2016, Volume 23 Issue 2
    15 March 2016
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    The strategic thinking of unconventional petroleum and gas in China.
    KANG Yu-Zhu, ZHOU Lei
    2016, 23(2): 1-7. 
    DOI: 10.13745/j.esf.2016.02.001

    Abstract ( 7845 )   PDF (1416KB) ( 17503 )  

    Based on the connotation of unconventional oil and gas, this paper analyzes the geological conditions of tight sandstone oil and gas and shale oil and gas reservoir, demonstrates huge potential for unconventional oil and gas resources, and discusses the strategic direction of unconventional hydrocarbon resources in China. The unconventional hydrocarbon reservoirs are continuous hydrocarbon accumulation consisting of selfgeneration and selfpreservation nanoporecrack system. Tight sandstone oil and gas and shale oil and gas reservoirs break the concept of reservoir trap distribution. Meanwhile, there is no significant “reservoir” boundary. The main characteristics of tight sandstone oil and gas are as follows. (1) Tight sandstone oil and gas are usually found in wide and slow tectonics which coexists with a widely distributed effective source rock. (2) Source rocks and reservoirs develop in the form of interactive multiple layers. (3) Hydrocarbon has short migration which is mainly dominated by nonDarcy flow. Shale oil and gas reservoir is a typical selfpreservation reservoir, but the concept of traps has been diluted. The shale oil and gas reservoirs have following characteristics: (1) shale oil and gas reservoir is mainly formed in the depression or slope of a basin. Therefore, shale has a large and continuous distribution area. (2) The organic matter has high TOC contents and high maturity. (3) The reservoir develops millimetercentimeter laminae, nanoporecrack system which has great brittleness coefficient and high formation pressure. The organicrich source rocks occurred from the Sinian to the Tertiary, deposited in terrestrial facies, marine facies, and terrestrialmarine facies. In a word, unconventional oil and gas resource has huge potential. Conventional and unconventional oil and gas coexist in a sequential distribution of time and space, forming a conventionalunconventional “sequentialaccumulation” system. “Sequentialexploitation” of conventional and unconventional oil and gas breakouts the traditional idea of hydrocarbon exploration, promoting the geological theories of hydrocarbon exploration from the “hot point”, “belt”, “two dimension” to “three dimension” and breaking the thinking of “rich first”.

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    The main factors of shale gas enrichment of Ordovician Wufeng FormationSilurian Longmaxi Formation in the Sichuan Basin and its adjacent areas.
    HE Chi-Liang, NIE Hai-Kuan, ZHANG Yu-Ying
    2016, 23(2): 8-17. 
    DOI: 10.13745/j.esf.2016.02.002

    Abstract ( 8039 )   PDF (2104KB) ( 17526 )  

    The main controlling factors of shale gas enrichment in the Ordovician Wufeng FormationSilurian Longmaxi Formation in the Sichuan Basin and its adjacent areas include: (1) High quality shale formed in favorable palaeoenvironment is the base for shale gas enrichment. Sichuan Basin and its adjacent areas experienced intracontinental depression in a weak compressional setting during the deposition of Wufeng and Longmaxi Fms. A spacious deep water shelf was formed during this period due to rapid global sealevel rising after the glacial epoch, providing a favorable setting for massive breeding of simple organisms. In the mean time, the obliterative bay provided a favorable geochemical environment for the preservation of organic matter, resulting in the high organic content in the strata. A large number of organic silicon, generated by special types of biology, formed rock framework with high compress strength in the early stage of diagenesis, which provided favorable space for crude oil generated in the early phase, as well as a material base for the formation and preservation of abundant organic pores in the stage of oiltogas. (2) Organic pores and special fractures can guarantee the enrichment of shale gas. High quality shale with high organic carbon content contains more organic pores and larger gas content, in which the proportion of free gas is higher. Special fractures include beddingparallel fractures and small scale fractures. Hydrocarbonforming organisms accumulating on bedding surface, such as graptolites and algae, promoted the development of beddingparallel fractures. Small scale fractures enlarged reservoir space and improved filtration capacity of shale, which was in favor of shale gas accumulation. (3) Effective preservation under moderate uplifting is the key factor for shale gas enrichment. However, if deformation and denudation of strata were too strong, the closed preservation system would be destroyed, both conventional and unconventional petroleum system might become invalid totally or partially. It would be the best if the microfractures caused by uplifting did not form large crossingbed fractures. The subdued strata with certain burial depth and without tectonic faults, especially opening faults, have favorable conditions for preservation of shale gas. The difference in preservation conditions between Sichuan Basin and its adjacent areas was mainly due to different tectonic deformation, sedimentation, uplifting and denudation, controlled by the middle Yanshanian tectonic movement. Shale gas play fairways of the Ordovician Wufeng FmSilurian Longmaxi Fm in Sichuan Basin and its adjacent areas are located in the composite region where thick black shale enriched in organic matter were deposited in the central area of deepwater shelf, the shale layers with prosperous organic pores, microfractures and beddingparallel fractures were well developed and the timing of uplifting in the Yanshanian was late and the amplitude of uplifting in the Himalayanian was relatively small.

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    Analyses and thoughts on accumulation mechanisms of marine and lacustrine shale gas: A case study in shales of Longmaxi Formation and Daanzhai Section of Ziliujing Formation in Sichuan Basin.
    GUO Xu-Sheng, HU Dong-Feng, LI Yu-Beng, WEI Xiang-Feng, LIU Re-Bing, LIU Zhu-Jiang, YAN Ji-Gong, WANG Qiang-Bei
    2016, 23(2): 18-28. 
    DOI: 10.13745/j.esf.2016.02.003

    Abstract ( 7890 )   PDF (1856KB) ( 20647 )  

    This article is dedicated to two shale gas intervals such as Longmaxi Formation and Daanzhai Section of Ziliujing Formation in the Sichuan Basin. In this study we analyzed and examined the basic conditions concerning the formation of marine and lacustrine shale gas, accumulation mechanisms and potential intervals, based on systematic experimental analysis of Longmaxi Formation in the Fuling Shale Gas Field and Daanzhai Section of Ziliujing Formation in Yuanba and Fuling areas and also based on the comparisons between six properties of shale reservoirs such as lithologies, geophysical properties, electric properties, shale gas contents, geochemical properties and brittle properties. It is considered that the differences between organic pores developed in marine and lacustrine shales are the main reasons for great differences in gas contents. Both marine and lacustrine shales have remarkable exploration prospects. Due to the differences among TOC, Ro and organic matter type, the organic pores develop better in marine shales. The intervals of organicrich mudstones or shales with streak or stripe limestones developed in shallowsemideep lacutrine are favorable facies belts for shale gas exploration. The lithofacies of grapholite shales with spicules and radiolarians deposited in deep shelf at the bottom of Longmaxi Formation are the most favorable for shale gas exploration. Furthermore, organicrich mudstones or shales are developed in shallow shelf, though the protecting conditions are destructed to a certain degree, the areas with high adsorbed gas still have potentials for shale gas exploration.

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    Analyses on the shale gas exploration prospect of the Niutitang Formation in northeastern Guizhou Area.
    LENG Ji-Gao, GONG Da-Jian, LI Fei, LI Feng
    2016, 23(2): 29-38. 
    DOI: 10.13745/j.esf.2016.02.004

    Abstract ( 8825 )   PDF (2359KB) ( 20042 )  

    The shale gas resources are rich in the northeastern Guizhou area, especially in the Niutitang Formation. Based on the former failed drilling wells, combined with abundant analytical data of outcrops and cores, this study systematically investigated the geological characters of the Niutitang Formation in the northeastern Guizhou area and further implemented the resource potential in the study area. The following understandings are obtained. The kerogen types of organic matter are mainly of typeⅠand typeⅡ1, of the Niutitang Formation in the northeastern Guizhou area. The TOC content is high, with an average value of 3.52%. The average value of Ro is 3.58%, which reflects that the source rock has entered high maturation stage. The reservoirs are characterized by low porosityultralow permeability and high specific surface area. The results show that the brittle and clay minerals are averaged at 64.2% and 19.6%, respectively. The high siliceous contents and great brittleness is favorable for reservoir alteration. The recoverable resource of shale gas is estimated at 0.12 billion cubic meters. Areas including Cen gong, Yanhe, Xiushan, Dejiang, Kaili, etc. can be selected for further exploration and evaluation in the northeastern Guizhou area.

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    The transitional facies shale gas formation selection and favorable area prediction in the western Henan.
    LI Zhong-Meng, ZHANG Dong, ZHANG Gu-Ban, CI Ma-Xian-Zhang, LIU Yan-Jie, WANG Hong, HONG Chao
    2016, 23(2): 39-47. 
    DOI: 10.13745/j.esf.2016.02.005

    Abstract ( 7651 )   PDF (1377KB) ( 18179 )  

    Shale gas is produced in mud shale formation with abundant organic matter. The transitional facies formation mud shale has large cumulative thickness and high hydrocarbon content. The gas accumulation potential is good in the western Henan, but the mud shale is characterized by thin single formation, multilayer and big transverse phase change. Because of the lack of large amount of gasbearing tests of the blank area, it is difficult to choose good shale gas formation. This paper takes the Upper Palaeozoic in western Henan province as a research object, makes a correlation and clustering analysis of the various parameters and air content of the mud shale, confirms that the main controlling factors of the air content of the shale are organic matter abundance, rock density, permeability, pyrite content and photoelectric absorption cross section index. A regression analysis is carried out with the air content to get a fitting equation, which has been validated to be good for the determination of fitting. Finally, the gasbearing of the transitional facies shale in the western Henan province has been determined by this method and a great number of gas data have been obtained. Comprehensive factor analysis method is proposed in this paper, making the gasbearing as a main factor, supplemented by secondary factors such as the organic matter maturity, porosity, coefficient of brittleness, thickness, burial depth and area. The reservoir benefit coefficient is calculated to choose a gasbearing horizon, and get the regional advantageous factor to predict favorable area. Use the measured and fitted data of the Upper Palaeozoic in the midwestern and western Henan province, favorable factor is calculated to predict the shale gas advantageous area of Zhuxianzhen, Gongyi and Mianchi by using the comprehensive factor analysis method.

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    The formation mechanism of overpressure reservoir and target screening index of the marine shale in the South China.
    LIU Hong-Lin, WANG Gong-Yan, FANG Chao-Ge, GUO Wei, SUN Sha-Sha
    2016, 23(2): 48-54. 
    DOI: 10.13745/j.esf.2016.02.006

    Abstract ( 8716 )   PDF (1048KB) ( 17613 )  

    In the process of exploration and development of shale gas, we find some areas as Development Zone, with high gas content and high resource abundance. The EUR of a single well is also high, and the economy is good. Since shale gas content equals to the adsorbed gas and free gas, in addition to dissolved gas, free gas, adsorbed gas and dissolved gas are closely correlated with pressure coefficient. In the United States, due to stable geological conditions, it is easy to carry out shale gas geological screening. The overpressure is not so important for shale gas field, normal pressure, even underpressure can be achieved commercially. So, In the United States shale gas geological screening index has no concept of pressure coefficient, or it is not a key indicator. However, due to the different geological formations in China and North America, the North American shale gas is mainly located in the basin of central Canada, and the background is very stable. In contrast, China consists of many blocks with complex structure and long time. Because of the high maturity of marine shale, the porosity is low and decreases. The tectonic movement is active with developed faults, and the preservation condition is relatively poor. For the shale with high maturity and low porosity, it is necessary to reach the same pressure coefficient of gasbearing formation, so that the ultimate recoverable reserves of single well can reach the economic limits, and the commercial development can be realized. South China has abundant marine shale gas, which is characterized by large thickness and stable distribution. The formation of low water saturation often occurs in the process of hydrocarbon generation. Pressure mechanism of the overpressure shale gas field in the Yangtze region mainly consists of uplifting construction, water pressure, the type of clay mineral dehydration, and hydrocarbon generation. The marine shale gas field is mainly resulting from the formation of super pressure. Changning shale gas field is a main hydrocarbongenerating pressurization field. Screening index of favorable area should include core area/enrichment area optimization index. Index value based on the geological characteristics of the super pressure gas field must match the significance of the parameters. Geological areas of North American shale gas need to consider the burial depth, shale thickness, TOC content, and the content of silica. Due to the simple geological conditions and moderate maturity of the North American shale, it can be realized under the condition of low pressure and under pressure, but in the background of high maturity and fault development, the formation pressure coefficient is especially important. Therefore, this paper considers that the basic parameters, such as depth (15004500 m), thickness (>30 m), total organic carbon content (>2%), and silica mineral content (>30%), should be considered as an important index to reflect the characteristics of marine shale gas in southern China.

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    Oil accumulation characteristics of China continental shale.
    NIE Hai-Kuan, ZHANG Pei-Xian, BIAN Rui-Kang, WU Xiao-Ling, DI Chang-Bo
    2016, 23(2): 55-62. 
    DOI: 10.13745/j.esf.2016.02.007

    Abstract ( 8618 )   PDF (1469KB) ( 17506 )  

    The accumulation mechanism and characteristics of shale oil were investigated. In comparison with shale gas, shale oil is more strict in accumulation conditions, more limited in distribution area, and more challenge in exploration. In the USA, shale oil is a kind of light oil in the marine shale and it is characterized by large distribution, high maturity, low density, low wax content and low viscosity. While in China, shale oil is a kind of heavy oil in the continental shale and it is characterized by small distribution area, low maturity, high density, high wax content and high viscosity. For the marine shale in USA, the quartz and carbonate were mostly biological sources. The quartz has a good positive correlation with the total organic carbon. It controls the oil content and is conducive to the fracturing. While for the continental shale in China, the quartz was of clastic source and the carbonate was chemical deposition. The quartz has a negative correlation with the total organic carbon and is not conducive to the fracturing. These differences may be the reasons of low shale oil production, which severely restricted the exploration and development of shale oil in China. It suggests that the shale oil exploration should focus on areas with relatively high maturity in central depressions and areas with highly developed sandstone interbed on slopes. The former features in ‘light oil, high pressure and easy fracturing’, while the latter is characterized by ‘well developed interbed and easy fracturing’.

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    Method and application of tectonic stress field simulation and fracture distribution prediction in shale reservoir.
    DING Wen-Long, CENG Wei-Te, WANG Er-Yue, JIU Kai, WANG Zhe, SUN Ya-Xiong, WANG Xin-Hua
    2016, 23(2): 63-74. 
    DOI: 10.13745/j.esf.2016.02.008

    Abstract ( 8715 )   PDF (2094KB) ( 17633 )  

    Fracture is a key factor for the enrichment and high production of shale gas. Compared with other types of reservoirs, shale reservoir is characterized by a relatively strong ductility and multitypes of structural and nonstructural fractures such as high dipangle tensionshear fracture, low dipangle slip fracture and bedding fracture. According to the characteristics of shale reservoirs and fractures from the perspective of geological origin, a method of tectonic stress field simulation and fracture distribution prediction was put forward and effectively applied in the Lower Silurian Longmaxi shale in the southeastern Chongqing area, the emphasis of which is the establishment of accurate geological, mechanical and mathematical Models. By the use of uniaxial and triaxial compression and acoustic emission tests, the paleostress, presentday stress and mechanical data were obtained to conduct a numerical simulation of the tectonic stress field. The rationality of the established models was examined and calibrated by the comparison of the simulation results and actual geological data. For the particular existence of tension and shear fractures in shale, Griffith and MohrCoulomb criteria were respectively used to calculate the tension and shear rupture rates. According to the proportions of the tension and shear fractures, a comprehensive rupture rate was introduced. By the combination of the comprehensive rupture rate and other dominant controlling factors of fractures, such as total organic carbon (TOC) and brittle mineral contents, the fracture developmental coefficient was proposed as an ultimate evaluating index to characterize the developmental degree and distribution of fractures. This method not only provides a new technical approach for the optimization of ‘sweet spot’, but also has important reference value for the design of horizontal wells and fracturing programs.

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    Shale uniaxial compressive failure property and the affecting factors of UCS.
    YIN Shuai, DING Wen-Long-*, SUN Ya-Xiong, WANG Xin-Hua, ZHANG Min, ZHANG Ning-Ji
    2016, 23(2): 75-95. 
    DOI: 10.13745/j.esf.2016.02.009

    Abstract ( 8709 )   PDF (3470KB) ( 18007 )  

    Correct understanding of the uniaxial compressive strength of shale failure characteristics and its UCS influencing factors has an important reference value in detecting shale failure mechanism, drilling and well completion, fracturing evaluation, micro crack prediction, logging interpretation and seismic response. In this paper, based on the systematic study and comprehensive analysis of the recent research results of shale uniaxial compressive characteristics and the UCS study, reviewed the shale uniaxial failure characteristics and its UCS affecting factors. The results show that, the shale inelastic deformation mechanism in uniaxial loading curve is affected by the sliding of micro cracks, the production and extension of micro cracks, and the pore collapse. The shale uniaxial compression characteristics present tensile or tensileshear fracture. The tensile fracture is easy to occur in location that has high rigidity and degree of consolidation. The shear fracture is easy to occur in location that has low rigidity and degree of consolidation. The S shape failure criterion can accurately describe the shale compressive failure strength variation from uniaxial to three axis failure. From the point of view of geology, making an induction and summary of shale UCS affecting factors, they are composition, bedding plane angle, sorting, micro fabric, organic matter content and its distribution, porosity, moisture content, and microcracks. The affecting mechanism of these factors are analyzed in detail. Among these factors, due to the complex distribution characteristics of micro cracks, the mechanism of micro cracks on shale UCS is not well understood. So, it is recommended that quantitative research of shale micro crack parameters and study of the influence mechanism of micro cracks on shale uniaxial compressional failure from the microscope scale should be strengthened in the future. This study can provide a scientific guidance for shale oil and gas exploration and development.

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    Lithofacies classification of shales of the Lower Paleozoic WufengLongmaxi Formations in the Sichuan Basin and its surrounding areas, China.
    DAN Bei, LIU Shu-Gen, SUN Wei, XIE Yue-Hao, QIU Jia-Wen, ZHANG Jian, YANG Di
    2016, 23(2): 96-107. 
    DOI: 10.13745/j.esf.2016.02.010

    Abstract ( 8023 )   PDF (1592KB) ( 17094 )  

    The Lower Paleozoic WufengLongmaxi shale in the Sichuan Basin and its surrounding areas, China, is a key point of Chinese shale gas industry which has been promoted by more and more related achievements since the finding of highyield industrial shale gas in the Jiaoshiba area. However, there has been significant controversy on the classification of lithofacies which is regarded as the basis of shale and shale gas. This study has proposed two core indexes for shale lithofacies classification, including the content of quartz and the lamination style, based on a comprehensive review of lithofacies classifications at home and abroad and combined with the research and exploration results for the WufengLongmaxi shale. Then nine lithofacies of the WufengLongmaxi shale have been recognized based on the complete lithofacies classification process: (1) siliceouspoor nonparallel laminated shale, (2) siliceousmoderate nonparallel laminated shale, (3) siliceousrich nonparallel laminated shale, (4) siliceouspoor parallel laminated shale, (5) siliceousmoderate parallel laminated shale, (6) siliceousrich parallel laminated shale, (7) siliceouspoor indistinctly laminated shale, (8) siliceousmoderate indistinctly laminated shale, (9) siliceousrich indistinctly laminated shale. Three unique lithologic characteristics in the favorable exploration section include high quartz content, high TOC content and high friability in the Sichuan Basin and its surrounding areas.

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    Lithofacies features of organicrich shale of the Triassic Yanchang Formation in Huachi Aera, Ordos Basin.
    ER Chen, LUO An-Xiang, DIAO Jing-Zhou, ZHANG Zhong-Xi, BAI Yu-Ban, CHENG Dang-Xing, TUN Wei-Chao, WEI Zhi-Kun, ZHANG Jie
    2016, 23(2): 108-117. 
    DOI: 10.13745/j.esf.2016.02.011

    Abstract ( 8517 )   PDF (1589KB) ( 17474 )  

    Organicrich shale and mudstone developed well in Chang7 Member of the Triassic Yanchang Formation, which has become an important prospecting target for shale gas and shale oil. Based on fine description of core, microstructure observation of thin section and grain analysis, three kinds of lithofacies of shale were determined, including black shale, laminar mudstone, and silty mudstone. Brittle minerals content of silty mudstone is higher than that of black shale and laminar mudstone. Pyrite content of the latter is higher than that of the former, and clay minerals content of the three lithofacies are nearly the same. Black shale is the most favorable lithofacies which has high organic abundance and greatest kerogen type (mainly type I). Laminar mudstone is the second favorable lithofacies. During the deposition of Chang7 Member, the layered anaerobic environment was beneficial to the preservation of organic matter. Lower grade aquatic lives were the main biological precursor of organic matter. Black shale and laminar mudstone developed in deep lacustrine environment which was quiet and not influenced by terrigenous coarse grains. However, silty mudstone developed in the environment that was influenced frequently by terrigenous coarse grains. As a result, organic matter types of silty mudstone are diverse and complicate. With the combination of fine description of core and logs, the vertical development characteristics of each kind of lithofacies were uncovered. Influenced by baselevel changing and sediment supply, the third section of Chang7 Member (C73) is composed of black shale and laminar mudstone, however, the second section and first section of Chang7 Member are mainly composed of laminar mudstone and silty mudstone. Black mudstone and shale in C73 have better lithofacies that bear lamellation fracture and lamina facies, better organic matter type and high abundance. C73 is the best prospect target for shale oil and shale gas.

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    The multianisotropy of shale oil and gas reservoirs in vertical and its influence on oilgas development.
    LI Yu-Chi, HE Jian-Hua, YIN Shuai, WANG Er-Yue, DAI Feng, DIAO Dong
    2016, 23(2): 118-125. 
    DOI: 10.13745/j.esf.2016.02.012

    Abstract ( 7369 )   PDF (1480KB) ( 15918 )  

    Shale oil and gas are a type of petroleum resource generated and accumulated in source rocks. The exploitability of this oilgas is obviously controlled by reservoir characteristics. The difference of depositional environment of various organicrich shale causes the multianisotropy of shale oil and gas reservoir in vertical, including lithology anisotropy, reservoir properties anisotropy, anisotropy of rock mechanical parameters, groupstress anisotropy and the anisotropy of gasbearing characteristics in vertical, which made the anisotropy of shale reservoir in vertical much stronger than that of shale reservoir in horizontal. The great variation of organic abundance, porosity, permeability, fracability, stress, gasbearing properties and ratio of free to adsorbed gas directly affects the design and implement of oilgas development strategies. The selection of advantaged objective layers for shale oil and gas exploitation should consider the following factors, including the single organicrich shale interval thickness (3050 m), TOC content with an average of >2.0%, high effective porosity (>2.0%), small poisson ration (<0.25), high brittleness, minor principle stress which is much smaller than other adjacent layers and good gasbearing properties. Moreover, the influence of this anisotropy must be fully considered for the selection of the types of shale oilgas development well, the design of horizontal drilling, the length of stage fracturing and the plan of perforation spacing.

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    The wholeaperture pore structure characteristics and its effect on gas content of the Longmaxi Formation shale in the southeastern Sichuan basin.
    JIANG Zhen-Hua, TANG Xiang-Lu, LI Zhuo, HUANG He-Xin, YANG Pei-Pei, YANG Xiao, LI Wei-Bing, HAO Jin
    2016, 23(2): 126-134. 
    DOI: 10.13745/j.esf.2016.02.013

    Abstract ( 8806 )   PDF (1616KB) ( 19158 )  

    Since shale gas mainly occurs in shale pores, research on the pore structure characteristics is key to understand shale gas accumulation mechanism. Based on the experiments of CO2 adsorption, N2 adsorption, CH4 isothermal adsorption and high pressure mercury injection, the wholeaperture pore structure of the Longmaxi Formation shale is characterized in the Southeastern Sichuan Basin and the controlling effects of pore structure on the gas content are explained. Micropores (<2.0 nm), mesopores (2.050.0 nm) and macropores (>50.0 nm) are developed in shale samples, and the distribution characters change obviously in each sample. In the aspect of pore volume, the mesopores have the biggest contribution to the whole pore volume, taking about 40.8%. It is followed by micropores, taking about 34.7%. The macropores have the minimum proportion in the whole pore volume, only taking 24.5%. In the aspect of surface area, the micropores have an absolute advantage in the whole surface area, accounting for about 76.87%. The second is mesopores, taking about 23.05%. The macropores only provide surface area of 0.07%. The main pore volume is provided by mesopores and micropores, which controls the content of free gas. The surface area of micropores has a good positive correlation with the largest CH4 adsorption contents, and makes up the main surface area in shale samples, which controls the content of adsorbed gas. The macropores are not dominant in pore volume and surface area, and its influence on the content of adsorbed gas and free gas is relatively weak. But the macropores can be the main channels for shale gas seepage. Therefore, understanding the distribution characteristics of micropores, mesopores and macropores, especially the contribution of micropores on the enrichment of adsorbed gas and free gas, has an important guiding significance to the shale gas exploration and development.

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    Reservoir characteristics and gasbearing capacity of the Lower Palaeozoic marine shales in Northwestern Hunan.
    2016, 23(2): 135-146. 
    DOI: 10.13745/j.esf.2016.02.014

    Abstract ( 7501 )   PDF (2631KB) ( 15566 )  

    Based on field geological and drilling data, the reservoir characteristics and gasbearing affecting factors of the Lower Paleozoic marine shale in the Northwestern Hunan were studied through the related experimental results. The results show as follows. The black shale of Niutitang Formation is formed in the deep water continental shelfmargin slope sedimentary environment, with thickness of 50250 m. The Longmaxi Formation is stranded bay deposit and the black shale is mainly developed at the bottom. The organic matter type in both formations is predominantly sapropelic. The Total Organic Carbon (TOC) content of the black shale from the two formations is averaged at 3.57% and 1.16%, respectively, with high equivalent vitrinite reflectance (Ro) of 2.61% and 2.08%, respectively. Black shale in both formations are characterized by high content of quartz, low content of clay minerals, and small amounts of carbonate minerals which is controlled by sedimentation and diagenesis. Shale reservoir spaces can be divided into three broad categories: mineral matrix pore, organic pore and microfracture. Influenced by factors such as organic matter and clay minerals, the pore structure parameters of shales are different. The micropores (< 2 nm) and mesopores (250 nm) are mainly developed, which have massive contribution to the pore specific surface area and pore volume where the shale gas adsorption mainly occur. The average methane adsorption capacities of shales in the Niutitang Formation are 1.98 cm3/g, a little higher than that of shales in the Longmaxi Formation (1.16 cm3/g).The organic matter and clay minerals both play a role in the methane adsorption, and high maturity and water content can reduce shale adsorption capacity.

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    The reservoir property of the Upper Paleozoic marinecontinental transitional shale and its gasbearing capacity in the Southeastern Ordos Basin.
    2016, 23(2): 147-157. 
    DOI: 10.13745/j.esf.2016.02.015

    Abstract ( 7639 )   PDF (1833KB) ( 20948 )  

    The Upper Paleozoic marinecontinental transitional shale is important gasrich shale in the Ordos Basin. A series of studies have been carried out on the gas generation and resource potential, but it lacks of detailed reservoir characterization and its impact on the gas content. This constrains the shale gas exploration and exploitation. A large number of shale samples were collected from the Upper Paleozoic Benxi Formation and Shanxi Formation to investigate the geochemical and mineral composition, pore type and distribution. Field canister gas desorption and isothermal adsorption experiments were performed to measure gas content and gas bearing capacity of shale samples. The results show that the Upper Paleozoic shale contains high TOC (0.5%11%) and high thermal maturity (1.0%3.0% Ro), and its organic matter belongs to type III kerogen. These shale samples are characterized by high level of clay mineral (up to 60%) and low porosity (2%8%). Some samples are relatively microfracturedeveloped. The pore is dominated by mesopore, which accounts for over 90% of all pore surface area and volume. TOC content also has close relationship to the pore surface area and volume, suggesting the organic matter pore makes significant contribution to all pore in the shale. The canister adsorption shows the gas content varies in a wide range from 0.591 m3/t to 4.05 m3/t, isothermal adsorption measurement shows the Langmuir gas volume ranges from 0.05 m3/t to 14 m3/t, both of which were seriously impacted by the TOC content. Besides, the clay mineral content might also contribute to the gas bearing capacity of shales.

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    Reservoir characteristics and its influence on continental shale: An example from Triassic Xujiahe Formation shale, Sichuan Basin.
    2016, 23(2): 158-166. 
    DOI: 10.13745/j.esf.2016.02.016

    Abstract ( 8673 )   PDF (1347KB) ( 19019 )  

    Based on drilling data, outcrop geologic survey around the area and laboratory test results of lots of rock samples, reservoir characteristics of Triassic Xujiahe Formation shale in the Sichuan basin are analyzed. Physical properties of the shale reservoir were tested by high pressure mercury intrusion method, nitrogen isothermal adsorption, and pulse permeability method. It is thought that Xujiahe Formation shale has a center of reservoir performance, and the porosity ranges from 0.95% to 4.77% with an average of 2.73%. A series of methods including direct observation method such as core and thin section observation, field emission scanning electron microscopy (FSEM) in combination with highpressure mercury injection, nitrogen isothermal adsorption experiment research have been used to research the reservoir space characteristics of Xujiahe Formation. Nanoscale matrix pore is the dominant reservoir space in the Xujiahe Formation shale, and pore with size less than 50 nm accounted for 83.9%. Matrix pores with pore size of 2100 nm include residual primary pores, intergranular pores, dissolved pores, and organic pores that only developed in local parts. Its pointed out that TOC content, clay mineral content and thermal maturity were the main controlling factors on reservoir characteristics of Xujiahe Formation shale.

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    Reservoir characteristics and enrichment conditions of shale gas in the CarboniferousPermian coalbearing formations of Qinshui Basin.
    2016, 23(2): 167-175. 
    DOI: 10.13745/j.esf.2016.02.017

    Abstract ( 8623 )   PDF (1571KB) ( 19029 )  

    Qinshui Basin, as one of the most important coalbearing basins in China, not only has plenty of coal and coalbed methane resources, but also has a lot of shale reservoirs. However, there is little research on the characteristics and potential evaluation of shale gas reservoirs in this basin. In this paper, we studied the characteristics of shale gas reservoirs in the Upper Paleozoic of Qinshui Basin, China. Comprehensive experimental methods, including Xray diffraction, NMR, FIBSEM, microscopic identification of thin sections and nitrogen adsorption etc. were applied to analyze the characteristics of organic geochemistry, rock and mineral composition and pores evolution of organicrich shale gas reservoirs. On this basis, the exploration and development potential of shale reservoirs in the study area is evaluated. The results show that different types of pores and micro fractures developed here, which provide enough spaces for the storage of shale gas. Mineral pores, mainly including intergranular pores and intercrystalline pores in shapes of plate, triangle or irregular are well developed, whereas only a small amount of organic pores in shapes of dot or occasional ellipse developed. Porosity has a large specific surface area, which has a range from 2.84 m2/g to 6.44 m2/g with an average of 4.26 m2/g. The average value of pore size distribution is between 3.64 nm and 10.34 nm, which means mainly mesopores developed. The appropriate ratio of mineral composition, which is composed of 57.5% of clay minerals and 41.3% of brittle minerals, is pretty good for the development of mircopores, gas absorption and fracturing. High value of TOC and Ro, caused by abnormal thermal gradient in Mesozoic, provided favorable conditions for shale gas formation and storage. On the whole, though the burial depth is shallow, there is great exploration and development potential for shale gas in the CP period in the Qinshui Basin because the organic chemical conditions, mineral composition and reservoir characteristics are quite suitable for the formation and storage of shale gas.

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    Reservoir characteristics of marine shale in the Malong block of eastern Yunnan Province and comparison analysis.
    2016, 23(2): 176-189. 
    DOI: 10.13745/j.esf.2016.02.018

    Abstract ( 4733 )   PDF (2666KB) ( 8978 )  

    Based on the latest drilling data, the laboratory test results of shale core samples from Well Maye1 and combined with the geologic survey of field outcrops, this paper systematically studies the reservoir characteristics of the Lower Cambrian Qiongzhusi shale in the Malong block of eastern Yunnan Province from organic geochemical characteristics, mineral constituents, reservoir properties and fracture characteristics. The Qiongzhusi shale of study area is characterized by high organic content with TOC over 2%. The black shale was all highover mature because of the old Qiongzhusi Formation. The major mineralogical compositions of shale are detrital minerals, carbonatite minerals and clay minerals. The black shale has a high brittleness mineral content and the brittleness index averages at 0.62. Clay minerals are mainly composed of illite, followed by the I/S layers and chlorite, and the kaolinite content is low. Qiongzhusi shale is characterized by low porosity and permeability and various pore types dominated by inkbottleshaped pores, platelike pores and slitshaped pores. Nanoscale mesopores in shale play an important role. The specific surface area and total pore volume are low with an average of 9.18 m2/g and 10.38×10-3cm3/g, respectively. The fissures of shale reservoir are mainly of high angle crack. Carbonaceous shale in the upper part of target layer is characterized by welldeveloped fissures and silty shale in the lower part of target layer possesses undeveloped fissures. TOC and brittle minerals contents promote the development of fissures. Compared with typical marine shale from home and abroad, the shale from Qiongzhusi Formation in the Malong block of eastern Yunnan Province is mainly composed of silty shale with some thin carbonaceous shale. Barnett shale from Fort Worth, Longmaxi shale from Jiaoshiba area and Niutitang shale from Cengong block are mainly carbonaceous and siliceous shale. So the lithofacies of Qiongzhusi shale is poorer than that of the other three kinds of marine shale. The TOC content of Qiongzhusi shale is moderate, lower than that of the other three kinds of marine shale. The brittleness minerals content of Qiongzhusi shale is similar to that of Longmaxi shale and slightly lower than that of Niutitang shale. Qiongzhusi shale is characterized by good brittleness. The reservoir property and development of organic matter pores of Barnett shale and Longmaxi shale are better than those of Qiongzhusi shale and Niutitang shale. The organic matter pores in Qiongzhusi shale mainly develop in the mixture of organic matter and clay. The fissure development of Qiongzhusi shale is poorer than that of Barnett shale, Longmaxi shale and Niutitang shale. In addition, the gas content of Qiongzhusi shale is lower than that of other three kinds of marine shale, and Qiongzhusi shale has a strong adsorption ability.

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    Early Paleozoic orogeny in the Himalayas: Evidences from the zircon U - Pb chronology and Hf isotope compositions of the Palung granitic gneiss in Nepal.
    2016, 23(2): 190-205. 
    DOI: 10.13745/j.esf.2016.02.019

    Abstract ( 7923 )   PDF (2216KB) ( 20236 )  

    The Palung granitic gneiss in Nepal is a part of the Kathmandu thrust sheet of which the major mineral compositions are: quartz, plagioclase, Kfeldspar, microcline and muscovite. Zircons from the granitic gneiss have corerim structures with inherited detrital cores and magmatic rims showing concentric oscillatory zoning. LAICPMS zircon UPb dating results of the rims gave weighted mean ages of 485.5±1.4 Ma and 455.1±3.1 Ma, hinting that the protolith of the gneiss was the early Paleozoic granite recording two episodes of magmatism. The εHf(t) values range from -8.7 to -3.5 and the calculated TCDM(twostage model age) vary from 2.01 Ga to 1.69 Ga. Combined with the petrological characteristics and compared with Hf isotope compositions of the metapelites and orthogneisses in the Greater Himalayan Complex(GHC)and the metasedimentary rocks in the Lesser Himalayan sequence(LHS), we propose that the source of granite was possibly generated from the partial melting of the metapelite in the GHC. Zircon UPb ages of the Palung granitic gneiss and the published geochronological results of the CambrianOrdovician granites/granitic gneisses demonstrate that the early Paleozoic orogeny was existed in the Himalayas. The early Paleozoic tectonic events preserved in the Himalayas are well compared with the contemporaneous ones in Lhasa terrane, Qiangtang terrane and BaoshanTengchong terrane located in the southeast of the Tibetan Plateau. Integrating the results from previous studies, we suggest that it is resulted from the Andeantype orogeny formed through the subduction of the protoTethys Ocean lithosphere along the northern margin of the Gondwana, rather than the PanAfrican orogeny which was related with the continentcontinent collision during the Gondwana assembly.

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    Geological characteristics and tectonic significance of the Indosinian granodiorites from the Zongwulong tectonic belt in North Qaidam.
    2016, 23(2): 206-221. 
    DOI: 10.13745/j.esf.2016.02.020

    Abstract ( 7648 )   PDF (2629KB) ( 17600 )  

    In order to research the Indosinian tectonic evolution features of the Zongwulong tectonic belt, the studies of petrology, geochronology and geochemistry were conducted for the Shailekeguolai granodiorite samples and Chahannuo granodiorite samples from that area. The results of zircon SHRIMP UPb dating of three samples for the Shailekeguolai granodiorite and Chahannuo granodiorite were 249.2±2.6 Ma, 242.7±1.9 Ma and 243.5±2.4 Ma respectively, which confirmed that the intermediateacidic intrusive rocks of the Zongwulong tectonic belt were formed in the Early and Middle Triassic, and the existence of Indosinian tectonicmagmatic activity in North Qaidam has been proved. The Shailekeguolai granodiorite and Chahannuo granodiorite are weak peraluminous Itype granites of middlehigh potassium calcalkaline series, characterized by high SiO2, high Na2O and high Al2O3, with A/CNK ratio ranging between 1.021.06 and 1.011.05, Rittmann index ranging between 1.541.73 and 1.071.61 respectively. The two granodiorites experienced a relatively insufficient crystallizationdifferentiation process, which is reflected by K/Rb(234 and 279 on average respectively) and DI(72.9576.06 and 64.4976.42 respectively). The rocks show LREE enrichment(LREE/HREE=6.839.70 and 3.297.40 respectively) and weak negative and positive Eu anomalies. The primitive mantle normalized trace element spider diagrams are characterized evidently by positive anomalies of Rb, U, La, Pb, Sr and negative of Nb, P, Ti. Microgranular mafic enclaves(MMEs) are developed in the Chahannuo granodiorite. Compositional and textural disequilibrium between plagioclase and hornblende in the MMEs and host rocks had been found, suggesting a magma mixing origin for the granodiorites. The granodiorites are products of lower crustmantle mixed magma due to the crustal thickening caused by active continental margin subduction and arccontinent collision during the Indosinian period in the North Qaidam. Based on the comparison of geologic features of the magmatites between the Zongwulong tectonic belt in North Qaidam and the Ela mountain tectonic belt in East Qaidam, the formation of the Zongwulong tectonic belt may have a close genetic relationship with the intense oblique collision of West Qinling along the Gonhe aulacogen towards Qaidam blocks.

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    Zircon U - Pb study of twostaged OligoMiocene migmatization along the Xianshuihe fault zone, East Tibet Plateau.
    2016, 23(2): 222-237. 
    DOI: 10.13745/j.esf.2016.02.021

    Abstract ( 7601 )   PDF (2905KB) ( 15755 )  

    The Xianshuihe (XSH) fault zone is an important lithospheric strikeslip fault in the eastern margin of the Tibet Plateau. A migmatite zone, about 120 km long and 35 km wide, developed along the fault. Kinematic and chronological studies reveal twostaged anatexis and metamorphism of the migmatite zone and indicate two periods of deformation of the XSH fault. The first stage migmatization occurred in 3227 Ma, suggesting that the Xianshuihe fault zone underwent intensive deformation during the Oligocene. The second stage migmatization occurred in 2520 Ma. Zircon UPb dating of two rock samples taken from the leucosome of the secondstage migmatite yields respectively the ages of ca. 25.06 Ma and ca. 20.9 Ma. Field investigation and microstructural study show a synshearing anatexis of the secondstage migmatite, with intensively developed horizontal lineations. Five zircon UPb dating of the granite intrusion, which closely related to the secondstage migmatite zone, yield crystalline ages of 2019 Ma, representing the ending of the migmatization. The new finding of the twostaged migmatization constrains the Cenozoic transformation from compressional regime to sinistral strikeslip regime of the XSH fault. And it confirms that the initiation of the Cenozoic strikeslip along the Xianshuihe fault zone occurred in 2725 Ma which is significant for understanding the processes of Cenozoic tectonic deformation in the east Tibet Plateau.

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    Worthy of giving attention to circular structure in remote sensing image in large or super large deposits exploration in Central Asia.
    2016, 23(2): 238-250. 
    DOI: 10.13745/j.esf.2016.02.022

    Abstract ( 7725 )   PDF (2929KB) ( 17541 )  

     There are many Gobi, desert, sand dunes in Central Asia, which provide more chances for remote sensing geological exploration. Some large or super large deposits have been found in Central Asia metallogenic zone and the remote sensing characteristics of them have been attracted great attention. We have analyzed and researched the remote sensing geology of some typical ore deposits in Central Asia by using the ETM+ data from the USA Landsat No.7, such as Muruntau giant gold deposits in Uzbekistan, Kounrad and Aktogai super largesized copper deposits in Kazakhstan, Oyu Tolgoi super largesized coppergold deposits in Mongolia and ChagangnuoerZhibo iron deposits in western Tianshan in Xinjiang, and have drawn a conclusion that some famous large or super large porphyry copper and gold deposits and volcanic iron deposits have deep relationship with circular structures several kms to tens of kms in diameter in the remote sensing image, and the deposits are mostly located in the margin of these circular structures. A very clear circular structure in the remote sensing image of Kusongmuqieke in western Tianshan in Xinjiang has been found which has the area of 2.9×2.3 km3. It has been confirmed as a tectonicmagmatic thermal dome by cross geological section survey. The dolomite and marble are located in the core, and the polymictic carbonate rock and fine grained clastic rocks are located in the marginal part. There are extrovergent normal faults between the core and the marginal part, and silicification and pyrite widely developed along faults. The circular structure found in the remote sensing image of Kusongmuqieke is coincided with the aeromagnetic composite anomaly, as well as the Co - Ni - W - Mo - Cu - Zn - Pb - Sb - Ag geochemical assemblage anomaly. There may be some very important prospecting targets of porphyryskarn type, or carlin/carlinlike type, or MVT copper, gold, iron, leadzinc large deposits. Therefore, the circular structure should be used fully and reasonably in some relatively large or super large mineral deposit exploration in the central and northern areas in Xinjiang.

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    Runout prediction of large thickbedded unstable rock: A case study of Daxiang unstable rock in Yangjiao town, Wulong county, Chongqing.
    WANG Lei, LI Bin, GAO Yang, SHU Sai-Nan
    2016, 23(2): 251-259. 
    DOI: 10.13745/j.esf.2016.02.023

    Abstract ( 8558 )   PDF (1842KB) ( 18006 )  

    Highspeed long runout landslidedebris flow is one of the most destructive failure modes of large unstable rock,which can be fast launching, run long distance and cover large area, so the runout prediction research of large unstable rock has great practical significance. Taking the Daxiang unstable rock as a study case, this project aimed at predicting the dynamic characteristics of long runout landslidedebris flow. Based on geological and geomorphological survey,the development characteristics and failure pattern of Daxiang unstable rock were analyzed. The DAN3D code and the rheological parameters calibrated through the inversion analysis of Jiweishan landslide were used for the analysis of the Daxiang unstable slope. The simulation results show that (1) the movement process of rockslidedebris avalanche could be divided into four stages as launching, deflection and throwing, crash and erosion, and long range accumulation. The whole process took 220 s, and travel distance was 2500 m; (2) the volume of the sliding mass was 530×104 m3, the total volume of the accumulation was 790×104 m3, the length of the accumulation was 1680 m and average depth was 6 m, the maximum erosion depth along the path was 8 m, and the maximum velocity was 60 m/s; (3) the debris could go though Yangjiao Town and reach the Wujiang River, which implies that the Yangjiao Town is in the danger zone; and (4) the simulated prediction could be used as a reference for landslide hazard quantitative assessment.

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    Distribution characteristics and genesis of fluoride groundwater in the Hetao basin,Inner Mongolia.
    MAO Re-Yu, GUO Hua-Meng-*, GU Yong-Feng, JIANG Yu-Xiao, CAO Yong-Sheng, DIAO Wei-Guang, WANG Zhen
    2016, 23(2): 260-268. 
    DOI: 10.13745/j.esf.2016.02.024

    Abstract ( 8660 )   PDF (1429KB) ( 18192 )  

    Not only high As groundwater but also high F- groundwater have been found in the Hetao basin of Inner Mongolia. Although much work has been done on high As groundwater, little is known about the distribution and genesis of high F- groundwater. Based on reviewing of previous data and hydrogeological setting, 406 groundwater samples were collected and analyzed from the Hetao Basin of Inner Mongolia. Mineral dissolution and precipitation, evaporation, competitive adsorption and desorption, and cation exchange were integrated to discuss the major mechanisms controlling the enrichment of groundwater fluoride in the plain and the piedmont areas in Hetao Basin with different hydrogeological conditions. Results show that over 59% of groundwater samples have fluoride concentration above the Chinas drinking water standards of 1.0 mg/L. Relatively more groundwater samples having fluoride concentrations greater than 1.0 mg/L in the piedmont area which is higher than those in the plain area. Highfluoride groundwater usually show high concentrations of Na+ and alkalinity and low concentration of Ca2+. In the flat plain, groundwater are normally higher in pH, HCO-3, δ18O, δD and TDS, and lower in Ca2+ and NO-3 than those in the piedmont area. The fluorite dissolution and calcite precipitation are the major factors controlling fluoride enrichment in groundwater at the piedmont area, while evaporation, cation exchange, competitive adsorption between OH-, HCO-3 and F- become the main controlling factors in groundwaters of the flat plain.

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    The preliminary quantitative study of paleo tectonic stress field of Yanshanian period in western Hubei Province.
    WANG Qian-Qian, MO Tian-Feng, YUAN Yu-Song, QIU De-Feng
    2016, 23(2): 269-279. 
    DOI: 10.13745/j.esf.2016.02.025

    Abstract ( 8650 )   PDF (2984KB) ( 17250 )  

    A series of NNE trending folds were formed by the major tectonic deformation in western Hubei Province and the major structural features of this region had been investigated systematically. However, a comprehensive study on paleotectonic stress field of the foldings has not been underway till now. Previous researchers had only studied on the direction of paleotectonic stress according to the fold features and fault slip directions and, had caused a number of different points of view on the Yanshanian tectonic evolution of Lichuan and Qiyueshan folds. The present paper gives a systematical research on the paleotectonic stress field of Yanshanian period including the stress direction and magnitude. According to the stratigraphic contact relationship in this region, the Jurassic and Triassic strata are in the same tectonic layer, due to their conformity relationships. However, the Cretaceous system is unconformably covered on the Jurassic and Triassic strata, which indicates that the tectonic event was occurred between the Late Jurassic and Early Cretaceous. On the basis of the data measured in the field on the occurrences of the conjugate shear joints and the attitude of the strata on both limbs of the foldings, combining with the bulk analysis on the characteristics of tectonic deformation to determine the compressive zone, it comes to the author that the directions of maximum principal compressive stress axes are generally NWSE trending. The quartz sandstone samples collected from the Jurassic and Triassic strata were tested to investigate and statistically analyze the intracrystalline free dislocation density by transmission electron microscope, then to calculate the differential stress valuesby using the empiric relationship formula. The results of the above research will provide a solid foundation for the quantitative research on paleotectonic stress field in that area.

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