Table of Content

08 June 2015, Volume 36 Issue 3

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Characteristics and development practice of fault-karst carbonate reservoirs in Tahe area,Tarim Basin

Lu Xinbian, Hu Wenge, Wang Yan, Li Xinhua, Li Tao, Lyu Yanping, He Xinming, Yang Debin

2015, 36(3):  347-355.  doi:10.11743/ogg20150301

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Various irregular fractured-vuggy reservoirs were formed along the large fault-karst belts in the area covered by the Upper Ordovician in Tahe area due to multi-phase tectonic deformations and karstifications of the carbonates.Using fine coherence, amplitude change rate, time slice and other properties of high-precision three-dimensional seismic, outcrops, drilling and production data, this paper first presented a theoretical concept of fault-karst trap, and elaborated its forming mechanism and geologic characteristics in this area.The fault-karst reservoirs can be divided into three types by their shapes and controlling factors:banded, sandwich and tabular reservoirs.According to recent development practices, the fault-karst reservoir is a very special reservoir type in this area.The development effectiveness of different fault-karst carbonate reservoirs is quite dissimilar, with the banded ones being the best in development performance.It is of great significance for the petroleum exploration and development of similar reservoirs in the Tarim Basin.

Reservoir-forming characteristics of stratigraphic and lithologic reservoir in Chunguang oilfield,western margin of Junggar Basin

Chen Xiang, Wang Ming, Wang Yong, Ding Jieying, Zhai Jingtian

2015, 36(3):  356-361.  doi:10.11743/ogg20150302

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The Chunguang oilfield is located in a simple structure named Chepaizi slope zone in western margin of Juggar Basin, northwestern China.The reservoirs are mainly stratigraphic and lithologic type of outside hydrocarbon source.The Neogene Shawan Formation, Paleogene, and Cretaceous, are all the exploration targets.Analyses of depositional characteristics show that the Shawan Formation developed mainly alluvial fan and braided river depositional system, the Paleogene and the Cretaceous grew braided river delta sedimentary system.A study based on semdimentary features of the area had been carried out to answer questions concerning on reservoiring conditions.Analyses of oil-source correlation show that the Changji sag in the east and Sikeshou sag in the south of the area had the potential to provide hydrocarbon and their Jurassic and Permian formaiotns were the major hydrocarbon-generating ‘factories'.Migration pathways for hydrocarbon were regarded as the major controlling factor for the reservoiring of oil in the area.Three relevent elements had been thoroughly studied(unconformity, sand sheet and fault).The result indicates the existence of a highly efficient pathway system.A hydrocarbon migration pattern was established for the area based on the study.Reserveroi features analyses of the area were used to determine the major controlling factors, establish of reservoring model and guide the exploration.

Hydrocarbon accumulation mechanism and play fairways of the Paleogene in Lunpola Basin,Tibet

Fan Xiaojun, Pan Lei, Li Feng, Li Jixuan, Hou Donglin, Hao Jingyu

2015, 36(3):  362-369,377.  doi:10.11743/ogg20150303

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Early exploration in Lunpola Basin shows a good exploration potential within the Paleogene Eocene Niubao and Dingqinghu Formations.However, most of the single well test results are low.The poor understanding of hydrocarbon accumulation mechanisms and their main controlling factors affects the early exploration.In order to clarify the accumulation mechanisms and predict play fairways, a comprehensive study was performed by integrating the geological and geophysical data.It is believed that Lunpola Basin has many good reservoir forming conditions such as multiple sets of fan delta front sandstone systems, favorable source-reservoir-cap rock assemblage, inherited palaeohigh(ancient slope), ste-reoscopic carrier systems and good timing of structure and hydrocarbon accumulation.Hydrocarbon accumulation in Lunpola Basin features in close proximity to the source rocks, multi periods of charging, damage of reservoirs with mid-shallow depth in late stage, in-situ enrichment of hydrocarbons in middle-deep layers.Six play fairways are identified in Lunpola Basin, their resource potential is estimated to be up to several hundred million tons based on calculation with the organic carbon method, and the resource abundance is relatively high, thus it has the potential to form mid-sized oil field.Especially, the Changshan litho-logic play has very favorable reservoir forming conditions and its resource potential is estimated to be up to 100 million tons.In addition, the oil shale is developed in the middle and lower Dingqinghu Formation within the play and its resource volume is three times as large as that of the conventional resources based on calculation with volume abundance method.As a whole, conventional and unconventional plays overlap in the Changshan lithologic zone, thus its exploration potential is huge.

Geochemical characteristics and accumulation models of different genetic types of natural gas in the Fangzheng Fault Depression

Liu Bo, Lu Jun, Lyu Yanfang, Fu Guang, Wang Shihui, Jin Wei

2015, 36(3):  370-377.  doi:10.11743/ogg20150304

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Because of the complicated genetic types of gas, accurate identification of the sources of the nature gas has great significance to gas exploration in the Fangzheng Fault Depression.First, the genetic types of natural gas were classified based on the gas components, alkane carbon isotopes and in combination with the actual geological conditions.Then, the thermal maturity of gas was correlated with source rocks in different tectonic units to reveal the gas sources based on identification of organic types and thermal evolution degree. The results show that the gas of this area can be divided into three types.Type A is dry gas and its genetic type is catalytic transitional zone gas generated by lacustrine mudstone in the Xin'ancun-Wuyun Formations.Type B is wet gas and its genetic type is thermal coal-related gas generated by coal measure mudstones.Type C is also wet gas and its genetic type is petroliferous gas generated partly by humic organic ma-tter.It is associated with the oil generated by humic organic matters and is of hybrid sources.Differential structural activity on two sides of Yihantong fault is the main factor leading to the different geochemical characteristics and accumulation patterns of natural gas between the east and west sags.

Timing of hydrocarbon accumulation of the Paleozoic reservoir in Rub Al Khali Basin

Zheng Lei, Jin Zhijun, Zhou Jin, Lu Xueyan, Liu Zhiqiang, Javed Ismail, Li Yanhua

2015, 36(3):  378-384.  doi:10.11743/ogg20150305

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In order to determine the main stages of the hydrocarbon accumulation of the Paleozoic reservoir in Rub Al Khali Basin, four key methods are applied in this paper including hydrocarbon generation and expulsion history simulation, measurements of fluid inclusions homogenization temperature and Illite K-Ar dating.The simulation of hydrocarbon generation and expulsion history of Well S2 shows that hydrocarbon generation and expulsion of the Silurian source rocks in the central depression peaked in the Triassic and Cretaceous.The simulation of hydrocarbon generation and expulsion history of Well A2 shows that the hydrocarbon generation and expulsion of the Silurian source rocks in the slope zone peaked in the Early Cretaceous.The analysis of homogenization temperature of fluid inclusions of Well S2 shows that most of the samples can be divided into two main stages and only some samples can be divided into three stages.In combination with the geothermal history, these three stages are the Triassic, Early Cretaceous and Late Cretaceous respectively.In contrast, the homogenization temperature of fluid inclusions of Well S2 in the slope zone can be separated into two stages, indicating that at least two periods of oil and gas charging occurred in the Ordovician.In combination with the geothermal history, the two periods are in the Early Cretaceous and Late Cretaceous respectively.The result of Illite K-Ar dating shows that the hydrocarbon accumulation in the Paleozoic of Well S2 in the central depression occurred mainly in the Triassic and Late Jurassic-Early Cretaceous.A comprehensive analysis indicates that the hydrocarbon accumulation of the Paleozoic reservoir in Rub Al Khali Basin mainly occurred in three periods.The first one is the Triassic, the second one is the Early Cretaceous and the last one is the Late Cretaceous.The hydrocarbon accumulations formed in the first stage are mainly distributed in the central depression, and that in the third stage are mainly distributed in the slope zone, and that in the second stage occurred in both the central depression and slope zone.

Sedimentary basin evolution and hydrocarbon accumulation conditions in Cuba

Chen Rong, Wu Chaodong, Shen Yanping

2015, 36(3):  385-392.  doi:10.11743/ogg20150306

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This paper compared the evolution and petroleum geological conditions of the foreland basin in northern Cuba and the basin in central Cuba based on the evolution history and paleogeography setting of the Cuba islands.The Meso-Cenozoic arc-continent collision of northern boundary of Caribbean Plate is thought to be the key factor controlling the oil and gas accumulation in Cuba.High quality source rocks were developed in Cuba islands and its surrounding platforms during the Late Jurassic rifting and the Cretaceous passive continental margin periods.The distribution of the source rocks was controlled by the paleogeography setting.The reservoir-cap rock assemblages were controlled by the collision between the Caribbean plate and North America plate in the Late Cretaceous-Paleocene.The effective regional cap rock was an important condition for oil accumulation in the foreland basin of northern Cuba.At the end of Cretaceous, the thrust of the Caribbean Arc over the North America plate promoted the maturation of the source rocks.The large thrust fault zone and faults resulted from arc-continent collision provided the pathways for hydrocarbon migrating to and accumulating in the reservoirs such as the fractured Jurassic-Cretaceous carbonates, fractured volcanic rocks, pyroclastic rock and Paleocene sandstone, leading to the formation of structural, stratigraphic, lithological and composite reservoirs.

A study on the genetic model of hydrothermal dolomitization in Taq Taq oilfield, Kurdistan region,Iraq—taking oilfield A in the Cretaceous in Zagros Basin as an example

Zhang Tao, Su Yushan, She Gang, Ahemaitijiang, Zhang Demin

2015, 36(3):  393-401.  doi:10.11743/ogg20150307

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Based on core petrographic description, fracture statistics, comprehensive interpretation of seismic and logging data, analogues with other confirmed examples, this paper analyzed the identification marks, development timing, genetic model and distribution of the hydrothermal dolomitization and its alteration on the reservoir quality, so as to analyze the abnormal distribution of dolomite in the Kometan Formation of the Cretaceous oilfield A in Zagros Basin.The most part of Kometan Formation and the lower part of the Shiranish Formation in two wells were altered by hydrothermal dolomitization.The matrix limestone there was replaced by hydrothermal flow with the crystal intergrowth, half automorphic, and coarse grain dolomite.Early extensional fractures were filled with saddle dolomite and anhydrite.Celestine-saddle dolomite-anhydrite is the main hydrothermal mineral assemblage and can be used to identify the hydrothermal origin.The hydrothermal dolomitization preferentially flow upwards along the extensional and transtensional fault systems, where dolomitization mainly occurs on the hanging walls(graben)and extends laterally in the porous and permeable layers.In this case, the geometry of altered rocks was with stratification, the limestone strata near the fractured zone were also altered by hydrothermal dolomitization which display great irregularity. The alteration of hydrothermal dolomitization on reservoir is complicated.The dolostone formed along the main fault has lower matrix porosity than dolomite a little far from main faults, because over-dolomitization usually happened in the position with more active hydrothermal fluid flow.Local reservoir quality is obviously improved with matrix porosity of about 6%.The dolomite is generally more fractured than the limestone, so dolomitization has greatly increased the fracture density and improve the flow capacity of the reservoir.This study is significant for reservoir modeling and production strategies.

Reconstruction effect of the Ordovician hydrothermal dissolution fluid on interior dolomite reservoirs in Maigaiti slope,Tarim Basin

Tian Lei, Cui Haifeng, Feng Xiaojun, Zhang Nianchun, Liu Jun

2015, 36(3):  402-408.  doi:10.11743/ogg20150308

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High-quality hydrothermal karst reservoirs are well developed in the Ordovician dolomite of Maigaiti slope in Tarim Basin.The reservoirs feature in karst fractures and cavities filled with saddle dolomite and hydrothermal minerals such as quartz, pyrite, celestineand siliceous and etc., and their physical properties were greatly improved by inter-crystal pores and dissolved pores formed during hydrothermal karst activities.Analyses of faults in the research area were combined with drilling data to study faulting activities associated with deep hydrothermal fluids and their effect on the transformation of dolomite reservoirs and characterize hydrothermol fluid on profiles.The results show that multi-staged deep and giant fault zones like Qunkuqiake fault zone, Mazatage fault zone and Madong thrust belt in the research area, were perfect places for hydrothermal fluid activities.Areas far from the fault zones and small extentional strike-slip faults may serve as the pathways for the fluids to flow by, and dolomite reservoirs presented themselves as a string of beads on seismic profiles and widely-distributed dots on the plane.Based on the above observation and reservoirsing conditions of the area, we suggest that the dolomite reservoirs in Qunkuqiake fault zone have the potential to be practical exploration targets and widely-distributed dolomite reservoirs controlled by tensional-shear faults in the area shall also be future exploration targets.

Carbonate reservoir characteristics of the Creataceous Sarvak Formation in southwestern Zagros Basin,Iran

Yan Jianping, Sima Liqiang, Tan Xuequn, Zhang Wencai, Liang Qiang, Yan Yu

2015, 36(3):  409-415.  doi:10.11743/ogg20150309

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In order to reveal the characteristics of the Cretaceous Sarvak Formation carbonate reservoir in the southwestern Zagros Basin, a comprehensive study was carried out by integrating the core, thin section, production test and well log data.Analyses of the reservoir rock types, reservoir space, physical property, electrical property and the factors influencing pore development show that the lithology types of the Sarvak reservoir includes chalky limestone, dolomitic limestone and grainstone.And the reservoir spaces are dominated by secondary dissolved pores and mold pores.The physical property of grainstone is the best.The chalk in chalky limestone is mainly planktonic foraminifera which have well-developed porosity.Generally, the oil-bearing property enhances with the improvement of physical property.The diagenesis also have great impact on reservoir's physical property, and the constructive diagenesis include dissolution, dolomitization, biological disturbance, stylolites of pressolution origin.The physical property of packstone and wackestone are greatly improved under the influences of these constructive diageneses.Microscopically, the development of reservoir's pore is mainly controlled by facies and diagenesis.Laterally, it is also related to tectonic location and sedimentary environment.The physical pro-perty of platform shoal microfacies on structural high is commonly better.The vertical logging response and the areal distribution of physical property of sublayers can be used to identify zones with better physical property and oil-bearing abundance, thus providing a basis for highly productive reservoirs.

Characteristics and origin of the Upper Sinian microbial carbonate reservoirs at the northwestern margin of Tarim Basin

Li Pengwei, Luo Ping, Chen Min, Song Jinmin, Jin Tingfu, Wang Guoqian

2015, 36(3):  416-428.  doi:10.11743/ogg20150310

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Through outcrop observation, thin section examination and physical property analysis, this paper studied the petrological and reservoir characteristics of the Upper Sinian microbial carbonates on the Shiairike section at the northwestern margin of the Tarim Basin and briefly discussed the origin of the microbial carbonate reservoirs.The microbial carbonates are dominated by microbial dolomites, accounting for 70.37% of the whole Sinian carbonates.Based on having stromatilithic structure or not, the microbial carbonates are divided into stromatolites and non-stromatolites.The stomatolites include stratiform, domal and small isolate columnar types, with the stratiform stromatolites as the main type and pelletoid and micritic lamination as their texture characteristics.In contrast, the non-stromatolites include non-stromatolic cynobactiarial pellet rock and cyanobacterial foam spongy rock, featuring in pelletoid and foam sponge textures.According to physical property, the Sinian microbial carbonate reservoir can be divided into two intervals, with the upper interval being better than the lower.Among the microbial carbonates, the stratiform stromatolites and non-stromatolitic cyanobacterial dolostones especially with foam sponge-like texture are the favorable reservoir rocks.The reservoirs are characterized by fenestal, pellet-associated, foam sponge-associated dissolved porosity as their main reservoir space.The formation and distribution of the microbial carbonate reservoirs are mainly controlled by microfabrics, dolomatization and dissolution.Of these influencing factors, the microfabicsisthe fundamental factor determining the types of the pore space and their texture;the dolomization and dissolution are the critical factors determining the formation of effective pore space.The higher quality of the upper microbial carbonate reservoirs is also attributed to the epigenetic kastification.

High resolution sequence stratigraphy of XingⅠ Formation in the Du 84 Block,Shu 1 area,Western Sag of Liaohe Depression

Wu Jun, Fan Tailiang, Liu Huiying, Gao Zhiqian

2015, 36(3):  429-436,446.  doi:10.11743/ogg20150311

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In order to demonstrate the characteristics of high resolution sequence stratigraphy of XingⅠ Formation in the Du 84 Block, cores and logging data were applied to conduct the research on the sequence boundaries reorganization, sequence analysis on single well profile and cross-well profiles of cored wells, interpretation of different level cycle types.We establish the chronostratigraphic sequence framework in the study area.One long-term sequence cycle(LSC1)and two mid-term sequence cycles(MSC1-MSC2)are identified according to unconformity, scour surface and flooding surface.Meanwhile, four short-term sequence cycles(SSC1-SSC4)are further identified according to the sedimentary transformation surfaces and rhythm conversion surfaces.These SSC are subdivided into three basic types and 7 sub-types according to the stacking patterns of cycles of various levels, planar and spatial distribution of sedimentary facies.The three basic types are deepening upward nonsymmetric type(typeA), shallowing upward nonsymmetric type(type B)and symmetric type(type C).Type A mainly develops in the MSC and LSC.And the type C develops in the SSC2.The strata in the whole basin belong to retrograding sequences formed during expansion of lake basin, featuring in multi-cycle mostly having only ascending half cycle and zonation in plane distribution during the SSC.The reservoir sands are best deve-loped at the bottom of the ascending half cycle(SSC1-SSC2).They consist of stacked underwater distributary channel sand bodies of different periods, and have good reservoir property, thus are the main targets of remaining oil potential tapping in the future.

Sequence stratigraphy and depositional system of the Baiyanghe Formation in the Laojunmiao structural belt,Yumen oilfield,Jiuxi Basin,Northwest China

Yu Chen, Wu Shenhe, Du Wenbo, Yue Dali, Chen Cheng, Qin Guoshen

2015, 36(3):  437-446.  doi:10.11743/ogg20150312

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Sequence-stratigraphic and sedimentologic theories and methods were employed in the study of sequence stratigraphic features and sedimentary system distributions in the Baiyanghe Formaiton of the Laojunmiao structural belt in Yumen oilfield, Jiuxi Basin, northwestern China.Data gathered through core and outsrrop observation and analyses, drilling and logging, and sesimic events, were resorted to establish sequence stratigraphic framework, determine the types and distribution of sedimenatry facies, and understand evolution pattern and controlling factors in the Formation.The result shows that the Formation can be described as a complete three-order sequence, which can be divided into 7 quasi-sequence sets.Sedimentary facies including alluvial fans, braided rivers, braided river deltas and lake depostis, were recognized in the sequence.Depositional facies varied vertically from alluvial fans to braided river delta and then to lake flooding mudstone and finally to delta.Horizontally, the facies presents itself as a near southeast-northwest sedimenatry system-a sedimentary sequence of water transgression and regression.Paleogeomorphology controlled the distribution of the sediments of lowstand system tract of the three-order sequence and climate affected the types of sediments and controlled the superimposed style and evolution pattern of the sediment in the Formation.

Reservoir characteristics and influences on poroperm characteristics of the Lower Cretaceous fan-delta facies in Chagan Depression

Wei Wei, Zhu Xiaomin, Tan Mingxuan, Guo Dianbin, Su Hui, Zhao Qilei, Jiang Feihu

2015, 36(3):  447-455.  doi:10.11743/ogg20150313

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In order to reveal the reservoir characteristics and their influences on poroperm characteristics of the Lower Cretaceous in Chagan Depression, core, thin-section, and reservoir analysis data were utilized to research the petrological characteristics, sedimentation and diagenesis of the reservoirs.The results show that the sandbodies of fan-delta facies in the Lower Cretaceous consist of lithicarkose and feldspathic litharenite with low compositional maturity, low maturity structure and high cement content, which are originated from proximal and rapid accumulation.The reservoir is relatively tight as a whole and is of ultra-low porosity and permeability reservoir type(with average porosity of 6.3% and permeability of 7.78×10^-3 μm²).Thin-tiny throats are well developed and the reservoir spaces are dominated by residual primary and dissolved intergranular pores, and their development are controlled by particle size, compaction, cementation, content of carbonate and the origin of organic acid.The favorable reservoir is mainly distributed in the sandstones(conglomerates)of the subaqueous distributary channel of fan delta front, followed by fine sandstones in sand sheet and mouth bar.Vertically, the secondary porosity zone is mainly developed in the depth interval of 2 100-2 800 m, which corresponds to the maturity stage of organic matters.The mature organic matter released large amount of organic acid which strongly dissolved the feldspar particles and carbonate cement, enlarged intergranular and intragranular pores and effectively enhanced reservoir quality.Obviously, favorable sedimentary microfacies, strong dissolution zone and secondary porosity zone are the main factors controlling favorable reservoir distribution.

Characteristics of lacustrine beach-bar sandstone reservoirs in the 3^rd Member of the Funing Formation in Zhangjiaduo oilfield

Yang Peng, Ding Xiaoqi, Zhang Shaonan, Han Meimei, Liu Xixiang, Zhan Xiaohong, Zhang Yongmei

2015, 36(3):  456-462.  doi:10.11743/ogg20150314

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Lacustrine beach-bar sandstone is generally adjacent to source rocks, and it is favorable for hydrocarbon accumulation under high differential pressure between the source rock and reservoir.In recent years, a large number of oil and gas reservoirs have been discovered in the Cenozoic lacustrine beach bar sandstones in eastern China.Distribution of beach-bar sands in the 3^rd Member of the Funing Formation was studied on the basis of the core observation.Mercury data, cast thin sections and scanning electron microscope were integrated to analyze the distribution of pore throat and the combinations of porosity types in reservoirs of different genetic types.The following results were obtained.①Three kinds of lithofacies were recognized in beach-bar sand and they can be organized into four kinds of lithofacies associations, which correspond to four kinds of logging facies;②The beach-bar sand has the characteristics of fine grain size, thin single layer, as well as interbedding, overlapping and lateral connection of the beach and barsands, and the potato-shaped bar sands are distributed in parallel with the lake shoreline;③The bar sands are dominated by fine sandstone with low matrix content;Primary pore and secondary pore are well developed, and clay minerals are rich in kaolinite and poor in chlorite and mixed layer;the beach sands are generally dominated by siltstone and very fine sandstone with high matrix content;Their pore structures are poor and secondary pores are underdeveloped, and the clay minerals are rich in mixed layer and poor in kaolinite and chlorite.

Factors controlling oil production from Paleogene shale in Jiyang depression

Song Guoqi, Xu Xingyou, Li Zheng, Wang Xiuhong

2015, 36(3):  463-471.  doi:10.11743/ogg20150315

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Industrial flow was obtained from 35 wells in Shahejie Formation of Paleogene shale in Jiyang Depression.The lower Es³ and upper Es⁴ were the major producing layers producing mostly shale oil.Lab analyzing results as well as well testing and logging data were used to study the geological factors that controlled oil production rates. It shows that factors controlling the production are complicated and a wise picking of sweet spots shall be based on various geological eletments, among which high TOC content is the material base for shale oil and gas to accumulate, matruity of organic matter controlled quantity and phase of the oil and gas, lamillar muddy limestone and lime mudstone with high content of organic matter are perfect home for oil land gas to gather, abnormal high pressure affected accumulation and production of shale oil and gas, and the distribtuion of interlayers, fractures growth as well as fluid flowability controoled the flow rates attainable from local shale oil and gas accumulations.

Discovery of high density methane inclusions in Jiaoshiba shale gas field and its significance

Gao Jian, He Sheng, Yi Jizheng

2015, 36(3):  472-480.  doi:10.11743/ogg20150316

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High density methane inclusions are discovered in the samples of quartz and calcite veins from Wufeng-Longmaxi Formation of Jiaoshiba shale gas field through micro-thermometric and Raman spectral analysis of fluid inclusions.The Raman scatter peak v₁ and the homogenization temperatures of methane inclusions are applied to calculate the density of pure methane inclusions.The Raman scatter peak v₁ is in the range from 2 910.57 to 2 911.27 cm^-1, and the homogenization temperatures(T_h)ranges from -95.8 to -88.2 ℃, and the corresponding density values range from 0.254 to 0.290 g/cm³, which signifies methane inclusions of high density.Taking the minimum homogenization temperatures of two-phase fluid inclusions paragenetic with high density pure methane inclusions as the trapping temperature of the latter, the state equation of CH₄ system is employed to calculate the trapping pressure for the high density pure methane inclusions in geologic history, and the calculated trapping pressure is 102.6-137.3 MPa and the corresponding pressure coefficients is 1.63-2.18, indicating medium-to-high overpressure characteristics.The abnormal high pressure and relatively high temperature during the formation of the high density methane inclusions may represent the temperature and overpressure of gas shale at the early stage of the Yanshanian uplifting.The discovery of high density pure methane inclusions can provide a key evidence for further studies on the formation and evolution of overpressure and the relationships between the enrichment of shale gas and the overpressure in the Wufeng-Longmaxi Formation of Jiaoshiba shale gas field.

Exploration potential for shale gas in the Upper Permian Longtan Formation in eastern Sichuan Basin

Liu Guangxiang, Jin Zhijun, Deng Mo, Zhai Changbo, Guan Honglin, Zhang Changjiang

2015, 36(3):  481-487.  doi:10.11743/ogg20150317

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Based on the previous studies and in combination with field geological investigation and drilling data analysis, the research indicates that the thickness of the organic rich shale in the Upper Permian Longtan Formation in the eastern Sichuan Basin is generally over 50 m with the maximum thickness of 140 m.Lithological association varies significantly in both vertical and horizontal direction:there mainly developed shale with limestone interbed in the Yunyang-Tongjiang area in the north, shale with coal seam and limestone interbeds in the Guang'an area in the central, as well as shale with sandstone and coal seam interbeds in the south.The total organic carbon contents(TOC)are generally higher than 2%;Research on carbon isotopic composition of the shale kerogen and the organic petrology indicates that the organic matters are mainly of type Ⅱ with excellent hydrocarbon generation potential.Analysis of X-ray diffraction and vitrinite reflectance indicates that the shale has a high content of brittle minerals such as quartz and displays a high evolution degree with favorable fracturability.The gas logging during drilling inthe Longtan Formation shale displays significant abnormity, reflecting the favorable gas potential.The prediction of shale gas resource suggests largeresource potential and exploration prospect for shale gas.A comprehensive analysis indicates that there have favorable exploration prospect for shale gas in Wanxian-Yilong-Tongjiang-Fengjie area in the north and the Yibin and Yongchuan-Xijiang-Chishui area in the south.

Evaluation of reservoirs in the Da'anzhai Member of the Jurassic Ziliujing Formation in eastern Sichuan Basin

Lu Bingxiong, Zheng Rongcai, Liang Xiwen, Xu Wenli

2015, 36(3):  488-496.  doi:10.11743/ogg20150318

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Reservoirs of interest in the Da'anzhai Member of the Ziliujing Formation in eastern Sichuan Basin were determined to be interbeds of shell limestone and carbonaceous shale of various thickness based on outcrop observation and thin section authentication with analyses of sedimentary facies, X-diffraction, physical properties, pore structure, and rock mechanics.The assemblage of lake regression limestone interbedded with shale of the sub-lacustrine-slope facies at the upper part of the second sub-member of the Da'anzhai was considered to be the relative good reservoirs as their content of brittle minerals were obviously higher than that of the lower part and were easily cracked and stimulated.Average TOC of the upper part was 1.07% contrasting with a 0.38% at the lower part.Measured total gas concentration of the upper was averaged at 0.71 m³/t, higher than 0.41 m³/t taken from the lower part.Thin section analyses, mercury injection test data as well as physical properties of the samples from the sub-member showed that the reservoirs were extra-low porosity and extra-low permeability.FESEM(field emission scanning electron microscopy)results confirmed the suspect of nano-scale pore structure.Interbedded pores of clay minerals among intergranular pores were considered to have the best connectivity in the sub-member and pores and cracks associated with organic matter as well as perimetral joints of rigid minerals were proved to be well developed at the upper part of the sub-member.The upper part of the sub-member also found to contain some sporadically distributed intragranular pores.It is therefore suggested that the upper part of the sub-member is more promising in terms of exploration potential than any other layers of the Da'anzhai Member.

Research on flow unit division rationality of Yan 9¹ oil reservoir in Yang 19 block of Suijing oilfield,Ordos Basin

Chen Zhe, Lu Jun, Zhao Yaohui, Zhang Wei, Zhang Chunsheng, Tian Qinghua

2015, 36(3):  497-503.  doi:10.11743/ogg20150319

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Currently, most of the flow unit divisions are only based on such static parameters as lithology and physical property, which make the division results deviate from the actual production practices.Besides, the verification method of the flow unit is single.In order to put forward a more reasonable division method of flow units, Yan 9¹ oil reservoir in Yang 19 block of Suijing Oilfield was taken as an example.Five groups of static parameters and three groups of dynamic parameters were selected to divide the flow unit of Yan 9¹ reservoir more accurately.By applying the Q type hierarchical clustering analysis method to each parameter, the reservoir can be divided into four types of flow unit including type A, type B, type C and type D.And the hit ratio of the result from discriminant analysis is 99.3%.The rationality of the results was demonstrated in respects of seepage characteristics, heterogeneity and spatial correlation, improving the verification method of the flow unit.The division results show that the physical characteristics correlate well with dynamic productions of each flow unit, indicating the rationality of the division of flow unit.The research shows that the flow units of Yan 9¹ reservoir are dominated by type B.The type A and type B units may be the emphasis of residual oil development.

Numerical analysis on hydraulic fracture initiation and penetration characteristics in directionally perforated horizontal wells

Li Zhichao, Li Lianchong, Tang Chun'an

2015, 36(3):  504-509.  doi:10.11743/ogg20150320

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In order to reveal the initiation mode and controlling factors of hydraulic fracture as well as its propagation characteristics near the interface between production layer and barrier, a FEM-based code is employed and several numerical models are built to emphatically discuss the possibility and necessary conditions of the formation of double fractures.The penetration phenomenon of hydraulic fracture near the interface between production layer and barrier is also numerically simulated.Numerical results show that the differential stress and perforation azimuth play an important role in the initiation mode of hydraulic fractures.Either a higher differential stress or a higher azimuth can decrease the possibility of fracture initiation and propagation along the perforation direction.If the cement sheath is failed, a fracture near the well may initiate along the orientation of maximum principal stress.If both mechanical and hydraulic conditions are satisfied, a double fracturing mode, i.e.two fractures initiating synchronously along the orientation of perforation and maximum principal stress, could be obtained.During propagating, a weak interface between production layer and barrier may terminate the fracture or induce the formation of T-shape fracture.A barrier with lower elastic modulus may help a fracture penetrate through the interface and continue to propagate.The numerical results in this study are expected to provide some references for the perforating parameters optimization and fracturing design of horizontal wells.

Sedimentary undation and hydrocarbon distribution features in northern and central deep-sea area of Kutei Basin,Indonesia

Wu Baonian, Jin Zhijun

2015, 36(3):  510-516.  doi:10.11743/ogg20150321

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The relationiship between sedimentary undation and hydrocarbon distribution in the formations above the mid-Miocence in northern and central deep-sea area of Kutei Basin, Indonesia, was idnetified through Milankovitch cycles da-ting of single wells, construction of chronostratigraphic framework, and calculatin of sedimentation rates in the study area.Four major undation periods(about 6, 3.7, 1.85 and 0.4 Ma)that had important relationships with hydrocarbon reser-voiring and distribution were recognized on fine sedimentation rate curves by using geological wave filtering methods.The undation period during 6 Ma was considered to control the formation of two plays(upper and lower).The upper play had the lower Pliocene-the Upper Miocene sandstone as the reservoirs and the bottom Lower Pleistocene-the middle Pliocene mudstone as the caprocks.And the lower play had the lower Upper Miocene-the top Middle Miocene as the reseservoirs and the middle Upper Miocene mudstone as the caprocks.Other undation periods also contributed to the development of reservoirs and caps controlled by the 6 Ma period.The undation period of 0.4 Ma was the long-eccentricity cycles among Milankovitch cycles and the major controlling factor for the formation of high-frequency sedimentary cycles.The study also shows that hydrocarbon distribution was controlled by the caprocks in the study area.All areas where favorable caprocks jointly controlled by the undation periods of 6 Ma and 3.7 Ma superimpose have oil/gas discoveries or abnormal seismic reflections.

Evaluation and selection system for petroleum exploration targets

Xu Xuhui, Cai Lixue, Liu Chaoying, Wu Minghui, Zou Wei

2015, 36(3):  517-524.  doi:10.11743/ogg20150322

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Evaluation and selection of potential exploration targets with limited capital support is an eternal theme for all the oil and gas explorers.Different exploration targets have to be dealt with in different stages of exploration, which means different evaluation methods and parameters.Based on a comparison of evaluation method both domestic and abroad, we proposed in this paper to quantitatively guide exploration with exploration extent index, and established several two-factor evaluation models(hydrocarbon accumulation conditions-resource strategic value model for blocks, hydrocarbon discovery probability-resource strategic value model for plays and hydrocarbon-bearing probability-resource strategic value model for traps)with intellectual property for different stages of exploration based on systematic analyses and parameters selection upon various exploration targets such as blocks, plays, traps and etc.The models are customized for oil and gas exploration in China and can be used to yield objective and quick evaluation and selection results for explorers and management staff.