2019 Vol. 44, No. 11
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2019, 44(11): 3583-3597.
doi: 10.3799/dqkx.2019.142
Abstract:
Core observation shows that high-angle and bed-parallel fractures of tectonic compression origin develop in the black shale of the second member of the Lower Cambrian Niutitang Formation in the southern limb of Huangling anticline,West Hubei. Typical fracture veins with different occurrences were selected,calcite vein was filled in high-angle fractures and calcite-dolomite composite vein was filled in bedding fractures under thin section microscopy. Through cathodic luminescence,fluid inclusion analysis and in-situ element determination,the evolutions of diagenetic environment of fractured veins were studied,and the effects of different occurrence fractures on local sealing of shale gas reservoirs were analyzed. The cathodic luminescence observation indicates that the high-angle calcite vein and bed-parallel calcite-dolomite composite vein were both formed by two phases of fluid activity. According to fluid inclusion analysis,the early vein-forming fluids of high-angle calcite vein were mainly deep-metamorphic stratum brine while the late vein-forming fluids were mixed with low-salinity fluids,however the two-stage vein-forming fluids of bed-parallel calcite-dolomite composite vein were not modified by low salinity fluids. The in-situ element determination results of carbonate minerals with different cathodoluminescence characteristics in fracture veins,and analyses of iron and manganese content,rare earth elements(REE) and redox discriminant parameters,show that the diagenetic environment of high-angle calcite vein has undergone a transformation from reductive environment to oxidative environment,while the diagenetic environment of bed-parallel calcite-dolomite composite vein has maintained a relatively reductive environment for a long time. Therefore,it is considered that high-angle fractures may have destructive effect on the local sealing conditions of shale gas reservoirs,resulting in the loss of shale gas to a certain extent. While bed-parallel fractures may have relatively limited destructive effect on the local sealing conditions. The study of fracture development characteristics and diagenetic evolution process can provide basis for the evaluation of self-sealing conditions of shale gas reservoirs and micro-preservation conditions of shale gas.
Core observation shows that high-angle and bed-parallel fractures of tectonic compression origin develop in the black shale of the second member of the Lower Cambrian Niutitang Formation in the southern limb of Huangling anticline,West Hubei. Typical fracture veins with different occurrences were selected,calcite vein was filled in high-angle fractures and calcite-dolomite composite vein was filled in bedding fractures under thin section microscopy. Through cathodic luminescence,fluid inclusion analysis and in-situ element determination,the evolutions of diagenetic environment of fractured veins were studied,and the effects of different occurrence fractures on local sealing of shale gas reservoirs were analyzed. The cathodic luminescence observation indicates that the high-angle calcite vein and bed-parallel calcite-dolomite composite vein were both formed by two phases of fluid activity. According to fluid inclusion analysis,the early vein-forming fluids of high-angle calcite vein were mainly deep-metamorphic stratum brine while the late vein-forming fluids were mixed with low-salinity fluids,however the two-stage vein-forming fluids of bed-parallel calcite-dolomite composite vein were not modified by low salinity fluids. The in-situ element determination results of carbonate minerals with different cathodoluminescence characteristics in fracture veins,and analyses of iron and manganese content,rare earth elements(REE) and redox discriminant parameters,show that the diagenetic environment of high-angle calcite vein has undergone a transformation from reductive environment to oxidative environment,while the diagenetic environment of bed-parallel calcite-dolomite composite vein has maintained a relatively reductive environment for a long time. Therefore,it is considered that high-angle fractures may have destructive effect on the local sealing conditions of shale gas reservoirs,resulting in the loss of shale gas to a certain extent. While bed-parallel fractures may have relatively limited destructive effect on the local sealing conditions. The study of fracture development characteristics and diagenetic evolution process can provide basis for the evaluation of self-sealing conditions of shale gas reservoirs and micro-preservation conditions of shale gas.
2019, 44(11): 3598-3615.
doi: 10.3799/dqkx.2019.179
Abstract:
Good gas shows in the Cambrian Shuijingtuo Formation indicate the resources potential in Middle Yangtze region. The weakness of basic research on the shale gas accumulation constrains gas exploration and development in this area. In this paper,it focuses on the geological characteristics of Shuijingtuo shale gas in Yichang area by integrating geological and geochemical data from latest exploration well and outcrop. The gas potential is discussed based on preliminary evaluation of lithofacies,geochemical characteristics,reservoir features,and shale gas content. These organic-rich intervals are concentrated along and between continental shelf and slope. Thermally mature strata of the Shuijingtuo shale attain thickness between 28 and 41 m,with a total organic carbon (TOC) exceeding 2%. Organic matter within Shuijingtuo shale is high,which contains an average of 2.65% TOC,with present-day thermal maturity between 2.4% and 3.2% equivalent vitrinite reflectance (Ro),which is in the high mature of dry thermogenic gases dominated stage. The Shuijingtuo shale is noted for having generally high silica content. Mineral composition of shale consists of 29.33% quartz,25.94% carbonatite calcite/dolomite,35.06% clay minerals. Illite smectite mixed layer is the major clay mineral. The gas shale reservoir has an extremely low porosity and permeability. Porosity ranges from 0.96% to 3.22%,with an average value of 2.08% at the bottom of Shuijingtuo Formation. The effective permeability in gas shale is (0.01-3.05)×10-3 μm2. Through scanning electron microscope observation and isothermal adsorption,pores in shale also show multiple genetic types and small size of multi-pore diameter. Fractal dimensions of the organic pores vary from 10 to 50 nm. Overlying formations and underlying strata are favorable for shale gas preserved. The tectonic stress field is regionally very stable and short of fault activity,which all indicates favorable preservation conditions for Shuijingtuo shale gas in gentle slope of Yichang area. Measurement of total hydrocarbon and methane through mud logging indicates anomaly. The measured gas content of the Shuijingtuo shale in Well Yiye-1 ranges between 0.31 to 5.48 m3/t. Thermally mature strata of the Shuijingtuo Formation attain thickness of 44.05 m,with a continuous gas content exceeding 2 m3/t. Well Yiye-1 tested an industrial gas flow after horizontal well fractured. Methane is the main constituent of gas sample and varies in concentration from 81.17% to 92.75%. Ethane ranges from 0.83% to 0.94%,nitrogen in non-hydrocarbon gas ranges from 5.86% to 9.37%,and carbon dioxide ranges from 0.05% to 2.25%. It is concluded that it could be the favorable area for shale gas accumulation in the Middle Yangtze region,and it's a new area for shale gas exploration outside Sichuan basin.
Good gas shows in the Cambrian Shuijingtuo Formation indicate the resources potential in Middle Yangtze region. The weakness of basic research on the shale gas accumulation constrains gas exploration and development in this area. In this paper,it focuses on the geological characteristics of Shuijingtuo shale gas in Yichang area by integrating geological and geochemical data from latest exploration well and outcrop. The gas potential is discussed based on preliminary evaluation of lithofacies,geochemical characteristics,reservoir features,and shale gas content. These organic-rich intervals are concentrated along and between continental shelf and slope. Thermally mature strata of the Shuijingtuo shale attain thickness between 28 and 41 m,with a total organic carbon (TOC) exceeding 2%. Organic matter within Shuijingtuo shale is high,which contains an average of 2.65% TOC,with present-day thermal maturity between 2.4% and 3.2% equivalent vitrinite reflectance (Ro),which is in the high mature of dry thermogenic gases dominated stage. The Shuijingtuo shale is noted for having generally high silica content. Mineral composition of shale consists of 29.33% quartz,25.94% carbonatite calcite/dolomite,35.06% clay minerals. Illite smectite mixed layer is the major clay mineral. The gas shale reservoir has an extremely low porosity and permeability. Porosity ranges from 0.96% to 3.22%,with an average value of 2.08% at the bottom of Shuijingtuo Formation. The effective permeability in gas shale is (0.01-3.05)×10-3 μm2. Through scanning electron microscope observation and isothermal adsorption,pores in shale also show multiple genetic types and small size of multi-pore diameter. Fractal dimensions of the organic pores vary from 10 to 50 nm. Overlying formations and underlying strata are favorable for shale gas preserved. The tectonic stress field is regionally very stable and short of fault activity,which all indicates favorable preservation conditions for Shuijingtuo shale gas in gentle slope of Yichang area. Measurement of total hydrocarbon and methane through mud logging indicates anomaly. The measured gas content of the Shuijingtuo shale in Well Yiye-1 ranges between 0.31 to 5.48 m3/t. Thermally mature strata of the Shuijingtuo Formation attain thickness of 44.05 m,with a continuous gas content exceeding 2 m3/t. Well Yiye-1 tested an industrial gas flow after horizontal well fractured. Methane is the main constituent of gas sample and varies in concentration from 81.17% to 92.75%. Ethane ranges from 0.83% to 0.94%,nitrogen in non-hydrocarbon gas ranges from 5.86% to 9.37%,and carbon dioxide ranges from 0.05% to 2.25%. It is concluded that it could be the favorable area for shale gas accumulation in the Middle Yangtze region,and it's a new area for shale gas exploration outside Sichuan basin.
2019, 44(11): 3616-3627.
doi: 10.3799/dqkx.2019.127
Abstract:
To find out the accumulation characteristics of the Cambrian Niutitang Formation shale gas in West Hubei,reservoir fracture characteristics,fluid inclusion testing of fracture-filling calcite veins,and detrital zircon U-Pb dating of Cambrian sedimentary rocks were conducted based on the data of Well XD1. This well contains developed,high-angle,mostly calcite-filled fractures. Inclusions inside the fractures include liquid inclusions typically consisting of H2O and CH4,and gas inclusions that contain CO2,H2S,CH4,N2 and H2. The fluid inclusions display a high level of divergence in their homogenization temperature,spanning from 168 to 293℃,and are roughly distinguished by three temperature intervals:168-175℃ low-temperature intervals,185-227℃ medium-temperature intervals,and 244-293℃ high-temperature intervals,suggesting a multistage history of reservoir formation. Most of the late secondary inclusions are found in the medium-temperature intervals and contain high levels of CH4,which indicates an origin of late secondary accumulation. According to the valid age data of 178 groups of detrital zircon obtained,the ages range from 2 638 to 330 Ma and mostly fall within five time intervals of 2 638-2 010 Ma,1 997-1 516 Ma,1 450-904 Ma,890-722 Ma and 699-330 Ma. It shows that XD1 has undergone multistage tectonic transformation. Well XD1 shale gas has the material basis of hydrocarbon generation. This suggests that extensive fracture and rupture zones resulting from multistage tectonic reformation in the area have led to destruction of shale gas preservation conditions,resulting in the loss of shale gas. Therefore,the stable structure regions are predicted as the favorable shale exploration areas in West Hubei.
To find out the accumulation characteristics of the Cambrian Niutitang Formation shale gas in West Hubei,reservoir fracture characteristics,fluid inclusion testing of fracture-filling calcite veins,and detrital zircon U-Pb dating of Cambrian sedimentary rocks were conducted based on the data of Well XD1. This well contains developed,high-angle,mostly calcite-filled fractures. Inclusions inside the fractures include liquid inclusions typically consisting of H2O and CH4,and gas inclusions that contain CO2,H2S,CH4,N2 and H2. The fluid inclusions display a high level of divergence in their homogenization temperature,spanning from 168 to 293℃,and are roughly distinguished by three temperature intervals:168-175℃ low-temperature intervals,185-227℃ medium-temperature intervals,and 244-293℃ high-temperature intervals,suggesting a multistage history of reservoir formation. Most of the late secondary inclusions are found in the medium-temperature intervals and contain high levels of CH4,which indicates an origin of late secondary accumulation. According to the valid age data of 178 groups of detrital zircon obtained,the ages range from 2 638 to 330 Ma and mostly fall within five time intervals of 2 638-2 010 Ma,1 997-1 516 Ma,1 450-904 Ma,890-722 Ma and 699-330 Ma. It shows that XD1 has undergone multistage tectonic transformation. Well XD1 shale gas has the material basis of hydrocarbon generation. This suggests that extensive fracture and rupture zones resulting from multistage tectonic reformation in the area have led to destruction of shale gas preservation conditions,resulting in the loss of shale gas. Therefore,the stable structure regions are predicted as the favorable shale exploration areas in West Hubei.
2019, 44(11): 3628-3638.
doi: 10.3799/dqkx.2019.183
Abstract:
Multiple shale gas intervals occur in the Qiongzhusi Formation in the Southwest Sichuan basin,where gas contents in upper shale section are significantly higher than those in the lower shale section. Main control factors of shale gas differential vertical enrichment in Qiongzhusi Formation were understood through analyzing geochemical feature,reservoir and sealing conditions with rock pyrolysis,physical experiements,XRD diffraction,and field-emission scanning electron microscopy. The main control factors can be summarized as follows. (1) TOC content. It is higher and enriched in the upper shale section but lower and scattered in the lower shale section,resulting in the difference in hydrocarbon generation,organic pores and micro-pore growth. (2) Mineral component and reservoir property. The upper shale is characterized by high clay mineral content,especially I/S content,which contributes to the absorbed gas. The porosity of upper shale is higher than that of lower shale,where organic pores are the main pore space. The lower shales are mainly composed of clay mineral pores,intergranular pores and micro-fractures. Compared with the lower shales,the clay mineral content in the upper shale is higher,which is dominated by I/S mixed layer that can make an important contribution to the enrichment of adsorbed gas. (3) Sealing conditions. The top and floor of the upper shale section are well developed,however,the bottom of the lower shale section is relatively weak due to the existence of paleo-weathering carbonate crust at the bottom of the shale. Therefore,high TOC,high clay mineral content and well-developed organic pores,good sealing conditions contribute to the enrichment of shale gas at upper shale section.
Multiple shale gas intervals occur in the Qiongzhusi Formation in the Southwest Sichuan basin,where gas contents in upper shale section are significantly higher than those in the lower shale section. Main control factors of shale gas differential vertical enrichment in Qiongzhusi Formation were understood through analyzing geochemical feature,reservoir and sealing conditions with rock pyrolysis,physical experiements,XRD diffraction,and field-emission scanning electron microscopy. The main control factors can be summarized as follows. (1) TOC content. It is higher and enriched in the upper shale section but lower and scattered in the lower shale section,resulting in the difference in hydrocarbon generation,organic pores and micro-pore growth. (2) Mineral component and reservoir property. The upper shale is characterized by high clay mineral content,especially I/S content,which contributes to the absorbed gas. The porosity of upper shale is higher than that of lower shale,where organic pores are the main pore space. The lower shales are mainly composed of clay mineral pores,intergranular pores and micro-fractures. Compared with the lower shales,the clay mineral content in the upper shale is higher,which is dominated by I/S mixed layer that can make an important contribution to the enrichment of adsorbed gas. (3) Sealing conditions. The top and floor of the upper shale section are well developed,however,the bottom of the lower shale section is relatively weak due to the existence of paleo-weathering carbonate crust at the bottom of the shale. Therefore,high TOC,high clay mineral content and well-developed organic pores,good sealing conditions contribute to the enrichment of shale gas at upper shale section.
2019, 44(11): 3639-3652.
doi: 10.3799/dqkx.2019.197
Abstract:
Understanding differences of shale gas generation in different sedimentary environments has great significance to fully elucidate genesis mechanisms and geochemical characteristics of shale gas. In this study,semi-closed pyrolysis experiments were conducted on two lower-mature shales,including a marine shale from Hongshuizhuang Formation of Mesoproterozoic and a terrestrial mudstone from the Chang 7 Member of Yanchang Formation of Upper Triassic. The pyrolyzed gas productions were performed for gas constituent and carbon isotope analysis,aiming to investigate influences on gas generation from the nature of organic matter,mineralogical characteristics and rock fabric. The results show the discrepancy of sources of organic matter exists in the two shales,causing the amount of gas generated from Hongshuizhuang shale was lower than that of the Chang 7 Member under the same pyrolysis temperature. Meanwhile,the secondary cracking content of gas productions in the Chang 7 Member mudstone was relatively high. Organic matter in Hongshuizhuang Formation is oil-prone,but organic matter in the Chang 7 Member mudstone is relatively gas-prone due to mixture of continental materials. Moreover,the transformation process from pyrite to pyrrhotine also can be conducive to advancing the generation of hydrocarbon gas in the Chang 7 Member mudstone. The rock fabrics used in the pyrolysis experiments would lead to different cracking behaviors of gas. In this scenario,the characteristics of high methane composition and rollover of carbon isotope of shale gas in the South China may be associated with higher retention of oil and gas in those thick shales.
Understanding differences of shale gas generation in different sedimentary environments has great significance to fully elucidate genesis mechanisms and geochemical characteristics of shale gas. In this study,semi-closed pyrolysis experiments were conducted on two lower-mature shales,including a marine shale from Hongshuizhuang Formation of Mesoproterozoic and a terrestrial mudstone from the Chang 7 Member of Yanchang Formation of Upper Triassic. The pyrolyzed gas productions were performed for gas constituent and carbon isotope analysis,aiming to investigate influences on gas generation from the nature of organic matter,mineralogical characteristics and rock fabric. The results show the discrepancy of sources of organic matter exists in the two shales,causing the amount of gas generated from Hongshuizhuang shale was lower than that of the Chang 7 Member under the same pyrolysis temperature. Meanwhile,the secondary cracking content of gas productions in the Chang 7 Member mudstone was relatively high. Organic matter in Hongshuizhuang Formation is oil-prone,but organic matter in the Chang 7 Member mudstone is relatively gas-prone due to mixture of continental materials. Moreover,the transformation process from pyrite to pyrrhotine also can be conducive to advancing the generation of hydrocarbon gas in the Chang 7 Member mudstone. The rock fabrics used in the pyrolysis experiments would lead to different cracking behaviors of gas. In this scenario,the characteristics of high methane composition and rollover of carbon isotope of shale gas in the South China may be associated with higher retention of oil and gas in those thick shales.
2019, 44(11): 3653-3661.
doi: 10.3799/dqkx.2019.212
Abstract:
In order to find out the reasons why there are obvious differences in the development effect of gas wells between upper gas reservoir (⑥-⑨ sublayers) and lower gas reservoirs (①-⑤ sublayers),in this paper it analyzes differences between upper and lower gas reservoirs in shale lithology,geochemical characteristics,pore type and reservoir physical properties based on fracturing data,field production performance,recoverable reserves prediction and geological analysis. Combined with the analysis of production characteristics of gas wells,it is believed that there may be a primary migration in the upper gas reservoir in the source rock,resulting in a high degree of natural gas enrichment in the upper part of the upper gas layer structure. This is the main reason for the difference of development effect between upper and lower gas reservoir gas wells. The high part of Jiaoshiba anticline is the favorable area for the development of upper gas reservoir,but its effective development scope needs to be delineated according to the recoverable reserves and economy of shale gas wells due to the limitations of technological level and gas price. Combining with the evaluation of stable production capacity and recoverable reserves of shale gas wells in upper gas reservoirs,it is considered that the development of upper gas reservoirs should start from the high part of the structure and gradually expand to the low part.
In order to find out the reasons why there are obvious differences in the development effect of gas wells between upper gas reservoir (⑥-⑨ sublayers) and lower gas reservoirs (①-⑤ sublayers),in this paper it analyzes differences between upper and lower gas reservoirs in shale lithology,geochemical characteristics,pore type and reservoir physical properties based on fracturing data,field production performance,recoverable reserves prediction and geological analysis. Combined with the analysis of production characteristics of gas wells,it is believed that there may be a primary migration in the upper gas reservoir in the source rock,resulting in a high degree of natural gas enrichment in the upper part of the upper gas layer structure. This is the main reason for the difference of development effect between upper and lower gas reservoir gas wells. The high part of Jiaoshiba anticline is the favorable area for the development of upper gas reservoir,but its effective development scope needs to be delineated according to the recoverable reserves and economy of shale gas wells due to the limitations of technological level and gas price. Combining with the evaluation of stable production capacity and recoverable reserves of shale gas wells in upper gas reservoirs,it is considered that the development of upper gas reservoirs should start from the high part of the structure and gradually expand to the low part.
2019, 44(11): 3662-3677.
doi: 10.3799/dqkx.2019.167
Abstract:
The Lower Cambrian Niutitang Formation in Xuefeng uplift and its peripheral areas is one of major shale gas reservoirs. To explore the gas-bearing capacity of Niutitang Formation shale in this area, the vertical variations of gas-bearing capacity, distribution and controlling factors of shale gas in western margin of Xuefeng uplift were studied in detail, based on the drilling data of Well XZD-1 and the testing gas content data. The gas content of desorption in Well XZD-1 increases gradually with the increase of depth with locally high gas abundance. The gas-bearing property of Niutitang Formation shale was controlled by various factors such as organic carbon content, mineral composition, development characteristics of pore and fracture, physical property and the decollement structure. The lower shale of Niutitang Formation has high content of organic carbon and brittle minerals, well-developed natural fractures and pores. Organic matter provides the main adsorption specific surface area, the brittle minerals contribute to the formation and preservation of pores and fractures. The fracture and pore with the decollement structure have effectively improved reservoir physical property, provided a large amount of reservoir space for free gas and ensured a high gas content in the lower Niutitang Formation. And free gas is the main component, accounting for 58%-82%. In addition, the content of adsorbed gas in the bottom decollement belt is very low. The influence of pore and fracture development is greater than that of organic carbon content. And the distribution of pores and fractures result in the locally enriched gas. The pore and fracture of upper shale in Niutitang Formation are under developed, and the contents of organic matter and brittle minerals are lower. The shale gas content in the upper shale of Niutitang Formation is poor and the proportion of adsorbed gas in the total gas content is slightly larger, which is mainly controlled by organic carbon content. In addition, the lower shale of Niutitang Formation has strong fracturability, which is conducive to later fracturing transformation, because it is brittle in rock mechanics, with late diagenesis, high thermal maturity and low difference between compressive strength and principal stress.
The Lower Cambrian Niutitang Formation in Xuefeng uplift and its peripheral areas is one of major shale gas reservoirs. To explore the gas-bearing capacity of Niutitang Formation shale in this area, the vertical variations of gas-bearing capacity, distribution and controlling factors of shale gas in western margin of Xuefeng uplift were studied in detail, based on the drilling data of Well XZD-1 and the testing gas content data. The gas content of desorption in Well XZD-1 increases gradually with the increase of depth with locally high gas abundance. The gas-bearing property of Niutitang Formation shale was controlled by various factors such as organic carbon content, mineral composition, development characteristics of pore and fracture, physical property and the decollement structure. The lower shale of Niutitang Formation has high content of organic carbon and brittle minerals, well-developed natural fractures and pores. Organic matter provides the main adsorption specific surface area, the brittle minerals contribute to the formation and preservation of pores and fractures. The fracture and pore with the decollement structure have effectively improved reservoir physical property, provided a large amount of reservoir space for free gas and ensured a high gas content in the lower Niutitang Formation. And free gas is the main component, accounting for 58%-82%. In addition, the content of adsorbed gas in the bottom decollement belt is very low. The influence of pore and fracture development is greater than that of organic carbon content. And the distribution of pores and fractures result in the locally enriched gas. The pore and fracture of upper shale in Niutitang Formation are under developed, and the contents of organic matter and brittle minerals are lower. The shale gas content in the upper shale of Niutitang Formation is poor and the proportion of adsorbed gas in the total gas content is slightly larger, which is mainly controlled by organic carbon content. In addition, the lower shale of Niutitang Formation has strong fracturability, which is conducive to later fracturing transformation, because it is brittle in rock mechanics, with late diagenesis, high thermal maturity and low difference between compressive strength and principal stress.
2019, 44(11): 3678-3691.
doi: 10.3799/dqkx.2019.208
Abstract:
The Xuefengshan Silurian foreland basin is located in the Central-Northwest Hunan-Sichuan basin, which is the main basin type of the Upper Yangtze plate. Sedimentary formation process and shale gas exploration potential of foreland basins in Northwest and Central Hunan are analyzed based on field data, logging data and testing data. The facies of foredeep include turbidite fan and shelf. Facies of back bulge basin include tidal flat, shelf, shore, delta and carbonate platform facies and so on. So, facies in back bulge basin are more abundant than in foredeep. Though the facies are different greatly in foredeep and back bulge basin, the sedimentary cycles in those systems are coherent. So foredeep and back bulge basin are connected and Xuefengshan obstructing is limited for the foredeep and back bulge basin distributed around Xufengshan. Based on geochemistry data and analysis data, TOC and organic matter type in study area are poorer than in Jiaoshiba area in Sichuan basin. Based on regional section correlation, black carbonaceous shale distributed at the bottom of Longmaxi Formation is absent in the study, causing TOC and organic matter type being poorer than in Jiaoshiba. The main reason for the poor geochemical indexes of Silurian shale in Hunan is the lack of black carbonaceous shale in the first cycle of Longmaxi Formation.
The Xuefengshan Silurian foreland basin is located in the Central-Northwest Hunan-Sichuan basin, which is the main basin type of the Upper Yangtze plate. Sedimentary formation process and shale gas exploration potential of foreland basins in Northwest and Central Hunan are analyzed based on field data, logging data and testing data. The facies of foredeep include turbidite fan and shelf. Facies of back bulge basin include tidal flat, shelf, shore, delta and carbonate platform facies and so on. So, facies in back bulge basin are more abundant than in foredeep. Though the facies are different greatly in foredeep and back bulge basin, the sedimentary cycles in those systems are coherent. So foredeep and back bulge basin are connected and Xuefengshan obstructing is limited for the foredeep and back bulge basin distributed around Xufengshan. Based on geochemistry data and analysis data, TOC and organic matter type in study area are poorer than in Jiaoshiba area in Sichuan basin. Based on regional section correlation, black carbonaceous shale distributed at the bottom of Longmaxi Formation is absent in the study, causing TOC and organic matter type being poorer than in Jiaoshiba. The main reason for the poor geochemical indexes of Silurian shale in Hunan is the lack of black carbonaceous shale in the first cycle of Longmaxi Formation.
2019, 44(11): 3692-3704.
doi: 10.3799/dqkx.2019.203
Abstract:
Mineral compositions control the type and key physical properties of shale gas reservoir. To analyze the characteristics of different types of quartz minerals in the longitudinal direction and their effects on shale gas enrichment and development, two graptolite shale zones are scrutinized including WF2-LM4 and LM5-LM8 of the Wufeng-Longmaxi Formations in the Sichuan basin and its surrounding areas. Three types of quartz are identified which are detrital quartz, biogenic quartz and quartz sourced from clay mineral reactions by means of thin section examination, scanning electron microscopy(SEM), mineral diagenesis and energy spectrum analysis. The contents of the three types of quartz vary in different shale intervals. Biogenic quartz is most abundant in the WF2-LM4 graptolite shale zone and gradually decreases upward to the LM5-LM8. In the WF2-LM4 graptolite shale zone, there is a clear positive correlation between biogenic quartz and organic carbon content, which is conducive not only to the formation of favorable shale reservoirs but also to the fracturing of shale reservoirs, realizing the integrity of shale gas enrichment and formation stimulation. The development areas of black shale from the Wufeng Formation and the first section of the Longmaxi Formation (WF2-LM4 graptolite shale zone) are identified as favorable targets providing abundant material basis for shale gas enrichment.
Mineral compositions control the type and key physical properties of shale gas reservoir. To analyze the characteristics of different types of quartz minerals in the longitudinal direction and their effects on shale gas enrichment and development, two graptolite shale zones are scrutinized including WF2-LM4 and LM5-LM8 of the Wufeng-Longmaxi Formations in the Sichuan basin and its surrounding areas. Three types of quartz are identified which are detrital quartz, biogenic quartz and quartz sourced from clay mineral reactions by means of thin section examination, scanning electron microscopy(SEM), mineral diagenesis and energy spectrum analysis. The contents of the three types of quartz vary in different shale intervals. Biogenic quartz is most abundant in the WF2-LM4 graptolite shale zone and gradually decreases upward to the LM5-LM8. In the WF2-LM4 graptolite shale zone, there is a clear positive correlation between biogenic quartz and organic carbon content, which is conducive not only to the formation of favorable shale reservoirs but also to the fracturing of shale reservoirs, realizing the integrity of shale gas enrichment and formation stimulation. The development areas of black shale from the Wufeng Formation and the first section of the Longmaxi Formation (WF2-LM4 graptolite shale zone) are identified as favorable targets providing abundant material basis for shale gas enrichment.
2019, 44(11): 3705-3716.
doi: 10.3799/dqkx.2019.143
Abstract:
In order to evaluate the thermal evolution degree of organic matter of Lower Paleozoic shale in South China and discuss its relationship with shale gas, gas chromatography-mass spectrometry analysis of aromatic compounds in 20 shale samples collected from 6 investigation wells and 3 outcrop profiles in the Central Yangtze region was made, and 6 samples representing different regions were determined by laser Raman spectroscopy. The results show that the parameters of Raman D and G bands can be used to calculate the maturity of organic matter from over-maturity to spheroidal graphite stage. The sub-bands of D band contain important information of aromatics content. The strength of D4 sub-band, which is related to aromatics content, decreases with the increase of thermal evolution degree of organic matter. The evolution regularities of phenanthrene series compounds and dibenzothiophene series compounds are remarkable in the range of RmcRo=2.73%-4.67%. Although the formula for maturity of methylphenanthrene is no longer applicable in this stage, the parameter F1 which characterizes the relative content of 3-MP+2-MP is still a good maturity index of organic matter. F1 gradually increases to about 0.74(Ro=3%) firstly, and then decreases with the increase of maturity at the over-maturity stage. The parameters of dibenzothiophene compounds, 2, 4-/1, 4-DMDBT and 4, 6-/1, 4-DMDBT, increase with maturity at the over-maturity stage. When the two ratios are 2 and 4.5 respectively, the Raman reflectance value of shale is RmcRo=4%. The isomerization and demethylation of aromatic hydrocarbon series compounds occur with the increase of thermal evolution degree of organic matter in the over-mature stage, which has a good coupling effect with the change of specific surface area of organic matter and a good correlation with analytical gas about investigation wells. The characteristics of aromatic hydrocarbon compounds have important indicative significance for shale gas generation at the over-mature stage, and can be used as an effective index for shale gas exploration in over-mature areas of Lower Paleozoic in South China.
In order to evaluate the thermal evolution degree of organic matter of Lower Paleozoic shale in South China and discuss its relationship with shale gas, gas chromatography-mass spectrometry analysis of aromatic compounds in 20 shale samples collected from 6 investigation wells and 3 outcrop profiles in the Central Yangtze region was made, and 6 samples representing different regions were determined by laser Raman spectroscopy. The results show that the parameters of Raman D and G bands can be used to calculate the maturity of organic matter from over-maturity to spheroidal graphite stage. The sub-bands of D band contain important information of aromatics content. The strength of D4 sub-band, which is related to aromatics content, decreases with the increase of thermal evolution degree of organic matter. The evolution regularities of phenanthrene series compounds and dibenzothiophene series compounds are remarkable in the range of RmcRo=2.73%-4.67%. Although the formula for maturity of methylphenanthrene is no longer applicable in this stage, the parameter F1 which characterizes the relative content of 3-MP+2-MP is still a good maturity index of organic matter. F1 gradually increases to about 0.74(Ro=3%) firstly, and then decreases with the increase of maturity at the over-maturity stage. The parameters of dibenzothiophene compounds, 2, 4-/1, 4-DMDBT and 4, 6-/1, 4-DMDBT, increase with maturity at the over-maturity stage. When the two ratios are 2 and 4.5 respectively, the Raman reflectance value of shale is RmcRo=4%. The isomerization and demethylation of aromatic hydrocarbon series compounds occur with the increase of thermal evolution degree of organic matter in the over-mature stage, which has a good coupling effect with the change of specific surface area of organic matter and a good correlation with analytical gas about investigation wells. The characteristics of aromatic hydrocarbon compounds have important indicative significance for shale gas generation at the over-mature stage, and can be used as an effective index for shale gas exploration in over-mature areas of Lower Paleozoic in South China.
2019, 44(11): 3717-3724.
doi: 10.3799/dqkx.2019.181
Abstract:
In order to clarify the equivalent conversion relationship between bitumen reflectance and vitrinite reflectance for evaluating the maturity of marine shale in the Lower Paleozoic in South China, a series of hydrocarbon generation simulation experiments were carried out in the temperature range of 350-525℃ using a shale from Hongshuizhuang Formation and a coal sample from Longtan Formation with similar maturity. An equivalent conversion relationship was established by measuring the reflectivity of bitumen from shale and vitrinite from coal at each temperature point, and also the accuracy of the method using the simulated sample and outcrop sample is validated. The result shows that they follow this relationship:VRo (equivalent vitrinite reflectance)=0.879 8Rb (bitumen reflectance) + 0.114 5 (VRo 0.61%-3.04%). The regression formula of bitumen reflectance can provide an important reference for accurately evaluating the maturity of marine shale strata without vitrinite in the South China.
In order to clarify the equivalent conversion relationship between bitumen reflectance and vitrinite reflectance for evaluating the maturity of marine shale in the Lower Paleozoic in South China, a series of hydrocarbon generation simulation experiments were carried out in the temperature range of 350-525℃ using a shale from Hongshuizhuang Formation and a coal sample from Longtan Formation with similar maturity. An equivalent conversion relationship was established by measuring the reflectivity of bitumen from shale and vitrinite from coal at each temperature point, and also the accuracy of the method using the simulated sample and outcrop sample is validated. The result shows that they follow this relationship:VRo (equivalent vitrinite reflectance)=0.879 8Rb (bitumen reflectance) + 0.114 5 (VRo 0.61%-3.04%). The regression formula of bitumen reflectance can provide an important reference for accurately evaluating the maturity of marine shale strata without vitrinite in the South China.
2019, 44(11): 3725-3735.
doi: 10.3799/dqkx.2019.098
Abstract:
The maturity of the Wufeng-Longmaxi Formation organic-rich shales with graptolites, which is now one of the most successful and important shale gas exploration targets in China, has been controversial due to the lack of vitrinite. In this paper, taking this formation shale located on the northern margin of Xuefeng Mountain as an example, the graptolite reflectance is used to represent the maturity characteristics. It is concluded that this shale is rich in graptolite, mainly composed of non-granular graptolites which have biaxial optical characteristics, and its maximum reflectance (GRmax) and bireflectance are positive. In addition, the higher the maturity of the graptolites, the greater the anisotropy of graptolite reflectance. At the same time, this formation is also rich in asphalt particles, and its random reflectance value is also positively correlated with the maximum and random reflectance of the graptolites, and its anisotropy is weaker than the former. However, the reflectance of asphalt particles is difficult to measure because of its complicated formation factor and smaller size. Relatively speaking, the graptolite reflectance is more dominant as a thermal maturity indicator. The Wufeng-Longmaxi Formation shales located on the northern margin of Xuefeng Mountain is a favorable area for shale gas exploration because of its high maturity. The equivalent vitrinite reflectance values (EqVRo) of this shale has reached more than 3.10%, reaching the over-mature stage.
The maturity of the Wufeng-Longmaxi Formation organic-rich shales with graptolites, which is now one of the most successful and important shale gas exploration targets in China, has been controversial due to the lack of vitrinite. In this paper, taking this formation shale located on the northern margin of Xuefeng Mountain as an example, the graptolite reflectance is used to represent the maturity characteristics. It is concluded that this shale is rich in graptolite, mainly composed of non-granular graptolites which have biaxial optical characteristics, and its maximum reflectance (GRmax) and bireflectance are positive. In addition, the higher the maturity of the graptolites, the greater the anisotropy of graptolite reflectance. At the same time, this formation is also rich in asphalt particles, and its random reflectance value is also positively correlated with the maximum and random reflectance of the graptolites, and its anisotropy is weaker than the former. However, the reflectance of asphalt particles is difficult to measure because of its complicated formation factor and smaller size. Relatively speaking, the graptolite reflectance is more dominant as a thermal maturity indicator. The Wufeng-Longmaxi Formation shales located on the northern margin of Xuefeng Mountain is a favorable area for shale gas exploration because of its high maturity. The equivalent vitrinite reflectance values (EqVRo) of this shale has reached more than 3.10%, reaching the over-mature stage.
2019, 44(11): 3736-3748.
doi: 10.3799/dqkx.2019.218
Abstract:
In order to study the evolution law of pore structure of over-matured shale, two groups of over-matured shales, which were collected from Cambrian Niutitang Formation and Silurian Longmaxi Formation in the Upper Yangtze region, were selected to carry out semi-closed thermal simulation experiments. Meanwhile, X-ray diffraction analysis, CO2 and N2 isotherm adsorption as well as FE-SEM observations were used to determine mineralogical compositions and study the nanopore evolution characteristics. The pore volume of Longmaxi samples increases to the maximum at 500℃, and the pore volume is 1.35 times higher than that of the original sample. The pore volume of shale samples in Niutitang Formation rises to the maximum at 450℃, which is 1.13 times higher than the original sample. Combined with N2 and CO2 adsorption data, the micro-meso-macro pore volume of the samples in the two groups was calculated. The micropore volume of the samples in the Niutitang Formation is 1.72 times higher than that in the Longmaxi Formation, and the mesopore volume of the samples in the Longmaxi Formation is 1.44 times higher than that in the Niutitang Formation. These results show that follows (1) The shale of Niutitang Formation has weak hydrocarbon generation potential and high original micropore volume, with little hydrocarbon generation and difficulty in discharging, resulting in relatively poor pore structure improvement.(2) Longmaxi Formation has high quartz content and strong compressive resistance, which is conducive to the development and preservation of meso-macropores, as well as hydrocarbon generation and subsequent extraction, so the pore volume is greatly improved.
In order to study the evolution law of pore structure of over-matured shale, two groups of over-matured shales, which were collected from Cambrian Niutitang Formation and Silurian Longmaxi Formation in the Upper Yangtze region, were selected to carry out semi-closed thermal simulation experiments. Meanwhile, X-ray diffraction analysis, CO2 and N2 isotherm adsorption as well as FE-SEM observations were used to determine mineralogical compositions and study the nanopore evolution characteristics. The pore volume of Longmaxi samples increases to the maximum at 500℃, and the pore volume is 1.35 times higher than that of the original sample. The pore volume of shale samples in Niutitang Formation rises to the maximum at 450℃, which is 1.13 times higher than the original sample. Combined with N2 and CO2 adsorption data, the micro-meso-macro pore volume of the samples in the two groups was calculated. The micropore volume of the samples in the Niutitang Formation is 1.72 times higher than that in the Longmaxi Formation, and the mesopore volume of the samples in the Longmaxi Formation is 1.44 times higher than that in the Niutitang Formation. These results show that follows (1) The shale of Niutitang Formation has weak hydrocarbon generation potential and high original micropore volume, with little hydrocarbon generation and difficulty in discharging, resulting in relatively poor pore structure improvement.(2) Longmaxi Formation has high quartz content and strong compressive resistance, which is conducive to the development and preservation of meso-macropores, as well as hydrocarbon generation and subsequent extraction, so the pore volume is greatly improved.
2019, 44(11): 3749-3756.
doi: 10.3799/dqkx.2019.221
Abstract:
The efficient development of shale gas with abundant resources is conducive to meeting the growing energy demand. However, it is very difficult to develop shale reservoirs because of their low porosity and low permeability in China. Supercritical carbon dioxide is a new kind of drilling and production fluid for shale gas which can effectively protect shale reservoirs, enhance shale gas recovery by displacement adsorption, and realize the geological storage of carbon dioxide. A set of device for developing shale gas by using supercritical carbon dioxide is developed, and the laboratory tests were carried out. Tests show that the rock strength decreases after the injection of supercritical carbon dioxide, and the higher the injection pressure and temperature, the greater the decreasing range. Under the experimental conditions, the rock-breaking volume of supercritical carbon dioxide jet is 1.73-6.51 times that of water jet, and the rock-breaking advantage is remarkable. The bottom ambient temperature has great influence on rock-breaking performance of supercritical carbon dioxide jet. It shows that the supercritical carbon dioxide can significantly improve the drilling speed of shale gas, and is expected to form an efficient shale gas development method with broad application potential.
The efficient development of shale gas with abundant resources is conducive to meeting the growing energy demand. However, it is very difficult to develop shale reservoirs because of their low porosity and low permeability in China. Supercritical carbon dioxide is a new kind of drilling and production fluid for shale gas which can effectively protect shale reservoirs, enhance shale gas recovery by displacement adsorption, and realize the geological storage of carbon dioxide. A set of device for developing shale gas by using supercritical carbon dioxide is developed, and the laboratory tests were carried out. Tests show that the rock strength decreases after the injection of supercritical carbon dioxide, and the higher the injection pressure and temperature, the greater the decreasing range. Under the experimental conditions, the rock-breaking volume of supercritical carbon dioxide jet is 1.73-6.51 times that of water jet, and the rock-breaking advantage is remarkable. The bottom ambient temperature has great influence on rock-breaking performance of supercritical carbon dioxide jet. It shows that the supercritical carbon dioxide can significantly improve the drilling speed of shale gas, and is expected to form an efficient shale gas development method with broad application potential.
2019, 44(11): 3757-3772.
doi: 10.3799/dqkx.2019.084
Abstract:
Taking transitional facies shale of Permian Longtan and Dalong Formations as the research object, 12 typical drilling core shale samples in Xiangzhong-Lianyuan depression were selected for tests including organic carbon content, rock-eval, X-ray diffraction, density porosity, high-pressure mercury intrusion, CO2/N2 adsorption while using field emission scanning electron microscopy(FE-SEM) to observe pore characteristics. In this study it focuses on the development of nano-microscale pore, pore structure characteristics and main control factors of the transitional facies shale through the combinations of qualitative description and quantitative measure method. The results show that the organic carbon content of Longtan and Dalong Formation shales is high, the degree of thermal evolution is in the early stage of generating condensate oil and wet gas, corresponding to Ro of 1.22%-1.43%; pore types of shale are mainly intergranular pores, intragranular pores, organic pores and micro-nanoscale cracks. There are differences in the pore morphology, pore size and control factors between Longtan and Dalong Formations. In Longtan Formation, N2 adsorption hysteresis loop is wide and the shapes of organic poresare mostly round and elliptic with larger pore diameter. The N2 adsorption hysteresis loop of the Dalong Formation is narrow and the shapes of the organic poresare irregular with small pore diameter. There is a positive correlation between TOC and clay mineral in both Longtan and Dalong Formation shales. The volume of micropore in both Longtan and Dalong Formation shales is positively correlated with TOC and clay mineral. The mesopore+macropore pore volume of Longtan Formation shale has a position linear relationship with TOC and clay mineral, but is negatively correlated with quartz+feldspar. Carbonate mineral in Dalong Formation has a significant influence on its pore structure, and the relationship of mesopore+macropore pore volume with TOC-clay mineral and quartz+feldspar in Dalong Formation shale is not obvious.
Taking transitional facies shale of Permian Longtan and Dalong Formations as the research object, 12 typical drilling core shale samples in Xiangzhong-Lianyuan depression were selected for tests including organic carbon content, rock-eval, X-ray diffraction, density porosity, high-pressure mercury intrusion, CO2/N2 adsorption while using field emission scanning electron microscopy(FE-SEM) to observe pore characteristics. In this study it focuses on the development of nano-microscale pore, pore structure characteristics and main control factors of the transitional facies shale through the combinations of qualitative description and quantitative measure method. The results show that the organic carbon content of Longtan and Dalong Formation shales is high, the degree of thermal evolution is in the early stage of generating condensate oil and wet gas, corresponding to Ro of 1.22%-1.43%; pore types of shale are mainly intergranular pores, intragranular pores, organic pores and micro-nanoscale cracks. There are differences in the pore morphology, pore size and control factors between Longtan and Dalong Formations. In Longtan Formation, N2 adsorption hysteresis loop is wide and the shapes of organic poresare mostly round and elliptic with larger pore diameter. The N2 adsorption hysteresis loop of the Dalong Formation is narrow and the shapes of the organic poresare irregular with small pore diameter. There is a positive correlation between TOC and clay mineral in both Longtan and Dalong Formation shales. The volume of micropore in both Longtan and Dalong Formation shales is positively correlated with TOC and clay mineral. The mesopore+macropore pore volume of Longtan Formation shale has a position linear relationship with TOC and clay mineral, but is negatively correlated with quartz+feldspar. Carbonate mineral in Dalong Formation has a significant influence on its pore structure, and the relationship of mesopore+macropore pore volume with TOC-clay mineral and quartz+feldspar in Dalong Formation shale is not obvious.
2019, 44(11): 3773-3782.
doi: 10.3799/dqkx.2019.107
Abstract:
In order to understand the transformation of microscopic pore structure and adsorption behavior of carbon dioxide (CO2) on shale under high pressure condition, using low-pressure N2 adsorption analysis and isothermal adsorption instrument based on gravimetric method, the microstructural characteristics before and after CO2 treatment, and the adsorption behavior of CO2 in Jiaoye 6 shale from Jiaoshiba area of Sichuan basin were studied. The results show that the shale specific surface area decreased, and the average pore size and pore volume increased with increasing CO2 treatment temperature. Besides, the proportions of micropore and mesopore decreased, and the proportion of macropore increased with increasing temperature. CO2 could change the pore structure of shale, and the degree of change is positively correlated with temperature. The results also show that the excess adsorption amount of CO2 increased with increasing pressure, reached a maximum value, and then decreased. The absolute adsorption amount of CO2 increased with increasing pressure, and then tended to be stable after 40 MPa. The adsorption behavior of CO2 on shale is related to temperature and pressure. Langmuir model can still fit CO2 adsorption on shale well under high pressure.
In order to understand the transformation of microscopic pore structure and adsorption behavior of carbon dioxide (CO2) on shale under high pressure condition, using low-pressure N2 adsorption analysis and isothermal adsorption instrument based on gravimetric method, the microstructural characteristics before and after CO2 treatment, and the adsorption behavior of CO2 in Jiaoye 6 shale from Jiaoshiba area of Sichuan basin were studied. The results show that the shale specific surface area decreased, and the average pore size and pore volume increased with increasing CO2 treatment temperature. Besides, the proportions of micropore and mesopore decreased, and the proportion of macropore increased with increasing temperature. CO2 could change the pore structure of shale, and the degree of change is positively correlated with temperature. The results also show that the excess adsorption amount of CO2 increased with increasing pressure, reached a maximum value, and then decreased. The absolute adsorption amount of CO2 increased with increasing pressure, and then tended to be stable after 40 MPa. The adsorption behavior of CO2 on shale is related to temperature and pressure. Langmuir model can still fit CO2 adsorption on shale well under high pressure.
2019, 44(11): 3783-3793.
doi: 10.3799/dqkx.2019.189
Abstract:
L11 sub-section shale reservoir is the major production layer in the South Sichuan shale gas block. For the horizontal well production, different well paths in the different layers can show quite big production gap, which may be due to the different shale crushabilities. However, the elastic modulus and brittle minerals for different layers in L11 sub-section have not shown much difference, so it is still impossible to evaluate the shale brittleness sufficiently with the conventional methods and models, Based on studies on the cause of earthquake, the steady & non-steady state failure is introduced to characterize the crushability for the different L11 layers in this paper. The new friction and steady & non-steady state experiments were designed to replace the conventional fault gauge testing method for the L11 outcrop samples. Firstly, the influence of the lamination, mineral constituents and normal stress on the friction for shale was studied and analyzed. Secondly, the steady & non-steady state behavior was characterized and quantified by the calculated a-b value for the shale with different mineral constituents. Thirdly, the critical value from velocity-weakening to velocity-strengthening was established by the overlay method. Taking Well YS108 field in Zhaotong shale block as the example, the different crushabilities for different layers were analyzed and discussed. It is found that L111-2 layers have better crushability that can cause the shear slide easily and generate the map cracking, while the L114 layers have worse crushability that generates the single cracking or cause the shear slide difficultly.
L11 sub-section shale reservoir is the major production layer in the South Sichuan shale gas block. For the horizontal well production, different well paths in the different layers can show quite big production gap, which may be due to the different shale crushabilities. However, the elastic modulus and brittle minerals for different layers in L11 sub-section have not shown much difference, so it is still impossible to evaluate the shale brittleness sufficiently with the conventional methods and models, Based on studies on the cause of earthquake, the steady & non-steady state failure is introduced to characterize the crushability for the different L11 layers in this paper. The new friction and steady & non-steady state experiments were designed to replace the conventional fault gauge testing method for the L11 outcrop samples. Firstly, the influence of the lamination, mineral constituents and normal stress on the friction for shale was studied and analyzed. Secondly, the steady & non-steady state behavior was characterized and quantified by the calculated a-b value for the shale with different mineral constituents. Thirdly, the critical value from velocity-weakening to velocity-strengthening was established by the overlay method. Taking Well YS108 field in Zhaotong shale block as the example, the different crushabilities for different layers were analyzed and discussed. It is found that L111-2 layers have better crushability that can cause the shear slide easily and generate the map cracking, while the L114 layers have worse crushability that generates the single cracking or cause the shear slide difficultly.
2019, 44(11): 3794-3811.
doi: 10.3799/dqkx.2019.156
Abstract:
The Upper Devonian Shetianqiao Formation shale is one of the most important shale gas exploration beds in Lianyuan sag of Xiangzhong depression. In order to discuss the organic matter enrichment mechanism of the Shetianqiao Formation shale, 20 shale core samples collected systematically from Well XXD-3 were chosen.The organic carbon content, major, trace and rare earth elements were analyzed to investigate the paleo-salinity, paleo-climate, paleo-redox and paleo-productivity characteristics of the Upper Devonian sedimentary environment in Lianyuan sag of Xiangzhong depression. Research illustrates that the organic carbon content is higher (1.28%-2.68%) at the bottom of Shetianqiao Formation, with an average of 1.69%. Major components of shale include SiO2(50.27%), Al2O3(13.66%), CaO (11.55%). Trace elements Rb, Sr and Zr are enriched while Co, Mo, Sc and Hf are depleted. The ratio of Sr/Ba, CIA, Th/U, V/Sc, V/Cr, and δU suggest that Shetianqiao Formation organic-rich shales should be deposited in fresh-brackish water, arid climate and suboxic to anoxic environment, while organic-poor shales were mostly deposited in salt water, arid to semi-arid climate and oxygen-enriched environment. Combining with the regional sequence stratigraphic characteristics, comprehensive comparison of the correlation among organic carbon content (TOC), paleo-redox and paleo-productivity conditions, it is revealed that the main controlling factors of organic matter enrichment of Shetianqiao Formation organic-rich shales are redox environment. The changes in organic matter content of Shetianqiao Formation organic-poor shales are predominantly controlled by terrigenous supply.
The Upper Devonian Shetianqiao Formation shale is one of the most important shale gas exploration beds in Lianyuan sag of Xiangzhong depression. In order to discuss the organic matter enrichment mechanism of the Shetianqiao Formation shale, 20 shale core samples collected systematically from Well XXD-3 were chosen.The organic carbon content, major, trace and rare earth elements were analyzed to investigate the paleo-salinity, paleo-climate, paleo-redox and paleo-productivity characteristics of the Upper Devonian sedimentary environment in Lianyuan sag of Xiangzhong depression. Research illustrates that the organic carbon content is higher (1.28%-2.68%) at the bottom of Shetianqiao Formation, with an average of 1.69%. Major components of shale include SiO2(50.27%), Al2O3(13.66%), CaO (11.55%). Trace elements Rb, Sr and Zr are enriched while Co, Mo, Sc and Hf are depleted. The ratio of Sr/Ba, CIA, Th/U, V/Sc, V/Cr, and δU suggest that Shetianqiao Formation organic-rich shales should be deposited in fresh-brackish water, arid climate and suboxic to anoxic environment, while organic-poor shales were mostly deposited in salt water, arid to semi-arid climate and oxygen-enriched environment. Combining with the regional sequence stratigraphic characteristics, comprehensive comparison of the correlation among organic carbon content (TOC), paleo-redox and paleo-productivity conditions, it is revealed that the main controlling factors of organic matter enrichment of Shetianqiao Formation organic-rich shales are redox environment. The changes in organic matter content of Shetianqiao Formation organic-poor shales are predominantly controlled by terrigenous supply.
2019, 44(11): 3812-3828.
doi: 10.3799/dqkx.2018.279
Abstract:
Yusupuleke pluton is one of the largest granite plutons in the south margin of the Altyn orogenic belt. It presents petrology, geochemistry, zircon U-Pb chronology to study the genesis and the evolution of the magmatism in this paper. The pluton is mainly composed of medium-coarse grained porphyritic biotite monzonitic granites and medium-fine grained phenocysts-bearing biotite monzonitic granites. The zircon U-Pb age of the former is 442-448 Ma while the latter is 423-430 Ma. The early granites belong to metaluminous series (A/CNK=0.97) and the late granites belong to weakly peraluminous series (A/CNK=1.04). Both of them show significant Ⅰ-type granite characteristics with depletion in HREE, Ba, P, Sr, Ti, enrichment in LREE, Rb, Th, K, and slightly negative Eu anomaly. Combined with the geochronological data and the regional geological background, It is inferred that the Yusupuleke granites formed in an active continental margin tectonic setting related to the northward subduction of the South Altyn Ocean in Early Paleozoic. In the process of the tectonic regime transition, along with the upwelling of the mantle component, the partial melting of the juvenile crust formed the parent magma and the Yusupuleke granites crystallized after the fractionation of the magma.
Yusupuleke pluton is one of the largest granite plutons in the south margin of the Altyn orogenic belt. It presents petrology, geochemistry, zircon U-Pb chronology to study the genesis and the evolution of the magmatism in this paper. The pluton is mainly composed of medium-coarse grained porphyritic biotite monzonitic granites and medium-fine grained phenocysts-bearing biotite monzonitic granites. The zircon U-Pb age of the former is 442-448 Ma while the latter is 423-430 Ma. The early granites belong to metaluminous series (A/CNK=0.97) and the late granites belong to weakly peraluminous series (A/CNK=1.04). Both of them show significant Ⅰ-type granite characteristics with depletion in HREE, Ba, P, Sr, Ti, enrichment in LREE, Rb, Th, K, and slightly negative Eu anomaly. Combined with the geochronological data and the regional geological background, It is inferred that the Yusupuleke granites formed in an active continental margin tectonic setting related to the northward subduction of the South Altyn Ocean in Early Paleozoic. In the process of the tectonic regime transition, along with the upwelling of the mantle component, the partial melting of the juvenile crust formed the parent magma and the Yusupuleke granites crystallized after the fractionation of the magma.
2019, 44(11): 3829-3844.
doi: 10.3799/dqkx.2018.558
Abstract:
Unconformably overlain by the Early Cretaceous volcanic rocks, the Shangcheng pluton is located in the central segment of the northern Huaiyang tectono-magmatic belt, Dabie orogen. It is of great importance to determine the emplacement age and petrogenesis of this pluton in terms of deciphering the Mesozoic tectonic evolution of the Dabie orogeny. In this paper, it reports the SHRIMP U-Pb zircon ages and whole rock geochemical data. For the central Sigudun unit of the pluton, thirteen zircon analysis spots out of fifteen yield zircon U-Pb ages of 130.2±1.7 Ma, representing the emplacement age of the pluton. The Shangcheng pluton displays high contents of Al2O3 and Sr, as well as high ratios of Sr/Y, and low abundances of Y and Yb, with Nb-Ta negative anomalies and pronounced LREE/HREE, but without obvious Eu anomalies (δEu=0.90~1.05), collectively pointing to an adakite affinity. Three units of Shangcheng pluton, from old to young, display a trend of gradually decreasing crystallization pressures corresponding to shallower emplacement depths step by step, suggesting that formed in an active emplacement background. The Shangcheng pluton results from the Early Cretaceous magmatic flare-up in the Dabie orogeny, and it is originated from the partial melting of the thickened lower crust. From the emplacement of the Shangcheng pluton to the eruption of the Jingangtai volcanics, this region has experienced rapid uplift and denudation. The process is exactly the surface response recorded by those two different geochemical signatures generated through thinning of the thickened lower crust. The 130 Ma is the time of tectonic regime transition of the Dabie orogen during the Mesozoic.
Unconformably overlain by the Early Cretaceous volcanic rocks, the Shangcheng pluton is located in the central segment of the northern Huaiyang tectono-magmatic belt, Dabie orogen. It is of great importance to determine the emplacement age and petrogenesis of this pluton in terms of deciphering the Mesozoic tectonic evolution of the Dabie orogeny. In this paper, it reports the SHRIMP U-Pb zircon ages and whole rock geochemical data. For the central Sigudun unit of the pluton, thirteen zircon analysis spots out of fifteen yield zircon U-Pb ages of 130.2±1.7 Ma, representing the emplacement age of the pluton. The Shangcheng pluton displays high contents of Al2O3 and Sr, as well as high ratios of Sr/Y, and low abundances of Y and Yb, with Nb-Ta negative anomalies and pronounced LREE/HREE, but without obvious Eu anomalies (δEu=0.90~1.05), collectively pointing to an adakite affinity. Three units of Shangcheng pluton, from old to young, display a trend of gradually decreasing crystallization pressures corresponding to shallower emplacement depths step by step, suggesting that formed in an active emplacement background. The Shangcheng pluton results from the Early Cretaceous magmatic flare-up in the Dabie orogeny, and it is originated from the partial melting of the thickened lower crust. From the emplacement of the Shangcheng pluton to the eruption of the Jingangtai volcanics, this region has experienced rapid uplift and denudation. The process is exactly the surface response recorded by those two different geochemical signatures generated through thinning of the thickened lower crust. The 130 Ma is the time of tectonic regime transition of the Dabie orogen during the Mesozoic.
2019, 44(11): 3845-3870.
doi: 10.3799/dqkx.2017.502
Abstract:
Siliceous rocks were widely deposited in many continents during an important geological period, Ediacaran-Cambriam transition. The well developed thin-bedded siliceous rocks in the bottom of Yurtus Formation, northwestern margin of Tarim basin, rich in residual grains, phosphatic nodules and barite concretions, are very special and rare, which is obviously different from conventional siliceous rocks reported at home and abroad. In order to reveal the causes and sedimentary model of this set of siliceous rocks, the advantages of petrological and geochemical methods were used, such as detailed profile measurement (Kule profile), SEM observation, energy spectrum probe, characteristics of main and trace elements, oxygen and silicon isotope distribution. The siliceous rock section can be divided into five units in vertical direction. Its main minerals are quartz and dolomite, and authigenic minerals are mainly pyrite, barite and zeolite; the microstructures of different siliceous rock units show obvious fabric variation, including residual grain structure, residual crystal structure, cryptocrystalline structure and micro-crystal structure. Siliceous rocks of measured profile are deposited in shallow continental shelf near the continental or paleo-uplift with high salinity (high Al2O3/(Al2O3+Fe2O3) ratios, high MgO/Al2O3 ratios), and their terrigenous clastics, affected by the dilution effect of SiO2 (Th/Ti and Al/Ti), are mainly from the weathering products of continental crust or basement granite. Redox sensitive elements (such as Ba, V, Ni, Cu, Zn and U) with different degrees of enrichment and redox indicators (V/Cr ratios from 0.81 to 8.34) indicate that siliceous rocks are developed in the oxidizing environment during early depositional period due to the strong water energy, also supported by many internal clastic particles and microbial mat fragments with good roundness seen under the microscope. And they experienced aerobic/anoxic stratified environment (negative Ce/Ce* anomaly) with limited water circulation during middle to late depositional period, also supported by well-development of microbial pellets, faecal pellets and phytoplankton (bonding) mass seen under the microscope with high organic matter content (TOC up to 2%). Characteristics of rare earth elements (low ∑REE, medium Ce negative anomaly, significant positive Y anomaly and positive Eu anomaly) and distribution range of δ30Si and δ18O values suggest that geochemical characteristics of siliceous rocks have mainly inherited from hydrothermal fluid and seawater, and the terrigenous influence is weak. The polymetallic and Si-rich hydrothermal fluid ascending from rift center near platform and terrigenous clastics provide plenty of nutrition which offers the material foundation for microbial prosperity and the mineralization of SiO2. The decreased solubility of silicon dissolved in water column (due to temperature decreased, the decrease of pH and increase of salinity) promotes the chemical precipitation of silica colloidal particles, and the metabolic activity of microorganisms (especially thermophilic microorganisms) has accelerated this process.
Siliceous rocks were widely deposited in many continents during an important geological period, Ediacaran-Cambriam transition. The well developed thin-bedded siliceous rocks in the bottom of Yurtus Formation, northwestern margin of Tarim basin, rich in residual grains, phosphatic nodules and barite concretions, are very special and rare, which is obviously different from conventional siliceous rocks reported at home and abroad. In order to reveal the causes and sedimentary model of this set of siliceous rocks, the advantages of petrological and geochemical methods were used, such as detailed profile measurement (Kule profile), SEM observation, energy spectrum probe, characteristics of main and trace elements, oxygen and silicon isotope distribution. The siliceous rock section can be divided into five units in vertical direction. Its main minerals are quartz and dolomite, and authigenic minerals are mainly pyrite, barite and zeolite; the microstructures of different siliceous rock units show obvious fabric variation, including residual grain structure, residual crystal structure, cryptocrystalline structure and micro-crystal structure. Siliceous rocks of measured profile are deposited in shallow continental shelf near the continental or paleo-uplift with high salinity (high Al2O3/(Al2O3+Fe2O3) ratios, high MgO/Al2O3 ratios), and their terrigenous clastics, affected by the dilution effect of SiO2 (Th/Ti and Al/Ti), are mainly from the weathering products of continental crust or basement granite. Redox sensitive elements (such as Ba, V, Ni, Cu, Zn and U) with different degrees of enrichment and redox indicators (V/Cr ratios from 0.81 to 8.34) indicate that siliceous rocks are developed in the oxidizing environment during early depositional period due to the strong water energy, also supported by many internal clastic particles and microbial mat fragments with good roundness seen under the microscope. And they experienced aerobic/anoxic stratified environment (negative Ce/Ce* anomaly) with limited water circulation during middle to late depositional period, also supported by well-development of microbial pellets, faecal pellets and phytoplankton (bonding) mass seen under the microscope with high organic matter content (TOC up to 2%). Characteristics of rare earth elements (low ∑REE, medium Ce negative anomaly, significant positive Y anomaly and positive Eu anomaly) and distribution range of δ30Si and δ18O values suggest that geochemical characteristics of siliceous rocks have mainly inherited from hydrothermal fluid and seawater, and the terrigenous influence is weak. The polymetallic and Si-rich hydrothermal fluid ascending from rift center near platform and terrigenous clastics provide plenty of nutrition which offers the material foundation for microbial prosperity and the mineralization of SiO2. The decreased solubility of silicon dissolved in water column (due to temperature decreased, the decrease of pH and increase of salinity) promotes the chemical precipitation of silica colloidal particles, and the metabolic activity of microorganisms (especially thermophilic microorganisms) has accelerated this process.
2019, 44(11): 3871-3881.
doi: 10.3799/dqkx.2018.371
Abstract:
The molar tooth structure(MTS), a special kind of microstructure consisting of pure equigranular micritic calcite or micritic dolomite, mainly developed in Meso-Neoproterozoic strata. During the field geologic investigation, the molar tooth structures were observed in the micritic limestone in the third member of Gaoyuzhuang Formation (Changcheng System) in Nankou, Beijing. Through detailed field observations and microscopic studies, a variety of MTSs were found. The boundaries between host rock and MTS show obvious distinction with a circular arc shape or a gulf-like shape. It is found by scanning electron microscopy (SEM) and energy disperse X-ray microanalysis(EDX) that the MTS consists of siliceous component, such as chalcedony and authigenic quartz. According to the morphology and the filling sequence, the MTS's formation is characterized by multi-genesis and multi-stage, and may be subdivided into four periods, such as crack forming period, crack filling period, crack transforming period, and crack refilling period. It's a key factor of the MTS's formation that the fissure systems are produced by the tectonic movement in semi-consolidated condition.
The molar tooth structure(MTS), a special kind of microstructure consisting of pure equigranular micritic calcite or micritic dolomite, mainly developed in Meso-Neoproterozoic strata. During the field geologic investigation, the molar tooth structures were observed in the micritic limestone in the third member of Gaoyuzhuang Formation (Changcheng System) in Nankou, Beijing. Through detailed field observations and microscopic studies, a variety of MTSs were found. The boundaries between host rock and MTS show obvious distinction with a circular arc shape or a gulf-like shape. It is found by scanning electron microscopy (SEM) and energy disperse X-ray microanalysis(EDX) that the MTS consists of siliceous component, such as chalcedony and authigenic quartz. According to the morphology and the filling sequence, the MTS's formation is characterized by multi-genesis and multi-stage, and may be subdivided into four periods, such as crack forming period, crack filling period, crack transforming period, and crack refilling period. It's a key factor of the MTS's formation that the fissure systems are produced by the tectonic movement in semi-consolidated condition.
2019, 44(11): 3882-3893.
doi: 10.3799/dqkx.2017.574
Abstract:
The study of the internal structure and its characteristics of fault zone shows that fault rock constitutes an important part of fault with universal distribution in fault, and the vertical sealing ability of fault is mainly determined by the difference of capillary entry pressure between fault rock and underlying reservoir rock. The fault is sealed when the capillary entry pressure of fault rock is not smaller than that of reservoir rock. In addition, the sealing ability is determined by the degree of capillary entry pressure difference, the greater the difference, the stronger the sealing ability of fault, and vice versa. The capillary entry pressure of fault rock depends on mud content, diagenetic degree and structure directionality of rock. The higher the mud content and the larger the degree of diagenesis, the smaller the angle between fault surface and vertical direction, which results in the greater the capillary entry pressure. Based on the fault vertical sealing mechanism and multiple geological factors, in combination with the results of capillary entry pressure of mudstone samples in different angles under laboratory conditions and the relation of rock mechanics decomposition, a set of method that could evaluate the fault vertical sealing ability is then established on the basis of determining the surrendering rock which has the same diagenetic degree with the target fault rock. Then the method was applied to evaluation of the fault sealing ability of 1st structure of Nanpu sag. The results indicate that the differences of capillary entry pressures of fault rock and reservoir rock in different survey lines of Fault f1 are from -0.114 MPa to 1.035 MPa, the capillary entry pressures of fault rock are larger than that of reservoir rock except for the survey Lines L1 to L7, that fault is sealed invertical direction, which is consistent with oil and gas distribution law. The method is proved more feasible and credible by comparison of the results with those calculated by method which ignores the structure directionality of rock.
The study of the internal structure and its characteristics of fault zone shows that fault rock constitutes an important part of fault with universal distribution in fault, and the vertical sealing ability of fault is mainly determined by the difference of capillary entry pressure between fault rock and underlying reservoir rock. The fault is sealed when the capillary entry pressure of fault rock is not smaller than that of reservoir rock. In addition, the sealing ability is determined by the degree of capillary entry pressure difference, the greater the difference, the stronger the sealing ability of fault, and vice versa. The capillary entry pressure of fault rock depends on mud content, diagenetic degree and structure directionality of rock. The higher the mud content and the larger the degree of diagenesis, the smaller the angle between fault surface and vertical direction, which results in the greater the capillary entry pressure. Based on the fault vertical sealing mechanism and multiple geological factors, in combination with the results of capillary entry pressure of mudstone samples in different angles under laboratory conditions and the relation of rock mechanics decomposition, a set of method that could evaluate the fault vertical sealing ability is then established on the basis of determining the surrendering rock which has the same diagenetic degree with the target fault rock. Then the method was applied to evaluation of the fault sealing ability of 1st structure of Nanpu sag. The results indicate that the differences of capillary entry pressures of fault rock and reservoir rock in different survey lines of Fault f1 are from -0.114 MPa to 1.035 MPa, the capillary entry pressures of fault rock are larger than that of reservoir rock except for the survey Lines L1 to L7, that fault is sealed invertical direction, which is consistent with oil and gas distribution law. The method is proved more feasible and credible by comparison of the results with those calculated by method which ignores the structure directionality of rock.
2019, 44(11): 3894-3909.
doi: 10.3799/dqkx.2018.250
Abstract:
Well PBX1 is located on Markit slope in the southwestern Tarim basin, and gets oil flow from the breccias upon the testing after oil show at the depth of 6 884-7 150 m.However, the stratigraphy age and formation reasons of the breccia still remains in dispute, which limits the exploration deployment and potential analysis in this area. Core observation and X-ray powder diffraction test show that the degree of breccia roundness and size classification are relatively poor. The compositions of breccia are white sparite psammitic composition (oolitic) limestone, light gray powder dolomite, grey powder dolomite, dark grey powder and a small amount of quartz and anhydrite, and its matrix mostly is cementation of carbonate gravels with fine grain. Many pollen microfossils are found in the lower part of objective formation, the age of which mainly is Cretaceous. Detrital zircon ages range from 2 529 to 127 Ma in the study area, and the age of sedimentation influenced by the terrigenous provenance is after 127 Ma. The comprehensive analyses of lithostratigraphy, biostratigraphy and isotope dating indicate that the age of breccia in Well PBX1 belongs to Yigeziya Formation of Late Cretaceous. The distribution scale of breccia is limited, which overlaps on the strata of Permian and is controlled by hot bottom split underground forming circular depression. Effected by the former caldera and later intrusive complex structure, Late Cretaceous platform facies carbonate fragmentate and deposit in the negative structures of north Pishan Mountain. The oil and gas resources of Well PSX1 were derived from Cambrian. The magmatic intrusion pierces the huge thickness of Paleozoic carbonate and clastic strata, forming a vertical unconformity surface which links up the source rock. The hydrocarbon migrates to the Mesozoic and Cenozoic reservoir-roof combination and gathering with the help of high angle faults, which were created by the volcanism, and form bottom-water structure formation oil reservoir. The Cenozoic of southwestern Tarim basin will be the next breakthrough of hydrocarbon exploration. Fault block traps around calderas edge and special traps which are sheltered by central arched-roof igneous-rock are the favorable targets of further hydrocarbon exploration.
Well PBX1 is located on Markit slope in the southwestern Tarim basin, and gets oil flow from the breccias upon the testing after oil show at the depth of 6 884-7 150 m.However, the stratigraphy age and formation reasons of the breccia still remains in dispute, which limits the exploration deployment and potential analysis in this area. Core observation and X-ray powder diffraction test show that the degree of breccia roundness and size classification are relatively poor. The compositions of breccia are white sparite psammitic composition (oolitic) limestone, light gray powder dolomite, grey powder dolomite, dark grey powder and a small amount of quartz and anhydrite, and its matrix mostly is cementation of carbonate gravels with fine grain. Many pollen microfossils are found in the lower part of objective formation, the age of which mainly is Cretaceous. Detrital zircon ages range from 2 529 to 127 Ma in the study area, and the age of sedimentation influenced by the terrigenous provenance is after 127 Ma. The comprehensive analyses of lithostratigraphy, biostratigraphy and isotope dating indicate that the age of breccia in Well PBX1 belongs to Yigeziya Formation of Late Cretaceous. The distribution scale of breccia is limited, which overlaps on the strata of Permian and is controlled by hot bottom split underground forming circular depression. Effected by the former caldera and later intrusive complex structure, Late Cretaceous platform facies carbonate fragmentate and deposit in the negative structures of north Pishan Mountain. The oil and gas resources of Well PSX1 were derived from Cambrian. The magmatic intrusion pierces the huge thickness of Paleozoic carbonate and clastic strata, forming a vertical unconformity surface which links up the source rock. The hydrocarbon migrates to the Mesozoic and Cenozoic reservoir-roof combination and gathering with the help of high angle faults, which were created by the volcanism, and form bottom-water structure formation oil reservoir. The Cenozoic of southwestern Tarim basin will be the next breakthrough of hydrocarbon exploration. Fault block traps around calderas edge and special traps which are sheltered by central arched-roof igneous-rock are the favorable targets of further hydrocarbon exploration.
2019, 44(11): 3910-3925.
doi: 10.3799/dqkx.2018.331
Abstract:
Apatite fission track dating and thermal history modeling were carried out on 12 granite samples collected from Kalamaili and Aokeshi Mountain in Eastern Junngar to investigate the uplift-denudation processes and characteristics of mountains, and then to discuss its control on sandstone U mineralization. Analyses results reveal the tectonic differential uplift-denudation of Kalamaili and Aokeshi Mountain, with Kalamaili area having been uplifting and being eroded since Late Triassic, much earlier than Aokeshi Mountain with uplifting in Late Jurassic, which plays an essential role in sandstone type U mineralization, including U source condition, the formation of tectonic-slope, favorable metallogenic structure and stable groundwater dynamics. The sandstone type U mineralization is different between the areas of Wucaiwan-Laojunmiao-Jiangjunmiao and Kamusite due to the differential uplift-denudation of the mountains under the tectonic background of transition from Indosinian to Yanshanian periods. Generally speaking, the conditions were better in Wucaiwan-Jiangjunmiao area in Early-Middle Jurassic while the conditions were better in the latter in Late Jurassic. Our study is a kind of sandstone type U mineralization which is going to provide the basic geology criteria for U resource prognosis.
Apatite fission track dating and thermal history modeling were carried out on 12 granite samples collected from Kalamaili and Aokeshi Mountain in Eastern Junngar to investigate the uplift-denudation processes and characteristics of mountains, and then to discuss its control on sandstone U mineralization. Analyses results reveal the tectonic differential uplift-denudation of Kalamaili and Aokeshi Mountain, with Kalamaili area having been uplifting and being eroded since Late Triassic, much earlier than Aokeshi Mountain with uplifting in Late Jurassic, which plays an essential role in sandstone type U mineralization, including U source condition, the formation of tectonic-slope, favorable metallogenic structure and stable groundwater dynamics. The sandstone type U mineralization is different between the areas of Wucaiwan-Laojunmiao-Jiangjunmiao and Kamusite due to the differential uplift-denudation of the mountains under the tectonic background of transition from Indosinian to Yanshanian periods. Generally speaking, the conditions were better in Wucaiwan-Jiangjunmiao area in Early-Middle Jurassic while the conditions were better in the latter in Late Jurassic. Our study is a kind of sandstone type U mineralization which is going to provide the basic geology criteria for U resource prognosis.
2019, 44(11): 3926-3938.
doi: 10.3799/dqkx.2019.166
Abstract:
This study focuses on the environmental background values in shallow groundwater in karst area of Guizhou. Firstly, the study area is divided into different groundwater environmental units according to the analysis data of 3 699 shallow groundwater chemical samples collected for the Guizhou Drought-Resistant Well-Drilling and Water Prospecting Project from 2007 to 2015, and the analysis of the geological background and hydrogeological conditions. Then, the box plot and the iteration standard deviation method are used to eliminate the abnormal values, and determine the distribution type of water chemical data in each hydrogeological area. Finally the 95th percentile of the data is taken as the upper threshhold of the environmental background values after deleting the outliers. The results show that the shallow groundwater in Guizhou karst area is neutral alkaline water, the cations are mainly Ca2+, Mg2+, the anions are mainly HCO3- and SO42- and the groundwater types are mainly HCO3-Ca·Mg type and HCO3-Ca type. The main sources of ions in groundwater are weathering and hydrolysis of rocks and minerals. The distribution types of SO42- and Cl- ions in groundwater are mainly normal distribution, followed by lognormal distribution and least skewed distribution. The environmental background threshold values of the SO42- ion of the Middle Triassic Guanling Formation and the Permian coal-bearing strata are 68.71-164.32 mg/L, while those of other areas are 19.42-39.05 mg/L. The threshold background values of Cl- ion range from 3.45 to 6.65 mg/L, and the regional variations are small.
This study focuses on the environmental background values in shallow groundwater in karst area of Guizhou. Firstly, the study area is divided into different groundwater environmental units according to the analysis data of 3 699 shallow groundwater chemical samples collected for the Guizhou Drought-Resistant Well-Drilling and Water Prospecting Project from 2007 to 2015, and the analysis of the geological background and hydrogeological conditions. Then, the box plot and the iteration standard deviation method are used to eliminate the abnormal values, and determine the distribution type of water chemical data in each hydrogeological area. Finally the 95th percentile of the data is taken as the upper threshhold of the environmental background values after deleting the outliers. The results show that the shallow groundwater in Guizhou karst area is neutral alkaline water, the cations are mainly Ca2+, Mg2+, the anions are mainly HCO3- and SO42- and the groundwater types are mainly HCO3-Ca·Mg type and HCO3-Ca type. The main sources of ions in groundwater are weathering and hydrolysis of rocks and minerals. The distribution types of SO42- and Cl- ions in groundwater are mainly normal distribution, followed by lognormal distribution and least skewed distribution. The environmental background threshold values of the SO42- ion of the Middle Triassic Guanling Formation and the Permian coal-bearing strata are 68.71-164.32 mg/L, while those of other areas are 19.42-39.05 mg/L. The threshold background values of Cl- ion range from 3.45 to 6.65 mg/L, and the regional variations are small.
2019, 44(11): 3939-3949.
doi: 10.3799/dqkx.2017.589
Abstract:
Rockslide avalanches usually cause catastrophic accidents. Quantitative study on the movement process of rockslide avalanches is of great significance to the study on the mechanism of landslide occurrence and the prediction of disaster scope. Based on the indoor physical model test, the PIV technique was used to analyze the photographs taken by the high-speed camera during the experiment, and the motion parameters such as the horizontal velocity, vertical velocity and displacement of the sliding particles were obtained. The evolution of rockslide avalanche motion was analyzed from angles of the whole landslide and single particles. The results show follows:(1) the front position of landslide shows high speed spot. The spot keeps high speed though the landslide is ending. (2) From the view of single particles, the front particle is the largest one in displacement and most frequent in velocity fluctuation. The front particles own high collision frequency and their energy gains multiple supplements. The displacement of the middle particles ranks the second place. The velocity of middle particles is fluctuating, but less frequent than those of front. The displacement of the rear particles is the smallest. The velocity and energy generally decrease constantly. It is concluded that there are collision and energy transmission between the sliding particles in the process of rockslide avalanches, combined with the facts found in Jiweishan and Black Rapids Glacier rockslide avalanches. The formation mechanism of rockslide avalanche is also discussed in depth, which is of practical significance to the disaster monitoring, prevention, and control.
Rockslide avalanches usually cause catastrophic accidents. Quantitative study on the movement process of rockslide avalanches is of great significance to the study on the mechanism of landslide occurrence and the prediction of disaster scope. Based on the indoor physical model test, the PIV technique was used to analyze the photographs taken by the high-speed camera during the experiment, and the motion parameters such as the horizontal velocity, vertical velocity and displacement of the sliding particles were obtained. The evolution of rockslide avalanche motion was analyzed from angles of the whole landslide and single particles. The results show follows:(1) the front position of landslide shows high speed spot. The spot keeps high speed though the landslide is ending. (2) From the view of single particles, the front particle is the largest one in displacement and most frequent in velocity fluctuation. The front particles own high collision frequency and their energy gains multiple supplements. The displacement of the middle particles ranks the second place. The velocity of middle particles is fluctuating, but less frequent than those of front. The displacement of the rear particles is the smallest. The velocity and energy generally decrease constantly. It is concluded that there are collision and energy transmission between the sliding particles in the process of rockslide avalanches, combined with the facts found in Jiweishan and Black Rapids Glacier rockslide avalanches. The formation mechanism of rockslide avalanche is also discussed in depth, which is of practical significance to the disaster monitoring, prevention, and control.
2019, 44(11): 3950-3960.
doi: 10.3799/dqkx.2019.110
Abstract:
Strength degradation mechanism of soft and hard interbedded rock mass of Badong Formation caused by rock/discontinuity degradation is the key issue to reveal progressive strength deterioration mechanism of soft and hard interbedded rock mass of Badong Formation in hydro-fluctuation belt of reservoir bank and to evaluate the stability of reservoir bank slope in the Three Gorges area. Sandstone and silty mudstone of the typical sliding-prone soft and hard interbedded rock masses of Badong Formation in the Three Gorges area were taken as the research object to conduct uniaxial compression numerical test, considering the deterioration of rock/discontinuity parameters under the condition of drying-wetting cycle, the contribution of soft rock/hard rock/bedding plane degradation to the uniaxial compression strength degradation of soft and hard interbedded rock masses in the Badong Formation and its relationship with the dip angle are analyzed. The results indicate that the influence of soft rock/hard rock/bedding plane deterioration on the uniaxial compression strength degradation of soft and hard interbedded rock mass in the Badong Formation has obvious difference under different dip angles. The dip angle is divided into soft rock control zone, soft rock-hard rock-bedding plane common control zone, slip failure zone along the bedding plane and hard rock control zone based on their contribution. The results reveal the mechanism of strength degradation of soft and hard interbedded rock mass caused by rock/discontinuity deterioration and the influence of dip angle, which provides the basis for revealing the progressive strength deterioration mechanism of soft and hard interbedded rock masses of the Badong Formation in hydro-fluctuation belt of reservoir bank.
Strength degradation mechanism of soft and hard interbedded rock mass of Badong Formation caused by rock/discontinuity degradation is the key issue to reveal progressive strength deterioration mechanism of soft and hard interbedded rock mass of Badong Formation in hydro-fluctuation belt of reservoir bank and to evaluate the stability of reservoir bank slope in the Three Gorges area. Sandstone and silty mudstone of the typical sliding-prone soft and hard interbedded rock masses of Badong Formation in the Three Gorges area were taken as the research object to conduct uniaxial compression numerical test, considering the deterioration of rock/discontinuity parameters under the condition of drying-wetting cycle, the contribution of soft rock/hard rock/bedding plane degradation to the uniaxial compression strength degradation of soft and hard interbedded rock masses in the Badong Formation and its relationship with the dip angle are analyzed. The results indicate that the influence of soft rock/hard rock/bedding plane deterioration on the uniaxial compression strength degradation of soft and hard interbedded rock mass in the Badong Formation has obvious difference under different dip angles. The dip angle is divided into soft rock control zone, soft rock-hard rock-bedding plane common control zone, slip failure zone along the bedding plane and hard rock control zone based on their contribution. The results reveal the mechanism of strength degradation of soft and hard interbedded rock mass caused by rock/discontinuity deterioration and the influence of dip angle, which provides the basis for revealing the progressive strength deterioration mechanism of soft and hard interbedded rock masses of the Badong Formation in hydro-fluctuation belt of reservoir bank.
