Globally,many lakes are drying up,leaving exposed lakebeds where wind erosion releases dust and sand rich in salt and harmful heavy metals into the atmosphere.Therefore,understanding the characteristics and spatial di...Globally,many lakes are drying up,leaving exposed lakebeds where wind erosion releases dust and sand rich in salt and harmful heavy metals into the atmosphere.Therefore,understanding the characteristics and spatial distribution of playa surface crusts is important to recognize the manifestation of salt dust storms.The objective of this study was to explore the playa surface crust types as well as their spatial distribution and evolution of Qehan Lake in Inner Mongolia Autonomous Region,China to understand the salt dust release potential of different types of playa surface crusts.Various crust characteristics were investigated by field sampling in Qehan Lake,and playa surface crusts were further divided into five types:vegetated areas,salt crusts,clay flats,curly crusts,and margins.It should be noted that curly crusts were distributed in clay flats and covered only a small area in Qehan Lake.The spatial distribution characteristics of playa surface crust types were obtained by supervised classification of remote sensing images,and the salt dust release potential of crusts was explored by the wind tunnel experiments.The field investigation of Qehan Lake revealed that playa surface crust types had a circum-lake band distribution from the inside to the outside of this lake,which were successively vegetated areas,clay flats,salt crusts,and margins.The spatial distribution patterns of playa surface crust types were mainly controlled by the hydrodynamics of the playa,soil texture,and groundwater.There was a significant negative correlation between crust thickness and electrical conductivity.The results of the wind tunnel experiments showed that the initial threshold of friction wind velocity for the salt dust release was higher in clay flats(0.7–0.8 m/s)than in salt crusts(0.5–0.6 m/s).Moreover,the particle leap impact processes occurring under natural conditions may reduce this threshold value.Salinity was the main factor controlling the difference in the initial threshold of friction wind velocity for the salt dust release of clay flats and salt crusts.This study provides a scientific reference for understanding how salt dust is released from a lakebed,which may be used for ecological restoration of dry salt lakes.展开更多
Lithological, petrographic, and morphoscopic studies were conducted on cuttings and cores from three boreholes drilled in the Loemé salt, Kanga site, Republic of the Congo, to determine 1) the preferential condit...Lithological, petrographic, and morphoscopic studies were conducted on cuttings and cores from three boreholes drilled in the Loemé salt, Kanga site, Republic of the Congo, to determine 1) the preferential conditions for crystallization of carnallite and associated salts and 2) to reconstruct paleoenvironmental and paleoclimatic conditions at the time of sedimentation. Sequential analysis of logs, sedimentary structures, carnallitite facies and associated salts concluded to the existence of a potassic carnallitite lagoon basin with low water cover, on a very wide and extensive plateau, affected by coastal waves and swells resulting from successive collapses. This basin evolved in two phases: confined and then open. The regular stratifications of halite, the rhythmicity of the halite-carnallitite elementary sequences are characteristic of salts that precipitated in relatively stable brines. These salts are therefore tectonosedimentary. The brecciated facies of the carnallitites sometimes associated with tachyhydrite result from the evolution of these deposits into salt crusts reworked by the surges into subaquatic allochemical gravelly cords under water. These crusts mark stages of partial and complete drying of the basin in a very hot and arid climate. Prolonged exposure of halite brines as well as their homogenization by surges accelerated evaporation and their abrupt evolution into carnallite brines obstructing the fossilization of sylvite. The precipitation of tachyhydrite marks the final stage of the successive complete drying of the basin.展开更多
Quaternary biogenic gas reservoirs are extensively developed in the Sanhu Depression of the Qaidam Basin,where the largest domestic biogenic gas production base has been built up.In recent years,however,the exploratio...Quaternary biogenic gas reservoirs are extensively developed in the Sanhu Depression of the Qaidam Basin,where the largest domestic biogenic gas production base has been built up.In recent years,however,the exploration of biogenic gas there encounters a variety of difficulties,such as the identification of true and false seismic abnormality,the determination of micro-relief structure and the identification and description of lithologic traps,which are the bottlenecks restricting its exploration breakthrough.In this paper,hydrocarbon accumulation patterns of biogenic gas were studied.Then,based on fine structure interpretation results,combined with laboratory experiments,the sealing capacity,distribution range,formation time and genesis of salt crust were discussed,and the salt crust covered hydrocarbon accumulation pattern of biogenic gas was put forward.Finally,combined with the conditions of source rocks and reservoirs,the exploration prospect of salt crust covered biogenic gas reservoirs was predicted.And the following research results were obtained.First,the Quaternary in the Sanhu Depression is composed of sandstone-mudstone interbeds of shore-shallow lake facies,with superior conditions of source rocks and reservoirs.Many source-reservoir-caprock assemblages are vertically formed.The biogenic gas has the characteristics of dynamic hydrocarbon accumulation,i.e.,continuous migration,accumulation,diffusion and re-accumulation.Second,under the effect of Himalayan movement,the climate changes frequently and the salinity of the ancient lake is zoned in the Sanhu Depression.A freshwater area is formed at the inlet of the river in the south and a brine area is formed in the north.Under the influence of evaporation,the phreatic water in the north is salinized continuously,and a set of extensively distributed salt crust with steady thickness and a strong sealing capacity is formed at the eastern part of Lingjian fault.Third,the biogenic gas generated by dark mudstone of lacustrine facies in the depression center migrates laterally and vertically to Lingjian fault zone and gets accumulated under the sealing of salt crust.In conclusion,high-quality source rocks and reservoirs and the salt crust with a strong sealing capacity in the Sanhu Depression constitute a good spatial-temporal configuration relationship of source rocks,reservoirs and cap rocks,so salt crust covered biogenic gas reservoirs can be formed to provide abundant natural gas resources with a broad exploration prospect.展开更多
基金funded by the National Natural Science Foundation of China (42067013, 41571090)
文摘Globally,many lakes are drying up,leaving exposed lakebeds where wind erosion releases dust and sand rich in salt and harmful heavy metals into the atmosphere.Therefore,understanding the characteristics and spatial distribution of playa surface crusts is important to recognize the manifestation of salt dust storms.The objective of this study was to explore the playa surface crust types as well as their spatial distribution and evolution of Qehan Lake in Inner Mongolia Autonomous Region,China to understand the salt dust release potential of different types of playa surface crusts.Various crust characteristics were investigated by field sampling in Qehan Lake,and playa surface crusts were further divided into five types:vegetated areas,salt crusts,clay flats,curly crusts,and margins.It should be noted that curly crusts were distributed in clay flats and covered only a small area in Qehan Lake.The spatial distribution characteristics of playa surface crust types were obtained by supervised classification of remote sensing images,and the salt dust release potential of crusts was explored by the wind tunnel experiments.The field investigation of Qehan Lake revealed that playa surface crust types had a circum-lake band distribution from the inside to the outside of this lake,which were successively vegetated areas,clay flats,salt crusts,and margins.The spatial distribution patterns of playa surface crust types were mainly controlled by the hydrodynamics of the playa,soil texture,and groundwater.There was a significant negative correlation between crust thickness and electrical conductivity.The results of the wind tunnel experiments showed that the initial threshold of friction wind velocity for the salt dust release was higher in clay flats(0.7–0.8 m/s)than in salt crusts(0.5–0.6 m/s).Moreover,the particle leap impact processes occurring under natural conditions may reduce this threshold value.Salinity was the main factor controlling the difference in the initial threshold of friction wind velocity for the salt dust release of clay flats and salt crusts.This study provides a scientific reference for understanding how salt dust is released from a lakebed,which may be used for ecological restoration of dry salt lakes.
文摘Lithological, petrographic, and morphoscopic studies were conducted on cuttings and cores from three boreholes drilled in the Loemé salt, Kanga site, Republic of the Congo, to determine 1) the preferential conditions for crystallization of carnallite and associated salts and 2) to reconstruct paleoenvironmental and paleoclimatic conditions at the time of sedimentation. Sequential analysis of logs, sedimentary structures, carnallitite facies and associated salts concluded to the existence of a potassic carnallitite lagoon basin with low water cover, on a very wide and extensive plateau, affected by coastal waves and swells resulting from successive collapses. This basin evolved in two phases: confined and then open. The regular stratifications of halite, the rhythmicity of the halite-carnallitite elementary sequences are characteristic of salts that precipitated in relatively stable brines. These salts are therefore tectonosedimentary. The brecciated facies of the carnallitites sometimes associated with tachyhydrite result from the evolution of these deposits into salt crusts reworked by the surges into subaquatic allochemical gravelly cords under water. These crusts mark stages of partial and complete drying of the basin in a very hot and arid climate. Prolonged exposure of halite brines as well as their homogenization by surges accelerated evaporation and their abrupt evolution into carnallite brines obstructing the fossilization of sylvite. The precipitation of tachyhydrite marks the final stage of the successive complete drying of the basin.
基金Project supported by the Key Program of National Natural Science Foundation of China“Fundamental study on tight gas reservoir formation drying and tight gas seepage capacity improvement”(No.:51534006).
文摘Quaternary biogenic gas reservoirs are extensively developed in the Sanhu Depression of the Qaidam Basin,where the largest domestic biogenic gas production base has been built up.In recent years,however,the exploration of biogenic gas there encounters a variety of difficulties,such as the identification of true and false seismic abnormality,the determination of micro-relief structure and the identification and description of lithologic traps,which are the bottlenecks restricting its exploration breakthrough.In this paper,hydrocarbon accumulation patterns of biogenic gas were studied.Then,based on fine structure interpretation results,combined with laboratory experiments,the sealing capacity,distribution range,formation time and genesis of salt crust were discussed,and the salt crust covered hydrocarbon accumulation pattern of biogenic gas was put forward.Finally,combined with the conditions of source rocks and reservoirs,the exploration prospect of salt crust covered biogenic gas reservoirs was predicted.And the following research results were obtained.First,the Quaternary in the Sanhu Depression is composed of sandstone-mudstone interbeds of shore-shallow lake facies,with superior conditions of source rocks and reservoirs.Many source-reservoir-caprock assemblages are vertically formed.The biogenic gas has the characteristics of dynamic hydrocarbon accumulation,i.e.,continuous migration,accumulation,diffusion and re-accumulation.Second,under the effect of Himalayan movement,the climate changes frequently and the salinity of the ancient lake is zoned in the Sanhu Depression.A freshwater area is formed at the inlet of the river in the south and a brine area is formed in the north.Under the influence of evaporation,the phreatic water in the north is salinized continuously,and a set of extensively distributed salt crust with steady thickness and a strong sealing capacity is formed at the eastern part of Lingjian fault.Third,the biogenic gas generated by dark mudstone of lacustrine facies in the depression center migrates laterally and vertically to Lingjian fault zone and gets accumulated under the sealing of salt crust.In conclusion,high-quality source rocks and reservoirs and the salt crust with a strong sealing capacity in the Sanhu Depression constitute a good spatial-temporal configuration relationship of source rocks,reservoirs and cap rocks,so salt crust covered biogenic gas reservoirs can be formed to provide abundant natural gas resources with a broad exploration prospect.
