2015 Vol. 33, No. 3
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Display Method:
2015, 33(3): 427-438.
doi: 10.14027/j.cnki.cjxb.2015.03.001
Abstract:
A major breakthrough of thick bedded sandstone oil and gas exploration is in China's western Xinjiang region of Jurassic and Cretaceous. Large areas of thick layer of sand body and red mudstone layer deposition formation mechanism have been a research focus by attention for a long time. Combined with much more information including southern margin of Junggar Basin sedimentary system of seasonal rivers, sand body distribution characteristics of analysis, and analysis of the lithofacies assemblages and rock color, sedimentary structure and formation mechanism of sandstone and mudstone of the Haojiagou-Toutun River section and Manasi River section of Toutun River formation of Middle Jurassic in upper part of Middle Jurassic Qigu and Kalazha Formation in the southern margin of the Junggar Basin, We think arid climate background ephemeral streams are the main sediment types of the period. An ephemeral streams sand body configuration and the genetic model have been established, and further understanding of ancient ephemeral streams sedimentary will provide the beneficial reference in China.
A major breakthrough of thick bedded sandstone oil and gas exploration is in China's western Xinjiang region of Jurassic and Cretaceous. Large areas of thick layer of sand body and red mudstone layer deposition formation mechanism have been a research focus by attention for a long time. Combined with much more information including southern margin of Junggar Basin sedimentary system of seasonal rivers, sand body distribution characteristics of analysis, and analysis of the lithofacies assemblages and rock color, sedimentary structure and formation mechanism of sandstone and mudstone of the Haojiagou-Toutun River section and Manasi River section of Toutun River formation of Middle Jurassic in upper part of Middle Jurassic Qigu and Kalazha Formation in the southern margin of the Junggar Basin, We think arid climate background ephemeral streams are the main sediment types of the period. An ephemeral streams sand body configuration and the genetic model have been established, and further understanding of ancient ephemeral streams sedimentary will provide the beneficial reference in China.
2015, 33(3): 448-458.
doi: 10.14027/j.cnki.cjxb.2015.03.003
Abstract:
Fluvial-delta reservoir architecture has been another geological hotspot over the past 20 years, and many scholars constructed geological models based on different perspectives and different research methods. However, the underground reservoirs are extremely complex which are composite sandbodies and reformed frequently, not single cause, such as there is erosion, cut and discarded phenomena etc. when channels swing and migrate, which make the sandbodies complicated in a certain extent. The wrong conclusions and understandings are drawn easily and make the complex reservoirs originally crude and simplistic if can not start from the causes of evolution, but describe results of the deposition directly. All of these will be not conducive to adjust for the late oilfield.The natural flow barrier from point-sandbar deposit of meandering river is a main controlling factors for residual oil, and its scale is small, difficult to identify, research difficulty and more need of information and other restrictions, which restricted the fine dissection of the point bar. Authors will rebuild the historical evolution of meandering rivers by reconstructing process of channels deposition process from semi-qualitative and semi-quantitative point of view in order to make the reconstruction and result more reasonable. The Yangdachengzi oil-bearing formation in Fuyu Oil Production Plant of Jilin Oilfield is main object of this study. Fuyu oilfield locates in No.3 Fuxin uplift structural belt in the eastern edge of the southern Songliao Basin, and the dome anticline is complicated by faults. The reservoir mainly is controlled by structure belonging to crack, low permeability lithologic reservoirs in which distribution are relatively stable, and the lithology are mainly siltstone and fine sandstone. The previous research results show that the meandering river deposition was most developmental facies type in Yangdachengzi oil-bearing formation in Fuyu field under fluvial-delta deposition background. The lateral accretion body size, orientation and inclination were identified by making full use of the core, logging, oil and other dense well net, point bar sand body identification, restoration, river fitting parameters and estimation methods based on previous sedimentary facies research, and then the course of sedimentary evolution was reconstructed according to the rule of meandering river development after the contemporaneous lateral accretion bodies were linked and built up from single stage fluvial sand bodies combined with geological conceptual model. This method could explain the problem of overlapping regular pattern and architectural structures of sandbodies from the angle of cause and process quite well, so, the explanation will be more reasonable and credible to predict the potential of residual oil based on architectural structures of sandbodies from the angle of deposition process and deposition result. By using the above methods, the reconstruction of meandering river sedimentary evolution history was completed in the thin layer small-scale. Practical results show that the evolution of the meandering point bar historical reconstruction provided the solid foundation for the fine anatomy of meandering channel sandbodies, and effectively guide the remaining oil forecast and tapping potential in advanced stage.
Fluvial-delta reservoir architecture has been another geological hotspot over the past 20 years, and many scholars constructed geological models based on different perspectives and different research methods. However, the underground reservoirs are extremely complex which are composite sandbodies and reformed frequently, not single cause, such as there is erosion, cut and discarded phenomena etc. when channels swing and migrate, which make the sandbodies complicated in a certain extent. The wrong conclusions and understandings are drawn easily and make the complex reservoirs originally crude and simplistic if can not start from the causes of evolution, but describe results of the deposition directly. All of these will be not conducive to adjust for the late oilfield.The natural flow barrier from point-sandbar deposit of meandering river is a main controlling factors for residual oil, and its scale is small, difficult to identify, research difficulty and more need of information and other restrictions, which restricted the fine dissection of the point bar. Authors will rebuild the historical evolution of meandering rivers by reconstructing process of channels deposition process from semi-qualitative and semi-quantitative point of view in order to make the reconstruction and result more reasonable. The Yangdachengzi oil-bearing formation in Fuyu Oil Production Plant of Jilin Oilfield is main object of this study. Fuyu oilfield locates in No.3 Fuxin uplift structural belt in the eastern edge of the southern Songliao Basin, and the dome anticline is complicated by faults. The reservoir mainly is controlled by structure belonging to crack, low permeability lithologic reservoirs in which distribution are relatively stable, and the lithology are mainly siltstone and fine sandstone. The previous research results show that the meandering river deposition was most developmental facies type in Yangdachengzi oil-bearing formation in Fuyu field under fluvial-delta deposition background. The lateral accretion body size, orientation and inclination were identified by making full use of the core, logging, oil and other dense well net, point bar sand body identification, restoration, river fitting parameters and estimation methods based on previous sedimentary facies research, and then the course of sedimentary evolution was reconstructed according to the rule of meandering river development after the contemporaneous lateral accretion bodies were linked and built up from single stage fluvial sand bodies combined with geological conceptual model. This method could explain the problem of overlapping regular pattern and architectural structures of sandbodies from the angle of cause and process quite well, so, the explanation will be more reasonable and credible to predict the potential of residual oil based on architectural structures of sandbodies from the angle of deposition process and deposition result. By using the above methods, the reconstruction of meandering river sedimentary evolution history was completed in the thin layer small-scale. Practical results show that the evolution of the meandering point bar historical reconstruction provided the solid foundation for the fine anatomy of meandering channel sandbodies, and effectively guide the remaining oil forecast and tapping potential in advanced stage.
2015, 33(3): 470-479.
doi: 10.14027/j.cnki.cjxb.2015.03.005
Abstract:
The stratum of Wutong Formation of Devonian is developed widely in Lower Yangtze area. Because it is at the early stage of transgression, there coexists, the continental and marine features which causes the difference in understanding sedimentary environment of this formation. The stratum of Wutong Formation of Devonian in northern Chaohu area of Anhui is a combination of thick sandstone with mudstone, and the depositional characteristics and depositional environment are unclear all the time. So, based on the research results of predecessors and analysis of outcrops, associated with the means of sedimentology, stratigraphy and grain size analysis under the microscope, we analyze the thick sandstone section in detail and find that Wutong Formation is developed in marine environment, that is it has backshore-foreshore of multi-segment pattern that is composed of rolling component and jumping component, foreshore-upper shoreface of bi-segment pattern that is composed of jumping component and suspending component, and mixed flat of siltstone and mudstone of bi-segment pattern that is composed of jumping component and suspending component. Combining with the characteristics of sedimentary sequences and sedimentary characteristics, we can draw a conclusion that the lower part of Guanshan Member in Wutong Formation is gravel beach deposition of backshore-foreshore subfacies, the upper part is sand beach deposition of foreshore-upper shoreface subfacies. The lower part of Leigutai Member in Wutong Formation is siltstone-mudstone deposition of mixed flat subfacies; the middle part is mudstone of bay mudflat subfacies and coastal marsh subfacies with sand beach deposition of foreshore subfacies; the upper part is chalybeate mixed flat deposition of littoral facies. This paper not only has theoretical value, but also has a certain teaching significance.
The stratum of Wutong Formation of Devonian is developed widely in Lower Yangtze area. Because it is at the early stage of transgression, there coexists, the continental and marine features which causes the difference in understanding sedimentary environment of this formation. The stratum of Wutong Formation of Devonian in northern Chaohu area of Anhui is a combination of thick sandstone with mudstone, and the depositional characteristics and depositional environment are unclear all the time. So, based on the research results of predecessors and analysis of outcrops, associated with the means of sedimentology, stratigraphy and grain size analysis under the microscope, we analyze the thick sandstone section in detail and find that Wutong Formation is developed in marine environment, that is it has backshore-foreshore of multi-segment pattern that is composed of rolling component and jumping component, foreshore-upper shoreface of bi-segment pattern that is composed of jumping component and suspending component, and mixed flat of siltstone and mudstone of bi-segment pattern that is composed of jumping component and suspending component. Combining with the characteristics of sedimentary sequences and sedimentary characteristics, we can draw a conclusion that the lower part of Guanshan Member in Wutong Formation is gravel beach deposition of backshore-foreshore subfacies, the upper part is sand beach deposition of foreshore-upper shoreface subfacies. The lower part of Leigutai Member in Wutong Formation is siltstone-mudstone deposition of mixed flat subfacies; the middle part is mudstone of bay mudflat subfacies and coastal marsh subfacies with sand beach deposition of foreshore subfacies; the upper part is chalybeate mixed flat deposition of littoral facies. This paper not only has theoretical value, but also has a certain teaching significance.
2015, 33(3): 486-499.
doi: 10.14027/j.cnki.cjxb.2015.03.007
Abstract:
This paper studied the age distribution of detrital zircons of sandstone in Maoniushan Formation of Upper Devoion of Wulan country from northern margin of Qaidam Basin using LA-ICP-MS U-Pb isotopic age of zircons. The results show that the detrital zircons of sandstone has a wide range of zircon age, which can be divided into 5 peak interval. This sequence of the strata possibly was deposited in the Late Devonian and not earlier than the end of Early Devonian according to the regional geological correlation and paleontological data. The age distribution of detrital zircons indicate that there may be events of five regional geological structure in this area, and the most prominent is the Early Paleozoic, followed by Neoproterozoic and Early Paleoproterozoic-Late New Archean, which imply that the three periods of metamorphism and magmatic activity is relatively active and provide the main source of zircon for this strata with a mixture of multi-source characteristics. The obtained age data indicate the multi-provenance of the sandstone. In addition, there are less Archean detrital zircon having a high degree of harmony, which has provided some basis for the possible existence of Archean old strata, but needs further research.
This paper studied the age distribution of detrital zircons of sandstone in Maoniushan Formation of Upper Devoion of Wulan country from northern margin of Qaidam Basin using LA-ICP-MS U-Pb isotopic age of zircons. The results show that the detrital zircons of sandstone has a wide range of zircon age, which can be divided into 5 peak interval. This sequence of the strata possibly was deposited in the Late Devonian and not earlier than the end of Early Devonian according to the regional geological correlation and paleontological data. The age distribution of detrital zircons indicate that there may be events of five regional geological structure in this area, and the most prominent is the Early Paleozoic, followed by Neoproterozoic and Early Paleoproterozoic-Late New Archean, which imply that the three periods of metamorphism and magmatic activity is relatively active and provide the main source of zircon for this strata with a mixture of multi-source characteristics. The obtained age data indicate the multi-provenance of the sandstone. In addition, there are less Archean detrital zircon having a high degree of harmony, which has provided some basis for the possible existence of Archean old strata, but needs further research.
2015, 33(3): 512-523.
doi: 10.14027/j.cnki.cjxb.2015.03.009
Abstract:
Based on Liuju copper deposit is one of the typical terrestrial sandstone-type deposits located in the Chuxiong red-bed basin of southwest China. The mineralization occurred in the interface between purple sandstone and grey sandstone of medium-fine grained sandstone strata, sandwiched between two purple silty mudstones. Besides, there coexists a horizontal metallic mineral zonation in this transitional zone from purple sandstone to grey sandstone:hematite, chalcocite, bornite, chalcopyrite and pyrite. Aiming at the relationship between mineralization and characteristics of cement and pore in sandstone, this paper has carried out the analysis of the statistical data of detrital contents, sorting coefficient, cement characteristics, pore types and the test results of porosity and permeability of each lithologic layer. The results shows that, the medium-fine grained feldspar quartz sandstone in the first Liuju sub-member of upper Cretaceous Matoushan group (K1ml1) was the most effective channel for fluid migration because of the high detrital content, low sorting coefficient, high porosity and high permeability. The place where organic matters was rich in locally in the sandstone strata of K1ml1 was changed into hydrocarbon source rocks during the middle diagenetic stage. The diagenetic pore water beared organic matters could evolve into acid reducing fluid by chemical reactions with wallrock. The acid reducing fluid and the alkaline oxidizing fluid from purple sandstone could form stable convection in the fluid migration channel of sandstone. Under the control of pH and Eh, cement zonation of ferruginous facies, calcite-dolomite carbonate facies, siliceous carbonate facies, siliceous facies formed in the sandstone strata from purple part to grey part. In the process of the water-rock interaction, the acid reducing fluid with hydrocarbons played a part in dissolving ferruginous and carbonate cements formed in the early diagenetic stage, which could open up inter grain pore for precipitation of copper sulfides. Besides, the process could also provide sulfur source by sulfate reduction. While, the alkaline oxidizing fluid was controlling the precipitation of the carbonate cements and copper sulfides in the interface of physicochemical conditions, which was the controlled conditions to the coexistence of cement zonation and metallic mineral zonation. When the hydrocarbon generation declined, the alkaline oxidizing traversed the neutral plane of Eh and pH value and conducted the corrosion of siliceous cements and quartz grains in grey sandstone, which could open up solution pore for more mineralization room and cause metasomatism between metallic sulfides. The water-rock interaction is the main factor of controlling the formation of pore for mineralization room and precipitation of cements and copper sulfides in diagenetic stages of sandstone strata.
Based on Liuju copper deposit is one of the typical terrestrial sandstone-type deposits located in the Chuxiong red-bed basin of southwest China. The mineralization occurred in the interface between purple sandstone and grey sandstone of medium-fine grained sandstone strata, sandwiched between two purple silty mudstones. Besides, there coexists a horizontal metallic mineral zonation in this transitional zone from purple sandstone to grey sandstone:hematite, chalcocite, bornite, chalcopyrite and pyrite. Aiming at the relationship between mineralization and characteristics of cement and pore in sandstone, this paper has carried out the analysis of the statistical data of detrital contents, sorting coefficient, cement characteristics, pore types and the test results of porosity and permeability of each lithologic layer. The results shows that, the medium-fine grained feldspar quartz sandstone in the first Liuju sub-member of upper Cretaceous Matoushan group (K1ml1) was the most effective channel for fluid migration because of the high detrital content, low sorting coefficient, high porosity and high permeability. The place where organic matters was rich in locally in the sandstone strata of K1ml1 was changed into hydrocarbon source rocks during the middle diagenetic stage. The diagenetic pore water beared organic matters could evolve into acid reducing fluid by chemical reactions with wallrock. The acid reducing fluid and the alkaline oxidizing fluid from purple sandstone could form stable convection in the fluid migration channel of sandstone. Under the control of pH and Eh, cement zonation of ferruginous facies, calcite-dolomite carbonate facies, siliceous carbonate facies, siliceous facies formed in the sandstone strata from purple part to grey part. In the process of the water-rock interaction, the acid reducing fluid with hydrocarbons played a part in dissolving ferruginous and carbonate cements formed in the early diagenetic stage, which could open up inter grain pore for precipitation of copper sulfides. Besides, the process could also provide sulfur source by sulfate reduction. While, the alkaline oxidizing fluid was controlling the precipitation of the carbonate cements and copper sulfides in the interface of physicochemical conditions, which was the controlled conditions to the coexistence of cement zonation and metallic mineral zonation. When the hydrocarbon generation declined, the alkaline oxidizing traversed the neutral plane of Eh and pH value and conducted the corrosion of siliceous cements and quartz grains in grey sandstone, which could open up solution pore for more mineralization room and cause metasomatism between metallic sulfides. The water-rock interaction is the main factor of controlling the formation of pore for mineralization room and precipitation of cements and copper sulfides in diagenetic stages of sandstone strata.
2015, 33(3): 537-542.
doi: 10.14027/j.cnki.cjxb.2015.03.011
Abstract:
The chroma and its major controlling factors of the Chafangcun loess-paleosol profile was studied in Danfeng, which is located on the southeast Shaanxi. Results show that lightness, redness and redness/yellowness are significantly different between loess and paleosol layers, with relatively low lightness values and high redness and redness/yellowness values in the paleosol layers. The lightness is strongly linked to the organic matter, By contrast the redness and redness/yellowness are strongly linked to the types(e.g., hematite and goethite)and concentrations of iron oxides. While variations in the lightness,redness and redness/yellowness are controlled by different color materials, these three proxies are closely associated with post-depositional processes such as chemical weathering and pedogenesis. And they are also good comparison between these chromaticity coefficients and magnetic susceptibility. Which indicates that the variation of chromaticity coefficients can indirectly reflect the change of climate and pedogenic environment.
The chroma and its major controlling factors of the Chafangcun loess-paleosol profile was studied in Danfeng, which is located on the southeast Shaanxi. Results show that lightness, redness and redness/yellowness are significantly different between loess and paleosol layers, with relatively low lightness values and high redness and redness/yellowness values in the paleosol layers. The lightness is strongly linked to the organic matter, By contrast the redness and redness/yellowness are strongly linked to the types(e.g., hematite and goethite)and concentrations of iron oxides. While variations in the lightness,redness and redness/yellowness are controlled by different color materials, these three proxies are closely associated with post-depositional processes such as chemical weathering and pedogenesis. And they are also good comparison between these chromaticity coefficients and magnetic susceptibility. Which indicates that the variation of chromaticity coefficients can indirectly reflect the change of climate and pedogenic environment.
2015, 33(3): 551-560.
doi: 10.14027/j.cnki.cjxb.2015.03.013
Abstract:
Rising sea levels caused by climate change is the major driving force in landward migration of mangrove communities, and its overlying plants can slow down the rate of sea-level rise deriving from sediment trapping. In the paper, six sediment cores were collected from the typical mangrove swamps in Guangxi, China. Based on moisture contents and 210Pb analysis, the average sedimentary rates were calculated using the CIC model in different cases of considering/no-considering sediment compaction. Compared between the rate of regional sea-level rise and the sedimentary rates, it reveals the relationship of landward mangrove migration in response to relative sea-level rise. The sediment compaction rates are between 0.16~0.78 cm/a, but no-considering sediment compaction rates are approximately 1.00~1.34 times (mean 1.12 times) more than the rates of sediment compaction. The sediment compaction rates are lower than the rate of regional sea-level rise in mangrove swamps of Yingluo Bay and Dandou Sea, however, the sediment compaction rates are obviously higher in the Maowei Sea. Owing to the seawall preventing the landward mangrove migration, the mangrove plants are currently under threat from sea-level rise in the Yingluo Bay and Dandou Sea. It is obviously different with previous reports. Taking no account of sediment compaction, the sediment rates were be overestimated in the recent studies.
Rising sea levels caused by climate change is the major driving force in landward migration of mangrove communities, and its overlying plants can slow down the rate of sea-level rise deriving from sediment trapping. In the paper, six sediment cores were collected from the typical mangrove swamps in Guangxi, China. Based on moisture contents and 210Pb analysis, the average sedimentary rates were calculated using the CIC model in different cases of considering/no-considering sediment compaction. Compared between the rate of regional sea-level rise and the sedimentary rates, it reveals the relationship of landward mangrove migration in response to relative sea-level rise. The sediment compaction rates are between 0.16~0.78 cm/a, but no-considering sediment compaction rates are approximately 1.00~1.34 times (mean 1.12 times) more than the rates of sediment compaction. The sediment compaction rates are lower than the rate of regional sea-level rise in mangrove swamps of Yingluo Bay and Dandou Sea, however, the sediment compaction rates are obviously higher in the Maowei Sea. Owing to the seawall preventing the landward mangrove migration, the mangrove plants are currently under threat from sea-level rise in the Yingluo Bay and Dandou Sea. It is obviously different with previous reports. Taking no account of sediment compaction, the sediment rates were be overestimated in the recent studies.
2015, 33(3): 568-577.
doi: 10.14027/j.cnki.cjxb.2015.03.015
Abstract:
The sedimentary characteristics, distribution characteristics, evolution laws and the controlling factors of the development of the Lower Cretaceous near-shore subaqueous fan, located in the steep slope of the Eastern Honghaoershute depression, were defined clearly based on the integrated information including cores, well-logging, logging and seismic data. The results show that three kinds of sub-facies, including upper fan, mid-fan and lower fan, can be identified in the nearshore subaqueous fan in the study area, the glutenite deposition is the most important deposition, including massive or grading middle-fine clast-supported conglomerate, turbidite bearing Bouma Sequence and slumps with slump structures. Besides, we also can find some seismite deposition. In the study area, the subaqueous fan began to develop from the upper part of the Aershan Formation, and it became the largest and shifted towards the north-east at the lower part of Tengger Formation by 3.5 km, however, the scale of the fan in the upper part of the Tengger Formation began to reduce with the weak of the tectonic activities and the shrink age of the basin and then the subaqueous fan became gradually changing into fan-delta deposition. The sedimentary characteristics, distribution and evolution laws were controlled by the multiple-staged tectonic activities and the palaeo-climates, which was hot and humid. The plate type boundary fault which is steep and active provides the favorable tectonic setting for the development of the near-shore subaqueous fans in the steep slope.
The sedimentary characteristics, distribution characteristics, evolution laws and the controlling factors of the development of the Lower Cretaceous near-shore subaqueous fan, located in the steep slope of the Eastern Honghaoershute depression, were defined clearly based on the integrated information including cores, well-logging, logging and seismic data. The results show that three kinds of sub-facies, including upper fan, mid-fan and lower fan, can be identified in the nearshore subaqueous fan in the study area, the glutenite deposition is the most important deposition, including massive or grading middle-fine clast-supported conglomerate, turbidite bearing Bouma Sequence and slumps with slump structures. Besides, we also can find some seismite deposition. In the study area, the subaqueous fan began to develop from the upper part of the Aershan Formation, and it became the largest and shifted towards the north-east at the lower part of Tengger Formation by 3.5 km, however, the scale of the fan in the upper part of the Tengger Formation began to reduce with the weak of the tectonic activities and the shrink age of the basin and then the subaqueous fan became gradually changing into fan-delta deposition. The sedimentary characteristics, distribution and evolution laws were controlled by the multiple-staged tectonic activities and the palaeo-climates, which was hot and humid. The plate type boundary fault which is steep and active provides the favorable tectonic setting for the development of the near-shore subaqueous fans in the steep slope.
2015, 33(3): 587-594.
doi: 10.14027/j.cnki.cjxb.2015.03.017
Abstract:
Combined with the South China Sea spreading history, based on regional 2D seismic and drilling data, the paper focuses on the research of major unconformities, evolution of the Pearl River Mouth Basin and its controlling effect on the evolution of the Pearl River sedimentary system, aiming to provide support for the deep-water hydrocarbon exploration in the basin. Results show that:besides the basement, three major unconformity surfaces are recognized in the basin, i.e. breakup unconformity,slope-migrating unconformity and slope-gradient-jumped unconformity; according to the above three unconformities, the evolution of the Pearl River sedimentary system can be divided into four stages:rifting stage mainly develops depositional system of fluvial, lacustrine; fault-slope stage mainly develops shelf-margin delta(steep foreset);gentle-slope depression stage also develops shelf-margin delta (gentle foreset); steep-slope depression stage mainly develops delta-submarine canyon-submarine fan; the exploration of shelf-margin delta developed in faulted-slope stage and gentle-slope depression stage should focus along the shelf break; the exploration for delta-submarine canyon-submarine fan in steep-slope depression stage should adopt vertical exploration ideas, that is, searching for oil and gas perpendicular to the strike of the shelf break.
Combined with the South China Sea spreading history, based on regional 2D seismic and drilling data, the paper focuses on the research of major unconformities, evolution of the Pearl River Mouth Basin and its controlling effect on the evolution of the Pearl River sedimentary system, aiming to provide support for the deep-water hydrocarbon exploration in the basin. Results show that:besides the basement, three major unconformity surfaces are recognized in the basin, i.e. breakup unconformity,slope-migrating unconformity and slope-gradient-jumped unconformity; according to the above three unconformities, the evolution of the Pearl River sedimentary system can be divided into four stages:rifting stage mainly develops depositional system of fluvial, lacustrine; fault-slope stage mainly develops shelf-margin delta(steep foreset);gentle-slope depression stage also develops shelf-margin delta (gentle foreset); steep-slope depression stage mainly develops delta-submarine canyon-submarine fan; the exploration of shelf-margin delta developed in faulted-slope stage and gentle-slope depression stage should focus along the shelf break; the exploration for delta-submarine canyon-submarine fan in steep-slope depression stage should adopt vertical exploration ideas, that is, searching for oil and gas perpendicular to the strike of the shelf break.
2015, 33(3): 607-615.
doi: 10.14027/j.cnki.cjxb.2015.03.019
Abstract:
The strong intensely syn-sedimentary faulting and thrust-nappe structures resulted in the northwestern margin of Junggar Basin belongs to the large-scale landlocked depression basin in Late Permian-Triassic Period, within multistage slope-break belt, which controled the development of fan body in Mabei region. Based on the core observation, rock thin sections and logging,combined with the stratigraphic overlap, the longitudinal lithologic combination and the distribution of sand body concluded that the typical fan delta deposits were developed in Triassic Baikouquan Formation of Mabei area. According to sedimentary microfacies markers and detailed depiction of internal sedimentation unit of fan delta can identify 3 subphases and 11 microfacies:three kinds of submicrofacies named fan delta plain, fan delta front and prodelta. The fan delta plain included super-aqueous mudslides conglomerate microfacies, braided channel glutenite microfacies, plain interchannel sand-mudstone microfacies. The fan delta front can be divided into sub-aqueous distributary channel conglomerate microfacies, underwater channel glutenite microfacies, sub-aqueous mudslides glutenite microfacies, underwater inter-channel sand-mudstone microfacies, the end of the underwater channel sandstone microfacies, mouth bar-distal sandbar sandstone microfacies, and as well as the prodelta can be include pro-fan delta siltstone microfacies, pro-fan delta mudstone microfacies. The fan delta system which formed sudden flood alternating with normal water flow obviously controlled by the slope breaks under the background of lake invasion in Mabei area, and also characterized by retrogradation deposition toward to the NE source direction. The fan body is a kind of a lake invasion retrogradtional fan delta in the study area.
The strong intensely syn-sedimentary faulting and thrust-nappe structures resulted in the northwestern margin of Junggar Basin belongs to the large-scale landlocked depression basin in Late Permian-Triassic Period, within multistage slope-break belt, which controled the development of fan body in Mabei region. Based on the core observation, rock thin sections and logging,combined with the stratigraphic overlap, the longitudinal lithologic combination and the distribution of sand body concluded that the typical fan delta deposits were developed in Triassic Baikouquan Formation of Mabei area. According to sedimentary microfacies markers and detailed depiction of internal sedimentation unit of fan delta can identify 3 subphases and 11 microfacies:three kinds of submicrofacies named fan delta plain, fan delta front and prodelta. The fan delta plain included super-aqueous mudslides conglomerate microfacies, braided channel glutenite microfacies, plain interchannel sand-mudstone microfacies. The fan delta front can be divided into sub-aqueous distributary channel conglomerate microfacies, underwater channel glutenite microfacies, sub-aqueous mudslides glutenite microfacies, underwater inter-channel sand-mudstone microfacies, the end of the underwater channel sandstone microfacies, mouth bar-distal sandbar sandstone microfacies, and as well as the prodelta can be include pro-fan delta siltstone microfacies, pro-fan delta mudstone microfacies. The fan delta system which formed sudden flood alternating with normal water flow obviously controlled by the slope breaks under the background of lake invasion in Mabei area, and also characterized by retrogradation deposition toward to the NE source direction. The fan body is a kind of a lake invasion retrogradtional fan delta in the study area.
2015, 33(3): 625-632.
doi: 10.14027/j.cnki.cjxb.2015.03.021
Abstract:
As a first proven big oil field in Xin'anbian area, Ordos Basin, the proved reserves of Xin'anbian oilfield tight oil is over hundred million tons. Based on previous study on sedimentary facies, source rock, reservoir feature and densification mechanism, by using thin sections, MICP, SEM, porosity & permeability, Micro-CT and other analysis methods, and through study on source rock characters, sand distribution, contact between source rock and reservoir, the geological characteristics and controlling factors on large-scale distribution of tight oil in Xin'anbian area were summarized to clarify the mechanism of tight oil accumulation and enrichment. Chang 72 tight sandstones are widely distributed and micrometer-scaled pores are the main reservoir space. The complex pore system consists of micrometer scaled pores and nanometer scaled throats, and the better pore-throat connectivity provide guarantee for oil flowing in micro-reservoir space. The oil quality is relatively good with characters of low density, low viscosity, low freezing point, no sulfur-containing and high mobility. Tight sandstones are close to high quality source rocks, which is favorable for near-sourced accumulation. Pressure increase during hydrocarbon generation process can provide sufficient power, and sandstones with high connectivity & fractures are migration pathway for hydrocarbon accumulation, resulting in high hydrocarbon charging percentage and large scaled tight oil play in Xin'anbian area.
As a first proven big oil field in Xin'anbian area, Ordos Basin, the proved reserves of Xin'anbian oilfield tight oil is over hundred million tons. Based on previous study on sedimentary facies, source rock, reservoir feature and densification mechanism, by using thin sections, MICP, SEM, porosity & permeability, Micro-CT and other analysis methods, and through study on source rock characters, sand distribution, contact between source rock and reservoir, the geological characteristics and controlling factors on large-scale distribution of tight oil in Xin'anbian area were summarized to clarify the mechanism of tight oil accumulation and enrichment. Chang 72 tight sandstones are widely distributed and micrometer-scaled pores are the main reservoir space. The complex pore system consists of micrometer scaled pores and nanometer scaled throats, and the better pore-throat connectivity provide guarantee for oil flowing in micro-reservoir space. The oil quality is relatively good with characters of low density, low viscosity, low freezing point, no sulfur-containing and high mobility. Tight sandstones are close to high quality source rocks, which is favorable for near-sourced accumulation. Pressure increase during hydrocarbon generation process can provide sufficient power, and sandstones with high connectivity & fractures are migration pathway for hydrocarbon accumulation, resulting in high hydrocarbon charging percentage and large scaled tight oil play in Xin'anbian area.
2015, 33(3): 439-447.
doi: 10.14027/j.cnki.cjxb.2015.03.002
Abstract:
In recent years, a special kind of delta was found in ancient Songliao Basin and modern Poyang Lake and other large depression lacustrine in China. It is shallow lacustrine fluvial-dominated delta. It is with great differences between normal deltas, including the skeleton sandbody types, vertical sedimentary sequence and facies differentiation etc. Especially, the characteristics of sandbody in delta front is thin thickness and small scale and diversification, which is compared to quite different with sedimentary model of normal fluvial-dominated delta that it include to large scale and thick debouch bar in delta front. In this context, sandbody distribution and depositional model in shallow lacustrine fluvial-dominated delta front, deserves further study. Through analysis of outcrop, modern sedimentary and cores, logging and seismic data, it is realized that underwater distributary channel sandbody as the framework of shallow lacustrine fluvial-dominated delta front is abundant, closely and narrow. It is continual than original understanding and it extends to the far underwater, until disappearing into thin debouch bar and sheet sand. Debouch bar sandbody is not well preserved and is fluvial-dominated. Debouch bar is located mainly in the underwater distributary channel on both sides and the front. It is consistent with the source direction, and has narrow banded morphology. Characteristics of debouch bar is more similar to thin sand under water. In each of the underwater distributary channel is formed in the center of the sequence of sedimentary microfacies. This sequence is underwater distributary channel→ the core of thin sand→ the edge of thin sand→underwater distributary bay from the center to the edge. The study also found that distribution of sandbody is controlled by the position of sedimentary facies in the front of shallow lacustrine fluvial dominated delta. It can be divided into transition zone between high level and low level, shallow water zone of the nearshore, medium depth zone of the shore and deepwater zone of the offshore. Sedimentary model of the nearshore is formed in the transition zone between high level and low level. Its main sedimentary features show that continuous and narrow fluvial-dominated banded deposition is the main sedimentary, with its restrictive and straight distributary channel sandbody as the center. And small scale discontinuous thin sand underwater is more. Sedimentary model of fluvial-dominated banded deposition is formed in the shallow water zone of the nearshore. Its main sedimentary features show that the sequence of sedimentary microfacies is formed with its less restrictive and dendritic underwater distributary channel sandbody as the center. This sequence is underwater distributary channel→ underwater thin sand (residual debouch bar) → underwater distributary bay from the center to the edge. Sedimentary model of terminal distributary channel and fluvial-dominated sheet sand is formed in the medium depth zone of the shore. Its main sedimentary features show that distribution of sheet sand is large area, and is fluvial-dominated. The sequence of sedimentary microfacies is formed with terminal underwater distributary channel sandbody as the center. This sequence is terminal underwater distributary channel→ the core of sheet sand → the edge of sheet sand→ underwater distributary bay from the center to the edge. Sedimentary model of wave-dominated sheet sand is formed in the deepwater zone of the offshore. Its main sedimentary features show that the distribution of single sheet sand is perpendicular to the source direction, and a plurality of sheet sand is arranged parallel to each other. An obvious strip and annulus distribution in the inner sheet sand is formed. The sequence of sedimentary microfacies is the core of sheet sand → the edge of sheet sand→ underwater distributary bay from the center to the edge. Wave-dominated sheet sand is relatively rare in the shallow lacustrine fluvial-dominated delta. Because the river is main effect, and the wave is relatively small in the shallow lacustrine.
In recent years, a special kind of delta was found in ancient Songliao Basin and modern Poyang Lake and other large depression lacustrine in China. It is shallow lacustrine fluvial-dominated delta. It is with great differences between normal deltas, including the skeleton sandbody types, vertical sedimentary sequence and facies differentiation etc. Especially, the characteristics of sandbody in delta front is thin thickness and small scale and diversification, which is compared to quite different with sedimentary model of normal fluvial-dominated delta that it include to large scale and thick debouch bar in delta front. In this context, sandbody distribution and depositional model in shallow lacustrine fluvial-dominated delta front, deserves further study. Through analysis of outcrop, modern sedimentary and cores, logging and seismic data, it is realized that underwater distributary channel sandbody as the framework of shallow lacustrine fluvial-dominated delta front is abundant, closely and narrow. It is continual than original understanding and it extends to the far underwater, until disappearing into thin debouch bar and sheet sand. Debouch bar sandbody is not well preserved and is fluvial-dominated. Debouch bar is located mainly in the underwater distributary channel on both sides and the front. It is consistent with the source direction, and has narrow banded morphology. Characteristics of debouch bar is more similar to thin sand under water. In each of the underwater distributary channel is formed in the center of the sequence of sedimentary microfacies. This sequence is underwater distributary channel→ the core of thin sand→ the edge of thin sand→underwater distributary bay from the center to the edge. The study also found that distribution of sandbody is controlled by the position of sedimentary facies in the front of shallow lacustrine fluvial dominated delta. It can be divided into transition zone between high level and low level, shallow water zone of the nearshore, medium depth zone of the shore and deepwater zone of the offshore. Sedimentary model of the nearshore is formed in the transition zone between high level and low level. Its main sedimentary features show that continuous and narrow fluvial-dominated banded deposition is the main sedimentary, with its restrictive and straight distributary channel sandbody as the center. And small scale discontinuous thin sand underwater is more. Sedimentary model of fluvial-dominated banded deposition is formed in the shallow water zone of the nearshore. Its main sedimentary features show that the sequence of sedimentary microfacies is formed with its less restrictive and dendritic underwater distributary channel sandbody as the center. This sequence is underwater distributary channel→ underwater thin sand (residual debouch bar) → underwater distributary bay from the center to the edge. Sedimentary model of terminal distributary channel and fluvial-dominated sheet sand is formed in the medium depth zone of the shore. Its main sedimentary features show that distribution of sheet sand is large area, and is fluvial-dominated. The sequence of sedimentary microfacies is formed with terminal underwater distributary channel sandbody as the center. This sequence is terminal underwater distributary channel→ the core of sheet sand → the edge of sheet sand→ underwater distributary bay from the center to the edge. Sedimentary model of wave-dominated sheet sand is formed in the deepwater zone of the offshore. Its main sedimentary features show that the distribution of single sheet sand is perpendicular to the source direction, and a plurality of sheet sand is arranged parallel to each other. An obvious strip and annulus distribution in the inner sheet sand is formed. The sequence of sedimentary microfacies is the core of sheet sand → the edge of sheet sand→ underwater distributary bay from the center to the edge. Wave-dominated sheet sand is relatively rare in the shallow lacustrine fluvial-dominated delta. Because the river is main effect, and the wave is relatively small in the shallow lacustrine.
2015, 33(3): 459-469.
doi: 10.14027/j.cnki.cjxb.2015.03.004
Abstract:
Volcanic-sedimentary rocks from the Dahalajunshan Formation of the Lower Carboniferous are widely exposed in the Yili area, western Tianshan. Large amounts of mineral deposits have been found in this association. However, there is still a considerable controversy on the tectonic setting where the Dahalajunshan Formation deposited. Through regional stratigraphic correlations and field observations, we discovered a regional angular unconformity between the Dahalajunshan Formation and its underlying strata in the study area. The lower Dahalajunshan Formation consists of conglomerate, coarse sandstone, sandstone, siltstone, mudstones, carbonate and andesite in an ascending order. In combination with sedimentological and stratigraphical analysis, we suggest that the terrestrial clastic rocks at the bottom of the Dahalajunshan Formation were formed in a fan-delta environment, which can be further divided into three subfacies:fan-delta plain, fan-delta front and pro-fan delta, and the carbonates were formed in carbonate platform. The stratigraphical sequences, in an ascending order, have creasing sediment sizes from coarse to fine, enlarging water depths from shallow to deep, but varying depositional environment from land to marine, and thus reflect an extensional setting. Therefore, we believe that the early Carboniferous Dahalajunshan Formation in western Tianshan could have formed in a post-collision rift environment.
Volcanic-sedimentary rocks from the Dahalajunshan Formation of the Lower Carboniferous are widely exposed in the Yili area, western Tianshan. Large amounts of mineral deposits have been found in this association. However, there is still a considerable controversy on the tectonic setting where the Dahalajunshan Formation deposited. Through regional stratigraphic correlations and field observations, we discovered a regional angular unconformity between the Dahalajunshan Formation and its underlying strata in the study area. The lower Dahalajunshan Formation consists of conglomerate, coarse sandstone, sandstone, siltstone, mudstones, carbonate and andesite in an ascending order. In combination with sedimentological and stratigraphical analysis, we suggest that the terrestrial clastic rocks at the bottom of the Dahalajunshan Formation were formed in a fan-delta environment, which can be further divided into three subfacies:fan-delta plain, fan-delta front and pro-fan delta, and the carbonates were formed in carbonate platform. The stratigraphical sequences, in an ascending order, have creasing sediment sizes from coarse to fine, enlarging water depths from shallow to deep, but varying depositional environment from land to marine, and thus reflect an extensional setting. Therefore, we believe that the early Carboniferous Dahalajunshan Formation in western Tianshan could have formed in a post-collision rift environment.
2015, 33(3): 480-485.
doi: 10.14027/j.cnki.cjxb.2015.03.006
Abstract:
The main emergence stratum of Paleogene in the Weihe Basin, which hold in the Ordos block and Qinlingorogenic belt, include Honghe Formation and Bailuyuan Formation. In recent years, helium gas in the basin found in the Cenozoic strata has a prospect, it's necessary for us to research on sedimentary environment. Through the analysis of major and trace elements of field samples, the Paleogene sedimentary environment was revealed by quantitative semiquantitative analysis involving calculation using Adams formula, equivalent boron suggested by Walker, B/Ga ratio, Sr/Ba ratio methods and the variation characteristics of chemical index of alteration CIA. The results indicate the range of palaeosalinity of Honghe Formation and Bailuyuan Formation is 2.2‰~11.7‰, and display that Weihe basin belongs fresh water lake, which are warm, moist climate overall, regional drought and salt water sedimentary environment. At the same time,we find that chemical index of alteration have negative correlation with salinity value. By the lacustrine environment in Honghe Formation to river and delta facies environment in Bailuyuan Formation, CIA index increases, and the salinity of the B/Ga ratio is reduced, which show that CIA values, to some extent, reflect the characteristics of salinity. Because of bioconcentration the samples have high Sr values, which result in abnormal points when Sr/Ba ratio reflect salinity.
The main emergence stratum of Paleogene in the Weihe Basin, which hold in the Ordos block and Qinlingorogenic belt, include Honghe Formation and Bailuyuan Formation. In recent years, helium gas in the basin found in the Cenozoic strata has a prospect, it's necessary for us to research on sedimentary environment. Through the analysis of major and trace elements of field samples, the Paleogene sedimentary environment was revealed by quantitative semiquantitative analysis involving calculation using Adams formula, equivalent boron suggested by Walker, B/Ga ratio, Sr/Ba ratio methods and the variation characteristics of chemical index of alteration CIA. The results indicate the range of palaeosalinity of Honghe Formation and Bailuyuan Formation is 2.2‰~11.7‰, and display that Weihe basin belongs fresh water lake, which are warm, moist climate overall, regional drought and salt water sedimentary environment. At the same time,we find that chemical index of alteration have negative correlation with salinity value. By the lacustrine environment in Honghe Formation to river and delta facies environment in Bailuyuan Formation, CIA index increases, and the salinity of the B/Ga ratio is reduced, which show that CIA values, to some extent, reflect the characteristics of salinity. Because of bioconcentration the samples have high Sr values, which result in abnormal points when Sr/Ba ratio reflect salinity.
2015, 33(3): 500-511.
doi: 10.14027/j.cnki.cjxb.2015.03.008
Abstract:
As one type of coated grains in the process of carbonate deposition, ooids and oolite are usually used as proxies for sedimentary background, hydrodynamic condition, paleoclimate, hydrocarbon reservoir, etc. In last two centuries, numerous studies were carried out promoting the understanding of such “charming” carbonate grains. However, the mineral composition and controlling factors of ooid have been neglected in Chinese literatures for a long time. The CaCO3 polymorph mineral of ooid had been undergone secular periodic variations in geological history. In Phanerozoic time, three “aragonite and high-Mg calcite” dominated intervals (also called “aragonite sea” periods) and two “low-Mg calcite” dominated intervals (also called “calcite sea” periods) were identified firstly in the light of the mineralogical differences between original aragonitic (with high-Mg calcitic) and low-Mg calcitic ooids. The primary mineralogy of ooids implies the great influence on cortical fabric, degree of conservation, as well as diagenetic history, and may further provide a clue for understanding the variation in paleo-oceanic chemistry. Interpretation of the original mineralogy of ooid cortices requires assessment of (1) morphology and orientation of crystallites in cortices, (2) manner of preservation of cortical layers, and (3) elemental concentration data, especially of Sr and Mg. Primary aragonite ooids exhibit poorly preserved morphologies and recrystallization of cortical fabrics, remaining relics with selective diagenetic dissolution fabrics with respect to aragonite, and high concentrations of Sr (generally >2 000 ppm); Primary high-Mg calcite ooids generally exhibit low-level deformation replacement of radial (or radial-concentric) fabrics, low concentrations of Sr (generally <1 000 ppm) and high values of Mg, sometimes containing microdolomite inclusions in cortical layers; Primary low-Mg calcite ooids exhibit well-preserved radial (or radial-concentric) fabrics, low concentrations of Sr and Mg. In addition, the composition of bimineralic ooids presumably has two patterns, one is consisted of calcitic inner cortex and aragonitic outer cortex, the other is alternated between calcitic and aragonitic layers. Manner of differences in fabrics and preservation styles could help us infer the bimineralic type. It is noted that the original mineralogy of ooid is thought to be strongly influenced by seawater chemistry, especially by Mg/Ca ratio, atmospheric CO2 partial pressure and carbonate saturation state. The Mg/Ca ratio plays a critical role in determining the original mineralogy of ooids in a long timescale. In some temporal evens, however, suggested other factors may induce the fluctuation of primary ooid mineralogy with the stabilized ratio of Mg/Ca. For instance, glacio-eustatic cycles caused temperature fluctuations (associated with CO2 fluctuations) and lately supposed to disturb the carbonate saturation state, extremely arid climate might increase local carbonate saturation state, and the volcanism released a large quantity of CO2 that elevated temperature and atmospheric CO2 partial pressure and finally causing the decreased in carbonate saturation state. Therefore, the study on features and controlling factors of original ooid mineralogy may provide a new perspective to understand the paleo-oceanic chemistry.
As one type of coated grains in the process of carbonate deposition, ooids and oolite are usually used as proxies for sedimentary background, hydrodynamic condition, paleoclimate, hydrocarbon reservoir, etc. In last two centuries, numerous studies were carried out promoting the understanding of such “charming” carbonate grains. However, the mineral composition and controlling factors of ooid have been neglected in Chinese literatures for a long time. The CaCO3 polymorph mineral of ooid had been undergone secular periodic variations in geological history. In Phanerozoic time, three “aragonite and high-Mg calcite” dominated intervals (also called “aragonite sea” periods) and two “low-Mg calcite” dominated intervals (also called “calcite sea” periods) were identified firstly in the light of the mineralogical differences between original aragonitic (with high-Mg calcitic) and low-Mg calcitic ooids. The primary mineralogy of ooids implies the great influence on cortical fabric, degree of conservation, as well as diagenetic history, and may further provide a clue for understanding the variation in paleo-oceanic chemistry. Interpretation of the original mineralogy of ooid cortices requires assessment of (1) morphology and orientation of crystallites in cortices, (2) manner of preservation of cortical layers, and (3) elemental concentration data, especially of Sr and Mg. Primary aragonite ooids exhibit poorly preserved morphologies and recrystallization of cortical fabrics, remaining relics with selective diagenetic dissolution fabrics with respect to aragonite, and high concentrations of Sr (generally >2 000 ppm); Primary high-Mg calcite ooids generally exhibit low-level deformation replacement of radial (or radial-concentric) fabrics, low concentrations of Sr (generally <1 000 ppm) and high values of Mg, sometimes containing microdolomite inclusions in cortical layers; Primary low-Mg calcite ooids exhibit well-preserved radial (or radial-concentric) fabrics, low concentrations of Sr and Mg. In addition, the composition of bimineralic ooids presumably has two patterns, one is consisted of calcitic inner cortex and aragonitic outer cortex, the other is alternated between calcitic and aragonitic layers. Manner of differences in fabrics and preservation styles could help us infer the bimineralic type. It is noted that the original mineralogy of ooid is thought to be strongly influenced by seawater chemistry, especially by Mg/Ca ratio, atmospheric CO2 partial pressure and carbonate saturation state. The Mg/Ca ratio plays a critical role in determining the original mineralogy of ooids in a long timescale. In some temporal evens, however, suggested other factors may induce the fluctuation of primary ooid mineralogy with the stabilized ratio of Mg/Ca. For instance, glacio-eustatic cycles caused temperature fluctuations (associated with CO2 fluctuations) and lately supposed to disturb the carbonate saturation state, extremely arid climate might increase local carbonate saturation state, and the volcanism released a large quantity of CO2 that elevated temperature and atmospheric CO2 partial pressure and finally causing the decreased in carbonate saturation state. Therefore, the study on features and controlling factors of original ooid mineralogy may provide a new perspective to understand the paleo-oceanic chemistry.
2015, 33(3): 524-536.
doi: 10.14027/j.cnki.cjxb.2015.03.010
Abstract:
The northwest margin of summer monsoon in China is one of the most sensitive areas to response long-time scale climate change, but the related researches between summer monsoon boundary changes and millennial-scale climate change driving mechanism are still lack of sufficient evidence. The temporal and spatial variation of types and content of saline minerals in lake sediments could speculate the characteristics of climate change in the northwest margin of summer monsoon. Yanchi Lake is located in the northern Qilian Mountains and the central Hexi Corridor, while Zhuye Lake is located in the eastern Hexi Corridor, which is a key research area for the long-term northern boundary changes of the Asian summer monsoon. It has important significance for clarifing monsoon change mechanism under millennial-scale and predict long-time scale climate change to study how the motion of the northwest border of summer monsoon impact climate change process in the northwest margin of summer monsoon. In this paper, we chose YC section in Yanchi Lake and QTH01 and QTH02 sections in Zhuye Lake, which located at different positions of Hexi Corridor, to conduct a millennial-scale comparative study of temporal and spatial variation of types and content of saline minerals. The results revealed that saline minerals in QTH01 and QTH02 sections are mainly carbonate minerals like calcite and aragonite, and there are only sporadic sulfate minerals, while sulfate minerals content in YC section is relatively high, and there also exist chloride type minerals which indicated the more arid environment in Yanchi Lake than in Zhuye Lake. During the late glacial and early Holocene, all of the three sections were influenced by monsoon conveying water vapor, carbonate minerals well sedimentated, and monsoon boundary expanded to the middle region of Qilian mountains in this period. The summer monsoon effect weakened in middle Holocene, Zhuye Lake retreated with carbonate mineral contents reached peak values, and Yanchi Lake showed extreme drought climate characteristics and the content of sulfate minerals decreased because of the “salt effect”. The northwestern border of summer monsoon should be between the Shiyang river drainage basin and the Yanchi drainage basin in middle Holocene. Yanchi Lake and Zhuye Lake were given priority to eolian deposition in late Holocene, carbonate minerals were difficult to conserve in such arid climate, sulfate and chloride mineral contents had high value, and the northwestern border of summer monsoon further retreated to south. In conclusion, the variations of salt mineral contents are well respond to Holocene climate change characteristics, and the northwestern border of summer monsoon swung between the Shiyang river drainage basin and the Yanchi drainage basin under millennial-scale during Holocene.
The northwest margin of summer monsoon in China is one of the most sensitive areas to response long-time scale climate change, but the related researches between summer monsoon boundary changes and millennial-scale climate change driving mechanism are still lack of sufficient evidence. The temporal and spatial variation of types and content of saline minerals in lake sediments could speculate the characteristics of climate change in the northwest margin of summer monsoon. Yanchi Lake is located in the northern Qilian Mountains and the central Hexi Corridor, while Zhuye Lake is located in the eastern Hexi Corridor, which is a key research area for the long-term northern boundary changes of the Asian summer monsoon. It has important significance for clarifing monsoon change mechanism under millennial-scale and predict long-time scale climate change to study how the motion of the northwest border of summer monsoon impact climate change process in the northwest margin of summer monsoon. In this paper, we chose YC section in Yanchi Lake and QTH01 and QTH02 sections in Zhuye Lake, which located at different positions of Hexi Corridor, to conduct a millennial-scale comparative study of temporal and spatial variation of types and content of saline minerals. The results revealed that saline minerals in QTH01 and QTH02 sections are mainly carbonate minerals like calcite and aragonite, and there are only sporadic sulfate minerals, while sulfate minerals content in YC section is relatively high, and there also exist chloride type minerals which indicated the more arid environment in Yanchi Lake than in Zhuye Lake. During the late glacial and early Holocene, all of the three sections were influenced by monsoon conveying water vapor, carbonate minerals well sedimentated, and monsoon boundary expanded to the middle region of Qilian mountains in this period. The summer monsoon effect weakened in middle Holocene, Zhuye Lake retreated with carbonate mineral contents reached peak values, and Yanchi Lake showed extreme drought climate characteristics and the content of sulfate minerals decreased because of the “salt effect”. The northwestern border of summer monsoon should be between the Shiyang river drainage basin and the Yanchi drainage basin in middle Holocene. Yanchi Lake and Zhuye Lake were given priority to eolian deposition in late Holocene, carbonate minerals were difficult to conserve in such arid climate, sulfate and chloride mineral contents had high value, and the northwestern border of summer monsoon further retreated to south. In conclusion, the variations of salt mineral contents are well respond to Holocene climate change characteristics, and the northwestern border of summer monsoon swung between the Shiyang river drainage basin and the Yanchi drainage basin under millennial-scale during Holocene.
2015, 33(3): 543-550.
doi: 10.14027/j.cnki.cjxb.2015.03.012
Abstract:
Taking modern deposit of Weihe River at Caotan, Xi'an, as an example, particle size, sedimentary facies, sedimentary sequences and depositional model were studied based on outcrops and trench observation, and test results of selected samples. The results indicate that modern Weihe River in Xi'an is a meandering river which composed by three sedimentary cycle, and sediments in the river include sandy and argillaceous sediments, and only a little of gravely sediments. There are 6 kinds of lithofacies identified in Caotan deposit of modern Weihe River, and they are coarse sandstone with some fine gravel (parallel bedding) lithofacies, medium to fine (trough cross bedding) sandstone lithofacies, medium to fine sandstone (parallel bedding) lithofacies, medium sandstone (massive bedding) lithofacies, medium sandstone with some gravel(cross bedding) lithofacies and mudstone (massive bedding) lithofacies. Three kinds of sedimentary microfacies developed well, including channel lag deposit, point bar and flood-plain microfacies, and three sedimentary sequences were composed by these sedimentary microfacies. Lower sedimentary sequence with large thickness of sandstone was composed mainly by coarse and medium sandstone. Middle sedimentary sequence is a whole meandering river sedimentary body, and is composed by channel lag deposit, point bar and flood-plain deposit. Upper sedimentary sequence is dominantly composed by point bar and flood-plain deposit. Grain size analysis show that diameter of particles in channel lag deposit is 0.2~1.2 mm, and 0.1~1.0 mm in point bar, and they are favorable sand orebody which used for building sand.
Taking modern deposit of Weihe River at Caotan, Xi'an, as an example, particle size, sedimentary facies, sedimentary sequences and depositional model were studied based on outcrops and trench observation, and test results of selected samples. The results indicate that modern Weihe River in Xi'an is a meandering river which composed by three sedimentary cycle, and sediments in the river include sandy and argillaceous sediments, and only a little of gravely sediments. There are 6 kinds of lithofacies identified in Caotan deposit of modern Weihe River, and they are coarse sandstone with some fine gravel (parallel bedding) lithofacies, medium to fine (trough cross bedding) sandstone lithofacies, medium to fine sandstone (parallel bedding) lithofacies, medium sandstone (massive bedding) lithofacies, medium sandstone with some gravel(cross bedding) lithofacies and mudstone (massive bedding) lithofacies. Three kinds of sedimentary microfacies developed well, including channel lag deposit, point bar and flood-plain microfacies, and three sedimentary sequences were composed by these sedimentary microfacies. Lower sedimentary sequence with large thickness of sandstone was composed mainly by coarse and medium sandstone. Middle sedimentary sequence is a whole meandering river sedimentary body, and is composed by channel lag deposit, point bar and flood-plain deposit. Upper sedimentary sequence is dominantly composed by point bar and flood-plain deposit. Grain size analysis show that diameter of particles in channel lag deposit is 0.2~1.2 mm, and 0.1~1.0 mm in point bar, and they are favorable sand orebody which used for building sand.
2015, 33(3): 561-567.
doi: 10.14027/j.cnki.cjxb.2015.03.014
Abstract:
North Yellow Sea Basin is a typical Meso-Cenozoic superimposed fault basin, which has very weak exploration and research in the offshore of China. The Eastern Depression is the secondary building unit which has the best exploration foreground in North Yellow Sea Basin. According to the core observation and logging facies analysis, combined with 3D seismic data, it is considered that fan delta, braided-river delta, delta and lake developed in the Mesozoic in Eastern Depression. Restricted by structural evolution, there was different sedimentary evolution in different tectonic phase in Mesozoic. Middle Jurassic was in the period of initial graben faulting. The sedimentary types were mainly semi-abyss and abyss. There were few fan deltas in depression margin. Late Jurassic was in the period of faulting extension. The vertical lithological sequence was an integral depositional cycle of progradation-retrogradation. There were delta in north gentle slope and fan delta in abrupt slope in early stage. Owing to uprising of lake level, there developed undercompensation lake facies whose lithology is mainly dark mudstone. North gentle slope developed small-scale delta front. Early Cretaceous was in the period of faulting abortion, and there were two normal cyclic depositional sequences. The sedimentary types of each cycle were mainly fan delta, braided-river delta in lower part, and shore-shallow lacustrine upward.
North Yellow Sea Basin is a typical Meso-Cenozoic superimposed fault basin, which has very weak exploration and research in the offshore of China. The Eastern Depression is the secondary building unit which has the best exploration foreground in North Yellow Sea Basin. According to the core observation and logging facies analysis, combined with 3D seismic data, it is considered that fan delta, braided-river delta, delta and lake developed in the Mesozoic in Eastern Depression. Restricted by structural evolution, there was different sedimentary evolution in different tectonic phase in Mesozoic. Middle Jurassic was in the period of initial graben faulting. The sedimentary types were mainly semi-abyss and abyss. There were few fan deltas in depression margin. Late Jurassic was in the period of faulting extension. The vertical lithological sequence was an integral depositional cycle of progradation-retrogradation. There were delta in north gentle slope and fan delta in abrupt slope in early stage. Owing to uprising of lake level, there developed undercompensation lake facies whose lithology is mainly dark mudstone. North gentle slope developed small-scale delta front. Early Cretaceous was in the period of faulting abortion, and there were two normal cyclic depositional sequences. The sedimentary types of each cycle were mainly fan delta, braided-river delta in lower part, and shore-shallow lacustrine upward.
2015, 33(3): 578-586.
doi: 10.14027/j.cnki.cjxb.2015.03.016
Abstract:
This paper discusses the research idea of mapping gravity flow depositional systems based on seismic sedimentology method. Case study on the thick layer sandstone of the first member of Shahejie Formation in Qinan slope, according to the theory and method of seismic sedimentology, this paper puts forward a program of seismic sedimentology suitable for China's continental fault basins with gravity flow depositional systems:first, the high frequency sequence stratigraphic framework are performed through time-frequency analysis and frequency decomposing technology; then application of seismic geomorphology and macroscopic attribute constraint source direction; Combining with core calibration to determine sedimentary facies types; and lastly, stratal slicing, seismic inversion and 3D visualization showing the spatial and temporal distribution of the gravity flow channel, application of this method and techniques to seismic sedimentology study, gravity flow channel sand body is clearly characterized. This study provides favorable exploration areas for finding hydrocarbon reservoirs in lacustrine mudstones in Qikou sag, good results have been produced and enriched fundamental research of seismic sedimentology.
This paper discusses the research idea of mapping gravity flow depositional systems based on seismic sedimentology method. Case study on the thick layer sandstone of the first member of Shahejie Formation in Qinan slope, according to the theory and method of seismic sedimentology, this paper puts forward a program of seismic sedimentology suitable for China's continental fault basins with gravity flow depositional systems:first, the high frequency sequence stratigraphic framework are performed through time-frequency analysis and frequency decomposing technology; then application of seismic geomorphology and macroscopic attribute constraint source direction; Combining with core calibration to determine sedimentary facies types; and lastly, stratal slicing, seismic inversion and 3D visualization showing the spatial and temporal distribution of the gravity flow channel, application of this method and techniques to seismic sedimentology study, gravity flow channel sand body is clearly characterized. This study provides favorable exploration areas for finding hydrocarbon reservoirs in lacustrine mudstones in Qikou sag, good results have been produced and enriched fundamental research of seismic sedimentology.
2015, 33(3): 595-606.
doi: 10.14027/j.cnki.cjxb.2015.03.018
Abstract:
A shelf-margin delta is built up on shelf-margin, where sediments pass across the shelf break and settle down to form the delta. Oil richness of shelf-margin delta has been confirmed by exploration in the world for its wide distribution and well-developed reservoirs. Based on analysis of seismic and drilling data, distribution and architecture of large shelf-margin delta in Zhuhai Formation in deep-water area have been systematically studied for the first time, as well as the main control factors and exploration significance. With “S”, oblique and imbricated progradation configuration in profile, interbedding of underwater distributary channel, mouth bar, sand sheet and prodelta clay on wells, the large shelf-margin delta striking NE is located in Baiyun and Heshan sag. In Baiyun sag, this delta is relatively small with mainly oblique progradation configuration. The delta in South Baiyun depression developed deepwater channel and fans with “S” progradation configuration. The segment in southern uplift show oblique and imbricated progradation configuration. In Heshan sag, the delta developed incised valley and fans with “S” progradation configuration. Shelf break developed firmly in deepwater area for quiescence of tectonic movement in Late Oligocene. Shelf-margin delta developed because of the abundant sediment from Paleo-Pearl River and falling of relative sea-level. The delta takes abundant terrestrial organic matter to marine mudstone and, moreover, mudstone in the delta is fair-good source rock. With wide distribution and big thickness, underwater distributary channel, mouth bar and sand sheet in shelf-margin delta are significant reservoir in deepwater area and the deepwater fans before delta are profitable target.
A shelf-margin delta is built up on shelf-margin, where sediments pass across the shelf break and settle down to form the delta. Oil richness of shelf-margin delta has been confirmed by exploration in the world for its wide distribution and well-developed reservoirs. Based on analysis of seismic and drilling data, distribution and architecture of large shelf-margin delta in Zhuhai Formation in deep-water area have been systematically studied for the first time, as well as the main control factors and exploration significance. With “S”, oblique and imbricated progradation configuration in profile, interbedding of underwater distributary channel, mouth bar, sand sheet and prodelta clay on wells, the large shelf-margin delta striking NE is located in Baiyun and Heshan sag. In Baiyun sag, this delta is relatively small with mainly oblique progradation configuration. The delta in South Baiyun depression developed deepwater channel and fans with “S” progradation configuration. The segment in southern uplift show oblique and imbricated progradation configuration. In Heshan sag, the delta developed incised valley and fans with “S” progradation configuration. Shelf break developed firmly in deepwater area for quiescence of tectonic movement in Late Oligocene. Shelf-margin delta developed because of the abundant sediment from Paleo-Pearl River and falling of relative sea-level. The delta takes abundant terrestrial organic matter to marine mudstone and, moreover, mudstone in the delta is fair-good source rock. With wide distribution and big thickness, underwater distributary channel, mouth bar and sand sheet in shelf-margin delta are significant reservoir in deepwater area and the deepwater fans before delta are profitable target.
2015, 33(3): 616-624.
doi: 10.14027/j.cnki.cjxb.2015.03.020
Abstract:
Flow barrier was rock mass which keep out fluid flow inside of reservoir system. Taking Yulou oil-bearing sets in some experimental area in the south end of westward slope of West depression in Liaohe Basin as an example, flow barrier were studied on the base of combining geological data and 400 well data and six well data of cores and water analysis data of ten wells. Types and distribution characteristics and its effects to thermal recovery of heavy oil reservoir were studied in detail. Flow barrier in reservoir of fan delta front of the aimed stratum in the study area were carved up into three types of sedimentary flow barrier and diagenesis flow barrier and sealing fault flow barrier by cause, and sedimentary flow barrier took the leading role. Controlled by sedimentary process, sedimentary flow barrier distributed from north-west to south-east like stripped noodles. They mainly lined in areas of underwater distributary channels and channel mouth bars. With distances changed more and more far, sediments granularity became smaller and sedimentary flow barrier developed levels were strengthened. Steam paths in steam flooding were complicated because of the existence of flow barrier. In this process, thermal and economical efficiency were reduced. Flow barriers also had very important influence to layer steam injection and other development measures carried out.
Flow barrier was rock mass which keep out fluid flow inside of reservoir system. Taking Yulou oil-bearing sets in some experimental area in the south end of westward slope of West depression in Liaohe Basin as an example, flow barrier were studied on the base of combining geological data and 400 well data and six well data of cores and water analysis data of ten wells. Types and distribution characteristics and its effects to thermal recovery of heavy oil reservoir were studied in detail. Flow barrier in reservoir of fan delta front of the aimed stratum in the study area were carved up into three types of sedimentary flow barrier and diagenesis flow barrier and sealing fault flow barrier by cause, and sedimentary flow barrier took the leading role. Controlled by sedimentary process, sedimentary flow barrier distributed from north-west to south-east like stripped noodles. They mainly lined in areas of underwater distributary channels and channel mouth bars. With distances changed more and more far, sediments granularity became smaller and sedimentary flow barrier developed levels were strengthened. Steam paths in steam flooding were complicated because of the existence of flow barrier. In this process, thermal and economical efficiency were reduced. Flow barriers also had very important influence to layer steam injection and other development measures carried out.
