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Mesoscale fracture behavior of Longmaxi outcrop shale with different bedding angles:Experimental and numerical investigations

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第2期12卷 297-309页

作者： Jianping Zuo Jingfang Lu Rojin Ghandriz Jintao Wang Yanhong Li Xiaoyan Zhang Jun Li Hongtao Li School of Mechanics and Civil Engineering China University of Mining and TechnologyBeijing100083China State Key Laboratory of Coal Resources and Safe Mining China University of Mining and TechnologyBeijing100083China Department of Mechanical Engineering University of MassachusettsDartmouth02747USA

The mechanical properties and fracturing mechanism of shale containing beddings are critically important in shale gas exploitation and wellbore stability.To investigate the effects of shale bedding on crack behavior and fracturing mechanism,scanning electron microscope(SEM)with a loading system was employed to carry out three-point bending tests on Longmaxi outcrop shale.The crack initiation and propagation of Longmaxi shale were observed and recorded by taking photos during loading.The cracking paths were extracted to calculate the crack length through a MATLAB program.The peak load,fracture toughness and fracture energy all increase with the bedding angle from 0°to 90°.The crack length and energy were also found to increase with the bedding angle in the range of 0°-600 and then drop slightly.The fracturing mechanism of shale includes the main crack affected by the bedding angle and disturbed by randomly distributed particles.The main cracking path was accompanied by several microcrack branches which could form an interconnected crack system.When the main crack encounters larger sedimentary particles,it will deflect around the particles and then restore to the initial direction.A numerical technique using extended finite element method(XFEM)coupled with anisotropic cohesive damage criteria was developed,which is able to capture the dependence of crack propagations on bedding angle and sedimentary particles.This study sheds light on understanding and predicting mesoscale fracture behavior of shale with different bedding angles.

关键词： Longmaxi shale Three-point bending test Fracture toughness Fracture energy Crack propagation Anisotropic cohesive damage Extended finite element method(XFEM)

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Formation Mechanism and Numerical Model of Quartz in Fine-Grained Organic-Rich Shales: A Case Study of Wufeng and Longmaxi Formations in Western Hubei Province, South China

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Journal of Earth Science 2020年第2期31卷 354-367页

作者： Bao Zhang Detian Yan Hassan Jasmine Drawarh Xiangrong Yang Jin He Liwei Zhang Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education China University of GeosciencesWuhan 430074China

The difference in quartz types in shales not only affects the porosity and permeability of the rocks,but also reflects the difference in the sedimentary environments.We established the formation mechanism and numerical model of quartz in shales of Wufeng and Longmaxi formations in the Wangjiawan Section,South China,based on thin-section studies using SEM(scanning electron microscope),SEM-CL(cathodoluminescence),XRD(X-ray diffraction)and geochemical analyses.There are two types of quartz in the shales:detrital quartz and authigenic quartz.Detrital quartz is mostly silt-size,typically ranging from 10 to 60μm in size and subangular to angular monocrystal in shape,and brighter than authigenic quartz by CL intensity;authigenic quartz is present in two phases in shape:grain overgrowths and crystallite grains.Overgrowth surfaces are subhedral.Crystallite grains are typically less than 10μm in size,euhedral or subhedral monocrystal in shape.Authigenic quartz can be subdivided into biogenic quartz and clay mineral transformed quartz according to the source of silicon.In the numerical model,the content of detrital quartz is relatively consistent(20%);the content of biogenic quartz ranges from 40%to 70%,with a sharp fall(0–30%)in the Guanyinqiao mudstone.During the Katian,a lower anoxic and dense water column make the dissolution of biogenic silica well preserved.Biogenic quartz is the major contributor to the sediment.During the early Hirnantian interval,due to the drop of sea level and the oxygenation of seafloor,the sediment is mainly composed of clay transformed quartz and detrital quartz.During the latest Hirnatian and Rhuddanian,rapid sea level rise and anoxic ocean enhance the preservation of the biogenic silica,thereby biogenic quartz re-emerges as the major contributors to the sediment.Authigenic crystallite grains and grain overgrowths have filled in primary pore space and have decreased the interparticle porosity,however,as a rigid framework,they can suppress compaction and maintain the internal pore structure.Th

关键词： brittle mineral quartz Wufeng and Longmaxi formations formation mechanism numerical simulation

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A Quantitative Evaluation of Shale Gas Content in Different Occurrence States of the Longmaxi Formation: A New Insight from Well JY-A in the Fuling Shale Gas Field,Sichuan Basin

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Acta Geologica Sinica(English Edition) 2019年第2期93卷 400-419页

作者： TANG Ling SONG Yan LI Qianwen PANG Xiongqi JIANG Zhenxue LI Zhuo TANG Xianglu YU Hailong SUN Yue FAN Shichao ZHU Lin State Key Laboratory of Petroleum Resources and Prospecting China University of Petroleum The Unconventional Natural Gas Institute China University of Petroleum Sinopec Petroleum Exploration and Production Research Institute

Comprehensive quantitative evaluation of shale gas content and the controlling factors in different occurrence states is of great significance for accurately assessing gas-bearing capacity and providing effective well-production strategies. A total of 122 core samples from well JY-A in the Fuling shale gas field were studied to reveal the characteristics of S_1 l shale,15 of which were selected to further predict the shale gas content in different occurrence states, which are dependent on geological factors in the thermal evolution process. Geological parameters were researched by a number of laboratory programs, and the factors influential in controlling shale gas content were extracted by both PCA and GRA methods and prediction models were confirmed by the BE method using SPSS software. Results reveal that the adsorbed gas content is mainly controlled by TOC, Ro, SSA, PD and pyrite content, and the free gas content is mainly controlled by S_2, quartz content, gas saturation and formation pressure for S_1 l in well JY-A. Three methods, including the on-site gas desorption method, the empirical formula method, and the multiple regression analysis method were used in combination to evaluate the shale gas capacity of well JY-A, all of which show that the overall shale gas content of well JY-A is in the range of 2.0–5.0 m^3/t and that the free gas ratio is about 50%, lower than that of well JY-1. Cause analysis further confirms the tectonics and preservation conditions of S_1 l in the geological processes, especially the influence of eastern boundary faults on well JY-A, as the fundamental reasons for the differences in shale gas enrichment in the Jiaoshiba area.

关键词： shale gas content on-site gas desorption multiple regression analysis controlling factors Longmaxi shales Fuling shale gas field Jiaoshiba area

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Differential Characteristics of the Upper Ordovician-Lower Silurian Wufeng-Longmaxi Shale Reservoir and its Implications for Exploration and Development of Shale Gas in/around the Sichuan Basin

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Acta Geologica Sinica(English Edition) 2019年第3期93卷 520-535页

作者： WANG Ruyue HU Zongquan LONG Shengxiang LIU Guangxiang ZHAO Jianhua DONG Li DU Wei WANG Pengwei YIN Shuai SINOPEC Petroleum Exploration and Production Research Institute Beijing 100083China SINOPEC Key Laboratory of Shale Gas/Oil Exploration&Production Beijing 100083China State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development Beijing 100083China School of Geosciences China University of Petroleum(East China)Qingdao 266580ShandongChina Shandong Provincial Key Laboratory of Depositional Mineralization&Sedimentary Minerals Shandong University of Science and TechnologyQingdao 266590ShandongChina

The Upper Ordovician Wufeng-Lower Silurian Longmaxi shale is widely distributed in the Sichuan Basin and its periphery,which is the key stratum for marine shale gas exploration and development(E&D)in China.Based on sedimentary environment,material basis,storage space,fracability and reservoir evolution data,the reservoir characteristics of the Wufeng-Longmaxi shale and their significance for shale gas E&D are systematically compared and analyzed in this paper.The results show that(1)the depocenter of the Wufeng(WF)-Longmaxi(LM)shale gradually migrates from east to west.The high-quality shale reservoirs in the eastern Sichuan Basin are mainly siliceous shales,which are primarily distributed in the graptolite shale interval of WF2-LM5.The high-quality reservoirs in the southern Sichuan Basin are mainly calcareous-siliceous and organic-rich argillaceous shales,which are distributed in the graptolite shale interval of WF2-LM7.(2)Deep shale gas(the burial depth>3500 m)in the Sichuan Basin has high-ultrahigh pressure and superior physical properties.The organic-rich siliceous,calcareous-siliceous and organic-rich argillaceous shales have suitable reservoir properties.The marginal area of the Sichuan Basin has a higher degree of pressure relief,which leads to the argillaceous and silty shales evolving into direct cap rocks with poor reservoir/good sealing capacity.(3)Combining shale gas exploration practices and impacts of lithofacies,depth,pressure coefficient and brittle-ductile transition on the reservoir properties,it is concluded that the favorable depth interval of the Wufeng-Longmaxi shale gas is 2200~4000 m under current technical conditions.(4)Aiming at the differential reservoir properties of the Wufeng-Longmaxi shale in the Sichuan Basin and its periphery,several suggestions for future research directions and E&D of shale gas are formulated.

关键词： shale gas reservoir physical property fracability evolution Wufeng Formation Longmaxi Formation,Sichuan Basin

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Laminae characteristics of gas-bearing shale fine-grained sediment of the Silurian Longmaxi Formation of Well Wuxi 2 in Sichuan Basin,SW China

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Petroleum Exploration and Development 2018年第2期45卷 358-368页

作者： SHI Zhensheng QIU Zhen DONG Dazhong LU Bin LIANG Pingping ZHANG Mengqi PetroChina Research Institute of Petroleum Exploration and Development Langfang 065007 China National Energy Shale Gas R&D (Experiment) Center Langfang 065007 China

Based on various test data, the composition, texture, structure and lamina types of gas-bearing shale were determined based on Well Wuxi 2 of the Silurian Longmaxi Formation in the Sichuan Basin. Four types of lamina, namely organic-rich lamina, organic-bearing lamina, clay lamina and silty lamina, are developed in the Longmaxi Formation of Well Wuxi 2, and they form 2 kinds of lamina set and 5 kinds of beds. Because of increasing supply of terrigenous clasts and enhancing hydrodynamics and associated oxygen levels, the contents of TOC and brittle mineral reduce and content of clay mineral increases gradually as the depth becomes shallow. Organic-rich lamina, organic-rich + organic-bearing lamina set and organic-rich bed dominate the small layers 1-3 of Member 1 of the Longmaxi Formation, suggesting anoxic and weak hydraulic depositional setting. Organic-rich lamina, along with organic-bearing lamina and silty lamina, appear in small layer 4, suggesting increased oxygenated and hydraulic level. Small layers 1-3 are the best interval and drilling target of shale gas exploration and development.

关键词： Sichuan Basin Longmaxi Formation fine-grained sediment shale gas lamina Well Wuxi 2

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Quantitative prediction of shale gas sweet spots based on seismic data in Lower Silurian Longmaxi Formation,Weiyuan area,Sichuan Basin,SW China

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Petroleum Exploration and Development 2018年第3期45卷 422-430页

作者： ZENG Qingcai CHEN Sheng HE Pei YANG Qing GUO Xiaolong CHEN Peng DAI Chunmeng LI Xuan GAI Shaohua DENG Yu HOU Huaxing Research Institute of Petroleum Exploration & Development PetroChina Beijing 100083 China China University of Petroleum Beijing 102249 China

Sweet spots in the shale reservoirs of the Lower Silurian Longmaxi Formation in Weiyuan 201 Block of Sichuan Basin were predicted quantitatively using seismic data and fuzzy optimization method. First, based on seismic and rock physics analysis, the rock physics characteristics of the reservoirs were determined, and elastic parameters sensitive to shale reservoirs with high gas content were selected. Second, data volumes with high precision of the elastic parameters were obtained from pre-stack simultaneous inversion. The horizontal distribution of key parameters for shale gas evaluation were calculated based on the results of rock physics analysis. Then, the fuzzy evaluation equation was established by fuzzy optimization method with test and logging data of horizontal wells with similar operation conditions. key parameters affecting the productivity of horizontal wells were sorted out and the weights of them in the sweet spots quantitative prediction were worked out by fuzzy optimization to set up a sweet spots evaluation system. Three classes of shale gas reservoirs which including two kinds of sweet spots were predicted with the above procedure, and the sweet spots have been predicted quantitatively by combining the above prediction results with the testing production. The testing results of 7 verification wells proved the reliability of the prediction results.

关键词： Sichuan Basin Lower Silurian Longmaxi Formation shale gas sweet spots quantitative prediction fuzzy optimization

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Investigating microstructure of Longmaxi shale in Shizhu area,Sichuan Basin, by optical microscopy, scanning electron microscopy and micro-computed tomography

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Nuclear Science and Techniques 2017年第11期28卷 226-235页

作者： Yu Wang Li-Hua Wang Jian-Qiang Wang Zheng Jiang Chan Jin Yan-Fei Wang Key Laboratory of Interfacial Physics and Technology Shanghai Institute of Applied Physics Chinese Academy of Sciences Shanghai 201800 China Shanghai Synchrotron Radiation Facility Shanghai Institute of Applied Physics Chinese Academy of SciencesShanghai 201204 China Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China

Microstructure of shale formation is the key to understanding its petrophysical and chemical properties.Optical microscopy, scanning electron microscopy and micro-computed tomography(μ-CT) have been combined for characterization of microstructure of Longmaxi(LMX)shale from Shizhu area, Sichan Basin. The results indicate that laminated LMX shale consists of mineral matrix-rich layers and organic matter(OM)-rich layers at micrometer scale in two and three dimensions. Mineral matrix layers,mainly consisting of interparticle pores and intraplatelet pores, are approximately parallel to the bedding plane.Pyrite-rich layer, mainly containing intercrystalline pores,shows a strong preferred orientation parallel to the bedding plane. OM-rich layer, mainly containing OM pores, seems to be discontinuous. In addition, intercrystalline pores are enriched in some layers, while OM pores are distributed irregularly in matrix layers. This vertical heterogeneity of pore microscopic structures in LMX shale is of great importance to understand its petrophysical and chemical properties.

关键词： Micro-computed tomography Pore microstructure Heterogeneity Matrix layers Longmaxi shale

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K-bentonite beds and high-resolution integrated strati- graphy of the uppermost Ordovician Wufeng and the lowest Silurian Longmaxi formations in South China

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Science China Earth Sciences 2003年第11期46卷 1121-1133页

作者：苏文博何龙清王永标龚淑云周湖云 School of Earth Sciences and Resources China University of Geosciences Beijing 100083 China Yichang Institute of Geology and Mineral Resources China Geological Survey Yichang 443003 China Faculty of Earth Sciences China University of Geosciences Wuhan 430074 China Test Center China University of Geosciences Wuhan 430074 China

More than 20 K-bentonite beds were discovered from the Wufeng Formation and the lowest Longmaxi Formation in two sections, both adjacent to the Ordovician-Silurian (O-S) bound-ary and located in Tongzi, Guizhou Province and Yichang, Hubei Province, some 500 km apart from each other in South China. This indicates that many volcanic eruptions occurred near the southeast margin of the Yangtze Platform between the latest Ordovician and the earliest Silurian. Mainly through biostratigraphic and sequence stratigraphic studies, it was found that almost all these far-apart K-bentonite beds may be correlated with each other. This is the first time that a succession of volcanic ash deposits with high potential of correlation was discovered within a strata interval on the main platforms of China. Therefore, these K-bentonite beds may afford ex-cellent event-marker beds helpful to high-resolution research in integrated stratigraphy as well as other lines of research on the O-S boundary in South China.

关键词： K-bentonite bed, event-marker, high-resolution integrated stratigraphy, Ordovician-Silurian Boundary, Wufeng & Longmaxi formations, Yangtze Platform.

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The progress and prospects of shale gas exploration and development in southern Sichuan Basin, SW China

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Petroleum Exploration and Development 2018年第1期45卷 172-182页

作者： MA Xinhua XIE Jun PetroChina Southwest Oil & Gas Field Company 610051 Chengdu China

The Ordovician Wufeng Formation-Silurian Longmaxi Formation organic-rich shales distributed widely and stably in Southern Sichuan Basin were investigated based on drilling data.Geological evaluation of wells show that the shale reservoirs have good properties in the Yibin,Weiyuan,Zigong,Changning,Luzhou,Dazu areas,with key parameters such as TOC,porosity,gas content similar to the core shale gas production zones.Moreover,these areas are stable in structure,good in preservation conditions and highly certain in resources.The shale reservoirs have a burial depth of 4 500 m or shallow,a total area of over 2×10~4 km^2 and estimated resource of over10×10^(12) m^3,so they are the most resource-rich and practical areas for shale gas exploitation in China.Through construction of the Changning-Weiyuan national demonstration region,the production and EUR of shale gas wells increased significantly,the cost of shale gas wells decreased remarkable,resulting in economic benefit better than expected.Moreover,the localized exploration and development technologies and methods are effective and repeatable,so it is the right time for accelerating shale gas exploitation.Based on the production decline pattern of horizontal wells at present and wells to be drilled in the near future,at the end of the 13th Five Year Plan,the production of shale gas in southern Sichuan Basin is expected to reach or exceed 10 billion cubic meters per year.The resources are sufficient for a stable production period at 30 billion cubic meters per year,which will make the South Sichuan basin become the largest production base of shale gas in China.

关键词： Sichuan Basin southern Sichuan Basin shale gas Ordovician Wufeng Formation Silurian Longmaxi Formation resource potential

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A review and research on comprehensive characterization of microscopic shale gas reservoir space

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China Geology 2019年第4期2卷 541-556页

作者： Yu-ru Yang Xiao-chen Liu Hui Zhang Gang-yi Zhai Jiao-dong Zhang Zhi-fang Hu Shu-jing Bao Cong Zhang Xiang-hua Wang Xiao Yang Zheng-zhuang Liu Ting Xie Juan Chen Liyu Fang Li-juan Qin Oil and Gas Survey China Geological SurveyBeijing 100083China Unconventional Petroleum Geology Laboratory of Oil and Gas Survey Ministry of Natural ResourcesChina Geological SurveyBeijing 100094China SGS-CSTC Standards Technical Services Co. Ltd.Beijing 100176China School of Energy Resources China University of Geosciences(Beijing)Beijing 100083China

In this paper,substantial domestic and foreign research results of microscopic shale reservoir space were systemically reviewed,the research history consisting of simple observation and qualitative classification,quantitative research,the combination of qualitative and quantitative research successively as well as the characteristics of each research stage were summarized.In addition,the current problems existing in the characterization methods of shale reservoir space were also analyzed.Furthermore,based on massive actual detection of typical core samples obtained from more than 50 global shale gas wells and relevant practical experience,a comprehensive characterization method of combining qualitative with the semiquantitative characterization was put forward.In detail,the indicators of the qualitative characterization include pore combination type and organic-matter microscopic morphology type,while the core elements of the semi-quantitative characterization include the percentage of the organic-matter area and the plane porosity of the pores of different types.Based on the reference of the naming and classification of rocks,the three-end-member diagram method was used to characterize microscopic shale reservoir space.This is achieved by plotting the three end-member diagram of 3 kinds of first-order critical reservoir spaces,i.e.,organic-matter pores,matrix pores,and micro-fractures,in order to intuitively present the features of the microscopic pore combination.Meanwhile,statistic histograms of organic-matter microscopic morphology type and the plane porosity of different types of pores were adopted to characterize the development degree of second-order pores quantitatively.By this comprehensive characterization method,the importance of both pore combination and the microscopic morphology of organic matter were emphasized,revealing the control of organic-matter microscopic morphology over the organic-matter pores.What is more,high-resolution FE-SEM was adopted to obtain semi-quantitative statistics results.In

关键词： Shale Shale gas Reservoir space Research status Types of pore combinations Oil-gas exploration engineering Longmaxi Formation Niutitang Formation Shahejie Formation Yanchang Formation China USA

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