2006 Vol. 24, No. 4
Display Method:
2006, 24(4): 461-467.
Abstract:
The models are currently applied to model the smectite-to-illite transformation in petroleum basins using time, temperature and the composition of fluids as controlling parameters. However, small number recent studies have indicated that overpressure will retard the clay mineral transformations and enhance the activity energy of kinetic reactions. Using the data collected from both the overpressured wells and the normally pressured wells, a new kinetic model incorporating overpressure was developed, in which overpressure modifies activity energy. The model was tested in the Banqiao Sag, the Qibei Sag and the Qinan Sag of the Bohaiwan basin, China. As the results show that the computed smectite contents S% in I/S mixedlayer are coincident with the measured data, but significantly different from that predicted by Pytter and Reynolds's model(1989), and the smectite contents S% in I/S mixed-layer are retarded by 15%~20% in the overpressure formations with the pressure coefficient of 1.2～1.7. Because lots of such cations as Si4+, Ca2+, Mg2+, Fe3+ and Na+ are yielded in the smectite-to-illite conversion, the retardations of mineral transformations lead to the decrease of the action productions in the mudstones and the postpone of the cementations in the adjacent sandstones, which is propitious to develop high-quality reservoirs and to form hydrocarbon pools in the deep overpressured basin.
The models are currently applied to model the smectite-to-illite transformation in petroleum basins using time, temperature and the composition of fluids as controlling parameters. However, small number recent studies have indicated that overpressure will retard the clay mineral transformations and enhance the activity energy of kinetic reactions. Using the data collected from both the overpressured wells and the normally pressured wells, a new kinetic model incorporating overpressure was developed, in which overpressure modifies activity energy. The model was tested in the Banqiao Sag, the Qibei Sag and the Qinan Sag of the Bohaiwan basin, China. As the results show that the computed smectite contents S% in I/S mixedlayer are coincident with the measured data, but significantly different from that predicted by Pytter and Reynolds's model(1989), and the smectite contents S% in I/S mixed-layer are retarded by 15%~20% in the overpressure formations with the pressure coefficient of 1.2～1.7. Because lots of such cations as Si4+, Ca2+, Mg2+, Fe3+ and Na+ are yielded in the smectite-to-illite conversion, the retardations of mineral transformations lead to the decrease of the action productions in the mudstones and the postpone of the cementations in the adjacent sandstones, which is propitious to develop high-quality reservoirs and to form hydrocarbon pools in the deep overpressured basin.
2006, 24(4): 476-482.
Abstract:
Implied integrated sequence stratigraphy and geophysical method to analyze the 13.8Ma palaeogeomorphology of Baiyun sag, Pearl River Mouth Basin(PRMB). Submarine fan systems distribution,deposit characteristics and sequence stratigraphy filling evolvement analysis on sequence development from 13.8Ma implied that Baiyun sag lies in wide-slow continental shelf's slope area and develop two types canyons/channels on the north shelf margin , that Baiyun sag became to flat and open, and that submarine fan deposition are mainly controlled by palaeogeomorphology、sediment supply and fluctuation of climate. At the same time, north of South China Sea continental slope deepwater area’s depositional topography has been similar characteristic from 13.8Ma to today, and today’s submarine valley topography by and large implicated depositional paleo-geomorphology environment. It is concluded that deepwater deposition, which are mainly controlled by paleo-topography and evolvement rather than sea level changes, had been similar depositional topography character with today.
Implied integrated sequence stratigraphy and geophysical method to analyze the 13.8Ma palaeogeomorphology of Baiyun sag, Pearl River Mouth Basin(PRMB). Submarine fan systems distribution,deposit characteristics and sequence stratigraphy filling evolvement analysis on sequence development from 13.8Ma implied that Baiyun sag lies in wide-slow continental shelf's slope area and develop two types canyons/channels on the north shelf margin , that Baiyun sag became to flat and open, and that submarine fan deposition are mainly controlled by palaeogeomorphology、sediment supply and fluctuation of climate. At the same time, north of South China Sea continental slope deepwater area’s depositional topography has been similar characteristic from 13.8Ma to today, and today’s submarine valley topography by and large implicated depositional paleo-geomorphology environment. It is concluded that deepwater deposition, which are mainly controlled by paleo-topography and evolvement rather than sea level changes, had been similar depositional topography character with today.
2006, 24(4): 488-495.
Abstract:
The Jishan sandbody of central uplift belt of Paleogene in Huimin depression has been studied in terms of core observation and image logging datum analysis. The results show that the sedimentary dynamic mechanism for Jishan sandbody is seism, rather than flood deposition. Jishan sandbody is mainly composed of seismites(seismically disturbed), similar tsunamites and seismoturbidite rocks. A corresponding seismic sedimentary sequence and model have been established. The seismically disturbed series is crucial for analyzing the origin of Jishan sandbody, and the seismoturbidite rocks are the main body of the series. Both layers are contact with seismic unconformity plane of varied scale. During early Sha-3 period, the seismic events are resulted directly from magmatic intrusions and the upward of deep magma in origin. Magmatic intrusions and seismic events happen simultaneously at the same time and space.
The Jishan sandbody of central uplift belt of Paleogene in Huimin depression has been studied in terms of core observation and image logging datum analysis. The results show that the sedimentary dynamic mechanism for Jishan sandbody is seism, rather than flood deposition. Jishan sandbody is mainly composed of seismites(seismically disturbed), similar tsunamites and seismoturbidite rocks. A corresponding seismic sedimentary sequence and model have been established. The seismically disturbed series is crucial for analyzing the origin of Jishan sandbody, and the seismoturbidite rocks are the main body of the series. Both layers are contact with seismic unconformity plane of varied scale. During early Sha-3 period, the seismic events are resulted directly from magmatic intrusions and the upward of deep magma in origin. Magmatic intrusions and seismic events happen simultaneously at the same time and space.
2006, 24(4): 502-510.
Abstract:
This paper studies coal gas reservoir sedimentology on the basis of establishing sequence stratigraphy framework. Coal gas pool stored in sandstone (compact sandstone) reservoir of Permian system becomes important natural gas pool. In Jiyang, sandy deposit, which is mainly featured by river facies and lacustrine coastal faces, develops in Wanshan, Kuishan and Xiaofu Member of the Upper Shihezi Formation. And these three members become the main reservoir of coal gas. The main reservoir sedimentary facies is channel fill formed by channel detention and marginal bank. The main reservoir space of coal gas is induced porosity. In this area sandstone diagenesis of Carbonic-Permian system is very strong and there are less protosomatic intergmular pores. Most intergranular pore space is shaped after corrosion. Matrix or cement filled in intergranular pore space suffered from after-corrosionand then formed such heterogeneousintergranular pore space. The direct cap rock of gas pool of Permian system is mainly fluvial facies of Lower Shihezi Formation, delta plain of Shanxi Formation and Taiyuan Formation and mudstone, coal and carbargilite of limnological facies.
This paper studies coal gas reservoir sedimentology on the basis of establishing sequence stratigraphy framework. Coal gas pool stored in sandstone (compact sandstone) reservoir of Permian system becomes important natural gas pool. In Jiyang, sandy deposit, which is mainly featured by river facies and lacustrine coastal faces, develops in Wanshan, Kuishan and Xiaofu Member of the Upper Shihezi Formation. And these three members become the main reservoir of coal gas. The main reservoir sedimentary facies is channel fill formed by channel detention and marginal bank. The main reservoir space of coal gas is induced porosity. In this area sandstone diagenesis of Carbonic-Permian system is very strong and there are less protosomatic intergmular pores. Most intergranular pore space is shaped after corrosion. Matrix or cement filled in intergranular pore space suffered from after-corrosionand then formed such heterogeneousintergranular pore space. The direct cap rock of gas pool of Permian system is mainly fluvial facies of Lower Shihezi Formation, delta plain of Shanxi Formation and Taiyuan Formation and mudstone, coal and carbargilite of limnological facies.
2006, 24(4): 521-530.
Abstract:
Rich paleo-environmental and paleo-climatic formation is recorded in Tertiary successive detrital deposition of Kuqa depression. Based on detail magnetstratigraphic chronology, the color of sediments and the clay minerals of Tertiary from Kuqa depression are tested systemically. The results illustrate that there has consistent alteration trends between the color of Tertiary sediments from Kuqa depression and Tertiary global temperature change. Along the falling of global temperature, the red index of sediments decreases. The assemblages and contents of clay minerals change dramatically at 13Ma. The assemblages of clay minerals before 13Ma are illite and chlorite, and are smectite, chlorite, illite and kaolinite after 13Ma, which indicate that the climate is arid before 13Ma and alternation between dry and cold climate and warm and wet climate after 13Ma. The climatic change is consistent with enhancement of Asian inland monsoon which shows that the Tertiary climatic change of Kuqa depression at 13Ma has intimate relation with the uplift of Tibetan plateau.
Rich paleo-environmental and paleo-climatic formation is recorded in Tertiary successive detrital deposition of Kuqa depression. Based on detail magnetstratigraphic chronology, the color of sediments and the clay minerals of Tertiary from Kuqa depression are tested systemically. The results illustrate that there has consistent alteration trends between the color of Tertiary sediments from Kuqa depression and Tertiary global temperature change. Along the falling of global temperature, the red index of sediments decreases. The assemblages and contents of clay minerals change dramatically at 13Ma. The assemblages of clay minerals before 13Ma are illite and chlorite, and are smectite, chlorite, illite and kaolinite after 13Ma, which indicate that the climate is arid before 13Ma and alternation between dry and cold climate and warm and wet climate after 13Ma. The climatic change is consistent with enhancement of Asian inland monsoon which shows that the Tertiary climatic change of Kuqa depression at 13Ma has intimate relation with the uplift of Tibetan plateau.
2006, 24(4): 540-548.
Abstract:
Delta sandbody is one of the most important continental-basin hydrocarbon reservoir in China. The establishment of delta sandbody framework model in sequence stratigraphic framework is very important to the prediction of delta sandbody. Detailed high-resolution sequence stratigraphy study has been carried out on the Upper Triassic fluvial delta outcrops along the eastern margin of Ordos Basin. The basal surface of incised fluvial valley has been recognized as the boundary of a 3rd order base level cycle. Furthermore, delta sandbody framework prototype model and the evolutionary model of deltaplain distributary channel style in a 3rd order base level cycle have been established. This study demonstrate that the incision, aggradation, migration, overflow and style change of delta plain distributary channel or fluvial channel should be happen regularly in response to different base-level rise and fall rate in a 3rd order base level cycle, which make difference to the type, shape, scale and connectivity of delta sandbody in sequence stratigrphic framework. The discovery of this rule is important to the prediction of delta sandbody and the stratigraphic-trap forming condition analysis. Furthermore study of sandbody distribution in sequence stratigrphic framework under different geological conditions is helpful to the realization of the study object of sequence stratigrphy-“interpretable in genesis and predictable in space-time”.
Delta sandbody is one of the most important continental-basin hydrocarbon reservoir in China. The establishment of delta sandbody framework model in sequence stratigraphic framework is very important to the prediction of delta sandbody. Detailed high-resolution sequence stratigraphy study has been carried out on the Upper Triassic fluvial delta outcrops along the eastern margin of Ordos Basin. The basal surface of incised fluvial valley has been recognized as the boundary of a 3rd order base level cycle. Furthermore, delta sandbody framework prototype model and the evolutionary model of deltaplain distributary channel style in a 3rd order base level cycle have been established. This study demonstrate that the incision, aggradation, migration, overflow and style change of delta plain distributary channel or fluvial channel should be happen regularly in response to different base-level rise and fall rate in a 3rd order base level cycle, which make difference to the type, shape, scale and connectivity of delta sandbody in sequence stratigrphic framework. The discovery of this rule is important to the prediction of delta sandbody and the stratigraphic-trap forming condition analysis. Furthermore study of sandbody distribution in sequence stratigrphic framework under different geological conditions is helpful to the realization of the study object of sequence stratigrphy-“interpretable in genesis and predictable in space-time”.
2006, 24(4): 555-561.
Abstract:
Tidal salt-marshes represent an important part in a coastal wetland system，and it also becomes a key study objective of land-ocean interaction in coastal zone due to the marked human activities and the sensitivity of the areas in response to global change. Sediment cores as a traditional and primary instrument for studying the sedimentary environments and depositional processes of tidal flat are taken generally by gravity corer in inter-tidal flat. Wherever sediment cores were collected by gravity corer，the length of the cores became shorter than the original length，and this compaction processes take place not only inside the sampling tube but also beneath the bottom of the sampling tube. Nine sediment cores were collected by gravity method in the inter-tidal flat of Wanggang which is located on the central coastline of Jiangsu Province，the depth variations of sampling tube were recorded in situ，and the samples were analyzed for grain size by a laser particle analyzer in laboratory. According to the field records and analysis results indoor，both compactions taking placing inside and beneath the sampling tube are linear process；the compaction ratio inside the sampling tube relate to water content of sediment and sorting coefficient，viz. the higher water content and the worse sorted，the higher compaction ratio. According to the calculated results，the length of the compaction beneath the sampling tube is 11% as much as that inside， the compaction length beneath the sampling tube increases with the increasing of compaction ratio inside，and the function of compaction taking placing beneath the sampling tube is more remarkable.
Tidal salt-marshes represent an important part in a coastal wetland system，and it also becomes a key study objective of land-ocean interaction in coastal zone due to the marked human activities and the sensitivity of the areas in response to global change. Sediment cores as a traditional and primary instrument for studying the sedimentary environments and depositional processes of tidal flat are taken generally by gravity corer in inter-tidal flat. Wherever sediment cores were collected by gravity corer，the length of the cores became shorter than the original length，and this compaction processes take place not only inside the sampling tube but also beneath the bottom of the sampling tube. Nine sediment cores were collected by gravity method in the inter-tidal flat of Wanggang which is located on the central coastline of Jiangsu Province，the depth variations of sampling tube were recorded in situ，and the samples were analyzed for grain size by a laser particle analyzer in laboratory. According to the field records and analysis results indoor，both compactions taking placing inside and beneath the sampling tube are linear process；the compaction ratio inside the sampling tube relate to water content of sediment and sorting coefficient，viz. the higher water content and the worse sorted，the higher compaction ratio. According to the calculated results，the length of the compaction beneath the sampling tube is 11% as much as that inside， the compaction length beneath the sampling tube increases with the increasing of compaction ratio inside，and the function of compaction taking placing beneath the sampling tube is more remarkable.
2006, 24(4): 570-578.
Abstract:
The study of the detrital minerals of Changjiang sediments indicates that the light minerals mainly consist of quartz, feldspar and lithic fragment. The light mineral assemblages are different between the tributaries, and the mature index increases downstream with an average of 2.0. The diagrams of QFL and QtFL show that the Changjiang sediments are primarily sourced from recycled orogenic provenance due to stronger tectonic erosion and weathering in the river basin. The main assemblages of heavy minerals include magnetite, common hornblende, augite, garnet, epidote, limonite and ilmenite. Among which, andalusite and apatite are characteristic minerals of the Jinshajiang, cyanite is typical in the Minjiang, sphene and zircon abound in the Fujiang and Xiangjiang respectively, while the Hanjiang is relatively rich in apatite, hypersthene and humite. The distributions of characteristic minerals in the tributaries are obviously controlled by source rock types in the drainage basins. The sediments from the Yalongjiang, Daduhe and Minjiang contribute little to the middle-lower Changjiang reaches. The indexes of heavy minerals indicate that the heavy minerals in the river upstream Fuling are mainly provided by sedimentary rocks whereas the river sediments downstream Fuling are mixed by different source rocks with a large contribution form local magmatic and metamorphic rocks. In contrast, the sediments from the Xiangjiang and Yuanjiang are largely provided from low-and medium-grade metamorphic rocks.
The study of the detrital minerals of Changjiang sediments indicates that the light minerals mainly consist of quartz, feldspar and lithic fragment. The light mineral assemblages are different between the tributaries, and the mature index increases downstream with an average of 2.0. The diagrams of QFL and QtFL show that the Changjiang sediments are primarily sourced from recycled orogenic provenance due to stronger tectonic erosion and weathering in the river basin. The main assemblages of heavy minerals include magnetite, common hornblende, augite, garnet, epidote, limonite and ilmenite. Among which, andalusite and apatite are characteristic minerals of the Jinshajiang, cyanite is typical in the Minjiang, sphene and zircon abound in the Fujiang and Xiangjiang respectively, while the Hanjiang is relatively rich in apatite, hypersthene and humite. The distributions of characteristic minerals in the tributaries are obviously controlled by source rock types in the drainage basins. The sediments from the Yalongjiang, Daduhe and Minjiang contribute little to the middle-lower Changjiang reaches. The indexes of heavy minerals indicate that the heavy minerals in the river upstream Fuling are mainly provided by sedimentary rocks whereas the river sediments downstream Fuling are mixed by different source rocks with a large contribution form local magmatic and metamorphic rocks. In contrast, the sediments from the Xiangjiang and Yuanjiang are largely provided from low-and medium-grade metamorphic rocks.
2006, 24(4): 585-589.
Abstract:
It is very significant to determine the maturation threshold of primary hydrocarbon generation of source rock for evaluating the resource quantity of natural gas in gas-bearing basin and determining the primary period of hydrocarbon generation. The authors have done some thermal simulating experiments (at 800℃) on fifteen humic coal samples with different maturity and measured the content of hydrogen, carbon and oxygen elements. The result indicates that total hydrocarbon generation of low maturation coal is high, the amount of the hydrocarbon generation reduce gradually with the increase of maturation, when the value of Ro is between 0.6% and 2.3%, the decreasing scope of hydrocarbon generation is very large, from 61 m3/t·TOC to 11m3/t·TOC, While the value of Ro reach 2.3%, the hydrocarbon generation is very low, it decrease slowly with the increase of maturation. At the same time, we can see the similar variety rule about the value of H/C with different maturation, when the value of Ro is less than 2.3%, the value of H/C decrease fast with the increase of maturation, the value of H/C reduce slowly. So it can be considered that maturation threshold of kerogen cracking gas generation of humic coal is that the value of Ro equal to 2.3%.
It is very significant to determine the maturation threshold of primary hydrocarbon generation of source rock for evaluating the resource quantity of natural gas in gas-bearing basin and determining the primary period of hydrocarbon generation. The authors have done some thermal simulating experiments (at 800℃) on fifteen humic coal samples with different maturity and measured the content of hydrogen, carbon and oxygen elements. The result indicates that total hydrocarbon generation of low maturation coal is high, the amount of the hydrocarbon generation reduce gradually with the increase of maturation, when the value of Ro is between 0.6% and 2.3%, the decreasing scope of hydrocarbon generation is very large, from 61 m3/t·TOC to 11m3/t·TOC, While the value of Ro reach 2.3%, the hydrocarbon generation is very low, it decrease slowly with the increase of maturation. At the same time, we can see the similar variety rule about the value of H/C with different maturation, when the value of Ro is less than 2.3%, the value of H/C decrease fast with the increase of maturation, the value of H/C reduce slowly. So it can be considered that maturation threshold of kerogen cracking gas generation of humic coal is that the value of Ro equal to 2.3%.
2006, 24(4): 596-606.
Abstract:
The symbiosis between hydrocarbon and evaporate indicate the affiliation of evaporate and generation of hydrocarbon. From the view of conservation of organic matter, the water body in evaporates basin takes on the character of density stratification; the niederschlag below mascon has high oxidationreduction potential, which contribute to the conservation of organic matter. From the view of generation of hydrocarbon, bacteria, algae and lithology on the bottom of salt-water basin play important role in generation of hydrocarbon; furthermore, clunch from the redbeds acting as catalyzer, alkali metals making the hydrocarbon mobile. Deep-water cause of evaporate formation indicate the large potential for oil and gas exploration in Dongpu Depression.
The symbiosis between hydrocarbon and evaporate indicate the affiliation of evaporate and generation of hydrocarbon. From the view of conservation of organic matter, the water body in evaporates basin takes on the character of density stratification; the niederschlag below mascon has high oxidationreduction potential, which contribute to the conservation of organic matter. From the view of generation of hydrocarbon, bacteria, algae and lithology on the bottom of salt-water basin play important role in generation of hydrocarbon; furthermore, clunch from the redbeds acting as catalyzer, alkali metals making the hydrocarbon mobile. Deep-water cause of evaporate formation indicate the large potential for oil and gas exploration in Dongpu Depression.
2006, 24(4): 468-475.
Abstract:
Transgressive storm-dominated shore-neritic sedimentary system was developed in the lower bitumen-bearing sandstone member during Silurian period of Tazhong area in Tarim basin. The types of sandbody are shore sandbody, neritic sand bar and shelf sand in the lower bitumen-bearing sandstone member. After the storm, the distribution of shelf sand became larger than before. The physical property of sandstone during progression is better than that of sandstone of tidal flat during marine regression. There are many different characters on the sand bodies, and the shoreneritic sand bodies are the very important reservoir for the stratigraphic traps.
Transgressive storm-dominated shore-neritic sedimentary system was developed in the lower bitumen-bearing sandstone member during Silurian period of Tazhong area in Tarim basin. The types of sandbody are shore sandbody, neritic sand bar and shelf sand in the lower bitumen-bearing sandstone member. After the storm, the distribution of shelf sand became larger than before. The physical property of sandstone during progression is better than that of sandstone of tidal flat during marine regression. There are many different characters on the sand bodies, and the shoreneritic sand bodies are the very important reservoir for the stratigraphic traps.
2006, 24(4): 483-487.
Abstract:
Crushed fracture in clastic rock is created under great press from the gravity of over layer or giant stress by sides, as the contact point of the grain bear big intensity of pressure than others. As the crushed fracture are distributed only within the grain, it can be distinguished from the fracture created by tectonic stress. By studying the crushed fracture in clastic rock of the oil & gas-bearing basin in the western China, it can be seen that the development degree of the crushed fracture has close relation to grain size, type of detrital minerals and the amount of interstitial material. The crushed fracture is easier developed in the coarse-sand rock and conglomerate, and the grains that developed crushed fracture are mostly rigid or come from tuff and lava. Under the same grain size and type of detrital minerals, the development degree of crushed fracture has close relation with the scale of interstitial material in rock. As the fracture can be created in the press of the gravity of overburden rock, and the fracture provide space for oil and gas, it will enlarge the field of petroleum exploration, at the same time, it have great significance in improving oil recovery.
Crushed fracture in clastic rock is created under great press from the gravity of over layer or giant stress by sides, as the contact point of the grain bear big intensity of pressure than others. As the crushed fracture are distributed only within the grain, it can be distinguished from the fracture created by tectonic stress. By studying the crushed fracture in clastic rock of the oil & gas-bearing basin in the western China, it can be seen that the development degree of the crushed fracture has close relation to grain size, type of detrital minerals and the amount of interstitial material. The crushed fracture is easier developed in the coarse-sand rock and conglomerate, and the grains that developed crushed fracture are mostly rigid or come from tuff and lava. Under the same grain size and type of detrital minerals, the development degree of crushed fracture has close relation with the scale of interstitial material in rock. As the fracture can be created in the press of the gravity of overburden rock, and the fracture provide space for oil and gas, it will enlarge the field of petroleum exploration, at the same time, it have great significance in improving oil recovery.
2006, 24(4): 496-501.
Abstract:
In the Yishu fault zone and its surrounding area, seismites have been discovered in four horizons, i.e. Sinian Shiwangzhuang Formation, Cambrian Mantou Formation, Paleogene Zhubidian Formation and Shahejie Formation. All of Seismites are seismo-depositional layers with the liquefied vein structure and other seismogenesis intra-layer structures. Through some correlation and analysis in many ways, it is confirmed that liquefied vein structures of different horizons possess some alike or common features, which reflects that the origin of liquefied vein structures is identical in different geological periods. It is considered that Precambrian“molar tooth structure” with common features of liquefied vein structures is called “liquefied vein structure of micrite-sparry limestone”best.
In the Yishu fault zone and its surrounding area, seismites have been discovered in four horizons, i.e. Sinian Shiwangzhuang Formation, Cambrian Mantou Formation, Paleogene Zhubidian Formation and Shahejie Formation. All of Seismites are seismo-depositional layers with the liquefied vein structure and other seismogenesis intra-layer structures. Through some correlation and analysis in many ways, it is confirmed that liquefied vein structures of different horizons possess some alike or common features, which reflects that the origin of liquefied vein structures is identical in different geological periods. It is considered that Precambrian“molar tooth structure” with common features of liquefied vein structures is called “liquefied vein structure of micrite-sparry limestone”best.
2006, 24(4): 511-520.
Abstract:
The Late Triassic Batang group in south Qinghai are located in the south of Jinshajiang suture, the research degree is relatively lower with the complicated geological structures, and still there are disputes in the division of the strata sequences. Based on 1∶〖KG-*2〗250000 regional geology investigation, the Batang group in this article was subdivided into lower Formation, middle Formation and upper Formation in ascending order by the actual section survey and the region contrast. This article analyzed the lithologic combination, the biota appearance, the geological age of the Batang group. At the same time, using the gravity current micrite, the pillow shape basalt, the Bouma sequence turbidite and the structure setting of volcanic rock, discuss preliminary the developing process of the sedimentary environments and tectonic settings in research area, our works have provided the basic data for the research of Batang group.
The Late Triassic Batang group in south Qinghai are located in the south of Jinshajiang suture, the research degree is relatively lower with the complicated geological structures, and still there are disputes in the division of the strata sequences. Based on 1∶〖KG-*2〗250000 regional geology investigation, the Batang group in this article was subdivided into lower Formation, middle Formation and upper Formation in ascending order by the actual section survey and the region contrast. This article analyzed the lithologic combination, the biota appearance, the geological age of the Batang group. At the same time, using the gravity current micrite, the pillow shape basalt, the Bouma sequence turbidite and the structure setting of volcanic rock, discuss preliminary the developing process of the sedimentary environments and tectonic settings in research area, our works have provided the basic data for the research of Batang group.
2006, 24(4): 531-539.
Abstract:
The grain size of loess and paleosol sequence is regarded as one of the most important proxies to reconstruct paleoenvironment. To obtain the reliable information of climate changes, it is necessary to measure the grain size accurately. Using Mastersize2000 Laser Grain-size Analyzer, grain size of loesspalaeosol samples taken from the typical S4 soil section of Luochuan is studied through multi-preparing processes. The results show that the error of grain size measurement originates from two kinds of aspects: measurement accuracy of the machine itself and samples pretreatment processes. On the experiment, pretreatment of samples is the primary influence factor. At the same time, it was found that credible data are not obtained only through one time measurement, but more time measurements are necessary, and the average result can be used as climate proxy. But this method may made the information of rapid climate changes lost, and made changing range of the grain size inconspicuous which is affected by smoothness of the wave crest shape.
The grain size of loess and paleosol sequence is regarded as one of the most important proxies to reconstruct paleoenvironment. To obtain the reliable information of climate changes, it is necessary to measure the grain size accurately. Using Mastersize2000 Laser Grain-size Analyzer, grain size of loesspalaeosol samples taken from the typical S4 soil section of Luochuan is studied through multi-preparing processes. The results show that the error of grain size measurement originates from two kinds of aspects: measurement accuracy of the machine itself and samples pretreatment processes. On the experiment, pretreatment of samples is the primary influence factor. At the same time, it was found that credible data are not obtained only through one time measurement, but more time measurements are necessary, and the average result can be used as climate proxy. But this method may made the information of rapid climate changes lost, and made changing range of the grain size inconspicuous which is affected by smoothness of the wave crest shape.
2006, 24(4): 549-554.
Abstract:
At Late Triassic, Ordos Basin is an asymmetry depressed-type lacustrine basin with gentle slope in the east and steep slope in the west. By the research of core, logging profiles and seismic data, four types of sedimentary facies have been recognized. Among these sedimentary facies, river facies and turbidity fans are found on the steep slope in the west of the depression, while braid river deltas are found on both the steep slope in the west and the gentle in the east of the depression. Based on the classic pattern of sequence stratigraphic framework, five three-order sequences have been identified in Yanchang formation, Longdong area. Five times of lake transgression can be distinguished. The sequence evolution is that they formed in early time, reached the maximum in middle time and declined in late time. Fischer's plots of Yanchang formation stratigraphy are scaled with retrieved stratigraphic thickness in Longdong area. There are well corresponding relations between the plots and five times of lake transgression. The classification of the sequence stratigraphy has been verified by using Fischer's plots, which may be a potential tool for sequence analysis.
At Late Triassic, Ordos Basin is an asymmetry depressed-type lacustrine basin with gentle slope in the east and steep slope in the west. By the research of core, logging profiles and seismic data, four types of sedimentary facies have been recognized. Among these sedimentary facies, river facies and turbidity fans are found on the steep slope in the west of the depression, while braid river deltas are found on both the steep slope in the west and the gentle in the east of the depression. Based on the classic pattern of sequence stratigraphic framework, five three-order sequences have been identified in Yanchang formation, Longdong area. Five times of lake transgression can be distinguished. The sequence evolution is that they formed in early time, reached the maximum in middle time and declined in late time. Fischer's plots of Yanchang formation stratigraphy are scaled with retrieved stratigraphic thickness in Longdong area. There are well corresponding relations between the plots and five times of lake transgression. The classification of the sequence stratigraphy has been verified by using Fischer's plots, which may be a potential tool for sequence analysis.
2006, 24(4): 562-569.
Abstract:
Field observation on the formation and development process of silt-mud couplets is carried out on tidal flat of the middle Jiangsu province. Combined the observation result with the calculation of sedimentation quantity and the analysis of grain-size and roundness of sedimentary particles, the mechanism of silt-mud couplets is revealed in this area. One thin silt-mud couplet with the thickness of millimeters is formed during a flood-ebb tidal cycle, and one thick couplet with the thickness of centimeters is formed during a spring-neap tidal cycle.In addition to the research on the formation of silt-mud couplets, the field observation on the tidal flat is carried out before and after the storm surge for typhoon No. 9711. The result shows that even during storm surge period, high tidal flat can still be in sedimentation over some places, no erosion occurred. Compared with the normal tidal flat sedimentation, the storm sedimentation has the characteristics of coarse particle, bad sorting, relatively high roundness, obviously graded bedding, typical parallel bedding, cross bedding.
Field observation on the formation and development process of silt-mud couplets is carried out on tidal flat of the middle Jiangsu province. Combined the observation result with the calculation of sedimentation quantity and the analysis of grain-size and roundness of sedimentary particles, the mechanism of silt-mud couplets is revealed in this area. One thin silt-mud couplet with the thickness of millimeters is formed during a flood-ebb tidal cycle, and one thick couplet with the thickness of centimeters is formed during a spring-neap tidal cycle.In addition to the research on the formation of silt-mud couplets, the field observation on the tidal flat is carried out before and after the storm surge for typhoon No. 9711. The result shows that even during storm surge period, high tidal flat can still be in sedimentation over some places, no erosion occurred. Compared with the normal tidal flat sedimentation, the storm sedimentation has the characteristics of coarse particle, bad sorting, relatively high roundness, obviously graded bedding, typical parallel bedding, cross bedding.
2006, 24(4): 579-584.
Abstract:
Based on analysis of total phosphorus, horizontal and vertical characteristics of sediments in Wuliangsuhai Lake are discussed. The results indicate that the content of total phosphorus in surface sediments ranges from 0.37 to 0.99 g·kg-1, with mean content of 0.75 g·kg-1. The horizontal distribution of TP had decreasing trend from bank to center and the content of TP in surface sediment of most the lake districts had certain ecological toxic effects. The vertical distribution of TP in the sediment core is various, which indicate that effluents from human activity influence TP contents. The sequence of TP contents is silt, clay＞very fine sand ＞fine sand＞medium sand, TP enriched in the sediments with grains smaller than 63 micron in diameter. The adsorption contribution rates of TP are under the control of adsorbability and mass percenage. Sediment internal load would be a dominant factor controlling water quality when external load was reduced or cut off in Wuliangsuhai Lake.
Based on analysis of total phosphorus, horizontal and vertical characteristics of sediments in Wuliangsuhai Lake are discussed. The results indicate that the content of total phosphorus in surface sediments ranges from 0.37 to 0.99 g·kg-1, with mean content of 0.75 g·kg-1. The horizontal distribution of TP had decreasing trend from bank to center and the content of TP in surface sediment of most the lake districts had certain ecological toxic effects. The vertical distribution of TP in the sediment core is various, which indicate that effluents from human activity influence TP contents. The sequence of TP contents is silt, clay＞very fine sand ＞fine sand＞medium sand, TP enriched in the sediments with grains smaller than 63 micron in diameter. The adsorption contribution rates of TP are under the control of adsorbability and mass percenage. Sediment internal load would be a dominant factor controlling water quality when external load was reduced or cut off in Wuliangsuhai Lake.
2006, 24(4): 590-595.
Abstract:
The main oils of Jiuxi Depression have single characteristics of biomarker, it shows that the tricyclic terpane, C29-norhopane, C30-rearranged hopane and diasterane's content of these oils are low, gammacerane's content is high relatively and the isomerization parameter of sterane is lower,it is from 0.45 to 0.5, So it didn′t close to the terminal point of isomerization and it's source rock′s maturity isn′t high. This type oil is mainly from the laminar algal shaly dolomite of Xiagou formation that deposited in the reduction environment of Qingxi Depression region. Besides, there have another type of oil which it′s biomarker characteristics are different from the main part. These oils have relatively higher content of tricyclic terpane, C29-norhopane, C30-rearranged hopane ,diasterane and gammacerane, and part of it (such as the oils from long8,long4 and long10 wells) have high maturity. The isomerization parameter of sterane of these oils may reach from 0.56 to 0.58(it has closed to the terminal point of isomerization); it is the highest maturity oil of Jiuxi Depression. Especially, the main oils of this type have higher amount of C29ββ/(ββ+αα), it means that this oils have long distance migration. According to the result of analysis of depositional environment and native source precursor and contrast it with the oils which mainly from the Chijinbu formation of Jiudong Depression, we hold that those oils which have unusual biomarker characteristics might be in relation to the Chijinbu formation from deep part of Qingxi Depression.This viewpoint will have practical significance to the exploration of deep oil and gas in Jiuquan basin.
The main oils of Jiuxi Depression have single characteristics of biomarker, it shows that the tricyclic terpane, C29-norhopane, C30-rearranged hopane and diasterane's content of these oils are low, gammacerane's content is high relatively and the isomerization parameter of sterane is lower,it is from 0.45 to 0.5, So it didn′t close to the terminal point of isomerization and it's source rock′s maturity isn′t high. This type oil is mainly from the laminar algal shaly dolomite of Xiagou formation that deposited in the reduction environment of Qingxi Depression region. Besides, there have another type of oil which it′s biomarker characteristics are different from the main part. These oils have relatively higher content of tricyclic terpane, C29-norhopane, C30-rearranged hopane ,diasterane and gammacerane, and part of it (such as the oils from long8,long4 and long10 wells) have high maturity. The isomerization parameter of sterane of these oils may reach from 0.56 to 0.58(it has closed to the terminal point of isomerization); it is the highest maturity oil of Jiuxi Depression. Especially, the main oils of this type have higher amount of C29ββ/(ββ+αα), it means that this oils have long distance migration. According to the result of analysis of depositional environment and native source precursor and contrast it with the oils which mainly from the Chijinbu formation of Jiudong Depression, we hold that those oils which have unusual biomarker characteristics might be in relation to the Chijinbu formation from deep part of Qingxi Depression.This viewpoint will have practical significance to the exploration of deep oil and gas in Jiuquan basin.
2006, 24(4): 607-615.
Abstract:
Rapid and continuous deposition and large thickness, as well as high heat flow, high geotherm and high content of organic matters characterize source rocks in Dongying depression. Large thickness of mudstones are developed in the main source rock intervals (3rd and 4th of Shahejie Formation). Source rocks are mainly deposited in the forms mudstone inlaid with sandstone, sandstone enclosed within mudstone and pure mudstones. As a result, over pressured systems are well developed in the main source rock intervals, and episodic expulsion becomes the fundamental mode of hydrocarbon expulsion in Dongying depression. The over-pressured systems form over-pressured fluid compartments (OPC) in vary levels that control the hydrocarbon migration and accumulation. The compartments could be divided into three parts according to the geochemical characteristics: the edge of compartment (seal), which hold up the hydrocarbon migration to outside; the favorable releasing zone for hydrocarbon, in which over-pressure was released to some degree and hydrocarbon was expelled efficiently; the stagnant zone for hydrocarbon, in which the over-pressure remains and the hydrocarbon is stagnant relatively. The episodic hydrocarbon-expulsion can be classified as “tectonic episode” and “pressure episode” based on the different mechanisms. The mechanism of “tectonic episode” is a destruction caused by tectonic activities, and hydrocarbons migrate along fault planes, while the mechanism of “pressure episode” is the accumulation and release of the “residual energy” in the over pressured systems, and hydrocarbons migrate along microfissures induced from fracturing. Episodic hydrocarbon-expulsion of OPC has important significance in petroleum exploration in Dongying depression, due to its characteristics of high energy and rapid migration.With the exception of the stagnant fluid dynamics system, there are two kinds of fluid dynamic systems in Dongying depression: normal-pressured open fluid dynamics system and OPC fluid dynamics system, which results in two accumulation dynamic mechanisms: one was self-sourced and sealed dynamic mechanism, another was outward-sourced and opened mechanism. OPC is moving and changing at all times, so all the geological behaviors should be investigated by historical and developmental eye.
Rapid and continuous deposition and large thickness, as well as high heat flow, high geotherm and high content of organic matters characterize source rocks in Dongying depression. Large thickness of mudstones are developed in the main source rock intervals (3rd and 4th of Shahejie Formation). Source rocks are mainly deposited in the forms mudstone inlaid with sandstone, sandstone enclosed within mudstone and pure mudstones. As a result, over pressured systems are well developed in the main source rock intervals, and episodic expulsion becomes the fundamental mode of hydrocarbon expulsion in Dongying depression. The over-pressured systems form over-pressured fluid compartments (OPC) in vary levels that control the hydrocarbon migration and accumulation. The compartments could be divided into three parts according to the geochemical characteristics: the edge of compartment (seal), which hold up the hydrocarbon migration to outside; the favorable releasing zone for hydrocarbon, in which over-pressure was released to some degree and hydrocarbon was expelled efficiently; the stagnant zone for hydrocarbon, in which the over-pressure remains and the hydrocarbon is stagnant relatively. The episodic hydrocarbon-expulsion can be classified as “tectonic episode” and “pressure episode” based on the different mechanisms. The mechanism of “tectonic episode” is a destruction caused by tectonic activities, and hydrocarbons migrate along fault planes, while the mechanism of “pressure episode” is the accumulation and release of the “residual energy” in the over pressured systems, and hydrocarbons migrate along microfissures induced from fracturing. Episodic hydrocarbon-expulsion of OPC has important significance in petroleum exploration in Dongying depression, due to its characteristics of high energy and rapid migration.With the exception of the stagnant fluid dynamics system, there are two kinds of fluid dynamic systems in Dongying depression: normal-pressured open fluid dynamics system and OPC fluid dynamics system, which results in two accumulation dynamic mechanisms: one was self-sourced and sealed dynamic mechanism, another was outward-sourced and opened mechanism. OPC is moving and changing at all times, so all the geological behaviors should be investigated by historical and developmental eye.
