The microstructural analysis of muds and mudrocks requires very high-resolution measurement. Recent advances in electron microscopy have contributed significantly to the improved characterisation of mudrock microstruc...The microstructural analysis of muds and mudrocks requires very high-resolution measurement. Recent advances in electron microscopy have contributed significantly to the improved characterisation of mudrock microstructures and their consequent petrophysical properties. However, imaging through electron microscopy is limited to small areas of coverage such that upscaling of these properties is a great challenge. In this paper, we develop a new methodology for multiple large-area imaging using scanning electron microscopy through automated acquisition and stitching from polished thin-sections and ion-milled samples. The process is fast, efficient and minimises user-input and bias. It can provide reliable, quantifiable data on sediment grain size, grain orientation, pore size and porosity. Limitations include the time involved for individual runs and manual segmentation, the large amount of computer memory required, and instrument resolution at the nano-scale. This method is applied to selected samples of Quaternary muddy sediments from the Iberian margin at IODP Site 1385. The section comprises finegrained(very fine clayey silts), mixed-composition, biogenic-terrigenous hemipelagites, with a pronounced but non-regular colour cyclicity. There is a multi-tiered and diverse trace fossil assemblage of the deep-water Zoophycos ichnofacies. The sediment microstructures show small-scale heterogeneity in all properties, and an overall random fabric with secondary preferred grain-alignment. These results on the fabric differ, in part, from previous studies of hemipelagic muds. Further work is underway on their comparison with other deep-water sediment facies.展开更多
Geochemical analysis of Neogene mudrocks from Sitakund anticline, Chittagong Tripura Fold Belt (CTFB), Bengal Basin, Bangladesh, was deployed to delineate the provenance, tectonics and depositional environments. Repre...Geochemical analysis of Neogene mudrocks from Sitakund anticline, Chittagong Tripura Fold Belt (CTFB), Bengal Basin, Bangladesh, was deployed to delineate the provenance, tectonics and depositional environments. Representative samples went through mineralogical and geochemical analysis concerning major, trace and rare earth element analysis. Rigaku ZSX Primus and NITON XL3t 800 XRF instruments were utilized for the determination of major and trace elements. The experiment results reveal that the Neogene mudrocks are rich in silica having concentration of 58.10% to 62.60% with an average of 59.90%. Therefore, the geochemical response from the experiments apparently proved the existence of the active continental margin setting for the Neogene mudrocks. Different concentrations and ratios of major oxides satisfy that the mudrocks were derived from felsic source rocks. In addition, chemical index of alteration (CIA) values for the Neogene mudrocks vary from 67.81 to 77.57 with an average 74.41 indicating significant weathering at the source areas. Moreover, U/Th, Cu/Zn, Ni/Co and V/Cr ratios designate that the mudrocks were deposited in oxidizing depositional environment.展开更多
Shales in deep lake basins have become the main focus of continental shale oil and gas exploration.In order to highlight the sedimentary dynamics of mud deposition in deep lake basins,a combination of core observation...Shales in deep lake basins have become the main focus of continental shale oil and gas exploration.In order to highlight the sedimentary dynamics of mud deposition in deep lake basins,a combination of core observation,thin section examination,X-ray diffraction,and QEMSCAN(quantitative evaluation of minerals by scanning electron microscopy)was used to analyze the depositional characteristics of mudrocks in the Chang-7 Member from the Yanchang Formation(Upper Triassic)in Ordos Basin,and to establish a depositional model for mud accumulation in deep lake basins.This study recognizes four mudrock lithofacies in the Chang-7 Member:(1)the laminated silt-bearing mudstone,which generally develops a binary composition of“silt-clay”or a ternary composition of“silt-clay-organic matter”;(2)the graded mudstone,mainly composed of dark gray and gray-black mudstone sandwiched by silt-bearing mudstone;(3)the massive mudstone,internally showing a uniform distribution of quartz,clay,and carbonate minerals,with also a small amount of organic detritus;and(4)the laminated shale,which is generally composed of clay laminae,and organic laminae of the former two.Sediment supply,topographic slope,and flood intensity combine to control the evolution of gravity flows and the transport and deposition of the mudrock in the Chang-7 Member.The influence of orogeny provides terrain gradient,water depth,abundant sediments at source areas,and triggering mechanism for the formation of gravity flows.Floods triggered by wetting events provide the impetus for sediment transport.Mud deposition in the Chang-7 Member was mainly related to the transport and sedimentation of mud by hyperpycnal flows and rapid sedimentation by buoyant plume flocculation.A comprehensive evolutionary model for shale accumulation in the deep lake basin is established by integrating various triggering mechanisms and mud transport sedimentary processes.展开更多
Nanoscale pore characteristics of the Upper Permian Longtan transitional mudrocks and their equivalent strata Wujiaping Formation marine mudrocks in and around the eastern Sichuan Basin was investigated using field em...Nanoscale pore characteristics of the Upper Permian Longtan transitional mudrocks and their equivalent strata Wujiaping Formation marine mudrocks in and around the eastern Sichuan Basin was investigated using field emission scanning electron microscopy(FE-SEM)and low-pressure N2 adsorption experiments.The results indicate that the Upper Permian mudrock is at a mature stage with total organic carbon(TOC)values ranging between 0.47%and 12.3%.The Longtan mudrocks mainly contain vitrinite,and their mineral composition is primarily clay.In contrast,the Wujiaping mudrocks are dominated by sapropelinite and solid bitumen,and their mineral compositions are mainly quartz and a notably high amount of pyrite.The FE-SEM reveals that clay mineral pores and microcracks are the common pore types in the Longtan mudrocks.The specific surface area and pore volume depend on the clay content but are negatively correlated with the TOC.The generation of nanometer pores in the Longtan mudrocks is caused by high clay mineral contents.Meanwhile,the Wujiaping mudrock mainly contains OM pores,and the pore parameters are positively correlated with the TOC.The OM pore development exhibits remarkable differences in the Longtan and Wujiaping mudrocks,which might be related to their sedimentary facies and maceral fractions.Vitrinite and inertinite appear as discrete particles in these mudrocks and cannot generate pores during thermal maturation.Sapropelinite often contains many secondary pores,and solid bitumen with large particles,usually with several pores,is not the major contributor to the pore system of the investigated mudrock.展开更多
An integrated approach to geomaterial characterization is advocated that combines geology, in-situ testing, fabric studies, routine index experiments and advanced laboratory testing. It is shown that advanced laborato...An integrated approach to geomaterial characterization is advocated that combines geology, in-situ testing, fabric studies, routine index experiments and advanced laboratory testing. It is shown that advanced laboratory testing can explore features such as kinematic yielding and anisotropy in stiffness or shear strength that would otherwise be impossible to quantify. A detailed study performed in London clay at the new Heathrow Terminal 5 site is used to illustrate the arguments made. It is shown that the London clay has strong anisotropy in stiffness, is highly non-linear over the strain range of engineering interest, has markedly anisotropic shear strength characteristics and exhibits a pronounced degree of brittleness. These features can impact significantly on the practical design and analysis of civil engineering works including shallow and deep foundations, tunnels and excavations, and the stability of slopes.展开更多
Squeezing ground conditions,which can lead to severe loads in tunnels,have historically been associated with the presence of clay minerals in the ground.Over the years,many methodologies have been proposed to predict ...Squeezing ground conditions,which can lead to severe loads in tunnels,have historically been associated with the presence of clay minerals in the ground.Over the years,many methodologies have been proposed to predict squeezing in tunnels based on tunnel depth,in situ stress,ground mineralogy,and ground strength and deformation behavior.This paper presents a comprehensive review of methodologies to predict tunnel squeezing in clay-rich rocks.A new methodology is proposed where ground conditions and squeezing potential are assessed based on the Stress History and Normalized Soil Engineering Properties(SHANSEP)approach adapted to clayrich rocks,Peck’s stability number and Hoek&Brown’s(1997)Geological Strength Index(GSI).A squeezing number S is suggested to classify ground conditions based on the level of squeezing that the ground may experience in response to tunneling.Finally,it is demonstrated that by combining the proposed classification system and an existing classification system for ground squeezing condition,an accurate estimate of tunnel strain can also be obtained.The proposed method is applied to four case studies of tunnels in squeezing ground in shale and mudstone.展开更多
The sources,transportation and depositional processes of lacustrine mudrock are still poorly understood.Existing studies have demonstrated the controlling effect of astronomical forcing on lacustrine mudrock depositio...The sources,transportation and depositional processes of lacustrine mudrock are still poorly understood.Existing studies have demonstrated the controlling effect of astronomical forcing on lacustrine mudrock deposition,but its depositional mechanism and evolution are still not systematically investigated.Most research related to astronomical forcing exclusively highlights the sedimentation of carbonate rocks in deep-water lacustrine setting,with insufficient attention paid to the thick organic-rich,deep-lake mudrock.With the increasing interest in exploration and development of shale oil and gas accumulations,it is urgent to deeply understand depositional rules of lacustrine mudrock.This study reviews sediment sources,depositional mechanism and evolution process of mudrock through expounding the correlations between the periodic changes of astronomical forces,the parameters of Earth orbital and mudrock compositions.By investigating the existing literature and using some actual data of Jiyang Depression,Bohai Bay Basin in East China,this study expounds on the influence of astronomical cycles on the deposition of lacustrine mudrock.Moreover,efforts are made to analyze the effects of various orbital parameters(e.g.,precession,obliquity,and eccentricity with the periods ranging from tens of thousands years to million years)on the deposition of mudrock from small-scale(decimeters to meters)to large-scale(10s to 100s meters).Further,it is feasible to apply the high-precision isochronous stratigraphic correlation into clarifying the distribution of favorable shale oil and gas reservoirs.To conclude,this study enunciates the sedimentation of mudrock from a new perspective(astronomical forcing)and provides a direction for the research on sedimentation of fine-grained sedimentary rocks.展开更多
基金the sponsorship received from Petroleum Technology Development Fund, Nigeria
文摘The microstructural analysis of muds and mudrocks requires very high-resolution measurement. Recent advances in electron microscopy have contributed significantly to the improved characterisation of mudrock microstructures and their consequent petrophysical properties. However, imaging through electron microscopy is limited to small areas of coverage such that upscaling of these properties is a great challenge. In this paper, we develop a new methodology for multiple large-area imaging using scanning electron microscopy through automated acquisition and stitching from polished thin-sections and ion-milled samples. The process is fast, efficient and minimises user-input and bias. It can provide reliable, quantifiable data on sediment grain size, grain orientation, pore size and porosity. Limitations include the time involved for individual runs and manual segmentation, the large amount of computer memory required, and instrument resolution at the nano-scale. This method is applied to selected samples of Quaternary muddy sediments from the Iberian margin at IODP Site 1385. The section comprises finegrained(very fine clayey silts), mixed-composition, biogenic-terrigenous hemipelagites, with a pronounced but non-regular colour cyclicity. There is a multi-tiered and diverse trace fossil assemblage of the deep-water Zoophycos ichnofacies. The sediment microstructures show small-scale heterogeneity in all properties, and an overall random fabric with secondary preferred grain-alignment. These results on the fabric differ, in part, from previous studies of hemipelagic muds. Further work is underway on their comparison with other deep-water sediment facies.
文摘Geochemical analysis of Neogene mudrocks from Sitakund anticline, Chittagong Tripura Fold Belt (CTFB), Bengal Basin, Bangladesh, was deployed to delineate the provenance, tectonics and depositional environments. Representative samples went through mineralogical and geochemical analysis concerning major, trace and rare earth element analysis. Rigaku ZSX Primus and NITON XL3t 800 XRF instruments were utilized for the determination of major and trace elements. The experiment results reveal that the Neogene mudrocks are rich in silica having concentration of 58.10% to 62.60% with an average of 59.90%. Therefore, the geochemical response from the experiments apparently proved the existence of the active continental margin setting for the Neogene mudrocks. Different concentrations and ratios of major oxides satisfy that the mudrocks were derived from felsic source rocks. In addition, chemical index of alteration (CIA) values for the Neogene mudrocks vary from 67.81 to 77.57 with an average 74.41 indicating significant weathering at the source areas. Moreover, U/Th, Cu/Zn, Ni/Co and V/Cr ratios designate that the mudrocks were deposited in oxidizing depositional environment.
基金co-funded by the National Natural Science Foundation of China (Grant No.42372141and Grant No.42072126)Open Fund (DGERA20241002) of Key Laboratory of Deep-time Geography and Environment Reconstruction and Applications of Ministry of Natural Resources,Chengdu University of Technologythe Science Development Fund of Dongying (Grant No.2024kyqd004).
文摘Shales in deep lake basins have become the main focus of continental shale oil and gas exploration.In order to highlight the sedimentary dynamics of mud deposition in deep lake basins,a combination of core observation,thin section examination,X-ray diffraction,and QEMSCAN(quantitative evaluation of minerals by scanning electron microscopy)was used to analyze the depositional characteristics of mudrocks in the Chang-7 Member from the Yanchang Formation(Upper Triassic)in Ordos Basin,and to establish a depositional model for mud accumulation in deep lake basins.This study recognizes four mudrock lithofacies in the Chang-7 Member:(1)the laminated silt-bearing mudstone,which generally develops a binary composition of“silt-clay”or a ternary composition of“silt-clay-organic matter”;(2)the graded mudstone,mainly composed of dark gray and gray-black mudstone sandwiched by silt-bearing mudstone;(3)the massive mudstone,internally showing a uniform distribution of quartz,clay,and carbonate minerals,with also a small amount of organic detritus;and(4)the laminated shale,which is generally composed of clay laminae,and organic laminae of the former two.Sediment supply,topographic slope,and flood intensity combine to control the evolution of gravity flows and the transport and deposition of the mudrock in the Chang-7 Member.The influence of orogeny provides terrain gradient,water depth,abundant sediments at source areas,and triggering mechanism for the formation of gravity flows.Floods triggered by wetting events provide the impetus for sediment transport.Mud deposition in the Chang-7 Member was mainly related to the transport and sedimentation of mud by hyperpycnal flows and rapid sedimentation by buoyant plume flocculation.A comprehensive evolutionary model for shale accumulation in the deep lake basin is established by integrating various triggering mechanisms and mud transport sedimentary processes.
基金supported by the National NaturalScience Foundation of China(Grant No.41802163,41503033)Hunan Provincial Natural Science Foundation of China(Grant No.2018JJ3152)+1 种基金the Science and Technology Plan Project of Sichuan province(Grant No.2018JZ0003)the State Petroleum and Gas Specific Project(Grant No.2016ZX05061001-001)
文摘Nanoscale pore characteristics of the Upper Permian Longtan transitional mudrocks and their equivalent strata Wujiaping Formation marine mudrocks in and around the eastern Sichuan Basin was investigated using field emission scanning electron microscopy(FE-SEM)and low-pressure N2 adsorption experiments.The results indicate that the Upper Permian mudrock is at a mature stage with total organic carbon(TOC)values ranging between 0.47%and 12.3%.The Longtan mudrocks mainly contain vitrinite,and their mineral composition is primarily clay.In contrast,the Wujiaping mudrocks are dominated by sapropelinite and solid bitumen,and their mineral compositions are mainly quartz and a notably high amount of pyrite.The FE-SEM reveals that clay mineral pores and microcracks are the common pore types in the Longtan mudrocks.The specific surface area and pore volume depend on the clay content but are negatively correlated with the TOC.The generation of nanometer pores in the Longtan mudrocks is caused by high clay mineral contents.Meanwhile,the Wujiaping mudrock mainly contains OM pores,and the pore parameters are positively correlated with the TOC.The OM pore development exhibits remarkable differences in the Longtan and Wujiaping mudrocks,which might be related to their sedimentary facies and maceral fractions.Vitrinite and inertinite appear as discrete particles in these mudrocks and cannot generate pores during thermal maturation.Sapropelinite often contains many secondary pores,and solid bitumen with large particles,usually with several pores,is not the major contributor to the pore system of the investigated mudrock.
基金Project supported by the UK Engineering and Physical Sciences Research Council (EPSRC)the British Airports Authority (BAA)the London Underground Limited (LUL),UK
文摘An integrated approach to geomaterial characterization is advocated that combines geology, in-situ testing, fabric studies, routine index experiments and advanced laboratory testing. It is shown that advanced laboratory testing can explore features such as kinematic yielding and anisotropy in stiffness or shear strength that would otherwise be impossible to quantify. A detailed study performed in London clay at the new Heathrow Terminal 5 site is used to illustrate the arguments made. It is shown that the London clay has strong anisotropy in stiffness, is highly non-linear over the strain range of engineering interest, has markedly anisotropic shear strength characteristics and exhibits a pronounced degree of brittleness. These features can impact significantly on the practical design and analysis of civil engineering works including shallow and deep foundations, tunnels and excavations, and the stability of slopes.
基金the University Transportation Center for Underground Transportation Infrastructure(UTC-UTI)at the Colorado School of Mines for funding this research under Grant No.69A3551747118 from the U.S.Department of Transportation(DOT).
文摘Squeezing ground conditions,which can lead to severe loads in tunnels,have historically been associated with the presence of clay minerals in the ground.Over the years,many methodologies have been proposed to predict squeezing in tunnels based on tunnel depth,in situ stress,ground mineralogy,and ground strength and deformation behavior.This paper presents a comprehensive review of methodologies to predict tunnel squeezing in clay-rich rocks.A new methodology is proposed where ground conditions and squeezing potential are assessed based on the Stress History and Normalized Soil Engineering Properties(SHANSEP)approach adapted to clayrich rocks,Peck’s stability number and Hoek&Brown’s(1997)Geological Strength Index(GSI).A squeezing number S is suggested to classify ground conditions based on the level of squeezing that the ground may experience in response to tunneling.Finally,it is demonstrated that by combining the proposed classification system and an existing classification system for ground squeezing condition,an accurate estimate of tunnel strain can also be obtained.The proposed method is applied to four case studies of tunnels in squeezing ground in shale and mudstone.
基金co-funded by the China National Key Research Project(Grant No.2017ZX05009-002)the National Natural Science Foundation of China(Grant Nos.41772090,41802130)the Foundation from Shandong Key Laboratory of Depositional Mineralization and Sedimentary Mineral,Shandong University of Science and Technology(Grant No.DMSM20190024)。
文摘The sources,transportation and depositional processes of lacustrine mudrock are still poorly understood.Existing studies have demonstrated the controlling effect of astronomical forcing on lacustrine mudrock deposition,but its depositional mechanism and evolution are still not systematically investigated.Most research related to astronomical forcing exclusively highlights the sedimentation of carbonate rocks in deep-water lacustrine setting,with insufficient attention paid to the thick organic-rich,deep-lake mudrock.With the increasing interest in exploration and development of shale oil and gas accumulations,it is urgent to deeply understand depositional rules of lacustrine mudrock.This study reviews sediment sources,depositional mechanism and evolution process of mudrock through expounding the correlations between the periodic changes of astronomical forces,the parameters of Earth orbital and mudrock compositions.By investigating the existing literature and using some actual data of Jiyang Depression,Bohai Bay Basin in East China,this study expounds on the influence of astronomical cycles on the deposition of lacustrine mudrock.Moreover,efforts are made to analyze the effects of various orbital parameters(e.g.,precession,obliquity,and eccentricity with the periods ranging from tens of thousands years to million years)on the deposition of mudrock from small-scale(decimeters to meters)to large-scale(10s to 100s meters).Further,it is feasible to apply the high-precision isochronous stratigraphic correlation into clarifying the distribution of favorable shale oil and gas reservoirs.To conclude,this study enunciates the sedimentation of mudrock from a new perspective(astronomical forcing)and provides a direction for the research on sedimentation of fine-grained sedimentary rocks.
