Surface sediment is one of the main sources of nutrients in overlying water environments, and these can also indirectly reflect the degree of eutrophication. In this paper, the spatial distribution characteristics of ...Surface sediment is one of the main sources of nutrients in overlying water environments, and these can also indirectly reflect the degree of eutrophication. In this paper, the spatial distribution characteristics of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in the surface sediments of 11 sections in the lower Lancang River during flood season are analyzed, as well as the distribution of phosphorus in different forms. The main sources of TOC and its correlation with TN and TP are discussed and, finally, the pollution levels of the surface sediments are evaluated. The results show that the average content of TOC in the surface sediments of the lower Lancang River is 9003.75 mg/kg. The average TN content is 893.79 mg/kg, while the average TP content is 521.35 mg/kg. The TOC in the surface sediments of the lower Lancang River is derived mainly from algae and plankton in the river, and the TN and TP have similar sources. The total phosphorus in the surface sediments of the lower Lancang River is composed mainly of calcium-bound phosphorus (Ca-P). The evaluations of the organic pollution index and comprehensive pollution index show that the surface sediment pollution degree at the upper sections of the Nuozhadu and Jinghong Dams are more serious than those below the dams. Furthermore, the tributary sections are all slightly polluted, with the exception of the Mengyang River, which is considered moderately polluted.展开更多
The coupling effect of temperature and confining pressure on fracture toughness is a critical issue in deep shale gas development that cannot be overlooked.Field and laboratory studies have shown that this coupling ef...The coupling effect of temperature and confining pressure on fracture toughness is a critical issue in deep shale gas development that cannot be overlooked.Field and laboratory studies have shown that this coupling effect significantly alters shale fracture toughness,but the underlying mechanisms of it remain poorly understood.To investigate the mechanisms of the temperature-pressure coupling effect on the fracture toughness of transversely isotropic shale,this study develops a thermal-mechanical DEM(discrete element method)model that integrates a customized thermal algorithm and a shining-lamp algorithm.The model validity is verified by using experimental results from high-temperature SCB(semi-circular bend)tests.Additionally,a series of SCB tests under different temperatures and confining pressures are simulated based on this model.The loading curves,fracture toughness evolution,crack morphology,and microcrack statistics results obtained from simulations are analyzed to provide insights into the mechanisms of the temperature-pressure coupling effect.The simulation results indicate that the stimulation of thermal-induced microcracks on crack propagation may be the primary microscopic mechanism behind the thermal-induced weakening of shale fracture toughness.Meanwhile,confining pressure has an inhibitory influence on the thermal effect of shale fracture toughness.The activation of shear microcracks under the application of confining pressure is identified as the leading microscopic mechanism of confining pressure inhibition.The findings in this study enhance the understanding of the fracture property evolution of deep shale reservoirs and provide guidance for site selection,engineering design,and reservoir stability assessment in deep shale gas development.展开更多
文摘Surface sediment is one of the main sources of nutrients in overlying water environments, and these can also indirectly reflect the degree of eutrophication. In this paper, the spatial distribution characteristics of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in the surface sediments of 11 sections in the lower Lancang River during flood season are analyzed, as well as the distribution of phosphorus in different forms. The main sources of TOC and its correlation with TN and TP are discussed and, finally, the pollution levels of the surface sediments are evaluated. The results show that the average content of TOC in the surface sediments of the lower Lancang River is 9003.75 mg/kg. The average TN content is 893.79 mg/kg, while the average TP content is 521.35 mg/kg. The TOC in the surface sediments of the lower Lancang River is derived mainly from algae and plankton in the river, and the TN and TP have similar sources. The total phosphorus in the surface sediments of the lower Lancang River is composed mainly of calcium-bound phosphorus (Ca-P). The evaluations of the organic pollution index and comprehensive pollution index show that the surface sediment pollution degree at the upper sections of the Nuozhadu and Jinghong Dams are more serious than those below the dams. Furthermore, the tributary sections are all slightly polluted, with the exception of the Mengyang River, which is considered moderately polluted.
基金supported by the National Natural Science Foundation of China(No.42320104003).
文摘The coupling effect of temperature and confining pressure on fracture toughness is a critical issue in deep shale gas development that cannot be overlooked.Field and laboratory studies have shown that this coupling effect significantly alters shale fracture toughness,but the underlying mechanisms of it remain poorly understood.To investigate the mechanisms of the temperature-pressure coupling effect on the fracture toughness of transversely isotropic shale,this study develops a thermal-mechanical DEM(discrete element method)model that integrates a customized thermal algorithm and a shining-lamp algorithm.The model validity is verified by using experimental results from high-temperature SCB(semi-circular bend)tests.Additionally,a series of SCB tests under different temperatures and confining pressures are simulated based on this model.The loading curves,fracture toughness evolution,crack morphology,and microcrack statistics results obtained from simulations are analyzed to provide insights into the mechanisms of the temperature-pressure coupling effect.The simulation results indicate that the stimulation of thermal-induced microcracks on crack propagation may be the primary microscopic mechanism behind the thermal-induced weakening of shale fracture toughness.Meanwhile,confining pressure has an inhibitory influence on the thermal effect of shale fracture toughness.The activation of shear microcracks under the application of confining pressure is identified as the leading microscopic mechanism of confining pressure inhibition.The findings in this study enhance the understanding of the fracture property evolution of deep shale reservoirs and provide guidance for site selection,engineering design,and reservoir stability assessment in deep shale gas development.
