A wave flume simulator was used to study internal nitrogen release from the surface sediment collected from Taihu Lake, China. Particulate nitrogen concentrations were positively correlated with the concentrations of ...A wave flume simulator was used to study internal nitrogen release from the surface sediment collected from Taihu Lake, China. Particulate nitrogen concentrations were positively correlated with the concentrations of suspended solids, primarily from surface erosion related to the shear stress and duration of wave action. In response to 4 cm- and 10 cm-high wave production representing waves generated in Taihu Lake by gentle and gusty winds, respectively, the mean dynamic release rate of ammonium （NH4＋） from the sediment to the overlying water was 1 × 10-3 mg/（m2.s） and the NH4＋ concentration in the overlying water increased by 0.016 mg/L, indicating that waves resulting from strong wind can induce the rapid release of dissolved nitrogen from Taihu Lake sediments. The decrease in interstitial NH4＋ concentrations at all sediment depths was associated with an increase in NH4＋ concentrations in the overlying water by 0.01 mg/L, showing that sediment below the eroded layer was the main source of internal nitrogen release. Changes in the interstitial dissolved oxygen and NH4＋ concentrations showed that wave-induced pore water movement can greatly increase the diffusion rate, and that these 15 cm. Diffusion induced by pore water movement sediment layer in Taihu Lake. effects can influence the sediment to a depth of at least may be very important for the formation of an active展开更多
The erosion mechanisms of abandoned coastal section are understood detailedly by flume experiment, which play an important role to the offshore engineering facilities. A movable-bed physical model has been used to inv...The erosion mechanisms of abandoned coastal section are understood detailedly by flume experiment, which play an important role to the offshore engineering facilities. A movable-bed physical model has been used to investigate the coastal erosion of an abandoned section of the Huanghe （Yellow） River Delta. The theory of physical scale models is discussed and a method for constructing the representative seabed section is developed. The results indicate that during the period initially after the abandonment of the delta the entire bed experienced rapid erosion because the seabed was steep and prone to liquefaction that resulted from storm wave action. After this initial period, a balance of erosion and accretion was established, and the beach profllc equilibrated with a point of balance present on the profile. The experimental results indicate that the volume of deposition was about half that of the erosion. Wave action may also induce significant stratal changes through its interaction with the soft seabed. The major morphological features developed in the model delta section were found to be qualitatively comparable with those observed in the prototype. A distorted modeling law that maintains the similarity of the modeled and prototype equilibrium beach profiles is proposed. Experimental results show that the distorted modeling is able to reproduce the beach-face slope in nature, and the model also successfully reproduced three historical evolutionary stages of erosion.展开更多
Based on recent advancements in shale oil exploration within the Ordos Basin,this study presents a comprehensive investigation of the paleoenvironment,lithofacies assemblages and distribution,depositional mechanisms,a...Based on recent advancements in shale oil exploration within the Ordos Basin,this study presents a comprehensive investigation of the paleoenvironment,lithofacies assemblages and distribution,depositional mechanisms,and reservoir characteristics of shale oil of fine-grained sediment deposition in continental freshwater lacustrine basins,with a focus on the Chang 7_(3) sub-member of Triassic Yanchang Formation.The research integrates a variety of exploration data,including field outcrops,drilling,logging,core samples,geochemical analyses,and flume simulation.The study indicates that:(1)The paleoenvironment of the Chang 7_(3) deposition is characterized by a warm and humid climate,frequent monsoon events,and a large water depth of freshwater lacustrine basin.The paleogeomorphology exhibits an asymmetrical pattern,with steep slopes in the southwest and gentle slopes in the northeast,which can be subdivided into microgeomorphological units,including depressions and ridges in lakebed,as well as ancient channels.(2)The Chang 7_(3) sub-member is characterized by a diverse array of fine-grained sediments,including very fine sandstone,siltstone,mudstone and tuff.These sediments are primarily distributed in thin interbedded and laminated arrangements vertically.The overall grain size of the sandstone predominantly falls below 62.5μm,with individual layer thicknesses of 0.05–0.64 m.The deposits contain intact plant fragments and display various sedimentary structure,such as wavy bedding,inverse-to-normal grading sequence,and climbing ripple bedding,which indicating a depositional origin associated with density flows.(3)Flume simulation experiments have successfully replicated the transport processes and sedimentary characteristics associated with density flows.The initial phase is characterized by a density-velocity differential,resulting in a thicker,coarser sediment layer at the flow front,while the upper layers are thinner and finer in grain size.During the mid-phase,sliding water effects cause the fluid front to rise and facilitate rapid forward transport.This process generates multiple“new fronts”,enabling the long-distance transport of fine-grained sandstones,such as siltstone and argillaceous siltstone,into the center of the lake basin.(4)A sedimentary model primarily controlled by hyperpynal flows was established for the southwestern part of the basin,highlighting that the frequent occurrence of flood events and the steep slope topography in this area are primary controlling factors for the development of hyperpynal flows.(5)Sandstone and mudstone in the Chang 7_(3) sub-member exhibit micro-and nano-scale pore-throat systems,shale oil is present in various lithologies,while the content of movable oil varies considerably,with sandstone exhibiting the highest content of movable oil.(6)The fine-grained sediment complexes formed by multiple episodes of sandstones and mudstones associated with density flow in the Chang 7_(3) formation exhibit characteristics of“overall oil-bearing with differential storage capacity”.The combination of mudstone with low total organic carbon content(TOC)and siltstone is identified as the most favorable exploration target at present.展开更多
基金Supported by the National Natural Science Foundation of China(Nos.41101458, 40825004,40871095,40801200)the Major Project for National Science and Technology Development(No.2010ZX03006-006)the "100-Talent Project" of Chinese Academy of Sciences,China(No.YOBROB045)
文摘A wave flume simulator was used to study internal nitrogen release from the surface sediment collected from Taihu Lake, China. Particulate nitrogen concentrations were positively correlated with the concentrations of suspended solids, primarily from surface erosion related to the shear stress and duration of wave action. In response to 4 cm- and 10 cm-high wave production representing waves generated in Taihu Lake by gentle and gusty winds, respectively, the mean dynamic release rate of ammonium （NH4＋） from the sediment to the overlying water was 1 × 10-3 mg/（m2.s） and the NH4＋ concentration in the overlying water increased by 0.016 mg/L, indicating that waves resulting from strong wind can induce the rapid release of dissolved nitrogen from Taihu Lake sediments. The decrease in interstitial NH4＋ concentrations at all sediment depths was associated with an increase in NH4＋ concentrations in the overlying water by 0.01 mg/L, showing that sediment below the eroded layer was the main source of internal nitrogen release. Changes in the interstitial dissolved oxygen and NH4＋ concentrations showed that wave-induced pore water movement can greatly increase the diffusion rate, and that these 15 cm. Diffusion induced by pore water movement sediment layer in Taihu Lake. effects can influence the sediment to a depth of at least may be very important for the formation of an active
基金Supported by The National Basic Research Program (973 Program) (Nos. 2005CB422304 and 2002CB412408)
文摘The erosion mechanisms of abandoned coastal section are understood detailedly by flume experiment, which play an important role to the offshore engineering facilities. A movable-bed physical model has been used to investigate the coastal erosion of an abandoned section of the Huanghe （Yellow） River Delta. The theory of physical scale models is discussed and a method for constructing the representative seabed section is developed. The results indicate that during the period initially after the abandonment of the delta the entire bed experienced rapid erosion because the seabed was steep and prone to liquefaction that resulted from storm wave action. After this initial period, a balance of erosion and accretion was established, and the beach profllc equilibrated with a point of balance present on the profile. The experimental results indicate that the volume of deposition was about half that of the erosion. Wave action may also induce significant stratal changes through its interaction with the soft seabed. The major morphological features developed in the model delta section were found to be qualitatively comparable with those observed in the prototype. A distorted modeling law that maintains the similarity of the modeled and prototype equilibrium beach profiles is proposed. Experimental results show that the distorted modeling is able to reproduce the beach-face slope in nature, and the model also successfully reproduced three historical evolutionary stages of erosion.
基金Supported by the CNPC Major Science and Technology Project(2021DJ1806).
文摘Based on recent advancements in shale oil exploration within the Ordos Basin,this study presents a comprehensive investigation of the paleoenvironment,lithofacies assemblages and distribution,depositional mechanisms,and reservoir characteristics of shale oil of fine-grained sediment deposition in continental freshwater lacustrine basins,with a focus on the Chang 7_(3) sub-member of Triassic Yanchang Formation.The research integrates a variety of exploration data,including field outcrops,drilling,logging,core samples,geochemical analyses,and flume simulation.The study indicates that:(1)The paleoenvironment of the Chang 7_(3) deposition is characterized by a warm and humid climate,frequent monsoon events,and a large water depth of freshwater lacustrine basin.The paleogeomorphology exhibits an asymmetrical pattern,with steep slopes in the southwest and gentle slopes in the northeast,which can be subdivided into microgeomorphological units,including depressions and ridges in lakebed,as well as ancient channels.(2)The Chang 7_(3) sub-member is characterized by a diverse array of fine-grained sediments,including very fine sandstone,siltstone,mudstone and tuff.These sediments are primarily distributed in thin interbedded and laminated arrangements vertically.The overall grain size of the sandstone predominantly falls below 62.5μm,with individual layer thicknesses of 0.05–0.64 m.The deposits contain intact plant fragments and display various sedimentary structure,such as wavy bedding,inverse-to-normal grading sequence,and climbing ripple bedding,which indicating a depositional origin associated with density flows.(3)Flume simulation experiments have successfully replicated the transport processes and sedimentary characteristics associated with density flows.The initial phase is characterized by a density-velocity differential,resulting in a thicker,coarser sediment layer at the flow front,while the upper layers are thinner and finer in grain size.During the mid-phase,sliding water effects cause the fluid front to rise and facilitate rapid forward transport.This process generates multiple“new fronts”,enabling the long-distance transport of fine-grained sandstones,such as siltstone and argillaceous siltstone,into the center of the lake basin.(4)A sedimentary model primarily controlled by hyperpynal flows was established for the southwestern part of the basin,highlighting that the frequent occurrence of flood events and the steep slope topography in this area are primary controlling factors for the development of hyperpynal flows.(5)Sandstone and mudstone in the Chang 7_(3) sub-member exhibit micro-and nano-scale pore-throat systems,shale oil is present in various lithologies,while the content of movable oil varies considerably,with sandstone exhibiting the highest content of movable oil.(6)The fine-grained sediment complexes formed by multiple episodes of sandstones and mudstones associated with density flow in the Chang 7_(3) formation exhibit characteristics of“overall oil-bearing with differential storage capacity”.The combination of mudstone with low total organic carbon content(TOC)and siltstone is identified as the most favorable exploration target at present.
