2004 Vol. 22, No. 2
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Display Method:
2004, 22(2): 183-192.
Abstract:
Progress in Chinese fluvial sedimentology, beginning with the initial issue of ACTA SEDIMENTOLOGICA SINICA in 1983, have been reviewed respectively from the aspects of classification of stream, modern present deposits investigation, fluvial facies and depositional models, fluvial deposits sequence stratigraphy, fluvial architecture element analysis and fluvial sedimentological simulation. The great achievements, which have been made in this duration by Chinese fluvial sedimentologists, including the application of the new concepts of anastomosing stream, architecture element analysis, lithofacies and facies assemblages, sedimentary structure research, outcrop investigation, physical and digital simulation of fluvial sedimentology and fluvial sequence stratigraphy, have been concluded in this paper. However, there are no our own new theory which has been known worldwide.To make Chinese fluvial sedimentology front rank in the world fluvial sedimentology, the organization of such research should be reinforced, achievements in geography and hydrology should be absorbed, the domain of the research should be expanded with the demanding of the gradual development of the social economy , international exchange activities should be encouraged positively.
Progress in Chinese fluvial sedimentology, beginning with the initial issue of ACTA SEDIMENTOLOGICA SINICA in 1983, have been reviewed respectively from the aspects of classification of stream, modern present deposits investigation, fluvial facies and depositional models, fluvial deposits sequence stratigraphy, fluvial architecture element analysis and fluvial sedimentological simulation. The great achievements, which have been made in this duration by Chinese fluvial sedimentologists, including the application of the new concepts of anastomosing stream, architecture element analysis, lithofacies and facies assemblages, sedimentary structure research, outcrop investigation, physical and digital simulation of fluvial sedimentology and fluvial sequence stratigraphy, have been concluded in this paper. However, there are no our own new theory which has been known worldwide.To make Chinese fluvial sedimentology front rank in the world fluvial sedimentology, the organization of such research should be reinforced, achievements in geography and hydrology should be absorbed, the domain of the research should be expanded with the demanding of the gradual development of the social economy , international exchange activities should be encouraged positively.
2004, 22(2): 206-215.
Abstract:
The Altun rift system, located in the western Qaidam Basin, is a key large-scale thrusting-sliding rift system, by which, the two great basins—Qaidam and Tarim are separated. The fan-delta, which is themain subject in this paper, is well developed in theTertiarystratum of the western Altun slope, next to the referredrift system above, that is in thenorth boundary of thewestern Qaidam Basin. With the help of the analyses of thetectonic dynamical evolution in Cenozoic era, thesupplying speed of thesediments, the augmentof the accommodation, thequalities of thebasin boundary, the distance between the source area and thebasin, as well as thedelicate description of theoutcrops and the discussion of their sedimentary characters, it is believed that, two kinds of sequenceseries are developed in thestudy area,i.e. the retrograded fan deltas and the prograded one. According to the studies above, two sedimentary models of thefan deltas have been illustrated considering the differences of the tectonic dynamicssettings. From our study, it is clear that, thecombination of the generating rocks, the reservoirsand the caprocks in thewestern parts of theAltun slope is fairly ideal. Thegyttjadark mudstones, distributed in theupside of the low-Gan Chaigou Group, are theprimary hydrocarbon source rocks; and thesand bodies of the subaquaticdistributary channels, the bars in the prograded fan delta and the braided channels in retrograded one can offer a good space for thepreserving and pooling of oil, and therefore, it is themost important object for theoil exploration in this area. The study of theTertiarfan deltas in the western Altun slope can offer a solid scientific base for the further study of thegeneration of theAltun Orogen.
The Altun rift system, located in the western Qaidam Basin, is a key large-scale thrusting-sliding rift system, by which, the two great basins—Qaidam and Tarim are separated. The fan-delta, which is themain subject in this paper, is well developed in theTertiarystratum of the western Altun slope, next to the referredrift system above, that is in thenorth boundary of thewestern Qaidam Basin. With the help of the analyses of thetectonic dynamical evolution in Cenozoic era, thesupplying speed of thesediments, the augmentof the accommodation, thequalities of thebasin boundary, the distance between the source area and thebasin, as well as thedelicate description of theoutcrops and the discussion of their sedimentary characters, it is believed that, two kinds of sequenceseries are developed in thestudy area,i.e. the retrograded fan deltas and the prograded one. According to the studies above, two sedimentary models of thefan deltas have been illustrated considering the differences of the tectonic dynamicssettings. From our study, it is clear that, thecombination of the generating rocks, the reservoirsand the caprocks in thewestern parts of theAltun slope is fairly ideal. Thegyttjadark mudstones, distributed in theupside of the low-Gan Chaigou Group, are theprimary hydrocarbon source rocks; and thesand bodies of the subaquaticdistributary channels, the bars in the prograded fan delta and the braided channels in retrograded one can offer a good space for thepreserving and pooling of oil, and therefore, it is themost important object for theoil exploration in this area. The study of theTertiarfan deltas in the western Altun slope can offer a solid scientific base for the further study of thegeneration of theAltun Orogen.
2004, 22(2): 225-233.
Abstract:
Sedimentation during stage of Chang-8 deposition was controlled by a lacustrine delta system.The Chang-8 member is an important finger-bar reservoir-sandstone in Qingyang area. Sandstone reservoirs can be classified as compositionally immature feldspathic lithareniteand lithic arkose. The main diagenetic minerals of thesandstones include: authigenetic clayminerals, calcite cement, quartz overgrowth, albiteand later ferroan carbonate. Authigenic quartz overgrowths and micro-crystals contain a variety of organic fluid inclusions that indicate the petroleum filling history. Petroleum filling history showsthat the significant later filling process affectedreservoir quality.Porosity preservation caused by grain-coating , authigenic chlorite. Wide porosity variations in sandstones correlate with an abundance of grain-coating chlorite and consequent inhibition of quartz cementation. Secondary porosity has created mainly by feldspar, rock fragment and clay matrix dissolution. The dissolution mechanisim is closely related to organic acids and transformation of clayminerals in adjacentsource rocks. Based on diagenetic events related to temperature, reservoir diagenetic stages can be dividedinto A-substage of later diagenesis. Reservoir quality is controlled mostly by sedimentary microfacies and diagenesis. Subaquoeus distributary channeland mouth barsandbodies commonly have high porosity and permeability, whereas interdistributary and distal sandsheets may have low petrophysical properties.The study shows that the Chang-8 sandstone locally retained excellent porosities controlled by diagenetic facies despite deep burial and thermal conditions.
Sedimentation during stage of Chang-8 deposition was controlled by a lacustrine delta system.The Chang-8 member is an important finger-bar reservoir-sandstone in Qingyang area. Sandstone reservoirs can be classified as compositionally immature feldspathic lithareniteand lithic arkose. The main diagenetic minerals of thesandstones include: authigenetic clayminerals, calcite cement, quartz overgrowth, albiteand later ferroan carbonate. Authigenic quartz overgrowths and micro-crystals contain a variety of organic fluid inclusions that indicate the petroleum filling history. Petroleum filling history showsthat the significant later filling process affectedreservoir quality.Porosity preservation caused by grain-coating , authigenic chlorite. Wide porosity variations in sandstones correlate with an abundance of grain-coating chlorite and consequent inhibition of quartz cementation. Secondary porosity has created mainly by feldspar, rock fragment and clay matrix dissolution. The dissolution mechanisim is closely related to organic acids and transformation of clayminerals in adjacentsource rocks. Based on diagenetic events related to temperature, reservoir diagenetic stages can be dividedinto A-substage of later diagenesis. Reservoir quality is controlled mostly by sedimentary microfacies and diagenesis. Subaquoeus distributary channeland mouth barsandbodies commonly have high porosity and permeability, whereas interdistributary and distal sandsheets may have low petrophysical properties.The study shows that the Chang-8 sandstone locally retained excellent porosities controlled by diagenetic facies despite deep burial and thermal conditions.
2004, 22(2): 244-253.
Abstract:
There widely exists paleokarst reservoir associated with regional unconformitiesduring the oil and gas exploration in China. Based on the analysis of the paleokarst reservoirs in Ordovician gas field in Ordos basin, Ordovician oil/gas field in Tarim basin and Sinian gas field in Sichuan basin, the authors have found that the paleokarst reservoirs in China are common in the following characteristics: (1) The paleokarst zone can be explicitly divided into three subzones in vertical, i.e. the surface remnant karst zone, the vertical vadose zone and the horizontal phreatic zone.(2) The reservoir space is remnant dissolved pores, vugs and fissures. The most favorable reservoir for oil and gas accumulation is the fissure-dissolved vug reservoir. (3)The distribution of paleokarst reservoirs is controlled by paleokarst morphologyand fault fissures. The most favorable place for reservoir development is on karst slopes and in fault belts.(4) Dissolution during deep burial coincides with the maturation of source rocks, hydrocarbon evolution and migration.Porosity enhancement related to the burial organic dissolution takes place just prior to the arrival of hydrocarbons in reservoirs, so it is of economic concern. (5) Karstification and burial organic dissolution are the most important diagenesis for the paleokarst reservoir development. The formeris a prerequesite factor, while the latteris adominant factorin the reservoir construction.The paleokarst reservoiris a new domain for the deep exploration of oil and gas in China.
There widely exists paleokarst reservoir associated with regional unconformitiesduring the oil and gas exploration in China. Based on the analysis of the paleokarst reservoirs in Ordovician gas field in Ordos basin, Ordovician oil/gas field in Tarim basin and Sinian gas field in Sichuan basin, the authors have found that the paleokarst reservoirs in China are common in the following characteristics: (1) The paleokarst zone can be explicitly divided into three subzones in vertical, i.e. the surface remnant karst zone, the vertical vadose zone and the horizontal phreatic zone.(2) The reservoir space is remnant dissolved pores, vugs and fissures. The most favorable reservoir for oil and gas accumulation is the fissure-dissolved vug reservoir. (3)The distribution of paleokarst reservoirs is controlled by paleokarst morphologyand fault fissures. The most favorable place for reservoir development is on karst slopes and in fault belts.(4) Dissolution during deep burial coincides with the maturation of source rocks, hydrocarbon evolution and migration.Porosity enhancement related to the burial organic dissolution takes place just prior to the arrival of hydrocarbons in reservoirs, so it is of economic concern. (5) Karstification and burial organic dissolution are the most important diagenesis for the paleokarst reservoir development. The formeris a prerequesite factor, while the latteris adominant factorin the reservoir construction.The paleokarst reservoiris a new domain for the deep exploration of oil and gas in China.
2004, 22(2): 261-266.
Abstract:
Through the grain size analysis of sand dunes in the lower reach of the Tumen River, it is found that the frequency cumulative distribution curves are the double peak and the Sk i of the grains are negative,moreover, the change of the grain size is great and the mean value of the standard deviation is 0.64Ф,the sedimentary environment of dunes by the grain size analysis is neriticenvironment; With the analysis of Transmission Eletronic Microscopy (TEM), the shape of the quartz grains are subangular and the principaltraces of mechanical action which underwent are conchoidal breakages and V-shaped percussion pit. The quartz grains havedeveloped chemical action, mainly are middle-strong chemical corrosion; The surface textures of the quartz grains indicate that the sediments are mainly embouchureenvironment; The result of sand dunes'TL age show that the sand dunes were affected by the change of the sea-level in Holocene epoch and experienced the weathering.
Through the grain size analysis of sand dunes in the lower reach of the Tumen River, it is found that the frequency cumulative distribution curves are the double peak and the Sk i of the grains are negative,moreover, the change of the grain size is great and the mean value of the standard deviation is 0.64Ф,the sedimentary environment of dunes by the grain size analysis is neriticenvironment; With the analysis of Transmission Eletronic Microscopy (TEM), the shape of the quartz grains are subangular and the principaltraces of mechanical action which underwent are conchoidal breakages and V-shaped percussion pit. The quartz grains havedeveloped chemical action, mainly are middle-strong chemical corrosion; The surface textures of the quartz grains indicate that the sediments are mainly embouchureenvironment; The result of sand dunes'TL age show that the sand dunes were affected by the change of the sea-level in Holocene epoch and experienced the weathering.
2004, 22(2): 276-280.
Abstract:
It is indicated that glauconites have been found in Cenozoic group strata in Zhan-che sag of Jiyang depression by a variety of thin section identification, and which are all in the primary state. Though deposited in different epochs, they are relatively concentrated in the study area, that is, mostly ccurred inthe strata of Cenozoic Paleogene from No.1 to No.4 of Shahejie Formation. Based on the analysis of biology fossils, it is considered that Zhan-che sag of Jiyang depression was ever invaded by the small-scalemarinetransgression under the background of the continental basin, which influenced sedimentary environment at that time, and occurred biologic variation and glauconite deposit to a certain extent. It is helpful to confirm the sedimentary environment by analyzing glauconite formation.
It is indicated that glauconites have been found in Cenozoic group strata in Zhan-che sag of Jiyang depression by a variety of thin section identification, and which are all in the primary state. Though deposited in different epochs, they are relatively concentrated in the study area, that is, mostly ccurred inthe strata of Cenozoic Paleogene from No.1 to No.4 of Shahejie Formation. Based on the analysis of biology fossils, it is considered that Zhan-che sag of Jiyang depression was ever invaded by the small-scalemarinetransgression under the background of the continental basin, which influenced sedimentary environment at that time, and occurred biologic variation and glauconite deposit to a certain extent. It is helpful to confirm the sedimentary environment by analyzing glauconite formation.
2004, 22(2): 288-294.
Abstract:
The reduction of water hardness, which occurs at waterfalls on rivers in karst areas, is considered to be a result of the waterfall effects. These consist of aeration, jet-flow and low-pressure effects. Waterfall effects bring about two physical changes in river water: an increase in the air-water interface and turbulence. A series of experiments was designed and implemented in order to investigate whether these effects and associated physical changes may cause a reduction of water hardness. From an experiment involving the enlargement of interface area, the plot of air-water interface areas against conductivity revealed that the higher the air-water interface, the more rapidly conductance declines (and Ca2+is precipitated). A bubble producer was designed and used to simulate bubbles that are produced by aeration and low-pressure effects and a faster decline of water hardness was observed at the location with bubbles in this experiment. When a supersaturated solution was passed through a jet-stream producer, a rapid reduction of water hardness and an increase of pH appeared. Field measurements were used to support the laboratory experiments. Work on the Ya He River and at the Dishuiyan Waterfalls revealed that places with aeration had the quickest hardness reduction and the highest average rate of calcite deposition.
The reduction of water hardness, which occurs at waterfalls on rivers in karst areas, is considered to be a result of the waterfall effects. These consist of aeration, jet-flow and low-pressure effects. Waterfall effects bring about two physical changes in river water: an increase in the air-water interface and turbulence. A series of experiments was designed and implemented in order to investigate whether these effects and associated physical changes may cause a reduction of water hardness. From an experiment involving the enlargement of interface area, the plot of air-water interface areas against conductivity revealed that the higher the air-water interface, the more rapidly conductance declines (and Ca2+is precipitated). A bubble producer was designed and used to simulate bubbles that are produced by aeration and low-pressure effects and a faster decline of water hardness was observed at the location with bubbles in this experiment. When a supersaturated solution was passed through a jet-stream producer, a rapid reduction of water hardness and an increase of pH appeared. Field measurements were used to support the laboratory experiments. Work on the Ya He River and at the Dishuiyan Waterfalls revealed that places with aeration had the quickest hardness reduction and the highest average rate of calcite deposition.
2004, 22(2): 302-309.
Abstract:
This paper discusses high-resolution sequence in fan-delta sedmentary system, exemplifying T76 fan-delta of the fourth upper member of Shhejie formation in Shengbei fault's downthrown side of Dongying depression.Research shows that the high resolution sequence stratigraphic units are divided into parasequence set,parasequence,bed set and bed in fan-delta. The authors particularly study types and comparative methods of parasequence and bed set. The type of bed set is divided into Fu,Cu and Cu-Fu types, and parasequence into Fu-Fu,Cu-Fu and Cu-Cu types. We have summrized two comparative methods of parasequence and bed set which are facies change paralleling to source area and incisement perpendicular to the source area.
This paper discusses high-resolution sequence in fan-delta sedmentary system, exemplifying T76 fan-delta of the fourth upper member of Shhejie formation in Shengbei fault's downthrown side of Dongying depression.Research shows that the high resolution sequence stratigraphic units are divided into parasequence set,parasequence,bed set and bed in fan-delta. The authors particularly study types and comparative methods of parasequence and bed set. The type of bed set is divided into Fu,Cu and Cu-Fu types, and parasequence into Fu-Fu,Cu-Fu and Cu-Cu types. We have summrized two comparative methods of parasequence and bed set which are facies change paralleling to source area and incisement perpendicular to the source area.
2004, 22(2): 319-324.
Abstract:
On the basis of investigations on the distribution of source-rock in the sequence stratigraphic framework, a method is introduced to evaluate source rocks by combining geochemical logging data with sequence stratigraphy. Through the practice of evaluating Jurassic source rocks in Jungar basin, it is shown that this method is available and practicable.
On the basis of investigations on the distribution of source-rock in the sequence stratigraphic framework, a method is introduced to evaluate source rocks by combining geochemical logging data with sequence stratigraphy. Through the practice of evaluating Jurassic source rocks in Jungar basin, it is shown that this method is available and practicable.
2004, 22(2): 332-336.
Abstract:
Pedological and stratigraphic observations indicate that there is one paleosol layer on the Holocene loess profile in DPG site,Co. Xiangfen of Shanxi province. CaCO3 , TFe and clay analysis prove that pedological process started at the beginning of the Holocene Magathermal. The major pedological process developed between 4450～3100aB.P, when climate was humid and stable, ancient people cultivated here and created the splendid culture of Taosi . The leaching of CaCO3 existed during the pedological process . The illuvial depth of CaCO3 is about 1.1m . The pedogenesis is not intense overall due to deep slope on palaeo-alluvial-pluvial fans. The type of paleosol here can be regarded as the one of Heilutu soil.
Pedological and stratigraphic observations indicate that there is one paleosol layer on the Holocene loess profile in DPG site,Co. Xiangfen of Shanxi province. CaCO3 , TFe and clay analysis prove that pedological process started at the beginning of the Holocene Magathermal. The major pedological process developed between 4450～3100aB.P, when climate was humid and stable, ancient people cultivated here and created the splendid culture of Taosi . The leaching of CaCO3 existed during the pedological process . The illuvial depth of CaCO3 is about 1.1m . The pedogenesis is not intense overall due to deep slope on palaeo-alluvial-pluvial fans. The type of paleosol here can be regarded as the one of Heilutu soil.
2004, 22(2): 343-347.
Abstract:
Changes in the delivery of nutrients from land usage and anthropogenic emissions, are known to result in eutrophication in lakes. Both accumulation rates of total organic carbon and total nitrogen concentrations show increasing trends since 1970s, and have increased by as much as 2.5, 2.9 times in Caohu lake sedimentary core. Based on total organic carbon, total nitrogen, the ratios of total organic carbon and total nitrogen , TARHC and OEP, the environmental evolutions have been reconstructed since 1898. From 1898 to 1946 the sedimentary organic matter in Caohu lake was attributed to the mixture of terrestrial plants and aquatic algae. From 1946 to 1972 the source of land plant dominated the organic matter and there may be petroleum pollution. From 1972 to present, the source of algae dominated the organic matter of Caohu lake sediment. It can be concluded that sediment organic matter recorded the beginning of eutrophication at Caohu lake since 1970s.
Changes in the delivery of nutrients from land usage and anthropogenic emissions, are known to result in eutrophication in lakes. Both accumulation rates of total organic carbon and total nitrogen concentrations show increasing trends since 1970s, and have increased by as much as 2.5, 2.9 times in Caohu lake sedimentary core. Based on total organic carbon, total nitrogen, the ratios of total organic carbon and total nitrogen , TARHC and OEP, the environmental evolutions have been reconstructed since 1898. From 1898 to 1946 the sedimentary organic matter in Caohu lake was attributed to the mixture of terrestrial plants and aquatic algae. From 1946 to 1972 the source of land plant dominated the organic matter and there may be petroleum pollution. From 1972 to present, the source of algae dominated the organic matter of Caohu lake sediment. It can be concluded that sediment organic matter recorded the beginning of eutrophication at Caohu lake since 1970s.
2004, 22(2): 354-358.
Abstract:
An understanding of the ratio variation of chain alkane molecular components of oils in petroleum reservoir is important for successful study on reservoir formation and petroleum geochemistry. Pressure-falling and gas-washing fractionations, which are two main process of reservoir formation , are simulated by PVT experiments. Measuring the molecular composition of chain alkane of the products formed in the different experiment stages, the analytical results show that: ①A great deal of condensates, which is not from thermal generation, most come from gas-washing fractionations; ② Pressure-drop and gas-washing fractionations are of similar variation in some alkane ratios of the oil, such as the decrease of ratios of Pr/Ph,(Pr+Ph)/(nC19+nC 20) and nC 10/(nC16+nC25); ③The difference between pressure-falling and gas-washing fractionations shows that some alkane parameters of the condensates from the two different processes change in diverse direction; ④Some routine geochemical parameters can be also affected by pressure-falling and gas-washing fractionations.
An understanding of the ratio variation of chain alkane molecular components of oils in petroleum reservoir is important for successful study on reservoir formation and petroleum geochemistry. Pressure-falling and gas-washing fractionations, which are two main process of reservoir formation , are simulated by PVT experiments. Measuring the molecular composition of chain alkane of the products formed in the different experiment stages, the analytical results show that: ①A great deal of condensates, which is not from thermal generation, most come from gas-washing fractionations; ② Pressure-drop and gas-washing fractionations are of similar variation in some alkane ratios of the oil, such as the decrease of ratios of Pr/Ph,(Pr+Ph)/(nC19+nC 20) and nC 10/(nC16+nC25); ③The difference between pressure-falling and gas-washing fractionations shows that some alkane parameters of the condensates from the two different processes change in diverse direction; ④Some routine geochemical parameters can be also affected by pressure-falling and gas-washing fractionations.
2004, 22(2): 193-197.
Abstract:
Techniques and methods used forprediction of reservoirs and description of pertoleum accumulation have important effect in exploration and exploitation of engineering of oil and gas resource. However, their more abundant base connotations are taken into account when advancement of method andinnovation of technique are paid attentionto. Especiallywhen the research objects are hiddenpetroleum accumulations such as lithologic and strata reservoirs, their core contents refer to theory problems of sedimentary geology. So,in this paper it aimsat the peculiarity of lithologic reservoirs of sedimentary system of fluvial-delta-lacutrine of terrigenous basin in our country, many sedimentary geologicalproblems in prediction of reservoirs and description of pertoleum accumulation are expounded. These problems include the background and geological basement of research objects, the description of reservoir facies architecture of pertoleum accumulation, genetic types and their description of reservoir at delta front, petrographical facies mapping on small scale, elements of reservoir formation and high grade target and the research of reservoir three dimensionalarchitecture taking the reservoir flow units as objects, and it emphasizes that techniques of prediction of reservoirs and description of pertoleum accumulationare dependent onsedimentary geology,which is the fundamental basis.
Techniques and methods used forprediction of reservoirs and description of pertoleum accumulation have important effect in exploration and exploitation of engineering of oil and gas resource. However, their more abundant base connotations are taken into account when advancement of method andinnovation of technique are paid attentionto. Especiallywhen the research objects are hiddenpetroleum accumulations such as lithologic and strata reservoirs, their core contents refer to theory problems of sedimentary geology. So,in this paper it aimsat the peculiarity of lithologic reservoirs of sedimentary system of fluvial-delta-lacutrine of terrigenous basin in our country, many sedimentary geologicalproblems in prediction of reservoirs and description of pertoleum accumulation are expounded. These problems include the background and geological basement of research objects, the description of reservoir facies architecture of pertoleum accumulation, genetic types and their description of reservoir at delta front, petrographical facies mapping on small scale, elements of reservoir formation and high grade target and the research of reservoir three dimensionalarchitecture taking the reservoir flow units as objects, and it emphasizes that techniques of prediction of reservoirs and description of pertoleum accumulationare dependent onsedimentary geology,which is the fundamental basis.
2004, 22(2): 216-224.
Abstract:
Genetic types of tertiary lacustrine algal(cyanobacteria) limestones reservoirs in the western Qaidam basin mainly include:algal(cyanobacteria) flat limestones in littoral lake and algal(cyanobacteria) mound limestones in shallow lake.There are of completely different sedimentation characteristics,lithological types and reservoir featares.Tertiary algal(cyanobacteria)limestones reservoirs in the western Qaidam basin are characterized by widespread distribution and being the most important in the carbonate reservoirs.Tertiary algal(cyanobacteria)limestone reservoirs in the western Qaidam basin have been found in Yuexi, Yuedong,Qigequan, Shizigou, Huatugou, Jiandingshan, Nanyishan and Dafengshan regions etc., and distributed from E23 to N22. Algal(cyanobacteria)limestones reservoirs in E23 and N1 distributed mainly in the west(southwest) region of Yingxionglingdepression, those in N12 and N22 distributed mainly in east(northeast) region of Yingxionglingdepression. Distribution of algal(cyanobacteria)limestones in the western Qaidam basin is mainly controlled by lake level changes,migration of sedimentation center and basin evolution.Reservoir spaces of algal(cyanobacteria)flatlimestones in littoral lake are predominant with secondary disolution pores and disolution fissures .They are possibly controlled by atmospheric water leaching.Reservoir spaces of algal(cyanobacteria)moundlimestones in shallow lake are predominant with secondary disolution pores and disolution fissures,and also developed primary algal tube pores.They are possibly controlled bydisolution along rupture zones and organic acid disolution.
Genetic types of tertiary lacustrine algal(cyanobacteria) limestones reservoirs in the western Qaidam basin mainly include:algal(cyanobacteria) flat limestones in littoral lake and algal(cyanobacteria) mound limestones in shallow lake.There are of completely different sedimentation characteristics,lithological types and reservoir featares.Tertiary algal(cyanobacteria)limestones reservoirs in the western Qaidam basin are characterized by widespread distribution and being the most important in the carbonate reservoirs.Tertiary algal(cyanobacteria)limestone reservoirs in the western Qaidam basin have been found in Yuexi, Yuedong,Qigequan, Shizigou, Huatugou, Jiandingshan, Nanyishan and Dafengshan regions etc., and distributed from E23 to N22. Algal(cyanobacteria)limestones reservoirs in E23 and N1 distributed mainly in the west(southwest) region of Yingxionglingdepression, those in N12 and N22 distributed mainly in east(northeast) region of Yingxionglingdepression. Distribution of algal(cyanobacteria)limestones in the western Qaidam basin is mainly controlled by lake level changes,migration of sedimentation center and basin evolution.Reservoir spaces of algal(cyanobacteria)flatlimestones in littoral lake are predominant with secondary disolution pores and disolution fissures .They are possibly controlled by atmospheric water leaching.Reservoir spaces of algal(cyanobacteria)moundlimestones in shallow lake are predominant with secondary disolution pores and disolution fissures,and also developed primary algal tube pores.They are possibly controlled bydisolution along rupture zones and organic acid disolution.
2004, 22(2): 234-243.
Abstract:
The Upper Ordovician Midale Field is located in the northern Williston Basinin southeastern Saskatchewan, Canada.It consists of a serious of low-relief structural traps. The oil source rocks are the same or older stratigraphy in the southern basin center. Thereservoirs are characterized by intercrystalline porosity in the dolomitized matrix with variable amount of vugs and fractures. Based on core examination and density and neutron log analysis, the carbonate reservoirs in the Red River Yeomen Formation can be divided into four zones.Zones1 and 2 are situatedin the upper part of the structural traps and usually bear oil. Although zones3 and 4 are thicker with higher porosity, they usually contain water only because they are located below the spill point of hydrocarbon traps.On a regional scale, however, zone 3 and 4 could be the attractive targets for the future exploration of possible stratigraphictraps where these zones pinch-outlaterally. Thickerzone 1 and 2 are characterized by high-amplitudeandhigh-frequency reflections on seismic profilesbased on examination of log cross-sections, their correspondingwell-linked 3 D seismic profiles,and forward modeling of seismic response. Zone3 and 4, where all four zones are present, can be identified by an additionalpeak beneath the original reservoir reflectionon seismic profiles. The terminationof this additional peak on a seismic profile is, therefore, an indication of pinchout of reservoir zone 3 and 4.This can be used to identify possible stratigraphic traps. The Ordovician oil pools of the Midale area are spatially associated with localized low-relief structuresand presence of the reservoirs zones.The driving mechanism for the Midale pools is interpreted to be a combination ofedge water and bottom waterdrive systems.Based on our analyses of 3D seismic dataand their implication on the stratigraphic and structural evolution in the region, these low relief structures are interpreted as the drape of Red Riverstrata over local Precambrianbasement highs that could have reactivated later. The traps were initiated during the Middle Silurian to the Early Devoniantime and finalized during the Late Cretaceous. Future explorationtargets of stratigraphic trap play are identifiedon thenortheastern wings of the nose structure that is close tohydrocarbon sources.
The Upper Ordovician Midale Field is located in the northern Williston Basinin southeastern Saskatchewan, Canada.It consists of a serious of low-relief structural traps. The oil source rocks are the same or older stratigraphy in the southern basin center. Thereservoirs are characterized by intercrystalline porosity in the dolomitized matrix with variable amount of vugs and fractures. Based on core examination and density and neutron log analysis, the carbonate reservoirs in the Red River Yeomen Formation can be divided into four zones.Zones1 and 2 are situatedin the upper part of the structural traps and usually bear oil. Although zones3 and 4 are thicker with higher porosity, they usually contain water only because they are located below the spill point of hydrocarbon traps.On a regional scale, however, zone 3 and 4 could be the attractive targets for the future exploration of possible stratigraphictraps where these zones pinch-outlaterally. Thickerzone 1 and 2 are characterized by high-amplitudeandhigh-frequency reflections on seismic profilesbased on examination of log cross-sections, their correspondingwell-linked 3 D seismic profiles,and forward modeling of seismic response. Zone3 and 4, where all four zones are present, can be identified by an additionalpeak beneath the original reservoir reflectionon seismic profiles. The terminationof this additional peak on a seismic profile is, therefore, an indication of pinchout of reservoir zone 3 and 4.This can be used to identify possible stratigraphic traps. The Ordovician oil pools of the Midale area are spatially associated with localized low-relief structuresand presence of the reservoirs zones.The driving mechanism for the Midale pools is interpreted to be a combination ofedge water and bottom waterdrive systems.Based on our analyses of 3D seismic dataand their implication on the stratigraphic and structural evolution in the region, these low relief structures are interpreted as the drape of Red Riverstrata over local Precambrianbasement highs that could have reactivated later. The traps were initiated during the Middle Silurian to the Early Devoniantime and finalized during the Late Cretaceous. Future explorationtargets of stratigraphic trap play are identifiedon thenortheastern wings of the nose structure that is close tohydrocarbon sources.
2004, 22(2): 254-260.
Abstract:
Kaijiang-Liangping trough existed for 700 My.controlled the deposition of Feixianguan Formation of lower Triassic in the northern Sichuan Basin. In the short period of the trough existed, relativelysymmetrical carbonate rock sedimentary system that be analogous to Wilson facies pattern could be formed in its both sides. Through researching on petrology data of detailled drilling, outcrop and so on, Feixianguan Formation mainly developed six types of sedimentary facies including evaporate platform, restricted platform, open-platform, platform marginbeach, slope and basin facies. The basin facies that was shallower than deep-sea basin which mainly developed dark marl and lime mudstone; the depositonal characteristics of the slope facies are distinct, but shelf facies poor developed which may be for the sake of the depth of the trough, because it is so small; with the gradual close of the trough, seawater became shallow, the characteristics of the depositional evolution from basin facies to slope, platform margin beach, open-platform, restricted platform and evaporate platform within the trough are dinstinct; to the top of the Member 4 of Feixianguan Formation, all of the Northern Sichuan basin were deposited equally by restricted platform facies or evaporate platform facies. The period of the trough existed is so short that the course of evolution of sedimentary facies is quite clear in plane and longitude. With the gradual close of the trough, seawater receded toward to open sea, platform margin oolitic beaches moved toward to trough too, that was open sea, growing horizons of them rised gradually at the same time.
Kaijiang-Liangping trough existed for 700 My.controlled the deposition of Feixianguan Formation of lower Triassic in the northern Sichuan Basin. In the short period of the trough existed, relativelysymmetrical carbonate rock sedimentary system that be analogous to Wilson facies pattern could be formed in its both sides. Through researching on petrology data of detailled drilling, outcrop and so on, Feixianguan Formation mainly developed six types of sedimentary facies including evaporate platform, restricted platform, open-platform, platform marginbeach, slope and basin facies. The basin facies that was shallower than deep-sea basin which mainly developed dark marl and lime mudstone; the depositonal characteristics of the slope facies are distinct, but shelf facies poor developed which may be for the sake of the depth of the trough, because it is so small; with the gradual close of the trough, seawater became shallow, the characteristics of the depositional evolution from basin facies to slope, platform margin beach, open-platform, restricted platform and evaporate platform within the trough are dinstinct; to the top of the Member 4 of Feixianguan Formation, all of the Northern Sichuan basin were deposited equally by restricted platform facies or evaporate platform facies. The period of the trough existed is so short that the course of evolution of sedimentary facies is quite clear in plane and longitude. With the gradual close of the trough, seawater receded toward to open sea, platform margin oolitic beaches moved toward to trough too, that was open sea, growing horizons of them rised gradually at the same time.
2004, 22(2): 267-275.
Abstract:
The Miocene Shanwang Formation in Linqu of Shandong Province consists mainly of lacustrine diatomaceous sediments. Detailed sedimentary study on the laminated diatomites in the Shanwang Formation is necessary for the furtherwork on reconstruction of high-frequency climatic cycle. Based on the major mineral composition and their ratios, the diatomaceous sediments in the Shanwang Formation are distinguished as three distinct laminae (clay laminae, diatomaceous laminae and organic matter laminae) and three lamina couplet types (organic matter-clay couplet, organic matter-diatomaceous couplet and diatomaceous couplet- clay couplet). The formation of diatomaceous laminae and lamina couples in the Shanwang Formation was controlled by sedimentary rate of terrigenous clays, diatom growth, and deposition and preservation of organic matters in the basin.
The Miocene Shanwang Formation in Linqu of Shandong Province consists mainly of lacustrine diatomaceous sediments. Detailed sedimentary study on the laminated diatomites in the Shanwang Formation is necessary for the furtherwork on reconstruction of high-frequency climatic cycle. Based on the major mineral composition and their ratios, the diatomaceous sediments in the Shanwang Formation are distinguished as three distinct laminae (clay laminae, diatomaceous laminae and organic matter laminae) and three lamina couplet types (organic matter-clay couplet, organic matter-diatomaceous couplet and diatomaceous couplet- clay couplet). The formation of diatomaceous laminae and lamina couples in the Shanwang Formation was controlled by sedimentary rate of terrigenous clays, diatom growth, and deposition and preservation of organic matters in the basin.
2004, 22(2): 281-287.
Abstract:
By the observation of drillng cores, the seismite is recognized which mainly occurredin the upper part of Member4 and Member 3 of Shahejie Formation inthe Lower Tertiary in Jiyang sub-basin. Many kinds of soft sedimentarydeformation structures have been found in seismite, such as step micro-faults, pleatedwithin layers,liquefactionsandstone and clay veins, vibrationalliquefaction deformation structure, seismic breccias and flame structure. Seismites mainly occur in the northern steep zoneof rift lacustrine basin. There develop more seismites in Member 3 than in the upper part of Member4. Away from the basin-controlling boundary fault, the sedimentary sequence integrity of seismites gets worse. This reflects that seismites are the direct resultsof earthquake which causedby the intenseactionof basin-controlling boundary fault .The repeated emergence of seismites in stratasection showsthat themovement of boundary faultshas periodicity and episodicity. The researchprovides theoretical foundation for the tectonic evolution studies and seismite recognization in continental rift lacustrine basin.
By the observation of drillng cores, the seismite is recognized which mainly occurredin the upper part of Member4 and Member 3 of Shahejie Formation inthe Lower Tertiary in Jiyang sub-basin. Many kinds of soft sedimentarydeformation structures have been found in seismite, such as step micro-faults, pleatedwithin layers,liquefactionsandstone and clay veins, vibrationalliquefaction deformation structure, seismic breccias and flame structure. Seismites mainly occur in the northern steep zoneof rift lacustrine basin. There develop more seismites in Member 3 than in the upper part of Member4. Away from the basin-controlling boundary fault, the sedimentary sequence integrity of seismites gets worse. This reflects that seismites are the direct resultsof earthquake which causedby the intenseactionof basin-controlling boundary fault .The repeated emergence of seismites in stratasection showsthat themovement of boundary faultshas periodicity and episodicity. The researchprovides theoretical foundation for the tectonic evolution studies and seismite recognization in continental rift lacustrine basin.
2004, 22(2): 295-301.
Abstract:
The controlling factors and formation mechanism of the continental sequences are important research field in continental sequence stratigraphy. A fault-depressed stagnant lacustrine basin as a unique basin has its own particular characteristics. In this paper, the author has studied the sedimentary evolution and the base-level changes of the Early Cretaceous fault-depressed stagnant lacustrine basin in Chagan Depression, and then considered that the controlling factors of the sequence in the fault-depressed stagnant lacustrine basin are dominantly the integration of tectonic and climatic factors, and, in the next place, the supply rate of the sediments and lake-level change. Under the control of the double factors, two types of sequences were formed: one was the compound type of fault-depression and climate, and another was climatic type.
The controlling factors and formation mechanism of the continental sequences are important research field in continental sequence stratigraphy. A fault-depressed stagnant lacustrine basin as a unique basin has its own particular characteristics. In this paper, the author has studied the sedimentary evolution and the base-level changes of the Early Cretaceous fault-depressed stagnant lacustrine basin in Chagan Depression, and then considered that the controlling factors of the sequence in the fault-depressed stagnant lacustrine basin are dominantly the integration of tectonic and climatic factors, and, in the next place, the supply rate of the sediments and lake-level change. Under the control of the double factors, two types of sequences were formed: one was the compound type of fault-depression and climate, and another was climatic type.
2004, 22(2): 310-318.
Abstract:
The early Triassic lithostratigraphy in southwestern margin of Yangtze Platform is divided into 4 depositional sequences by studying the structure and stacking pattern of stratigraphic bodies, the features of unconformity-bound. The depositional sequences are subdivided into lowstand system tract, transgressive system tract and highstand system tract. After researching the data about conodonts obtained, and correlating them with Triassic conodont biozones established by Haq et al., the boundary ages of sequence and system tract are determined initially (lower boundary age of sequence 1 is 251Ma; lower boundary age of sequence 2 is 245.2Ma; lower boundary age of sequence 3 is 243Ma; lower boundary age is 240.5Ma, upper boundary age is 239.4Ma in sequence 4). Thus early Triassic stratigraphic framework with higher resolution is established in this area. The characters of sequence-combination in framework are displayed clearly in carbonate platform margin.The platform margin retreated successively toward continent during highstand system tracts of sequence 1-2, showing combinatorial relation overlapped. While platform margin advanced orderly in highstand systems tract stage of sequence 3-4, showing combinatorial relation offlaped. The characters of sequence-combinations mentioned over were controlled by the tectonic subsidence of sedimentary basin and the change of up-down subcycle of 2 order sea level. The sequences showed retrograding combinatorial relation when the tectonic subsidence was accelerated and sea level rised; on the contrary, the sequence appeared prograding combinatorial relation when the tectonic subsidence was gentle and sea level declined. In addition, the change law of carbon-oxygen isotope researched in sequence 1-bottom sequence 3 in slop zone (Gaimao, Guiyang) is as follow: The change of carbon-oxygen isotope composition isnot large in transgressive system tracts-highstand system tracts. δ13C is mainly positive, but it move obviously to negative direction in top highstand system tracts. The change of carbon-oxygen isotope composition is very big and negative number in lowstand system tracts. These geochemical characters provide basis for dividing stratigraphy.
The early Triassic lithostratigraphy in southwestern margin of Yangtze Platform is divided into 4 depositional sequences by studying the structure and stacking pattern of stratigraphic bodies, the features of unconformity-bound. The depositional sequences are subdivided into lowstand system tract, transgressive system tract and highstand system tract. After researching the data about conodonts obtained, and correlating them with Triassic conodont biozones established by Haq et al., the boundary ages of sequence and system tract are determined initially (lower boundary age of sequence 1 is 251Ma; lower boundary age of sequence 2 is 245.2Ma; lower boundary age of sequence 3 is 243Ma; lower boundary age is 240.5Ma, upper boundary age is 239.4Ma in sequence 4). Thus early Triassic stratigraphic framework with higher resolution is established in this area. The characters of sequence-combination in framework are displayed clearly in carbonate platform margin.The platform margin retreated successively toward continent during highstand system tracts of sequence 1-2, showing combinatorial relation overlapped. While platform margin advanced orderly in highstand systems tract stage of sequence 3-4, showing combinatorial relation offlaped. The characters of sequence-combinations mentioned over were controlled by the tectonic subsidence of sedimentary basin and the change of up-down subcycle of 2 order sea level. The sequences showed retrograding combinatorial relation when the tectonic subsidence was accelerated and sea level rised; on the contrary, the sequence appeared prograding combinatorial relation when the tectonic subsidence was gentle and sea level declined. In addition, the change law of carbon-oxygen isotope researched in sequence 1-bottom sequence 3 in slop zone (Gaimao, Guiyang) is as follow: The change of carbon-oxygen isotope composition isnot large in transgressive system tracts-highstand system tracts. δ13C is mainly positive, but it move obviously to negative direction in top highstand system tracts. The change of carbon-oxygen isotope composition is very big and negative number in lowstand system tracts. These geochemical characters provide basis for dividing stratigraphy.
2004, 22(2): 325-331.
Abstract:
Some dry lakes widely distributed in the north of China has been investigated in this paper based on analysis of grain-size distribution of the sediments of these dry lakes, including Manas Lake in Junggar Basin, Juyan Lake in the Alxa Plateau, Yezhu Lake in Minqin Basin and so on. The analyzed results are as followed: the total volume-percentage of the particles (10 μm) of dry lake-bed surface sediments is above 60%. There are plenty of clay particles (10 μm) on the surface of sandy grassland developed from dry lake-bed and the content amount to about 50%. The tiny particles on the surface of abandoned land can be blown away easily and rapidly, so the content of clay particles in Minqin Basin is less than 13.9%. The grain-size distribution of active dune in northwest of China is the fewness of particles (63 μm) and very little of the particles(10 μm). Frequently, sands of active dune in northwest desert areas have weak influence on North China and East China. It is considered that although the weather of sand-dust storm, blowing-sand and suspending-dust occur originally in the western desert, sandy areas of the Alxa Plateau, the north of Hexi Corridor and the east, center of Mongolia, it is the sand-dust materials(63μm),especially those dust(10μm) really influence North China and East China for limitation of transportation distance and height of coarse particles. It is concluded that material sources that influence the sand-dust weather of East Asia are not only inland deserts, more importantly, but also the dry lake, abandoned land and bare sand-gravel grassland.
Some dry lakes widely distributed in the north of China has been investigated in this paper based on analysis of grain-size distribution of the sediments of these dry lakes, including Manas Lake in Junggar Basin, Juyan Lake in the Alxa Plateau, Yezhu Lake in Minqin Basin and so on. The analyzed results are as followed: the total volume-percentage of the particles (10 μm) of dry lake-bed surface sediments is above 60%. There are plenty of clay particles (10 μm) on the surface of sandy grassland developed from dry lake-bed and the content amount to about 50%. The tiny particles on the surface of abandoned land can be blown away easily and rapidly, so the content of clay particles in Minqin Basin is less than 13.9%. The grain-size distribution of active dune in northwest of China is the fewness of particles (63 μm) and very little of the particles(10 μm). Frequently, sands of active dune in northwest desert areas have weak influence on North China and East China. It is considered that although the weather of sand-dust storm, blowing-sand and suspending-dust occur originally in the western desert, sandy areas of the Alxa Plateau, the north of Hexi Corridor and the east, center of Mongolia, it is the sand-dust materials(63μm),especially those dust(10μm) really influence North China and East China for limitation of transportation distance and height of coarse particles. It is concluded that material sources that influence the sand-dust weather of East Asia are not only inland deserts, more importantly, but also the dry lake, abandoned land and bare sand-gravel grassland.
2004, 22(2): 337-342.
Abstract:
The distribution of clay mineral in the sediments of ODP Leg 184 Site 1148, located on the north slope of the South China Sea and recovered 32.8Ma sediments,shows different character between 32.8-15.5 Ma and since 15.5-0Ma periods. In 32.8-15.5 Ma the sediments are dominated by smectite,whose relative abundance is as high as 70 percent,while the abundance of illite and chlorite increase gradually with the decrease of smectite into the last 15.5 Ma. Thus, the evolution of clay mineral in the sediments can be divided into two stages. 32.8-15.5 Ma is tectonic-controlled stage,in which the clay mineral record the speading history of South China Sea.Whereas the climate controlled the distribution of clay mineral since last 15.5 Ma.In this climate-controlled stage the distribution of clay mineral indicated that the temperature decreased gradually and droped rapidly at 3Ma.This result is well consistent with that of δ18O of benthic foraminifera.
The distribution of clay mineral in the sediments of ODP Leg 184 Site 1148, located on the north slope of the South China Sea and recovered 32.8Ma sediments,shows different character between 32.8-15.5 Ma and since 15.5-0Ma periods. In 32.8-15.5 Ma the sediments are dominated by smectite,whose relative abundance is as high as 70 percent,while the abundance of illite and chlorite increase gradually with the decrease of smectite into the last 15.5 Ma. Thus, the evolution of clay mineral in the sediments can be divided into two stages. 32.8-15.5 Ma is tectonic-controlled stage,in which the clay mineral record the speading history of South China Sea.Whereas the climate controlled the distribution of clay mineral since last 15.5 Ma.In this climate-controlled stage the distribution of clay mineral indicated that the temperature decreased gradually and droped rapidly at 3Ma.This result is well consistent with that of δ18O of benthic foraminifera.
2004, 22(2): 348-353.
Abstract:
According to characteristics of compositions and abundances, the dibenzothiophene series of Cambrian and Ordovician carbonate source rocks(marls, muddy limestone and dolomites) from four wells (KN1, LN46, TZ12 and TaCl) in Tabei and Tazhong areas, Tarim basin can be divided into three different types. They are:Ⅰ dibenzothiophene, methyldibenzoth iophene type; Ⅱ dibenzothiophene, methyldibenzothiophene, dimethyldi benzothiophene+trimethylfluorene mixture type; and Ⅲ dibenzothioph ene, methyldibenzothiophene, dimethyldibenzothiophene and trimethyl dibenzothiophene type. The distribution patterns of dibenzothiophene series of eleven marine crude oil samples from Tabei and Tazhong uplifts are, without exception, dibenzothiophene, methyldibenzothiophene, dimethyldibenzothiophene and trimethyldibenzothiophene types, which are very identical to Ⅲ types of above Cambrian and Ordovician marine carbonate source rock samples. Hence, it is inferred that the eight marine crude oil samples from Tabei uplift are thought mainly to possibly derive from Lower Ordovician marine source rocks of Tabei Lunnan area, the three marine crude oil samples from Tazhong uplift possibly from Middle-Upper Ordovician marine source rocks of Tahzhong area.
According to characteristics of compositions and abundances, the dibenzothiophene series of Cambrian and Ordovician carbonate source rocks(marls, muddy limestone and dolomites) from four wells (KN1, LN46, TZ12 and TaCl) in Tabei and Tazhong areas, Tarim basin can be divided into three different types. They are:Ⅰ dibenzothiophene, methyldibenzoth iophene type; Ⅱ dibenzothiophene, methyldibenzothiophene, dimethyldi benzothiophene+trimethylfluorene mixture type; and Ⅲ dibenzothioph ene, methyldibenzothiophene, dimethyldibenzothiophene and trimethyl dibenzothiophene type. The distribution patterns of dibenzothiophene series of eleven marine crude oil samples from Tabei and Tazhong uplifts are, without exception, dibenzothiophene, methyldibenzothiophene, dimethyldibenzothiophene and trimethyldibenzothiophene types, which are very identical to Ⅲ types of above Cambrian and Ordovician marine carbonate source rock samples. Hence, it is inferred that the eight marine crude oil samples from Tabei uplift are thought mainly to possibly derive from Lower Ordovician marine source rocks of Tabei Lunnan area, the three marine crude oil samples from Tazhong uplift possibly from Middle-Upper Ordovician marine source rocks of Tahzhong area.
2004, 22(2): 359-364.
Abstract:
There are mainly two sets of source rocks in the Bozhong Depression of the Bohaiwan Basin: Es 3 source rock and Ed 2 source rock. Since the source rocks in the most area of the depression are buried with a great depth, little work on petroleum generation pattern and history of the source rocks have been done. In this paper, a petroleum generation modeling method which is based on hydrocarbon generation kinetics was applied to investigate petroleum generation history of the source rocks from the depression center and the slope area. The results have shown that the Es 3 source rock from the depression center was matured to the main stage of oil generation and the main stage of gas generation occurred over stage of 20～14 Ma and 15～10 Ma, respectively. The Ed 2 source rock from the depression center passed its oil window during 10～5 Ma, and has a present maturation level of gas peak generation stage. In the slope area of the depression, the situation is quite different. The Es 3 and Ed 2 source rocks entered the main stage of oil generation during 10～5 my and after 2 my, respectively, and the current maturation level of the Es 3 source rock is still in the main stage of gas generation. With the combination of reservoir-cap features, and trapping, migration and accumulation conditions in this depression, it was believed that the oil and gas pools discovered around and inside the depression was related to petroleum generation from the source rocks after 10 my, and the source areas include Es 3 source rocks from the slope area and Ed 2 source rock throughout the depression. The Es 3 source rock from the depression center has a contribution to natural gas accumulation in oil and gas pools.
There are mainly two sets of source rocks in the Bozhong Depression of the Bohaiwan Basin: Es 3 source rock and Ed 2 source rock. Since the source rocks in the most area of the depression are buried with a great depth, little work on petroleum generation pattern and history of the source rocks have been done. In this paper, a petroleum generation modeling method which is based on hydrocarbon generation kinetics was applied to investigate petroleum generation history of the source rocks from the depression center and the slope area. The results have shown that the Es 3 source rock from the depression center was matured to the main stage of oil generation and the main stage of gas generation occurred over stage of 20～14 Ma and 15～10 Ma, respectively. The Ed 2 source rock from the depression center passed its oil window during 10～5 Ma, and has a present maturation level of gas peak generation stage. In the slope area of the depression, the situation is quite different. The Es 3 and Ed 2 source rocks entered the main stage of oil generation during 10～5 my and after 2 my, respectively, and the current maturation level of the Es 3 source rock is still in the main stage of gas generation. With the combination of reservoir-cap features, and trapping, migration and accumulation conditions in this depression, it was believed that the oil and gas pools discovered around and inside the depression was related to petroleum generation from the source rocks after 10 my, and the source areas include Es 3 source rocks from the slope area and Ed 2 source rock throughout the depression. The Es 3 source rock from the depression center has a contribution to natural gas accumulation in oil and gas pools.
