement with drilling data.

Risk-value assessment of existing overseas exploration projects

Ji Zhifeng, Li Fuheng, Pan Xiaohua, Shi Lei, Wu Yiping, Hou Ping, Luo Dongkun, Guo Rui, Yang Zi

2016, 37(6):  990-996.  doi:10.11743/ogg20160621

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Despite a great progress has been achieved in overseas business in recent years,Chinese oil companies have been facing problems in recovering their exploration investments.The situation has been exacerbated by falling oil price started in mid 2014.It seems that the companies are in an urgent need of a risk-value assessment method for their overseas exploration projects so as to avoid investment losses and improve exploration deployment.There are many risks in the operation of the existing exploration projects,including internal risks,namely geological risk and exploration technology risk,and external risks,like political risk,security risk in host country of the resources,and contract risk from the project itself.The risk-value assessment method proposed here focuses on the resource potential of the exploration projects concerned,with consideration of both the internal and external risks.Four types of project characteristics combinations,including low risk-low value projects,low risk-high value projects,high risk-low value projects and high risk-high value projects,are also proposed before putting forward a strategy and suggestion for optimizing exploration business.The merits of the method have been verified through applications in controlling project risks,adding reserves,and implementing economic targets.It is also proven useful in optimization of exploration assets and business deployment.