Large numbers of gas reservoirs have been discovered in overpressure basins.Fluid charging has a close relationship with paleo-pressure evolution,affecting the migration of gas reservoirs.To study fluid charging and t...Large numbers of gas reservoirs have been discovered in overpressure basins.Fluid charging has a close relationship with paleo-pressure evolution,affecting the migration of gas reservoirs.To study fluid charging and the related pressure system,we analyzed burial histories and fluid inclusion(PVTx)simulations and conducted basin modeling of the Ledong Slope Zone in the Yinggehai Basin as an example.On the basis of fluid-inclusion assemblages(FIAs),homogenization temperature(Th),final melting temperature(Tm,ice)and Raman spectroscopy in fluid inclusions,there are three stages of fluid charging:during the first and second stage,methane-dominated fluid was charged at 2.2–1.7 Ma and 1.7–0.9 Ma,respectively.In the third stage,CO_(2)-rich hydrothermal fluid was charged since 0.9 Ma.It could be concluded from the well-logging data that the disequilibrium compaction in the Yinggehai Fm.,along with the fluid expansion and clay diagenesis in the Huangliu and Meishan formations,resulted in the overpressure in the Ledong slope zone.The evolution of paleo-pressure was affected by the sedimentation rate of the Yinggehai Fm.,as well as the hydrocarbon generation rate.Additionally,the Ledong Slope Zone is less affected by diapir activity than the nearby diapir area.Based on fluid inclusions,paleo-pressure,basin modeling and geological background,the gas migration history of the Ledong Slope Zone can be divided into four stages:in the first stage,excess pressure was formed around 5 Ma;from 2.2 to 1.7 Ma,there was a reduction in the charging of hydrocarbon fluid and steadily increasing excess pressure;during the 1.7–0.9 Ma period a large amount of hydrocarbon was generated,excess pressure increasing significantly and hydraulic fractures forming in mudstones,With gas reservoirs developing in structural highs;since 0.9 Ma,CO_(2)-rich hydrothermal fluid accumulated in reservoirs adjacent to faults and the pressure coefficient remained stable.The research results are helpful in the study of fluid migration and accumulation mechanisms in overpressure basins.展开更多
Background,aim,and scope Certain physicochemical indexes of topsoil are closely related to climatic factors including temperature,and precipitation.Understanding the relationship between modern topsoil properties and ...Background,aim,and scope Certain physicochemical indexes of topsoil are closely related to climatic factors including temperature,and precipitation.Understanding the relationship between modern topsoil properties and climatic factors is essential for quantitative paleoclimate reconstruction.Motuo located in the eastern Himalayas,exhibits a significant elevation gradient of over 7000 m from Nnamjagbarwa Peak(7782 m a.s.l.)to the Baxika(150 m a.s.l.).This region features a complete vertical zonation of vegetation,from alpine meadow to tropical forest,presenting an ideal place to investigate the relationships among vegetation,soil and climate conditions across altitudinal gradients.This study aims to explore the vertical variations in the physicochemical composition of topsoil and its relationship with temperature and precipitation.Materials and methods Twenty-seven topsoil samples were collected at 100 m intervals from 800 m to 3600 m a.s.l.along the southern slope of the Himalayas.Grain size,magnetic susceptibility and geochemical elements were measured to discuss the vertical variation characteristics of topsoil composition and their correlation with climatic factors.Results(1)The grain size of topsoil at different altitudes in Motuo is mainly composed of sand accounting for an averaged 53.2%,followed by silt and clay.(2)In the mixed forest zone,frequency dependent magnetic susceptibility(χfd%)shows a clear relationship with altitude,and clay is positively correlated with both altitude and climatic factors.(3)The oxides of topsoil in this area mainly consist of SiO_(2),Al_(2)O_(3) and Fe_(2)O_(3),followed by MgO,CaO,Na_(2)O and K_(2)O,with slight variations in the primary components at different altitudes.The sensitivity of elements to climate varies across different altitudes and vegetation zone,likely due to the region’s complex topography and vegetation.(4)Physical and biological weathering dominates in the broad-leaved forest zone of Motuo,while chemical weathering is more prominent in the coniferous forest zone,with the mixed forest zone falling in between.Discussion The formation of topsoil across the three vegetation zones is influenced by various factors,including parent material,vegetation,and climate.In the broad-leaved forest zone,physical weathering(precipitation,root wedging etc.)and pedogenesis dominate,resulting in finer grain size.The χ_(fd)% increases with altitude likely due to the high temperature and abundant precipitation in this zone,which facilitate the transformation of strong magnetic miners into weaker ones,particularly when the soil is oversaturated.Zirconium(Zr),primarily found in zircon,is depleted at lower altitudes by strong current erosion.Barium(Ba)is similarly reduced at low altitudes in this zone.In mixed forest zone,clay content is the lowest,indicating weaker physical weathering conditions than broad-leaved forest zone.The coarser grain size may result from the combined effects of topography and vegetation coverage.Magnetic susceptibility and organic matter show a positive correlation with altitude.Zr concentration is higher than that in the broad-leaved forest zone,likely resulting from decreased precipitation.In the coniferous zone,the clay content shows considerable fluctuations,with grain size generally becoming finer as altitude increases.This trend may be explained by intensified soil disintegration from seasonal freeze-thaw cycles.The χ_(fd)% values lack a clear trend or pattern,possibly due to soil erosion causing the migration of magnetic minerals or insufficient iron precipitation,which reduces the concentration of magnetic minerals in the soil.Additionally,a positive correlation is observed between altitude and organic matter content,with higher altitudes associated with greater organic matter accumulation.This may be attributed to lower microbial activity in colder conditions,which slows the decomposition and transformation of organic matter.Conclusions The variations in grain size,magnetic susceptibility,and geochemical elements differ across altitudes and vegetation zones,closely connected to the complex interplay of terrain,vegetation,and climate in Motuo.In the mixed forest,altitude has a significant impact onχfd%,and the clay component is particularly sensitive to changes in altitude,mean annual temperature,and precipitation.Zr shows a strong correlation with altitude and climate factors,making it a valuable indicator for assessing changes in atmospheric precipitation within specific altitude ranges.Recommendations and perspectives This study enhances our understanding of the relationships between the physicochemical properties of topsoil and climate conditions,offering valuable insights for paleoclimate reconstruction in Motuo.展开更多
The purpose of this study is to forecast the profitable oil and gas reservoir,which is the key of finding hydrocarbon,based on the conception of special geologic bodies.With the guiding methodology of the research thi...The purpose of this study is to forecast the profitable oil and gas reservoir,which is the key of finding hydrocarbon,based on the conception of special geologic bodies.With the guiding methodology of the research thinking of integration of point-line-surface by using the methods and techniques of logging,seismic,seismic attribute,and logging constrained inversion in 3D data volume,the special geologic bodies of Member 3 of Dongying Formation in Littoral Slope Zone of Qikou Sag,which has important hydrocarbon exploration potential,are recognized and described under the constraint of sequence stratigraphic framework.As a result,the developed scale,geometric shape and space distribution feature of the special geologic bodies are forecasted;the inner structure and sequence structure patterns of the geologic bodies are also ascertained.From the lowstand system tract (LST) and lacustrine expanding system tract (EST) to the highstand system tract (HST),the geologic bodies have evolved from relative centralization of lake basin reducing period to three relative dispersive isolated parts of broad lake basin period.According to the relevance and regularity of the development of geologic bodies,the conclusions can be obtained that three types of potential profitable reservoir traps,including the lithologic lens traps,lithologic updip pinchout traps and structural-lithologic composite traps,are forecasted.In addition,scientific basis for further hydrocarbon exploration in new area (few-well area and no-well area) is offered in the guidance of sequence stratigraphic model.展开更多
Rainfall, as one of the most significant factors triggering the residual soil slope failure, leads to not only the reduction of soil shear strength, but also the increase of soil weight and the decrease of matric suct...Rainfall, as one of the most significant factors triggering the residual soil slope failure, leads to not only the reduction of soil shear strength, but also the increase of soil weight and the decrease of matric suction as well. All these modifications in soil properties have important influence on the slope stability. The water infiltration and redistribution inside the slope are the preconditions of the slope stability under rainfall conditions. Based on the numerical simulation via finite element method, the water infiltration process under rainfall conditions was studied in the present work. The emphases are the formation, distribution and dissipation of transient saturated zone. As for the calculation parameters, the SWCC and the saturated permeability have been determined by pressure plate test and variable head test respectively. The entire process(formation, development, dissipation) of the transient saturated zone was studied in detail. The variations of volumetric water content, matric suction and hydraulic gradient inside the slope, and the eventually raise of groundwater table were characterized and discussed, too. The results show that the major cause of the formation of transient saturated zone is ascribed to the fact that the exudation velocity of rainwater on the wetting front is less than the infiltration velocity of rainfall; as a result, the water content of the soil increases. On the other hand, the formation and extension of transient saturated zone have a close relationship with rainfall intensity and duration. The results can help the geotechnical engineers for the deeper understanding of the failure of residual slope under rainfall condition. It is also suggested that the proper drainage system in the slope may be the cost-effective slope failure mitigation method.展开更多
Multi-beam bathymetry and seismic sequence surveys in the northern slope of the South China Sea reveal detailed geomorphology and seismic stratigraphy characteristics of canyons, gullies, and mass movements. Modern ca...Multi-beam bathymetry and seismic sequence surveys in the northern slope of the South China Sea reveal detailed geomorphology and seismic stratigraphy characteristics of canyons, gullies, and mass movements. Modern canyons and gullies are roughly elongated NNW–SSW with U-shaped cross sections at water depths of 400–1000 m. Mass movements include slide complexes, slide scars, and debris/turbidity flows. Slide complexes and slide scars are oriented in the NE–SW direction and cover an area of about 1790 and 926 km^2, respectively. The debris/turbidity flows developed along the lower slope. A detailed facies analysis suggests that four seismic facies exist, and the late Cenozoic stratigraphy above the acoustic basement can be roughly subdivided into three sequences separated by regional unconformities in the study area. The occurrence of gas hydrates is marked by seismic velocity anomalies, bottom-simulating reflectors, gas chimneys, and pockmarks in the study area. Seismic observations suggest that modern canyons and mass movements formed around the transition between the last glacial period and the current interglacial period. The possible existence and dissociation of gas hydrates and the regional tectonic setting may trigger instability and mass movements on the seafloor. Canyons may be the final result of gas hydrate dissociation. Our study aims to contribute new information that is applicable to engineering construction required for deep-water petroleum exploration and gas hydrate surveys along any marginal sea.展开更多
Various factors controlling the accumulation of natural gas hydrates(NGHs)form various enrichment and accumulation modes through organic combination.This study mainly analyzes the geological and geophysical characteri...Various factors controlling the accumulation of natural gas hydrates(NGHs)form various enrichment and accumulation modes through organic combination.This study mainly analyzes the geological and geophysical characteristics of the NGHs occurrence in the uplifts and their slope zones within the deep-water area in the Qiongdongnan(QDN)Basin(also referred to as the study area).Furthermore,it investigates the dominant governing factors and models of NGHs migration and accumulation in the study area.The results are as follows.(1)The uplifts and their slope zones in the study area lie in the dominant pressure-relief direction of fluids in central hydrocarbon-rich sags in the area,which provide sufficient gas sources for the NGHs accumulation and enrichment through pathways such as gas chimneys and faults.(2)The top and flanks of gas chimneys below the bottom simulating reflectors(BSRs)show high-amplitude seismic reflections and pronounced transverse charging of free gas,indicating the occurrence of a large amount of gas accumulation at the heights of the uplifts.(3)Chimneys,faults,and high-porosity and high-permeability strata,which connect the gas hydrate temperature-pressure stability zones(GHSZs)with thermogenic gas and biogenic gas,form the main hydrate migration system.(4)The reservoir system in the study area comprises sedimentary interlayers consisting of mass transport deposits(MTDs)and turbidites.In addition,the reservoir system has developed fissure-and pore-filling types of hydrates in the pathways.The above well-matched controlling factors of hydrate accumulation enable the uplifts and their slope zones in the study area to become the favorable targets of NGHs exploration.展开更多
The development, evolution and formation mechanism of faults and their control on the migration and accumulation of Mesozoic oil and gas in the middle-shallow layers of the slope zone of Mahu sag were studied by the i...The development, evolution and formation mechanism of faults and their control on the migration and accumulation of Mesozoic oil and gas in the middle-shallow layers of the slope zone of Mahu sag were studied by the interpretation of seismic and drilling data. Two types of faults, normal and strike-slip, are developed in the middle-shallow layers of the slope zone of the Mahu sag and they are mostly active in the Yanshanian period. They are divided into four grade faults: The grade I strike-slip faults with NWW to near EW direction are related to the left-lateral transpressive fault zones in the northwest of Junggar Basin since the end of the Triassic. The grade II faults with NE to NNE direction are the normal faults located at the junction of the fault zone and the slope zone, and their formation is related to the extension at the top of the nose-like structures in the fault zone. The grade III faults, which are also the normal faults, are the result of the extension at the top of the lower uplifts in the slope zone and differential compaction. The grade IV faults with NE direction are normal faults, which may be related to the extension environment at the tip of the lower uplifts. Faults not only are the channel for the vertical migration of oil and gas, but also control the oil-gas accumulation. There are two types of oil-gas reservoirs in the middle-shallow layers of slope zone of Mahu sag: fault block reservoirs and fault-lithologic reservoirs. They have large traps and promising exploration potential.展开更多
The key of finding hydrocarbon reservoir is to find the profitable oil and gas reservoir.This paper uses the conception of"special geologic bodies"to study the profitable reservoir.Constrained by the sequenc...The key of finding hydrocarbon reservoir is to find the profitable oil and gas reservoir.This paper uses the conception of"special geologic bodies"to study the profitable reservoir.Constrained by the sequence stratigraphy framework,this paper recognizes and describes the special geologic bodies of the Member 3 of Dongying Formation in Littoral Slope Zone of Qikou Sag,which have important展开更多
The instability of a pit mine slope diagnostic caused by the slipping of a localized deep shear zone is described. The slope was designed on ultra basic, serpentine and metabasite rock formations with an angle varying...The instability of a pit mine slope diagnostic caused by the slipping of a localized deep shear zone is described. The slope was designed on ultra basic, serpentine and metabasite rock formations with an angle varying from 40 to 45 de- grees. The perturbed slope zone was classified as RMR 12 and the non-perturbed zone as RMR 75. The boundary of these zones is defined as the shear zone. The pit slope was field mapped in detail and the mechanical properties of the rock were obtained through a laboratory test. The lab data were further processed using the RMR mechanical classifi- cation system. The Distinct Elements Code numerical modeling and simulation software was used to design the pit slope. The model was calibrated through topographic mapping of the points on the ground. The task of calibrating a numerical model is far from simple. Exhaustive attempts to find points of reference are required. The mechanical be- havior in function of the time factor is a problem that has yet to be solved. The instant deformation generated in the numerical model generated functions that can be compared with the deformations of quick shifts acquired in the topog- raphic monitoring. SMR is indeed more often recommended for Pit Slopes, though the fact that we have used RMR does not invalidate the classification for the modeling effect. The main parameters such as spacing, filling, diving direc- tion and continuity allow for compartmentalization of the modeled area. The objective of the modeling was not to pro- ject slopes because this massif was undergoing a progressive slow rupture. The objective of the modeling was to study the movement of the mass of rock and its progressive rupture caused by a shear zone.展开更多
三峡库区周期性水位升降引起的消落带岩体劣化对典型危岩岸坡稳定性具有重大影响。基于野外调研及地勘资料,采用通用离散单元法程序(universal distinct element code,简称UDEC)研究了消落带劣化区形态对近水平层状高陡危岩岸坡的稳定...三峡库区周期性水位升降引起的消落带岩体劣化对典型危岩岸坡稳定性具有重大影响。基于野外调研及地勘资料,采用通用离散单元法程序(universal distinct element code,简称UDEC)研究了消落带劣化区形态对近水平层状高陡危岩岸坡的稳定性影响。研究表明:目前三峡库区巫山段的近水平层状危岩岸坡消落带岩体劣化严重,在不同消落带劣化区存在紧密层状、松散碎裂状、溶蚀凹腔状、含挤压碎裂带等典型消落带劣化区形态;含有第1种消落带劣化区形态的危岩岸坡稳定性较好,危岩体位移较小,失稳模式为滑移破坏;含有第2种消落带劣化区形态的危岩岸坡危岩体先向坡内偏移,其后随着消落带岩体支撑强度弱化向坡外倾倒破坏;含有第3种消落带劣化区形态的危岩岸坡危岩体向坡外位移较大,失稳模式为倾倒破坏;含有第4种消落带劣化区形态的危岩岸坡稳定性主要受挤压破碎带的力学性质控制,易产生沿破碎带切割面的旋转滑移破坏;通过对以上4种劣化区形态的危岩岸坡增加防治加固措施,危岩体的变形位移得到了不同程度的有效控制。展开更多
基金supported by the‘Research on Exploration and Development Technology and New Exploration Fields of high Temperature and High-pressure Gas Reservoirs in the West of the South China Sea’,a subject of the key technology projects of the CNOOC‘Key Technologies for Producing 20 million m~3 of Oil in the Western South China Sea Oilfield’(No.CNOOC-KJ 135 ZDXM 38 ZJ 02 ZJ)The financial support from CNOOC(Hainan)。
文摘Large numbers of gas reservoirs have been discovered in overpressure basins.Fluid charging has a close relationship with paleo-pressure evolution,affecting the migration of gas reservoirs.To study fluid charging and the related pressure system,we analyzed burial histories and fluid inclusion(PVTx)simulations and conducted basin modeling of the Ledong Slope Zone in the Yinggehai Basin as an example.On the basis of fluid-inclusion assemblages(FIAs),homogenization temperature(Th),final melting temperature(Tm,ice)and Raman spectroscopy in fluid inclusions,there are three stages of fluid charging:during the first and second stage,methane-dominated fluid was charged at 2.2–1.7 Ma and 1.7–0.9 Ma,respectively.In the third stage,CO_(2)-rich hydrothermal fluid was charged since 0.9 Ma.It could be concluded from the well-logging data that the disequilibrium compaction in the Yinggehai Fm.,along with the fluid expansion and clay diagenesis in the Huangliu and Meishan formations,resulted in the overpressure in the Ledong slope zone.The evolution of paleo-pressure was affected by the sedimentation rate of the Yinggehai Fm.,as well as the hydrocarbon generation rate.Additionally,the Ledong Slope Zone is less affected by diapir activity than the nearby diapir area.Based on fluid inclusions,paleo-pressure,basin modeling and geological background,the gas migration history of the Ledong Slope Zone can be divided into four stages:in the first stage,excess pressure was formed around 5 Ma;from 2.2 to 1.7 Ma,there was a reduction in the charging of hydrocarbon fluid and steadily increasing excess pressure;during the 1.7–0.9 Ma period a large amount of hydrocarbon was generated,excess pressure increasing significantly and hydraulic fractures forming in mudstones,With gas reservoirs developing in structural highs;since 0.9 Ma,CO_(2)-rich hydrothermal fluid accumulated in reservoirs adjacent to faults and the pressure coefficient remained stable.The research results are helpful in the study of fluid migration and accumulation mechanisms in overpressure basins.
文摘Background,aim,and scope Certain physicochemical indexes of topsoil are closely related to climatic factors including temperature,and precipitation.Understanding the relationship between modern topsoil properties and climatic factors is essential for quantitative paleoclimate reconstruction.Motuo located in the eastern Himalayas,exhibits a significant elevation gradient of over 7000 m from Nnamjagbarwa Peak(7782 m a.s.l.)to the Baxika(150 m a.s.l.).This region features a complete vertical zonation of vegetation,from alpine meadow to tropical forest,presenting an ideal place to investigate the relationships among vegetation,soil and climate conditions across altitudinal gradients.This study aims to explore the vertical variations in the physicochemical composition of topsoil and its relationship with temperature and precipitation.Materials and methods Twenty-seven topsoil samples were collected at 100 m intervals from 800 m to 3600 m a.s.l.along the southern slope of the Himalayas.Grain size,magnetic susceptibility and geochemical elements were measured to discuss the vertical variation characteristics of topsoil composition and their correlation with climatic factors.Results(1)The grain size of topsoil at different altitudes in Motuo is mainly composed of sand accounting for an averaged 53.2%,followed by silt and clay.(2)In the mixed forest zone,frequency dependent magnetic susceptibility(χfd%)shows a clear relationship with altitude,and clay is positively correlated with both altitude and climatic factors.(3)The oxides of topsoil in this area mainly consist of SiO_(2),Al_(2)O_(3) and Fe_(2)O_(3),followed by MgO,CaO,Na_(2)O and K_(2)O,with slight variations in the primary components at different altitudes.The sensitivity of elements to climate varies across different altitudes and vegetation zone,likely due to the region’s complex topography and vegetation.(4)Physical and biological weathering dominates in the broad-leaved forest zone of Motuo,while chemical weathering is more prominent in the coniferous forest zone,with the mixed forest zone falling in between.Discussion The formation of topsoil across the three vegetation zones is influenced by various factors,including parent material,vegetation,and climate.In the broad-leaved forest zone,physical weathering(precipitation,root wedging etc.)and pedogenesis dominate,resulting in finer grain size.The χ_(fd)% increases with altitude likely due to the high temperature and abundant precipitation in this zone,which facilitate the transformation of strong magnetic miners into weaker ones,particularly when the soil is oversaturated.Zirconium(Zr),primarily found in zircon,is depleted at lower altitudes by strong current erosion.Barium(Ba)is similarly reduced at low altitudes in this zone.In mixed forest zone,clay content is the lowest,indicating weaker physical weathering conditions than broad-leaved forest zone.The coarser grain size may result from the combined effects of topography and vegetation coverage.Magnetic susceptibility and organic matter show a positive correlation with altitude.Zr concentration is higher than that in the broad-leaved forest zone,likely resulting from decreased precipitation.In the coniferous zone,the clay content shows considerable fluctuations,with grain size generally becoming finer as altitude increases.This trend may be explained by intensified soil disintegration from seasonal freeze-thaw cycles.The χ_(fd)% values lack a clear trend or pattern,possibly due to soil erosion causing the migration of magnetic minerals or insufficient iron precipitation,which reduces the concentration of magnetic minerals in the soil.Additionally,a positive correlation is observed between altitude and organic matter content,with higher altitudes associated with greater organic matter accumulation.This may be attributed to lower microbial activity in colder conditions,which slows the decomposition and transformation of organic matter.Conclusions The variations in grain size,magnetic susceptibility,and geochemical elements differ across altitudes and vegetation zones,closely connected to the complex interplay of terrain,vegetation,and climate in Motuo.In the mixed forest,altitude has a significant impact onχfd%,and the clay component is particularly sensitive to changes in altitude,mean annual temperature,and precipitation.Zr shows a strong correlation with altitude and climate factors,making it a valuable indicator for assessing changes in atmospheric precipitation within specific altitude ranges.Recommendations and perspectives This study enhances our understanding of the relationships between the physicochemical properties of topsoil and climate conditions,offering valuable insights for paleoclimate reconstruction in Motuo.
基金Project(40872077) supported by the National Natural Science Foundation of ChinaProject(2008CDA098) supported by the Key Natural Science Foundation of Hubei Province,China+1 种基金Project(TPR-2010-01) supported by the Open Project Foundation of Key Laboratory of Tectonics and Petroleum Resources,Ministry of Education,Chinasupported by the research institute exploration and development,PetroChina Dagang Oilfield Company
文摘The purpose of this study is to forecast the profitable oil and gas reservoir,which is the key of finding hydrocarbon,based on the conception of special geologic bodies.With the guiding methodology of the research thinking of integration of point-line-surface by using the methods and techniques of logging,seismic,seismic attribute,and logging constrained inversion in 3D data volume,the special geologic bodies of Member 3 of Dongying Formation in Littoral Slope Zone of Qikou Sag,which has important hydrocarbon exploration potential,are recognized and described under the constraint of sequence stratigraphic framework.As a result,the developed scale,geometric shape and space distribution feature of the special geologic bodies are forecasted;the inner structure and sequence structure patterns of the geologic bodies are also ascertained.From the lowstand system tract (LST) and lacustrine expanding system tract (EST) to the highstand system tract (HST),the geologic bodies have evolved from relative centralization of lake basin reducing period to three relative dispersive isolated parts of broad lake basin period.According to the relevance and regularity of the development of geologic bodies,the conclusions can be obtained that three types of potential profitable reservoir traps,including the lithologic lens traps,lithologic updip pinchout traps and structural-lithologic composite traps,are forecasted.In addition,scientific basis for further hydrocarbon exploration in new area (few-well area and no-well area) is offered in the guidance of sequence stratigraphic model.
基金Projects(51508040,51578079,51678074,51678073)supported by the National Natural Science Foundation of ChinaProject(KFJ160601)supported by the Open Fund of Engineering Laboratory of Spatial Information Technology of Highway Geological Disaster Early Warning in Hunan Province(Changsha University of Science and Technology),China
文摘Rainfall, as one of the most significant factors triggering the residual soil slope failure, leads to not only the reduction of soil shear strength, but also the increase of soil weight and the decrease of matric suction as well. All these modifications in soil properties have important influence on the slope stability. The water infiltration and redistribution inside the slope are the preconditions of the slope stability under rainfall conditions. Based on the numerical simulation via finite element method, the water infiltration process under rainfall conditions was studied in the present work. The emphases are the formation, distribution and dissipation of transient saturated zone. As for the calculation parameters, the SWCC and the saturated permeability have been determined by pressure plate test and variable head test respectively. The entire process(formation, development, dissipation) of the transient saturated zone was studied in detail. The variations of volumetric water content, matric suction and hydraulic gradient inside the slope, and the eventually raise of groundwater table were characterized and discussed, too. The results show that the major cause of the formation of transient saturated zone is ascribed to the fact that the exudation velocity of rainwater on the wetting front is less than the infiltration velocity of rainfall; as a result, the water content of the soil increases. On the other hand, the formation and extension of transient saturated zone have a close relationship with rainfall intensity and duration. The results can help the geotechnical engineers for the deeper understanding of the failure of residual slope under rainfall condition. It is also suggested that the proper drainage system in the slope may be the cost-effective slope failure mitigation method.
基金funded by the China Geological Survey Project (Nos. GZH201500207 1212010611302 DD20160 138)
文摘Multi-beam bathymetry and seismic sequence surveys in the northern slope of the South China Sea reveal detailed geomorphology and seismic stratigraphy characteristics of canyons, gullies, and mass movements. Modern canyons and gullies are roughly elongated NNW–SSW with U-shaped cross sections at water depths of 400–1000 m. Mass movements include slide complexes, slide scars, and debris/turbidity flows. Slide complexes and slide scars are oriented in the NE–SW direction and cover an area of about 1790 and 926 km^2, respectively. The debris/turbidity flows developed along the lower slope. A detailed facies analysis suggests that four seismic facies exist, and the late Cenozoic stratigraphy above the acoustic basement can be roughly subdivided into three sequences separated by regional unconformities in the study area. The occurrence of gas hydrates is marked by seismic velocity anomalies, bottom-simulating reflectors, gas chimneys, and pockmarks in the study area. Seismic observations suggest that modern canyons and mass movements formed around the transition between the last glacial period and the current interglacial period. The possible existence and dissociation of gas hydrates and the regional tectonic setting may trigger instability and mass movements on the seafloor. Canyons may be the final result of gas hydrate dissociation. Our study aims to contribute new information that is applicable to engineering construction required for deep-water petroleum exploration and gas hydrate surveys along any marginal sea.
基金funded by the projects initiated by the China Geological Survey(DD20190217 and DD20190230)the key special project for introduced talent team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(GML2019ZD0102)Guangdong Major project of Basic and Applied Basic Research(2020B0301030003).
文摘Various factors controlling the accumulation of natural gas hydrates(NGHs)form various enrichment and accumulation modes through organic combination.This study mainly analyzes the geological and geophysical characteristics of the NGHs occurrence in the uplifts and their slope zones within the deep-water area in the Qiongdongnan(QDN)Basin(also referred to as the study area).Furthermore,it investigates the dominant governing factors and models of NGHs migration and accumulation in the study area.The results are as follows.(1)The uplifts and their slope zones in the study area lie in the dominant pressure-relief direction of fluids in central hydrocarbon-rich sags in the area,which provide sufficient gas sources for the NGHs accumulation and enrichment through pathways such as gas chimneys and faults.(2)The top and flanks of gas chimneys below the bottom simulating reflectors(BSRs)show high-amplitude seismic reflections and pronounced transverse charging of free gas,indicating the occurrence of a large amount of gas accumulation at the heights of the uplifts.(3)Chimneys,faults,and high-porosity and high-permeability strata,which connect the gas hydrate temperature-pressure stability zones(GHSZs)with thermogenic gas and biogenic gas,form the main hydrate migration system.(4)The reservoir system in the study area comprises sedimentary interlayers consisting of mass transport deposits(MTDs)and turbidites.In addition,the reservoir system has developed fissure-and pore-filling types of hydrates in the pathways.The above well-matched controlling factors of hydrate accumulation enable the uplifts and their slope zones in the study area to become the favorable targets of NGHs exploration.
基金Supported by the China National Science and Technology Major Project(2017ZX05008-001,2011ZX05003-003)
文摘The development, evolution and formation mechanism of faults and their control on the migration and accumulation of Mesozoic oil and gas in the middle-shallow layers of the slope zone of Mahu sag were studied by the interpretation of seismic and drilling data. Two types of faults, normal and strike-slip, are developed in the middle-shallow layers of the slope zone of the Mahu sag and they are mostly active in the Yanshanian period. They are divided into four grade faults: The grade I strike-slip faults with NWW to near EW direction are related to the left-lateral transpressive fault zones in the northwest of Junggar Basin since the end of the Triassic. The grade II faults with NE to NNE direction are the normal faults located at the junction of the fault zone and the slope zone, and their formation is related to the extension at the top of the nose-like structures in the fault zone. The grade III faults, which are also the normal faults, are the result of the extension at the top of the lower uplifts in the slope zone and differential compaction. The grade IV faults with NE direction are normal faults, which may be related to the extension environment at the tip of the lower uplifts. Faults not only are the channel for the vertical migration of oil and gas, but also control the oil-gas accumulation. There are two types of oil-gas reservoirs in the middle-shallow layers of slope zone of Mahu sag: fault block reservoirs and fault-lithologic reservoirs. They have large traps and promising exploration potential.
文摘The key of finding hydrocarbon reservoir is to find the profitable oil and gas reservoir.This paper uses the conception of"special geologic bodies"to study the profitable reservoir.Constrained by the sequence stratigraphy framework,this paper recognizes and describes the special geologic bodies of the Member 3 of Dongying Formation in Littoral Slope Zone of Qikou Sag,which have important
文摘The instability of a pit mine slope diagnostic caused by the slipping of a localized deep shear zone is described. The slope was designed on ultra basic, serpentine and metabasite rock formations with an angle varying from 40 to 45 de- grees. The perturbed slope zone was classified as RMR 12 and the non-perturbed zone as RMR 75. The boundary of these zones is defined as the shear zone. The pit slope was field mapped in detail and the mechanical properties of the rock were obtained through a laboratory test. The lab data were further processed using the RMR mechanical classifi- cation system. The Distinct Elements Code numerical modeling and simulation software was used to design the pit slope. The model was calibrated through topographic mapping of the points on the ground. The task of calibrating a numerical model is far from simple. Exhaustive attempts to find points of reference are required. The mechanical be- havior in function of the time factor is a problem that has yet to be solved. The instant deformation generated in the numerical model generated functions that can be compared with the deformations of quick shifts acquired in the topog- raphic monitoring. SMR is indeed more often recommended for Pit Slopes, though the fact that we have used RMR does not invalidate the classification for the modeling effect. The main parameters such as spacing, filling, diving direc- tion and continuity allow for compartmentalization of the modeled area. The objective of the modeling was not to pro- ject slopes because this massif was undergoing a progressive slow rupture. The objective of the modeling was to study the movement of the mass of rock and its progressive rupture caused by a shear zone.
文摘三峡库区周期性水位升降引起的消落带岩体劣化对典型危岩岸坡稳定性具有重大影响。基于野外调研及地勘资料,采用通用离散单元法程序(universal distinct element code,简称UDEC)研究了消落带劣化区形态对近水平层状高陡危岩岸坡的稳定性影响。研究表明:目前三峡库区巫山段的近水平层状危岩岸坡消落带岩体劣化严重,在不同消落带劣化区存在紧密层状、松散碎裂状、溶蚀凹腔状、含挤压碎裂带等典型消落带劣化区形态;含有第1种消落带劣化区形态的危岩岸坡稳定性较好,危岩体位移较小,失稳模式为滑移破坏;含有第2种消落带劣化区形态的危岩岸坡危岩体先向坡内偏移,其后随着消落带岩体支撑强度弱化向坡外倾倒破坏;含有第3种消落带劣化区形态的危岩岸坡危岩体向坡外位移较大,失稳模式为倾倒破坏;含有第4种消落带劣化区形态的危岩岸坡稳定性主要受挤压破碎带的力学性质控制,易产生沿破碎带切割面的旋转滑移破坏;通过对以上4种劣化区形态的危岩岸坡增加防治加固措施,危岩体的变形位移得到了不同程度的有效控制。
