2015 Vol. 33, No. 6
Display Method:
2015, 33(6): 1063-1073.
doi: 10.14027/j.cnki.cjxb.2015.06.001
Abstract:
Provenance studies of aeolian sand seas not only have great theoretical and practical significance in aeolian geomorphology, but also are essential for understanding the complex linkages between dust emission, loess accumulation, climate system, and ocean biogeochemistry cycles. A brief historical survey of Chinese deserts illustrates the limitations of modern provenance research. The state of the art in basic ideas, techniques, and their applications in provenance analysis of sediments are reviewed across Chinese sand seas. Traditionally sediment provenance studies are deductive approach, which depend on compositional and textural sediment properties based on geochemistry, mineralogy, and petrography, and its main difficulty stems from the fact that sediments are not a one-to-one image of their source, implying that factors other than parent lithology determine their final composition. Combined with the future research trend on quantitative provenance analysis(QPA) of sediments, some problems on data-acquisition and processing methodologies in provenance studies across global sand seas is presented, such as sampling design and physicochemical analysis of sediment, grain-size dependence of sediment composition and environmental bias, compositional data statistically treated with the log-ratio method for avoiding the well-known problems of spurious correlation and negative bias, limitations of typical Dickinson diagrams, and so on. Generally, current more attention has been paid to the inverse approach based on compositional properties, which dominates the field of quantitative provenance analysis, whereas applicable process-based forward model of sediment generation, which could predict simultaneous evolution of the grain-size distribution, as well as the petrographic, mineralogical and chemical composition of weathering products of specific parent rocks under a range of climatic and tectonic conditions, do not yet exist. Unraveling the history of sediments is a complex and challenging task which needs multidisciplinary efforts like sedimentology, petrography, mineralogy, geochemistry, geochronology, structural geology, stratigraphy, mathematical geology, and geomorphology. It is concluded from this review that the QPA of Chinese sand seas over historic and geologic timescale is still in its infancy and future provenance studies is needed to towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with uplift, climate and denudation in mountain belts as well as transfer of sediments from the continents to the atmosphere and oceans. These include(i) to build sedimentary compositional data bases using a uniform sampling design and analytical measurements across sand seas of China, to develop and use mathematically rigorous methods of statistical analysis and numerical modeling of sediment composition when dealing with compositional data such as data in percentages, concentrations or proportions,(ii) to construct a process-based sediment generation model(Forward model) capable of predicting the simultaneous evolution of the texture, as well as the petrographic, mineralogical and geochemical composition of weathering products of specific parent rocks under a range of climatic and tectonic conditions, using typical sand deserts of China which have available parent lithology, tectonic setting, regional geography, and climatic-physiographic data sets, to calibrate and validate forward models by sufficient high-quality data bases established at similar temporal and spatial scales,(iii) to assess contribution ratios and transport pathways of four possible proximal sources in Chinese deserts, to reveal mechanism of the formation and production of desert loess and silt quartz grains, to compare aeolian sand sources of Chinese deserts with most of the worldwide low-latitude deserts,(iv) to establish internal connections between deserts, wind-blown dust emission, loess accumulation, and climate system and ocean biogeochemical cycles at historic and geologic scales, and to build a Earth system model coupling with continent, atmosphere and ocean for understanding the Earth surface processes.
Provenance studies of aeolian sand seas not only have great theoretical and practical significance in aeolian geomorphology, but also are essential for understanding the complex linkages between dust emission, loess accumulation, climate system, and ocean biogeochemistry cycles. A brief historical survey of Chinese deserts illustrates the limitations of modern provenance research. The state of the art in basic ideas, techniques, and their applications in provenance analysis of sediments are reviewed across Chinese sand seas. Traditionally sediment provenance studies are deductive approach, which depend on compositional and textural sediment properties based on geochemistry, mineralogy, and petrography, and its main difficulty stems from the fact that sediments are not a one-to-one image of their source, implying that factors other than parent lithology determine their final composition. Combined with the future research trend on quantitative provenance analysis(QPA) of sediments, some problems on data-acquisition and processing methodologies in provenance studies across global sand seas is presented, such as sampling design and physicochemical analysis of sediment, grain-size dependence of sediment composition and environmental bias, compositional data statistically treated with the log-ratio method for avoiding the well-known problems of spurious correlation and negative bias, limitations of typical Dickinson diagrams, and so on. Generally, current more attention has been paid to the inverse approach based on compositional properties, which dominates the field of quantitative provenance analysis, whereas applicable process-based forward model of sediment generation, which could predict simultaneous evolution of the grain-size distribution, as well as the petrographic, mineralogical and chemical composition of weathering products of specific parent rocks under a range of climatic and tectonic conditions, do not yet exist. Unraveling the history of sediments is a complex and challenging task which needs multidisciplinary efforts like sedimentology, petrography, mineralogy, geochemistry, geochronology, structural geology, stratigraphy, mathematical geology, and geomorphology. It is concluded from this review that the QPA of Chinese sand seas over historic and geologic timescale is still in its infancy and future provenance studies is needed to towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with uplift, climate and denudation in mountain belts as well as transfer of sediments from the continents to the atmosphere and oceans. These include(i) to build sedimentary compositional data bases using a uniform sampling design and analytical measurements across sand seas of China, to develop and use mathematically rigorous methods of statistical analysis and numerical modeling of sediment composition when dealing with compositional data such as data in percentages, concentrations or proportions,(ii) to construct a process-based sediment generation model(Forward model) capable of predicting the simultaneous evolution of the texture, as well as the petrographic, mineralogical and geochemical composition of weathering products of specific parent rocks under a range of climatic and tectonic conditions, using typical sand deserts of China which have available parent lithology, tectonic setting, regional geography, and climatic-physiographic data sets, to calibrate and validate forward models by sufficient high-quality data bases established at similar temporal and spatial scales,(iii) to assess contribution ratios and transport pathways of four possible proximal sources in Chinese deserts, to reveal mechanism of the formation and production of desert loess and silt quartz grains, to compare aeolian sand sources of Chinese deserts with most of the worldwide low-latitude deserts,(iv) to establish internal connections between deserts, wind-blown dust emission, loess accumulation, and climate system and ocean biogeochemical cycles at historic and geologic scales, and to build a Earth system model coupling with continent, atmosphere and ocean for understanding the Earth surface processes.
2015, 33(6): 1074-1086.
doi: 10.14027/j.cnki.cjxb.2015.06.002
Abstract:
A set of Neogene thick continental clastic sedimentary rocks develops in Baicheng County, Xinjiang province, in which a large-scale sedimentary copper ore occurs in the upper part of Kangcun Formation. Obviously, it is of important significance in the formation of copper deposits to the sedimentary environment and its evolution of the Kangcun Formation. Based on detailed sedimentological studies in field and laboratory, two major types of sedimentary system, alluvial fan-fan delta type and lacustrine type, are identified for Jidike Formation, Kangcun Formation and Kuqa Formation of Neogene in the study area. The sedimentary systems are further divided into subfacies of fan delta plain, fan delta front, front fan delta, shore shallow lacustrine, gypsum-salt lacustrine and some microfacies. The sedimentary framework of the Kangcun stage approximately inherited that of the Jidike stage. The types of sedimentary facies were mainly fan delta facies in the study area during the Kangcun stage, while sediments of lacustrine facies occurred in warm humid climate could fill the whole study area. Main ore-bearing beds are in the transitional strata of red rocks to gray rocks in the upper part of Kangcun Formation. And the sedimentary characteristics of ore-bearing beds indicate that the depositional environment have experienced a process from fan delta front facies to shore shallow lacustrine facies.
A set of Neogene thick continental clastic sedimentary rocks develops in Baicheng County, Xinjiang province, in which a large-scale sedimentary copper ore occurs in the upper part of Kangcun Formation. Obviously, it is of important significance in the formation of copper deposits to the sedimentary environment and its evolution of the Kangcun Formation. Based on detailed sedimentological studies in field and laboratory, two major types of sedimentary system, alluvial fan-fan delta type and lacustrine type, are identified for Jidike Formation, Kangcun Formation and Kuqa Formation of Neogene in the study area. The sedimentary systems are further divided into subfacies of fan delta plain, fan delta front, front fan delta, shore shallow lacustrine, gypsum-salt lacustrine and some microfacies. The sedimentary framework of the Kangcun stage approximately inherited that of the Jidike stage. The types of sedimentary facies were mainly fan delta facies in the study area during the Kangcun stage, while sediments of lacustrine facies occurred in warm humid climate could fill the whole study area. Main ore-bearing beds are in the transitional strata of red rocks to gray rocks in the upper part of Kangcun Formation. And the sedimentary characteristics of ore-bearing beds indicate that the depositional environment have experienced a process from fan delta front facies to shore shallow lacustrine facies.
2015, 33(6): 1087-1096.
doi: 10.14027/j.cnki.cjxb.2015.06.003
Abstract:
Deepwater siliceous rocks developed during the Early Cambrian in Zhushan area which located on the north margin of the Yangtze block. These rocks mainly comprise pure siliceous rocks, with little dolomite and shale. The siliceous rocks are composed of microcrystalline quartz(content of more than 85%) and some carbon, flint and sericite. They show high SiO2 content(93.4%, on average) by geochemical analysis. Contents of Al2O3 and TiO2, are as low as 0.19%~1.45% and 0.01%~0.09%, respectively. And TFe2O3 accounts for 0.053%~0.342%. The ratio of Al/(Al+Fe+Mn) is from 0.58 to 0.83(0.73, on average), with Eu/Eu* being in 0.74~3.61 range(1.65, on average), which indicates the silicon comes from biological activities and hydrothermal injection. Meanwhile, the ratio of TFe2O3/TiO2 and Al2O3/(Al2O3+Fe2O3) are evidently low to 2.16~12.56 and 0.65~0.87 Y is positive anomaly(Y/Ho value is 34.81~60.19) and Ce is negative anomaly(Ce/Ce* value is 0.28~0.92), implying that these rocks were deposited in an ocean basin with no input of terrigenous materials. Negative anomaly of Ce are less evident to upside, which records the expansion of the passive continental margin rift basin on the northern Yangtze block.
Deepwater siliceous rocks developed during the Early Cambrian in Zhushan area which located on the north margin of the Yangtze block. These rocks mainly comprise pure siliceous rocks, with little dolomite and shale. The siliceous rocks are composed of microcrystalline quartz(content of more than 85%) and some carbon, flint and sericite. They show high SiO2 content(93.4%, on average) by geochemical analysis. Contents of Al2O3 and TiO2, are as low as 0.19%~1.45% and 0.01%~0.09%, respectively. And TFe2O3 accounts for 0.053%~0.342%. The ratio of Al/(Al+Fe+Mn) is from 0.58 to 0.83(0.73, on average), with Eu/Eu* being in 0.74~3.61 range(1.65, on average), which indicates the silicon comes from biological activities and hydrothermal injection. Meanwhile, the ratio of TFe2O3/TiO2 and Al2O3/(Al2O3+Fe2O3) are evidently low to 2.16~12.56 and 0.65~0.87 Y is positive anomaly(Y/Ho value is 34.81~60.19) and Ce is negative anomaly(Ce/Ce* value is 0.28~0.92), implying that these rocks were deposited in an ocean basin with no input of terrigenous materials. Negative anomaly of Ce are less evident to upside, which records the expansion of the passive continental margin rift basin on the northern Yangtze block.
2015, 33(6): 1097-1110.
doi: 10.14027/j.cnki.cjxb.2015.06.004
Abstract:
There is a special and extensively developed type of dolomite in Dengying Formation and its corresponding formations of Upper Sinian in Yangtze region, which is with an odd-looking like renal globule, ellipsoid, grape-like body and sphere in irregular shape(hereinafter referred to as the "grapes"). Many scholars in China believed that this kind of dolomite was affected by atmospheric fresh water during formation. "Grapes" are like pieces of tufa on the macro, distributed along interfaces of rock strata and fractures. On the basis of the detailed observation and description of outcrops, and using polarized light microscope, cathodoluminescence and scanning electron microscopy(SEM), the characteristics and genesis of grape-like dolomite in the First section of Sinian Dengying Formation in Yangba Town of Nanjiang County, were studied. The results show that the grapes were as the fillings in surrounding rocks through diagenetic ways into rocks. The grapes are usually like hemispheroids with cores and alternated dark and bright shells, and composed mostly of dolomite and a little of authigenic quartz. The cores and dark shells were formed from biological and chemical processes in sea water, according to the algal binding aggregates with irregular microbial filaments, high carbon elements in the mineral components, and in combination with the existence of the seabed hard ground. The bright shells were composed by fiber cements, which in the same thickness and formed the outer layers of grapes. Grapes are with polyhedral intersection and filled with fiber cements in the residual space, so the outer of grapes are forming in marine phreatic water and mainly due to cementation. Cores were the irregular bumps on the wall of dissolution holes and seams, the characteristics of grapes were closely related to the size and shape of bumps and the features of growth space. The fixed point and regular structure indicate that grapes were formed in stable water. Aragonite or high-magnesian calcite was the original component, because of the dolomitization, the grape-like dolomite was formed and with crystalline-granular texture. The characteristics cathode luminescence of grapes are similar to surrounding rocks, and according to the occurrence and the morphological characteristics of the grapes, the hemispheroids with cores and alternated dark and bright shells are identified as an sedimentary structure and named grape-like structure. The sedimentary structure is a deposition-diagenetic structure and due to biological and chemical effect, and formed in the stable sea environment.
There is a special and extensively developed type of dolomite in Dengying Formation and its corresponding formations of Upper Sinian in Yangtze region, which is with an odd-looking like renal globule, ellipsoid, grape-like body and sphere in irregular shape(hereinafter referred to as the "grapes"). Many scholars in China believed that this kind of dolomite was affected by atmospheric fresh water during formation. "Grapes" are like pieces of tufa on the macro, distributed along interfaces of rock strata and fractures. On the basis of the detailed observation and description of outcrops, and using polarized light microscope, cathodoluminescence and scanning electron microscopy(SEM), the characteristics and genesis of grape-like dolomite in the First section of Sinian Dengying Formation in Yangba Town of Nanjiang County, were studied. The results show that the grapes were as the fillings in surrounding rocks through diagenetic ways into rocks. The grapes are usually like hemispheroids with cores and alternated dark and bright shells, and composed mostly of dolomite and a little of authigenic quartz. The cores and dark shells were formed from biological and chemical processes in sea water, according to the algal binding aggregates with irregular microbial filaments, high carbon elements in the mineral components, and in combination with the existence of the seabed hard ground. The bright shells were composed by fiber cements, which in the same thickness and formed the outer layers of grapes. Grapes are with polyhedral intersection and filled with fiber cements in the residual space, so the outer of grapes are forming in marine phreatic water and mainly due to cementation. Cores were the irregular bumps on the wall of dissolution holes and seams, the characteristics of grapes were closely related to the size and shape of bumps and the features of growth space. The fixed point and regular structure indicate that grapes were formed in stable water. Aragonite or high-magnesian calcite was the original component, because of the dolomitization, the grape-like dolomite was formed and with crystalline-granular texture. The characteristics cathode luminescence of grapes are similar to surrounding rocks, and according to the occurrence and the morphological characteristics of the grapes, the hemispheroids with cores and alternated dark and bright shells are identified as an sedimentary structure and named grape-like structure. The sedimentary structure is a deposition-diagenetic structure and due to biological and chemical effect, and formed in the stable sea environment.
2015, 33(6): 1111-1125.
doi: 10.14027/j.cnki.cjxb.2015.06.005
Abstract:
Limestone conglomerates are widely distributed in Cambrian-Ordovician North China Platform, and only a portion of limestone conglomerates have shape of bamboo leaf viewing from cross section. These limestone conglomerates were mixed with other pebbles. Ancient continental sea was environmental foundation for limestone conglomerates formed. Tidal flat and open marine platform were basic geomorphic units in continental sea, and the main place for limestone conglomerates formed. The ancient plate-motion indicated that North China plate situated in low latitude and has frequent storm wave and hurricane tide, which was the main power for limestone layers broken. In addition, compaction and dewatering also provided power for limestone layers broken. Limestone layers interbedded with mudstone layers or argillaceous limestone was material base for limestone becoming bamboo leaf shaped conglomerates. Limestone conglomerates in North China Platform can be classified and genetically interpreted in terms of color, shapes, the degree of grinding, support structure of limestone conglomerates, filling types. In short, limestone conglomerates in Cambrian-Ordovician North China Platform has many genesis and should be make a difference between various kinds of limestone conglomerates.
Limestone conglomerates are widely distributed in Cambrian-Ordovician North China Platform, and only a portion of limestone conglomerates have shape of bamboo leaf viewing from cross section. These limestone conglomerates were mixed with other pebbles. Ancient continental sea was environmental foundation for limestone conglomerates formed. Tidal flat and open marine platform were basic geomorphic units in continental sea, and the main place for limestone conglomerates formed. The ancient plate-motion indicated that North China plate situated in low latitude and has frequent storm wave and hurricane tide, which was the main power for limestone layers broken. In addition, compaction and dewatering also provided power for limestone layers broken. Limestone layers interbedded with mudstone layers or argillaceous limestone was material base for limestone becoming bamboo leaf shaped conglomerates. Limestone conglomerates in North China Platform can be classified and genetically interpreted in terms of color, shapes, the degree of grinding, support structure of limestone conglomerates, filling types. In short, limestone conglomerates in Cambrian-Ordovician North China Platform has many genesis and should be make a difference between various kinds of limestone conglomerates.
2015, 33(6): 1126-1139.
doi: 10.14027/j.cnki.cjxb.2015.06.006
Abstract:
The Upper Carboniferous-Lower Permian Taiyuan Formation in the middle-south Shanxi province is a set of coal-bearing formation with marine-terrigenous facies. Abundant ichnofossils are discovered in carbonate rocks of this formation.10 ichnogena and 14 ichnospecies has been recognized and described from the observation of the outcrop sections in Xishan area of Taiyuan city and near Fucheng of Lingchuan county, which include Fodinichnia(10 ichnospecies), Pascichnia(2 ichnospecies) and Domichnia(2 ichnospecies) according to the ethological classification. Based on the composition, occurrence and size of ichnofossils as well as the components and color of burrow filling, and combined with lithologic characteristics of host rock, four types of ichnofabrics and their sedimentary environment model can be established, i.e., Type A, the large-sized Zoophycos-Thalassinoides ichnofabric, which is formed in restricted bay or lagoon sedimentary environment; Type B, the large-sized Zoophycos-Planolites ichnofabric, which occurrs in the upper shallow marine environment between sea level and fair-weather wave base or restricted carbonate platform environment with shallow and relatively calm water body; Type C, medium-sized Zoophycos-Teichichnus ichnofabric, which is generated in middle shallow sea between fair-weather wave base and storm wave base; Type D, small sized Zoophycos-Chondrites ichnofabric, which is developed in the lower zone of shallow sea below the storm wave base, showing the low oxygen and deeper water environment. The result will provide biologic information in order for the detailed studies on sedimentary environmental evolution of the Taiyuan Formation and can also provide scientific evidence for the study of coal and coalbed gas formation palaeoenvironment in this area.
The Upper Carboniferous-Lower Permian Taiyuan Formation in the middle-south Shanxi province is a set of coal-bearing formation with marine-terrigenous facies. Abundant ichnofossils are discovered in carbonate rocks of this formation.10 ichnogena and 14 ichnospecies has been recognized and described from the observation of the outcrop sections in Xishan area of Taiyuan city and near Fucheng of Lingchuan county, which include Fodinichnia(10 ichnospecies), Pascichnia(2 ichnospecies) and Domichnia(2 ichnospecies) according to the ethological classification. Based on the composition, occurrence and size of ichnofossils as well as the components and color of burrow filling, and combined with lithologic characteristics of host rock, four types of ichnofabrics and their sedimentary environment model can be established, i.e., Type A, the large-sized Zoophycos-Thalassinoides ichnofabric, which is formed in restricted bay or lagoon sedimentary environment; Type B, the large-sized Zoophycos-Planolites ichnofabric, which occurrs in the upper shallow marine environment between sea level and fair-weather wave base or restricted carbonate platform environment with shallow and relatively calm water body; Type C, medium-sized Zoophycos-Teichichnus ichnofabric, which is generated in middle shallow sea between fair-weather wave base and storm wave base; Type D, small sized Zoophycos-Chondrites ichnofabric, which is developed in the lower zone of shallow sea below the storm wave base, showing the low oxygen and deeper water environment. The result will provide biologic information in order for the detailed studies on sedimentary environmental evolution of the Taiyuan Formation and can also provide scientific evidence for the study of coal and coalbed gas formation palaeoenvironment in this area.
2015, 33(6): 1140-1148.
doi: 10.14027/j.cnki.cjxb.2015.06.007
Abstract:
High-resolution δ18O records from two annually-laminated stalagmites(QT16 and QT40) from Qingtian Cave, Mt. Shengnongjia reveal a detailed Asian monsoon(AM) variability throughout the Younger Dryas(YD) and the 8.2 ka event. During the mid-YD, the AM variability exhibits three centennial oscillations, while the 8.2 ka event is characterized by two 20-year weak AM events separated by one 40-year AM strengthening event. The general pattern of AM variability in two time windows at this site agree well with other cave records from the AM area and the Greenland records. To quantitatively evaluate the structure of the YD and 8.2 ka event, two mathematical methods are applied. In these analyses, both climate events show an asymmetrical structure, i.e., a gradual transition into the event and an abrupt ending. These transitional patterns are further supported by previous stalagmite records in the AM area. However, the AM changes during these events are significantly different from the temperature changes over the Greenland. To some degree, the gradual AM decline at the onset is similarly reflected by low-latitude terrestrial or oceanic records regarding their onsets. This implicates that a forcing factor associated with hydrological circulations in the tropical ocean might modulate the AM evolution during these events.
High-resolution δ18O records from two annually-laminated stalagmites(QT16 and QT40) from Qingtian Cave, Mt. Shengnongjia reveal a detailed Asian monsoon(AM) variability throughout the Younger Dryas(YD) and the 8.2 ka event. During the mid-YD, the AM variability exhibits three centennial oscillations, while the 8.2 ka event is characterized by two 20-year weak AM events separated by one 40-year AM strengthening event. The general pattern of AM variability in two time windows at this site agree well with other cave records from the AM area and the Greenland records. To quantitatively evaluate the structure of the YD and 8.2 ka event, two mathematical methods are applied. In these analyses, both climate events show an asymmetrical structure, i.e., a gradual transition into the event and an abrupt ending. These transitional patterns are further supported by previous stalagmite records in the AM area. However, the AM changes during these events are significantly different from the temperature changes over the Greenland. To some degree, the gradual AM decline at the onset is similarly reflected by low-latitude terrestrial or oceanic records regarding their onsets. This implicates that a forcing factor associated with hydrological circulations in the tropical ocean might modulate the AM evolution during these events.
2015, 33(6): 1149-1158.
doi: 10.14027/j.cnki.cjxb.2015.06.008
Abstract:
A series of significant geological, climatological, and biological events have been documented during the Triassic period(252~201 Ma). Influenced by the tectonic movement, the sedimentary environment changed from marine to continental in the Upper Yangtze region and the rudiment of the Sichuan Basin was preliminary formed during the Middle-Late Triassic transition. The Middle to Upper Triassic deposits in the Sichuan Basin probably recorded the major changes of sedimentary environment and biodiversity variations during this period. The Middle-Late Triassic marine and non-marine transitional strata are well developed and outcropped in Qilixia, Xuanhan, NE Sichuan representing the perfect profile for investigating the evolution of marine and continental environment during the Middle-Late Triassic in the Sichuan Basin. The basal part of the section(bed 1) is represented by the gray and thick muddy dolomite deposit of the Middle Triassic Leikoupo Formation, inferring an evaporative platform miocrofacies. The systematic study on the 1st member of the Upper Triassic Xujiahe Formation shows that the lithologic characters are dominated mainly by dark grey, black mudstone and shale; there are few sandy, silty mudstone and no conglomerate. Mudstones are medium to thin layers and the parallel beddings are common; mud cracks, biological disturb and lebensspur are also founded at the surface of the rock. The root clay is also distributed in the mudstone with coal inclusions and charcoalified plants; some thin layers of siderite concretions and calcic concretions are developed at the bottom and top of the mudstone; in addition, gypsum is locally distributed. The lithological association reflects the regularity of the sedimentary environment from marine to terrestrial. The pollen data analysis shows that most of the vegetation species are ferns, conifers and cycads in the Xuanhan region during the Late Triassic. The plant community represents a subtropical and tropical climate condition and the subaquatic environment. Sedimentary environment and facies of the 1st member of the Upper Triassic Xujiahe Formation could be divided from evaporative platform, lagoon-tidal flat, coastal marsh to estuarine sandbar based on evidences of lithology, color, structure, lens, carbon isotope, paleontology and coal accumulation. The regular evolutionary model shows that the strata of the formation had an unbroken transgressive and regressive cycle during the Norian-Rhaetian. Influenced by the Indosinian Movement, a great regression happened, the typical marine deposition of shallow-water carbonates in the Upper Yangtze platform ended and most of the Sichuan Basin uplifted to the land, the carbonaceous Lower and Middle Triassic series were weathered and eroded. The continual transgression started in the Carnian age didn't arrive at Xuanhan region until the Late Norian age. Once the transgression arrived, the bar-built estuarine environment began to take shape and the muddy facies deposited. At the end of the Norian age, the regression event controlled by the orogenic uplift of the Qinling Mt. and the strong crumpling of the North-China Plate happened again, the seashore and lakeshore swamp occurred and the muskey and lakeshore swamp facies covered the muddy facies formed before. With the continuous regression, the rivers originated from the Daba Mt. were dominated at the Rhaetian age. The riverine environment, a typical terrestrial sedimentary environment, occupied the entire Xuanhan region and its adjacent area and the riverine sedimentary facies occurred. The evolutionary process of the paleoenvironment is an essential reflection of the changes in NE Sichuan Basin during the Middle-Late Triassic.
A series of significant geological, climatological, and biological events have been documented during the Triassic period(252~201 Ma). Influenced by the tectonic movement, the sedimentary environment changed from marine to continental in the Upper Yangtze region and the rudiment of the Sichuan Basin was preliminary formed during the Middle-Late Triassic transition. The Middle to Upper Triassic deposits in the Sichuan Basin probably recorded the major changes of sedimentary environment and biodiversity variations during this period. The Middle-Late Triassic marine and non-marine transitional strata are well developed and outcropped in Qilixia, Xuanhan, NE Sichuan representing the perfect profile for investigating the evolution of marine and continental environment during the Middle-Late Triassic in the Sichuan Basin. The basal part of the section(bed 1) is represented by the gray and thick muddy dolomite deposit of the Middle Triassic Leikoupo Formation, inferring an evaporative platform miocrofacies. The systematic study on the 1st member of the Upper Triassic Xujiahe Formation shows that the lithologic characters are dominated mainly by dark grey, black mudstone and shale; there are few sandy, silty mudstone and no conglomerate. Mudstones are medium to thin layers and the parallel beddings are common; mud cracks, biological disturb and lebensspur are also founded at the surface of the rock. The root clay is also distributed in the mudstone with coal inclusions and charcoalified plants; some thin layers of siderite concretions and calcic concretions are developed at the bottom and top of the mudstone; in addition, gypsum is locally distributed. The lithological association reflects the regularity of the sedimentary environment from marine to terrestrial. The pollen data analysis shows that most of the vegetation species are ferns, conifers and cycads in the Xuanhan region during the Late Triassic. The plant community represents a subtropical and tropical climate condition and the subaquatic environment. Sedimentary environment and facies of the 1st member of the Upper Triassic Xujiahe Formation could be divided from evaporative platform, lagoon-tidal flat, coastal marsh to estuarine sandbar based on evidences of lithology, color, structure, lens, carbon isotope, paleontology and coal accumulation. The regular evolutionary model shows that the strata of the formation had an unbroken transgressive and regressive cycle during the Norian-Rhaetian. Influenced by the Indosinian Movement, a great regression happened, the typical marine deposition of shallow-water carbonates in the Upper Yangtze platform ended and most of the Sichuan Basin uplifted to the land, the carbonaceous Lower and Middle Triassic series were weathered and eroded. The continual transgression started in the Carnian age didn't arrive at Xuanhan region until the Late Norian age. Once the transgression arrived, the bar-built estuarine environment began to take shape and the muddy facies deposited. At the end of the Norian age, the regression event controlled by the orogenic uplift of the Qinling Mt. and the strong crumpling of the North-China Plate happened again, the seashore and lakeshore swamp occurred and the muskey and lakeshore swamp facies covered the muddy facies formed before. With the continuous regression, the rivers originated from the Daba Mt. were dominated at the Rhaetian age. The riverine environment, a typical terrestrial sedimentary environment, occupied the entire Xuanhan region and its adjacent area and the riverine sedimentary facies occurred. The evolutionary process of the paleoenvironment is an essential reflection of the changes in NE Sichuan Basin during the Middle-Late Triassic.
2015, 33(6): 1159-1169.
doi: 10.14027/j.cnki.cjxb.2015.06.009
Abstract:
According to the result of grain-size analysis which combine with the characteristics of stratigraphical sequence, texture, structure and lithological properties, there are four kinds of sedimentary environments in the Carboniferous to the Permian could be discerned in Xingcheng, Western Liaoning. Each kind of sedimentary environments have distinct characteristics of grain-size. First one is meandering river environment whose layers are in Benxi Formation and middle and lower Shihezi Formation, the average grain-sizes of sediments are mainly 3φ and sediments have a good gradation. Their frequency curves are slight skewed positive distribution. There are two kinds of grain-size probability cumulative curves. The one of distributary channel is typical bi-segment pattern and another of crevasse splay is "low suspension" bi-segment pattern. Second one is delta plain environment. It is identified in Taiyuan Formation and Shanxi Formation. The sediments of swamy have better gradation whose average grain-size is about 3.2φ and their grain-sizes are more fine than distributary channel's which is similar to meandering river. The frequency curves of sediments of delta plain reveal both positive and negative skewness. The grain-size probability cumulative curves of distributary channel manifest as "low-suspension" bi-segment pattern but ones of swamp are one-segment pattern which reflect vertical-accretion process. Third one is braided river environment. It is distinguished in upper Shihezi Formation and its average grain-size is near 2.5φ. The gradation is middle to better and the frequency curve of it is slight skewed positive distribution. The type of grain-size probability cumulative curves is between typical bi-segment pattern and "high suspension" bi-segment pattern. Fourth one is alluvial fan environment in Hamashan Formation. It has middle gradation and its average grain-size is about 2φ. According to common and extreme skewed positive distribution and of its frequency curves, it shows that most of sediments are composed of coarse component. "High suspension" bi-segment pattern of probability cumulative curves show that the hydrodynamic condition of the time was strong. Considering paleohydrodynamic condition and evolution of sedimentary environment, this area was a basin in close-shore environment which was warm and moist during Late Carboniferous to the middle of Middle Permian. With the Earth's crust uplift, the environment changed in direction of inland environment progressively from late Middle Permian. Up to the end of Late Permian, the environment had turned into inland which was dry and torrid.
According to the result of grain-size analysis which combine with the characteristics of stratigraphical sequence, texture, structure and lithological properties, there are four kinds of sedimentary environments in the Carboniferous to the Permian could be discerned in Xingcheng, Western Liaoning. Each kind of sedimentary environments have distinct characteristics of grain-size. First one is meandering river environment whose layers are in Benxi Formation and middle and lower Shihezi Formation, the average grain-sizes of sediments are mainly 3φ and sediments have a good gradation. Their frequency curves are slight skewed positive distribution. There are two kinds of grain-size probability cumulative curves. The one of distributary channel is typical bi-segment pattern and another of crevasse splay is "low suspension" bi-segment pattern. Second one is delta plain environment. It is identified in Taiyuan Formation and Shanxi Formation. The sediments of swamy have better gradation whose average grain-size is about 3.2φ and their grain-sizes are more fine than distributary channel's which is similar to meandering river. The frequency curves of sediments of delta plain reveal both positive and negative skewness. The grain-size probability cumulative curves of distributary channel manifest as "low-suspension" bi-segment pattern but ones of swamp are one-segment pattern which reflect vertical-accretion process. Third one is braided river environment. It is distinguished in upper Shihezi Formation and its average grain-size is near 2.5φ. The gradation is middle to better and the frequency curve of it is slight skewed positive distribution. The type of grain-size probability cumulative curves is between typical bi-segment pattern and "high suspension" bi-segment pattern. Fourth one is alluvial fan environment in Hamashan Formation. It has middle gradation and its average grain-size is about 2φ. According to common and extreme skewed positive distribution and of its frequency curves, it shows that most of sediments are composed of coarse component. "High suspension" bi-segment pattern of probability cumulative curves show that the hydrodynamic condition of the time was strong. Considering paleohydrodynamic condition and evolution of sedimentary environment, this area was a basin in close-shore environment which was warm and moist during Late Carboniferous to the middle of Middle Permian. With the Earth's crust uplift, the environment changed in direction of inland environment progressively from late Middle Permian. Up to the end of Late Permian, the environment had turned into inland which was dry and torrid.
2015, 33(6): 1170-1181.
doi: 10.14027/j.cnki.cjxb.2015.06.010
Abstract:
Fan deltas and braided river deltas are widely developed along the direction of minor axis in half-graben rift lake basin of East China. Both of them can form good oil and gas reservoir, but the identifications of them in well core and geophysical data are easy to confuse. Through the comparison and analysis of sedimentary features, geophysical data, oil-gas-bearing and controlling factors, we conclude that fan deltas are formed by alluvial fans running into lake along steep-slope zone and its seismic reflection characters is wedge foreset. The sediment composition maturity and structural maturity of fan deltas are lower than that of braided river deltas. The sedimentary features of fan deltas reflect the gravity current and tractive current sediments combined effection. Braided river deltas are formed by braided river flow into lake far away along gentle slope zone and its seismic reflection characters is imbricate foreset. The sedimentary characters of braided river deltas reflect the tractive current sediments effection. Fan deltas can form fault-lithologic reservoir and lithologic reservoir. Its favorable reservoir zone includes underwater distributary channel, sheet-like sand of fan delta front and slump turbid fan formed in pre-fan delta. Braided river deltas can form strata-lithologic reservoir and lithologic reservoir of which favorable reservoir includes braid-river channel of braid river delta plain and underwater distributary channel, mouth bar, sheet-like sand of braid river delta front. Besides above, turbidity sandstone is also favorable reservoir in fairly deep lake. The sedimentary features of fan deltas and braid river deltas are controlled by palaeoclimate, tectonic-palaeogeomorphology and lake level fluctuations; Tectonic-palaeogeomorphology is the critical factor among them. The depositional model of fan deltas and braided river deltas in half-graben rift lake basin of East China is established by combining the sedimentary features difference between them so as to provide guidance to analysis and research for them in similar geological background.
Fan deltas and braided river deltas are widely developed along the direction of minor axis in half-graben rift lake basin of East China. Both of them can form good oil and gas reservoir, but the identifications of them in well core and geophysical data are easy to confuse. Through the comparison and analysis of sedimentary features, geophysical data, oil-gas-bearing and controlling factors, we conclude that fan deltas are formed by alluvial fans running into lake along steep-slope zone and its seismic reflection characters is wedge foreset. The sediment composition maturity and structural maturity of fan deltas are lower than that of braided river deltas. The sedimentary features of fan deltas reflect the gravity current and tractive current sediments combined effection. Braided river deltas are formed by braided river flow into lake far away along gentle slope zone and its seismic reflection characters is imbricate foreset. The sedimentary characters of braided river deltas reflect the tractive current sediments effection. Fan deltas can form fault-lithologic reservoir and lithologic reservoir. Its favorable reservoir zone includes underwater distributary channel, sheet-like sand of fan delta front and slump turbid fan formed in pre-fan delta. Braided river deltas can form strata-lithologic reservoir and lithologic reservoir of which favorable reservoir includes braid-river channel of braid river delta plain and underwater distributary channel, mouth bar, sheet-like sand of braid river delta front. Besides above, turbidity sandstone is also favorable reservoir in fairly deep lake. The sedimentary features of fan deltas and braid river deltas are controlled by palaeoclimate, tectonic-palaeogeomorphology and lake level fluctuations; Tectonic-palaeogeomorphology is the critical factor among them. The depositional model of fan deltas and braided river deltas in half-graben rift lake basin of East China is established by combining the sedimentary features difference between them so as to provide guidance to analysis and research for them in similar geological background.
2015, 33(6): 1182-1191.
doi: 10.14027/j.cnki.cjxb.2015.06.011
Abstract:
In southern Sichuan Basin, with a number of wells drilled through Maokou Formation, the data obtained is difficult to meet the needs of the study for sedimentary microfacies due to the old materials with poor quality. This paper presents Mao 2A, B, C sub-members all develop a stable bioclastic shoal layer composed of thin stratified-blocky and light gray-gray sparry bioclastic limestones, respectively, which has several typical characteristics:multiple thin shoal bodies with sequences of shallowing and coarsening upwards superimpose frequently in the vertical, the thickness of single shoal body is generally small(less than 3m), the phenomenon of syngenetic exposure is rare through observation and analysis for cores and thin sections of Mao-2 member from only 10 cored wells in southern Sichuan Basin. The Gamma logging character of the multicycle superimposed, thin shoal bodies generally presents the comprehensive response of low value in the high value setting, thus it is difficult to accurately identify and calculate the thickness of grain shoals via logging data. Further analysis found that, during the development of non-exposed shoals inside carbonate platform, the grain shoals develop in microtopographic highs and have a relatively larger deposition rate, thus the depositional microtopographic highs can be approximately portrayed by the thickness variation of isochronal geological bodies that mainly composed of grainstones. Based on analysis of correlation between the thickness of isochronal geological bodies or the depositional microtopography and weathering crust karst reservoirs' development, point out the high-energy bioclastic shoals mainly present along the zonal distibutions of Luzhou-Jiangjin, Zigong-Dazu and Qingshen-Zizhong, which is controlled by the rudiment of Luzhou palaeohigh and Leshan-Longnvsi inherited palaeohigh. The results indicate that the restoration of depositional microtopography has important significance for the study of sedimentary microfacies in highly-developed borehole areas, where the drilling activity has been conducted to a high degree and only low quality of the study material can be used. This may also offer new reference to the prediction of favorable reservoir and the developing potential to the highly development layers.
In southern Sichuan Basin, with a number of wells drilled through Maokou Formation, the data obtained is difficult to meet the needs of the study for sedimentary microfacies due to the old materials with poor quality. This paper presents Mao 2A, B, C sub-members all develop a stable bioclastic shoal layer composed of thin stratified-blocky and light gray-gray sparry bioclastic limestones, respectively, which has several typical characteristics:multiple thin shoal bodies with sequences of shallowing and coarsening upwards superimpose frequently in the vertical, the thickness of single shoal body is generally small(less than 3m), the phenomenon of syngenetic exposure is rare through observation and analysis for cores and thin sections of Mao-2 member from only 10 cored wells in southern Sichuan Basin. The Gamma logging character of the multicycle superimposed, thin shoal bodies generally presents the comprehensive response of low value in the high value setting, thus it is difficult to accurately identify and calculate the thickness of grain shoals via logging data. Further analysis found that, during the development of non-exposed shoals inside carbonate platform, the grain shoals develop in microtopographic highs and have a relatively larger deposition rate, thus the depositional microtopographic highs can be approximately portrayed by the thickness variation of isochronal geological bodies that mainly composed of grainstones. Based on analysis of correlation between the thickness of isochronal geological bodies or the depositional microtopography and weathering crust karst reservoirs' development, point out the high-energy bioclastic shoals mainly present along the zonal distibutions of Luzhou-Jiangjin, Zigong-Dazu and Qingshen-Zizhong, which is controlled by the rudiment of Luzhou palaeohigh and Leshan-Longnvsi inherited palaeohigh. The results indicate that the restoration of depositional microtopography has important significance for the study of sedimentary microfacies in highly-developed borehole areas, where the drilling activity has been conducted to a high degree and only low quality of the study material can be used. This may also offer new reference to the prediction of favorable reservoir and the developing potential to the highly development layers.
2015, 33(6): 1192-1203.
doi: 10.14027/j.cnki.cjxb.2015.06.012
Abstract:
Based on a combination of core information, thin-section identification, an analysis of core properties and related analysis-testing data, the diagenesis of Palaeogene glutenite reservoir and its control on physical property in the north zone of Chezhen sag have been studied. Studies have shown that diagenesis is characterized by compaction, cementation, dissolution, lime-mud matrix recrystallization and metasomatism, the diagenetic environment underwent an evolution of alkalescence→acid→alkalescence→acid→alkalescence, and the corresponding diagenetic evolution sequence is compaction→feldspar dissolution/early quartz overgrowth→carbonate cementation/quartz dissolution→feldspar dissolution/carbonate dissolution/late quartz overgrowth→pyrite cementation. The glutenite reservoirs in research area have low porosity and permeability, and the reservoir space is mainly composed of secondary pores and cracks. The difference in lithofacies and diagenesis of different subfacies results in the difference in physical property. The inner fan is mainly composed of matrix-supported or grain-supported conglomerate,whose diagenesis is characterized by compaction or lime-mud matrix recrystallization, so dry layers develop widely in this kind of subfacies. Dissolution is intense in the middle fan, which effectively improves the reservoirs' property, so the rate of effective reservoir is high in this part. As for the fan marginal subfacies, intense cementation makes the property worse, regional dissolution makes the reservoir effective.
Based on a combination of core information, thin-section identification, an analysis of core properties and related analysis-testing data, the diagenesis of Palaeogene glutenite reservoir and its control on physical property in the north zone of Chezhen sag have been studied. Studies have shown that diagenesis is characterized by compaction, cementation, dissolution, lime-mud matrix recrystallization and metasomatism, the diagenetic environment underwent an evolution of alkalescence→acid→alkalescence→acid→alkalescence, and the corresponding diagenetic evolution sequence is compaction→feldspar dissolution/early quartz overgrowth→carbonate cementation/quartz dissolution→feldspar dissolution/carbonate dissolution/late quartz overgrowth→pyrite cementation. The glutenite reservoirs in research area have low porosity and permeability, and the reservoir space is mainly composed of secondary pores and cracks. The difference in lithofacies and diagenesis of different subfacies results in the difference in physical property. The inner fan is mainly composed of matrix-supported or grain-supported conglomerate,whose diagenesis is characterized by compaction or lime-mud matrix recrystallization, so dry layers develop widely in this kind of subfacies. Dissolution is intense in the middle fan, which effectively improves the reservoirs' property, so the rate of effective reservoir is high in this part. As for the fan marginal subfacies, intense cementation makes the property worse, regional dissolution makes the reservoir effective.
2015, 33(6): 1204-1216.
doi: 10.14027/j.cnki.cjxb.2015.06.013
Abstract:
Kaolinite is a common clay mineral of the Shahejie sandstone reservoir in Dongying sag, which has an important influence on the reservoir properties. However, the characteristics and origin of kaolinite are poorly understood. Based on data of structural evolution, fluid history and diagenetic sequence of Dongying sag, types, characteristics and origin of kaolinite were studied by using a series of techniques-rock slice, scanning electron microscope(SEM), energy dispersive X-ray(EDX) and cathodoluminescence(CL). Research results show that there are mainly two kinds of kaolinite. The first kind kaolinite has perfect crystal form and pure elements, it appears in scaly-vermiform shape under single polar and the tightly packed aggregate of kaolinite occurs as vermiform or booklet under SEM. The crystal form of the second kind kaolinite is not so perfect as the first, it appears in scaly shape under single polar light. Under the SEM some laminae is curved and the aggregate of kaolinite occurs as accordion which is packed loosely. Except for Al, Si, O, the second kind of kaolinite contains little Fe and Ca. These two kinds kaolinite in Dongying sag are mainly authigenic kaolinite, whick have been precipitated from the dissolution of feldspar in the strata acidic media relevant to the evolution of organic matter. These two kinds of kaolinite have different formation period, origin and formation circumstance, the first and the second kinds kaolinite are relative to the twice oil and gas charging of Dongying sag, respectively, which occurs in late Dongying period, late Guantao and Minghuazhen period. When the second kind kaolinite forms, sandstone enters the late diagenesis A substage period and large amounts of smectite transfer to illite, causing more Fe and Ca cation dissolved in the acid fluid.
Kaolinite is a common clay mineral of the Shahejie sandstone reservoir in Dongying sag, which has an important influence on the reservoir properties. However, the characteristics and origin of kaolinite are poorly understood. Based on data of structural evolution, fluid history and diagenetic sequence of Dongying sag, types, characteristics and origin of kaolinite were studied by using a series of techniques-rock slice, scanning electron microscope(SEM), energy dispersive X-ray(EDX) and cathodoluminescence(CL). Research results show that there are mainly two kinds of kaolinite. The first kind kaolinite has perfect crystal form and pure elements, it appears in scaly-vermiform shape under single polar and the tightly packed aggregate of kaolinite occurs as vermiform or booklet under SEM. The crystal form of the second kind kaolinite is not so perfect as the first, it appears in scaly shape under single polar light. Under the SEM some laminae is curved and the aggregate of kaolinite occurs as accordion which is packed loosely. Except for Al, Si, O, the second kind of kaolinite contains little Fe and Ca. These two kinds kaolinite in Dongying sag are mainly authigenic kaolinite, whick have been precipitated from the dissolution of feldspar in the strata acidic media relevant to the evolution of organic matter. These two kinds of kaolinite have different formation period, origin and formation circumstance, the first and the second kinds kaolinite are relative to the twice oil and gas charging of Dongying sag, respectively, which occurs in late Dongying period, late Guantao and Minghuazhen period. When the second kind kaolinite forms, sandstone enters the late diagenesis A substage period and large amounts of smectite transfer to illite, causing more Fe and Ca cation dissolved in the acid fluid.
2015, 33(6): 1217-1223.
doi: 10.14027/j.cnki.cjxb.2015.06.014
Abstract:
Through conventional section, cast section, SEM samples and constant-rate mercury injection technology, characteristics of He 8 reservoir in Gaoqiao area of Ordos Basin were studied, and its origin mechanism of tightness was analysed based on pore evolution. The following conclusions were obtained. The rock types of He 8 reservoir were mainly lithic quartz sandstone, quartz sandstone and lithic sandstone, the compositional maturity and the textural maturity of sandstone were high, but its reservoir property was low. The selectivity of sandstone was good, the initial porosity overall was higher, about 34.7% on average. On the one hand, due to the effects of rock components, buried depth, acidic fluids of coal measure hydrocarbon source rock, and the compaction was strong, 20.4% primary porosity was destructed. On the other hand, cementation destroyed 13.9% of the remaining primary porosity, leading to the complete loss of most primary pore. The compaction was destructive for the pore formed by the early dissolution, at the same time, the later dissolution was weak, only increased by 3.4% secondary porosity, it was hard to improve the reservoir property remarkably. So, in the diagenesis stage, the complete loss of most primary pore and the less formation of secondary pore common lead to the tight reservoir.
Through conventional section, cast section, SEM samples and constant-rate mercury injection technology, characteristics of He 8 reservoir in Gaoqiao area of Ordos Basin were studied, and its origin mechanism of tightness was analysed based on pore evolution. The following conclusions were obtained. The rock types of He 8 reservoir were mainly lithic quartz sandstone, quartz sandstone and lithic sandstone, the compositional maturity and the textural maturity of sandstone were high, but its reservoir property was low. The selectivity of sandstone was good, the initial porosity overall was higher, about 34.7% on average. On the one hand, due to the effects of rock components, buried depth, acidic fluids of coal measure hydrocarbon source rock, and the compaction was strong, 20.4% primary porosity was destructed. On the other hand, cementation destroyed 13.9% of the remaining primary porosity, leading to the complete loss of most primary pore. The compaction was destructive for the pore formed by the early dissolution, at the same time, the later dissolution was weak, only increased by 3.4% secondary porosity, it was hard to improve the reservoir property remarkably. So, in the diagenesis stage, the complete loss of most primary pore and the less formation of secondary pore common lead to the tight reservoir.
2015, 33(6): 1224-1234.
doi: 10.14027/j.cnki.cjxb.2015.06.015
Abstract:
The third member of Xujiahe Formation has been considered the source rocks. However, the well obtained 120.8×108 m3/d yield in gas production of the member, showing the exploration prospect being bright within the source rock of tight gas, especially in the third member of Xujiahe Formation. This article aims to use the multi-information integrated research method, to elaborately analyze sedimentary microfacies, features and sediment evolution of different sand groups, and characterize their relation with tight gas sandstone reservoir, based on the data of drilling cores, loggings and analysis assay. The result shows that braided fluvial delta was developed in the west of the study area and meandering fluvial delta was developed in the east. Among those different microfacies, braided channel, subaqueous braided main channel and subaqueous distributary channel are relatively favorable reservoirs. Meanwhile, the difference of east and west sedimentary facies configuration are obvious. In the east, thick set of subaqueous distributary channel resevoirs are distributed at the bottom, and thin set of sandstone and coal bed superimposed each other at the top. In the west, the distribution of braided channel and subaqueous braided channel sandstone are widely and stacked. And carbonaceous mudstone and coal bed with sandstone superimposed each other, appearing as a "thousand layers cake" like stacking pattern. Comparing to the east, the source rock and reservoir are closely proximity, so the west has favorable accumulation condition. The present study suggested that the future exploration would be focused on the west.
The third member of Xujiahe Formation has been considered the source rocks. However, the well obtained 120.8×108 m3/d yield in gas production of the member, showing the exploration prospect being bright within the source rock of tight gas, especially in the third member of Xujiahe Formation. This article aims to use the multi-information integrated research method, to elaborately analyze sedimentary microfacies, features and sediment evolution of different sand groups, and characterize their relation with tight gas sandstone reservoir, based on the data of drilling cores, loggings and analysis assay. The result shows that braided fluvial delta was developed in the west of the study area and meandering fluvial delta was developed in the east. Among those different microfacies, braided channel, subaqueous braided main channel and subaqueous distributary channel are relatively favorable reservoirs. Meanwhile, the difference of east and west sedimentary facies configuration are obvious. In the east, thick set of subaqueous distributary channel resevoirs are distributed at the bottom, and thin set of sandstone and coal bed superimposed each other at the top. In the west, the distribution of braided channel and subaqueous braided channel sandstone are widely and stacked. And carbonaceous mudstone and coal bed with sandstone superimposed each other, appearing as a "thousand layers cake" like stacking pattern. Comparing to the east, the source rock and reservoir are closely proximity, so the west has favorable accumulation condition. The present study suggested that the future exploration would be focused on the west.
2015, 33(6): 1235-1246.
doi: 10.14027/j.cnki.cjxb.2015.06.016
Abstract:
To clear the sedimentary characteristics of glutenite and the distribution of favourable accumulation facies, With the integrated study of core, logging, seismic and experimental analysis, this paper draw conclusions that the sedimentation in T1b, Mabei Slope subordinate to fan delta deposition, including five sedimentary microfacies as follows:braided-stream channel in fan delta plain, sandy-debris flow in fan delta plain or fan delta front, nearshore underwater-distributary channel, offshore underwater-distributary channel, and estuary dam in fan delta front. There developed two mechanism named tractive current and gravity current, and mainly developed Xiazijie fan and Huangyangquan fan. Xiazijie fan is divided into three branch-fans named FN10, XIA72, MA7. FN10 branch-fan and MA7 branch-fan are mainly developed sandy-debris flow. XIA72 branch-fan locate in Mabei heave. The slow grooves developed in Mabei heave controlled the distribution of tractive current. The intensity of reservoir diagenesis(compaction and cementation) is closely related to deposition(matrix content and granularity). Matrix content and granularity are main controlling factor of accumulation property. Transportation mechanism and sedimentary microfacies controlled the distribution of favourable accumulation facies. Sandy-debris flow deposition is poor reservoir. The different sedimentary facies belt in tractive current have different accumulation property. Braided-stream channel in fan delta plain and offshore underwater-distributary channel are sub-poor reservoir. Nearshore underwater-distributary channel and estuary dam in fan delta front are the best reservoirs. High-quality reservoir are mainly located in nearshore underwater-distributary channel, and fan delta front.
To clear the sedimentary characteristics of glutenite and the distribution of favourable accumulation facies, With the integrated study of core, logging, seismic and experimental analysis, this paper draw conclusions that the sedimentation in T1b, Mabei Slope subordinate to fan delta deposition, including five sedimentary microfacies as follows:braided-stream channel in fan delta plain, sandy-debris flow in fan delta plain or fan delta front, nearshore underwater-distributary channel, offshore underwater-distributary channel, and estuary dam in fan delta front. There developed two mechanism named tractive current and gravity current, and mainly developed Xiazijie fan and Huangyangquan fan. Xiazijie fan is divided into three branch-fans named FN10, XIA72, MA7. FN10 branch-fan and MA7 branch-fan are mainly developed sandy-debris flow. XIA72 branch-fan locate in Mabei heave. The slow grooves developed in Mabei heave controlled the distribution of tractive current. The intensity of reservoir diagenesis(compaction and cementation) is closely related to deposition(matrix content and granularity). Matrix content and granularity are main controlling factor of accumulation property. Transportation mechanism and sedimentary microfacies controlled the distribution of favourable accumulation facies. Sandy-debris flow deposition is poor reservoir. The different sedimentary facies belt in tractive current have different accumulation property. Braided-stream channel in fan delta plain and offshore underwater-distributary channel are sub-poor reservoir. Nearshore underwater-distributary channel and estuary dam in fan delta front are the best reservoirs. High-quality reservoir are mainly located in nearshore underwater-distributary channel, and fan delta front.
2015, 33(6): 1247-1257.
doi: 10.14027/j.cnki.cjxb.2015.06.017
Abstract:
This paper studies on the lithofacies, sedimentary facies, depositional models and reservoir architecture of the rudist-bearing zone of Creatures Sarvak Formation in South Azadegan oilfield of Iran by utilizing the coring, thin section, XRD data of 5 coring wells. Firstly, identified the lithofacies by the Dunham classification. Secondly, clarified the rudist-mound and tidal flat are the main microfacies in Sar-3 depositional time. Based on the regional depositional setting, we built the depositional model of Sar-3, which highlight four key points:① The rudist-buildup forming was controlled by the paleo-high; ②The build-up without the landward colonize by the regression and formation uplift, and they reach the wave-base and eroded by the high energy current, the rudist fragments were dispersed and re-deposited, forming the moundy allochthonous deposition; ③The tidal flat exists widely in the upper Sar-3 and the duration time depends on the paleo-structure, in the lower part could develop tidal deposit of several stages vertically; ④The exposure within the leaching effect by the meteoric water occurred in the late cycle, which is the main controlling factor to the reservoir architecture. From the model, we can obtain the following findings:the Sar-3 featured as the dualistic architecture layer, the lower is the rudist bearing limestone of reservoir and the upper is the tidal dense limestone of interlayer, and the thickness of each is controlled by the paleo-geomorphology, and the paleo-high is the preferential exploitable area. According to this, we proposed the horizontal well development strategy that keeping the trajectory in the middle of the oil-zone in the pale-high, in the paleo-low, assure the forepart trajectory crossing the oil-zone and then keep it in the lower part.
This paper studies on the lithofacies, sedimentary facies, depositional models and reservoir architecture of the rudist-bearing zone of Creatures Sarvak Formation in South Azadegan oilfield of Iran by utilizing the coring, thin section, XRD data of 5 coring wells. Firstly, identified the lithofacies by the Dunham classification. Secondly, clarified the rudist-mound and tidal flat are the main microfacies in Sar-3 depositional time. Based on the regional depositional setting, we built the depositional model of Sar-3, which highlight four key points:① The rudist-buildup forming was controlled by the paleo-high; ②The build-up without the landward colonize by the regression and formation uplift, and they reach the wave-base and eroded by the high energy current, the rudist fragments were dispersed and re-deposited, forming the moundy allochthonous deposition; ③The tidal flat exists widely in the upper Sar-3 and the duration time depends on the paleo-structure, in the lower part could develop tidal deposit of several stages vertically; ④The exposure within the leaching effect by the meteoric water occurred in the late cycle, which is the main controlling factor to the reservoir architecture. From the model, we can obtain the following findings:the Sar-3 featured as the dualistic architecture layer, the lower is the rudist bearing limestone of reservoir and the upper is the tidal dense limestone of interlayer, and the thickness of each is controlled by the paleo-geomorphology, and the paleo-high is the preferential exploitable area. According to this, we proposed the horizontal well development strategy that keeping the trajectory in the middle of the oil-zone in the pale-high, in the paleo-low, assure the forepart trajectory crossing the oil-zone and then keep it in the lower part.
2015, 33(6): 1258-1264.
doi: 10.14027/j.cnki.cjxb.2015.06.018
Abstract:
The study of gas shale is the hot spot in unconventional oil and gas resources exploration at home and abroad. The effective porosity of shale is an important parameter to access the reservoir property which is always the bottleneck problem and difficulty in reservoir description. It is difficult to drill a perfect cylinder from the weathered and breakable shale. Many people comminuted the samples to different sizes to get the shale porosity by measuring bulk density and skeletal density and nitrogen adsorption method. But no validated difference and effectiveness of the results between the cylinder and broken samples measurement have been shown until now. We chose twelve shale cylinders and broke the samples around the cylinders to 40~60 mesh, measurements were conducted with the three methods above, respectively. The results showed that three groups of values were different, they may be mainly controlled by experiment parameters and sample integrity. One-way analysis of variance in mathematical statistics was adopted to analyse the effectiveness of the results from the three measurement methods. Mathematical analysis showed cylinder porosity by gas expansion method and broken sample porosity in 40~60 mesh by density method and nitrogen adsorption method had no marked difference, they were consistent and effective. But, a large number of effective porosity will be destroyed in the process of crushing the samples. Overall, effective porosity measured by cylinder method is superior to the other two.
The study of gas shale is the hot spot in unconventional oil and gas resources exploration at home and abroad. The effective porosity of shale is an important parameter to access the reservoir property which is always the bottleneck problem and difficulty in reservoir description. It is difficult to drill a perfect cylinder from the weathered and breakable shale. Many people comminuted the samples to different sizes to get the shale porosity by measuring bulk density and skeletal density and nitrogen adsorption method. But no validated difference and effectiveness of the results between the cylinder and broken samples measurement have been shown until now. We chose twelve shale cylinders and broke the samples around the cylinders to 40~60 mesh, measurements were conducted with the three methods above, respectively. The results showed that three groups of values were different, they may be mainly controlled by experiment parameters and sample integrity. One-way analysis of variance in mathematical statistics was adopted to analyse the effectiveness of the results from the three measurement methods. Mathematical analysis showed cylinder porosity by gas expansion method and broken sample porosity in 40~60 mesh by density method and nitrogen adsorption method had no marked difference, they were consistent and effective. But, a large number of effective porosity will be destroyed in the process of crushing the samples. Overall, effective porosity measured by cylinder method is superior to the other two.
2015, 33(6): 1265-1274.
doi: 10.14027/j.cnki.cjxb.2015.06.019
Abstract:
Based on routine physical properties, carbon isotope and molecular geochemical analysis, this paper elaborated geochemical characteristics of heavy oil in Chagan depression and the main controlling factors of its formation systematically. There are two types of heavy oils:the primary and the secondary. The nonhydrocarbon content of primary heavy oil is higher than the saturated hydrocarbon content. Family component of heavy oils enriched lighter carbon isotope, C29 regular steranes series enriched ααα configuration, low abundance of αββ configuration steranes and no rearranged steranes. It has low tricyclene/pentacyclic terpene value, high gammacerane content, low Pr/Ph value, the oil-forming matrixes were formed under the reducing and high salt water environment, a variety of geochemical parameters indicated that the primary heavy oil derived from the hydrocarbon expulsion of hydrocarbon source rocks at low evolutionary stages. Secondary heavy oil formed after oil and gas migration and accumulation, which has high density, high viscosity and low freezing point due to the change of late preservation condition and secondary reconstruction. The depth of secondary heavy oil was generally less than 1200 meters, most of which were biodegradated oils and some of biodegradated oils experienced multiple period of accumulation. The n-alkanes and isoprenoid of secondary heavy oil suffered from degradation of different level, it indicates that the oil have reached moderate degree of degradation as steranes and terpanes distribute completely. Studies have shown that the thickening of crude oil is the result of a variety of factors worked together, biodegradation is the main formation mechanism of heavy oil in the study area, the later tectonic uplift provide necessary conditions for the crude oil thickened, and active water conditions provide both fine oxidation environment and nutrients for shallow aerobic microbe.
Based on routine physical properties, carbon isotope and molecular geochemical analysis, this paper elaborated geochemical characteristics of heavy oil in Chagan depression and the main controlling factors of its formation systematically. There are two types of heavy oils:the primary and the secondary. The nonhydrocarbon content of primary heavy oil is higher than the saturated hydrocarbon content. Family component of heavy oils enriched lighter carbon isotope, C29 regular steranes series enriched ααα configuration, low abundance of αββ configuration steranes and no rearranged steranes. It has low tricyclene/pentacyclic terpene value, high gammacerane content, low Pr/Ph value, the oil-forming matrixes were formed under the reducing and high salt water environment, a variety of geochemical parameters indicated that the primary heavy oil derived from the hydrocarbon expulsion of hydrocarbon source rocks at low evolutionary stages. Secondary heavy oil formed after oil and gas migration and accumulation, which has high density, high viscosity and low freezing point due to the change of late preservation condition and secondary reconstruction. The depth of secondary heavy oil was generally less than 1200 meters, most of which were biodegradated oils and some of biodegradated oils experienced multiple period of accumulation. The n-alkanes and isoprenoid of secondary heavy oil suffered from degradation of different level, it indicates that the oil have reached moderate degree of degradation as steranes and terpanes distribute completely. Studies have shown that the thickening of crude oil is the result of a variety of factors worked together, biodegradation is the main formation mechanism of heavy oil in the study area, the later tectonic uplift provide necessary conditions for the crude oil thickened, and active water conditions provide both fine oxidation environment and nutrients for shallow aerobic microbe.
