2003 Vol. 21, No. 2
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Display Method:
2003, 21(2): 191-197.
Abstract:
Qinghai-Tibetan Plateau is composed of many sutures and basins. The late Triassic northern Qiangtang foreland basin system is peripheral foreland system in the front of Jinshajiang suture and can be divided into four tectonic units from north to south, including the Jinshajiang suture, Hoh Xil thrust belt, Qiangtang foreland basin and the forebulge (center uplift). The Late Triassic northern Qiangtang foreland basin is filled with more than 2500 m strata and can be divided into two tectonic sequences bounded by unconformities. In a transverse section there is wedge-shaped sedimentary body and the depocenter was located in north part of the basin . There were double paleocurrent and double provenances in the basin. Based on the youngest age of ophiolite, collision granite, Flysch, Molasss, carbonate ramp on forebulge and clast in sandstone and conglomerate, unconformity between Flysch facies and Molasse facies, it has been suggested that the time of the major collision between Qiangtang block and Euasian block is between Norian and Rhaetian.
Qinghai-Tibetan Plateau is composed of many sutures and basins. The late Triassic northern Qiangtang foreland basin system is peripheral foreland system in the front of Jinshajiang suture and can be divided into four tectonic units from north to south, including the Jinshajiang suture, Hoh Xil thrust belt, Qiangtang foreland basin and the forebulge (center uplift). The Late Triassic northern Qiangtang foreland basin is filled with more than 2500 m strata and can be divided into two tectonic sequences bounded by unconformities. In a transverse section there is wedge-shaped sedimentary body and the depocenter was located in north part of the basin . There were double paleocurrent and double provenances in the basin. Based on the youngest age of ophiolite, collision granite, Flysch, Molasss, carbonate ramp on forebulge and clast in sandstone and conglomerate, unconformity between Flysch facies and Molasse facies, it has been suggested that the time of the major collision between Qiangtang block and Euasian block is between Norian and Rhaetian.
2003, 21(2): 205-210.
Abstract:
According to observational data of viscous debris flows with hyper-concentration , distinct causes of formation for different graded bedding in debris flow deposits have been analyzed by use of its rheology and the ratio of flow plug . The paper specially analyzed that the gravel in squirm condition of hyper-concentration viscous flows would tend to have vertical motion due to the effect of Weissenberg , then they would form the bedding structure of the gravel accumulated at surface, and they are different from rough bedding structure.
According to observational data of viscous debris flows with hyper-concentration , distinct causes of formation for different graded bedding in debris flow deposits have been analyzed by use of its rheology and the ratio of flow plug . The paper specially analyzed that the gravel in squirm condition of hyper-concentration viscous flows would tend to have vertical motion due to the effect of Weissenberg , then they would form the bedding structure of the gravel accumulated at surface, and they are different from rough bedding structure.
2003, 21(2): 228-233.
Abstract:
Taking modern deposit of Nenjiang river at Damagang,Fuyu,Heilongjiang,as an example,this paper studied in detail the intrior lithofacies,sedimentary microfacies,sedimentary sequences and model of modern deposit of Nenjiang river at Damagang,by fine dissection of digging exploration troughs and pits and densely collecting samples. The study indicates that Damagang deposit is a complex consisting of sediments from the braided stream and meandering river,with pebby bar of the braided stream in the lower and the low-energy meandering river deposit in the upper.There are 16 kinds of lithofacies identified in Damagang deposit of modern Nenjiang river:Gm,St1,St2,Ft,Ssd,Sh,St,Stcb,Shcs,Sw,Sm,Fw,Fm,Fsc1,Fsc2,Mm and Mpr.Five kinds of subfacies and six kinds of sedimentary microfacies were developed well,including fluvial flood-plain microfacies,crevasse-splay microfacies,natural levee microfacies,point bar microfacies of the meandering river,and flood-plain microfacies and mid-channel bar microfacies of the braided river.These sedimentary microfacies form three sets of different sedimentary sequences in vertical in Damagang deposit,i.e. the lower sequence consist mainly of pebby sediments of braided river the middle sequence is an integrated meandering river deposit,consisting of sand of point-bar and shale of flood-plain of meandering river,and the upper sequence consists of flodd-plain and crevasses-splay of meandering river.By analysing sedimentary microfacise and sedimentary sequences,this paper built a new fluvial complex sedimentary model and it will contribute to the theory of fluvial sedimentology.
Taking modern deposit of Nenjiang river at Damagang,Fuyu,Heilongjiang,as an example,this paper studied in detail the intrior lithofacies,sedimentary microfacies,sedimentary sequences and model of modern deposit of Nenjiang river at Damagang,by fine dissection of digging exploration troughs and pits and densely collecting samples. The study indicates that Damagang deposit is a complex consisting of sediments from the braided stream and meandering river,with pebby bar of the braided stream in the lower and the low-energy meandering river deposit in the upper.There are 16 kinds of lithofacies identified in Damagang deposit of modern Nenjiang river:Gm,St1,St2,Ft,Ssd,Sh,St,Stcb,Shcs,Sw,Sm,Fw,Fm,Fsc1,Fsc2,Mm and Mpr.Five kinds of subfacies and six kinds of sedimentary microfacies were developed well,including fluvial flood-plain microfacies,crevasse-splay microfacies,natural levee microfacies,point bar microfacies of the meandering river,and flood-plain microfacies and mid-channel bar microfacies of the braided river.These sedimentary microfacies form three sets of different sedimentary sequences in vertical in Damagang deposit,i.e. the lower sequence consist mainly of pebby sediments of braided river the middle sequence is an integrated meandering river deposit,consisting of sand of point-bar and shale of flood-plain of meandering river,and the upper sequence consists of flodd-plain and crevasses-splay of meandering river.By analysing sedimentary microfacise and sedimentary sequences,this paper built a new fluvial complex sedimentary model and it will contribute to the theory of fluvial sedimentology.
2003, 21(2): 247-254.
Abstract:
The Late Ordovician Wenchang Fm. is subdivided into two members. Member I (M I, the lower section), characterized by presence of thick massive sandstone layers intercalated with thin mudstone layers and brachiopodous, bryozoan and crinoidea assemblage, is interpreted as nearshore to shallow-marine deposits. Member Ⅱ(M Ⅱ, the upper section), is further subdivided two parts: M Ⅱ-1 (the lower one), consisting of sandstone intercalated with conglomerate lenses; M Ⅱ-2 (the upper section), composed of muddy sandstone or sandy mudstone with well-developed tidal bedding. There are two opposite opinions concerning the sedimentary environment of M Ⅱ. Some consider that M Ⅱ-1 is debris-flow deposits on the basin slope owing to biological assemblage containing graptolite, and M Ⅱ-2 is deep-water internal-tide deposits. Others interpret M Ⅱ-1 as near-shore subaqueous channel deposits based on its biological assemblage dominated by shallow-water species and conformity contact with the underlying M Ⅰ in the region, and M Ⅱ-2 as tidal-flat deposits. M Ⅱ-2 is characterized by alternations of sand and mud laminae, and of sand- and mud-dominated layers. In this study, raindrop imprints were observed on some bedding-planes, exhibiting the periodic subaerial exposure of sedimentation facies. The presence of symmetrical oscillation ripples shows wave activities were common at the study area. Mud pebbles are inferred to form on the intertidal flats during storms in comparison with studies on the modern tidal flats margining the Changjiang Delta. M Ⅱ-2 is, therefore, not deep-water internal-tide deposits but normal tidal-flat deposits with strong storm influence. The sand-dominated layers (SDL), several to several tens of cm thick, are interpreted as storm deposits based on the presence of: 1) scour features, 2) numerous intraformation mud-pebbles, 3) oscillation ripples, 4) relatively thick sand laminae at the lower part with an upward trend of thinning toward the adjacent mud-dominated layer. The mud-dominated layers (MDL), consisting of thin sand/mud alternating laminae, deposit after storms when sedimentary environments return to tidal regime. A small sequence, consisting of a SDL and a MDL, is thus a storm succession. Facies transition is gradual among the three units of the formation (M I, M Ⅱ-1,M Ⅱ-2). Dip directions and angles are close to each other. Detrital composition analyses show that they have similar provenance from the Cathaysian Block. It is inferred that sedimentary environments should have no much change during deposition of three different units. Sedimentological study suggested a shallowing-upward progradational succession from high-energy shallow-marine deposits to low-energy tidal-flat deposits. Upward increases of clay content indicate that sedimentary environments get closer to the shoreline. M Ⅱ-1, interlayered between neritic facies and tidal-flat deposits, is thus interpreted nearshore facies with conglomerate layers of event subaqueous channel deposits.
The Late Ordovician Wenchang Fm. is subdivided into two members. Member I (M I, the lower section), characterized by presence of thick massive sandstone layers intercalated with thin mudstone layers and brachiopodous, bryozoan and crinoidea assemblage, is interpreted as nearshore to shallow-marine deposits. Member Ⅱ(M Ⅱ, the upper section), is further subdivided two parts: M Ⅱ-1 (the lower one), consisting of sandstone intercalated with conglomerate lenses; M Ⅱ-2 (the upper section), composed of muddy sandstone or sandy mudstone with well-developed tidal bedding. There are two opposite opinions concerning the sedimentary environment of M Ⅱ. Some consider that M Ⅱ-1 is debris-flow deposits on the basin slope owing to biological assemblage containing graptolite, and M Ⅱ-2 is deep-water internal-tide deposits. Others interpret M Ⅱ-1 as near-shore subaqueous channel deposits based on its biological assemblage dominated by shallow-water species and conformity contact with the underlying M Ⅰ in the region, and M Ⅱ-2 as tidal-flat deposits. M Ⅱ-2 is characterized by alternations of sand and mud laminae, and of sand- and mud-dominated layers. In this study, raindrop imprints were observed on some bedding-planes, exhibiting the periodic subaerial exposure of sedimentation facies. The presence of symmetrical oscillation ripples shows wave activities were common at the study area. Mud pebbles are inferred to form on the intertidal flats during storms in comparison with studies on the modern tidal flats margining the Changjiang Delta. M Ⅱ-2 is, therefore, not deep-water internal-tide deposits but normal tidal-flat deposits with strong storm influence. The sand-dominated layers (SDL), several to several tens of cm thick, are interpreted as storm deposits based on the presence of: 1) scour features, 2) numerous intraformation mud-pebbles, 3) oscillation ripples, 4) relatively thick sand laminae at the lower part with an upward trend of thinning toward the adjacent mud-dominated layer. The mud-dominated layers (MDL), consisting of thin sand/mud alternating laminae, deposit after storms when sedimentary environments return to tidal regime. A small sequence, consisting of a SDL and a MDL, is thus a storm succession. Facies transition is gradual among the three units of the formation (M I, M Ⅱ-1,M Ⅱ-2). Dip directions and angles are close to each other. Detrital composition analyses show that they have similar provenance from the Cathaysian Block. It is inferred that sedimentary environments should have no much change during deposition of three different units. Sedimentological study suggested a shallowing-upward progradational succession from high-energy shallow-marine deposits to low-energy tidal-flat deposits. Upward increases of clay content indicate that sedimentary environments get closer to the shoreline. M Ⅱ-1, interlayered between neritic facies and tidal-flat deposits, is thus interpreted nearshore facies with conglomerate layers of event subaqueous channel deposits.
2003, 21(2): 260-265.
Abstract:
The weathering crust of Majiagou Formation in Ordovician of Changqing Gasfield in Ordos Basin is the major pay zone with the evaporated marginal sea facies. Solution spots and holes with millimeter and centimeter size are developed and its occurrence, composition and fillings in the holes are very complex. Some of them have multi-stage fillings such as gypsum, quartz, calcite, dolomite, kaolinite and pyrite,and so on. The lower part of the solution hole remains dolomite crystalline just like geopetal structure of vadose sands in the clastic rock. As shown, the solution spots are formed not only with suitable lithofacies, paleogeographic environment and complexed evolutional genetic history, but also the karstification related to original deposit and different geologic historical stages.
The weathering crust of Majiagou Formation in Ordovician of Changqing Gasfield in Ordos Basin is the major pay zone with the evaporated marginal sea facies. Solution spots and holes with millimeter and centimeter size are developed and its occurrence, composition and fillings in the holes are very complex. Some of them have multi-stage fillings such as gypsum, quartz, calcite, dolomite, kaolinite and pyrite,and so on. The lower part of the solution hole remains dolomite crystalline just like geopetal structure of vadose sands in the clastic rock. As shown, the solution spots are formed not only with suitable lithofacies, paleogeographic environment and complexed evolutional genetic history, but also the karstification related to original deposit and different geologic historical stages.
2003, 21(2): 272-277.
Abstract:
The thick sandstones in Chang 8 oil Formation of Yanchang group may be divided into two types by the research on sedimentary petrology and sequence stratigraphy. One is made up of single genetic distributary channel sandstones that is stacked with multiple stages sandstone. The other is consist with many microfacies , including underwater distributary channel, river mouth bar, sheet sand over mouth bar and slump sandstone. They pile up as thick sandbody by different stacking patterns. It has been first proposed that only the sandstone called as sheet sand over mouth bar may become high-quality reservoir with relative high porosity and permeability under the background of high accommodations and high sediment alimentations.
The thick sandstones in Chang 8 oil Formation of Yanchang group may be divided into two types by the research on sedimentary petrology and sequence stratigraphy. One is made up of single genetic distributary channel sandstones that is stacked with multiple stages sandstone. The other is consist with many microfacies , including underwater distributary channel, river mouth bar, sheet sand over mouth bar and slump sandstone. They pile up as thick sandbody by different stacking patterns. It has been first proposed that only the sandstone called as sheet sand over mouth bar may become high-quality reservoir with relative high porosity and permeability under the background of high accommodations and high sediment alimentations.
2003, 21(2): 283-287.
Abstract:
Under the guidance of theory of sequence stratigraphy originated from the study of marine basins in continental margin, this paper analyzed thoroughly the characteristics of basin texture and sediment filling sequence in Chinese Mesozoic-Cenozoic depression and faulted down lake basins, used the geological and geophysical data,took the Junggar ,Qaidam , Shongliao and Bohaibay basins as the cases for studying sequence stratigraphy, and pointed out the key of continental sequence stratigraphy study is to determine sequence boundary, first and maximum lake flooding surfaces. It does show that topographic break may be recognized in some depression and faulted down lacustrine basins. Therefore, the sequence stratigraphic models have been built in depression lake basin with or without topographic break. One sequence in depression lake basin with topographic break is composed of lowstand, transgressive and highstand systems tracts, but the sequence in depression lake basin without topographic break only is made up of transgressive and regressive systems tracts. In faulted down lake basin, there are some growth faults in gentle slope of a basin, the different activity of the growth fault produced a topographic change and formed a topographic break, so the sequence stratigraphic model of faulted down lake basin with topographic break has been built, which consists of lowstand, trangressive and highstand systems tracts .Also, this paper has discussed how to determine first and maximum flooding surfaces and sequence boundary according to geological, well-logging and seismic data.
Under the guidance of theory of sequence stratigraphy originated from the study of marine basins in continental margin, this paper analyzed thoroughly the characteristics of basin texture and sediment filling sequence in Chinese Mesozoic-Cenozoic depression and faulted down lake basins, used the geological and geophysical data,took the Junggar ,Qaidam , Shongliao and Bohaibay basins as the cases for studying sequence stratigraphy, and pointed out the key of continental sequence stratigraphy study is to determine sequence boundary, first and maximum lake flooding surfaces. It does show that topographic break may be recognized in some depression and faulted down lacustrine basins. Therefore, the sequence stratigraphic models have been built in depression lake basin with or without topographic break. One sequence in depression lake basin with topographic break is composed of lowstand, transgressive and highstand systems tracts, but the sequence in depression lake basin without topographic break only is made up of transgressive and regressive systems tracts. In faulted down lake basin, there are some growth faults in gentle slope of a basin, the different activity of the growth fault produced a topographic change and formed a topographic break, so the sequence stratigraphic model of faulted down lake basin with topographic break has been built, which consists of lowstand, trangressive and highstand systems tracts .Also, this paper has discussed how to determine first and maximum flooding surfaces and sequence boundary according to geological, well-logging and seismic data.
2003, 21(2): 297-306.
Abstract:
There is a great change of paleogeography setting resulted from the Caledonian orogeny at the end of Silurian in Guizhou and Guangxi area in south China, the Dianqiangui oldland in early Paleozoic evolved as the Dianqiangui sea in late Plaeozoic. In the initial stage of Devonian Period, seawater is onlaped gradually from the south to the north caused by transgression, so the bottom part of Devonian system is constituted by a set of transgressive clastic sedimentary rock. The great scale transgressive event at the end of the early Epoch of Devonian forms evident differentiation of depositional facies in Guizhou and Guangxi province, a lot of isolated carbonate platforms are developed in Dianqiangui Basin, the special paleogeographic setting marked by "platforms-basins-hills-trough" is formed and lasted to the early stage of the late Epoch of Devonian. The strata of the upper Epoch of Devonian become regressive thin out from paleosea to oldland resulted from the Ziyun epeirogeny that took place in the transitional period from Devonian Period to Carboniferous Period. On the basis of the study on the evolutional natures of sediments in time and the distribution characters of sedimentary facies in space, 13 third-order sedimentary sequences are discerned in Devonian strata in Guizhou and Guangxi province, which could be grouped into one second-order tectonic sequence. In terms of the correlation on biostratigraphy, the sea-level changes delegated by third-order sequences with different architecture natures of facies-succession also could be correlative in research region, in the end, the framework of sequence stratigraphy could be constructed. Many characters such as two elementary natures of third-order sequences——“the regularity of facies-succession in space and the synchronism of the changes of sedimentary environment in time”, two kinds of diachronism that are relative to two types of facies-changing surfaces——“the diachronism of facies-changing surfaces caused by static facies-changing surface and the diachronism of punctuated surfaces formed by dynamic facies-changing surfaces" in strtigraphic records, are clearly demonstrated in the framework of sequence stratigraphy.
There is a great change of paleogeography setting resulted from the Caledonian orogeny at the end of Silurian in Guizhou and Guangxi area in south China, the Dianqiangui oldland in early Paleozoic evolved as the Dianqiangui sea in late Plaeozoic. In the initial stage of Devonian Period, seawater is onlaped gradually from the south to the north caused by transgression, so the bottom part of Devonian system is constituted by a set of transgressive clastic sedimentary rock. The great scale transgressive event at the end of the early Epoch of Devonian forms evident differentiation of depositional facies in Guizhou and Guangxi province, a lot of isolated carbonate platforms are developed in Dianqiangui Basin, the special paleogeographic setting marked by "platforms-basins-hills-trough" is formed and lasted to the early stage of the late Epoch of Devonian. The strata of the upper Epoch of Devonian become regressive thin out from paleosea to oldland resulted from the Ziyun epeirogeny that took place in the transitional period from Devonian Period to Carboniferous Period. On the basis of the study on the evolutional natures of sediments in time and the distribution characters of sedimentary facies in space, 13 third-order sedimentary sequences are discerned in Devonian strata in Guizhou and Guangxi province, which could be grouped into one second-order tectonic sequence. In terms of the correlation on biostratigraphy, the sea-level changes delegated by third-order sequences with different architecture natures of facies-succession also could be correlative in research region, in the end, the framework of sequence stratigraphy could be constructed. Many characters such as two elementary natures of third-order sequences——“the regularity of facies-succession in space and the synchronism of the changes of sedimentary environment in time”, two kinds of diachronism that are relative to two types of facies-changing surfaces——“the diachronism of facies-changing surfaces caused by static facies-changing surface and the diachronism of punctuated surfaces formed by dynamic facies-changing surfaces" in strtigraphic records, are clearly demonstrated in the framework of sequence stratigraphy.
2003, 21(2): 313-317.
Abstract:
Guided with the theory of sequence stratigraphy, the characteristics of sequence stratigraphy of Jiangling shallow to semi-deep water depressional lake basin has been studied systematically. The study indicates that the regional unconformable and sedimentary transformation interfaces are the main interfaces of Ⅲ-order sequence. Though lowstand, highstand and lake transgressive system tracts developed in the studied sequence, the development degrees of different system tracts are quite different, which result in the asymmetric distribution of sequential cycles. The sedimentary facies in different system tracts consist of mainly fluvial delta and shallow lake facies, with alluvial fan and fan delta underdeveloped. The lake water body has experienced no obvious expansion and shrinkage. The fluctuation of water level of the lake has caused no regional changes of sedimentary facies belts. Two particular filling model of sequence stratigraphy have been constructed on the basis of the study results.
Guided with the theory of sequence stratigraphy, the characteristics of sequence stratigraphy of Jiangling shallow to semi-deep water depressional lake basin has been studied systematically. The study indicates that the regional unconformable and sedimentary transformation interfaces are the main interfaces of Ⅲ-order sequence. Though lowstand, highstand and lake transgressive system tracts developed in the studied sequence, the development degrees of different system tracts are quite different, which result in the asymmetric distribution of sequential cycles. The sedimentary facies in different system tracts consist of mainly fluvial delta and shallow lake facies, with alluvial fan and fan delta underdeveloped. The lake water body has experienced no obvious expansion and shrinkage. The fluctuation of water level of the lake has caused no regional changes of sedimentary facies belts. Two particular filling model of sequence stratigraphy have been constructed on the basis of the study results.
2003, 21(2): 324-327.
Abstract:
The author aimed at the character of the continental stratum development to discuss the feasibility of the application of classical sequence stratigraphy to continental stratum .We point out that the compulsory lake regresson often appears in later period of continental stratum development ,so large progradational stratum wedge come into being when lake level fall from the high relatively stable water level to the low water level, the bottom interface of this compulsory stratum wedge is conformable down lapping surface, it's top-interface is regional erosional boundary ,in this circumstance ,it is not feasible to take the bottom interface as sequence boundary ,and the top interface as sequence boundary is more correspond to the theory of classic sequence stratigraphy. Compulsory regressive stratum should be a new system tract on high level system tract in continental third grade sequence element ,continental sequence stratigraphy third grade element should be classified to four parts ;the element of the scheme of four division can not only be distinguished,but also has significance in theory and in practice.
The author aimed at the character of the continental stratum development to discuss the feasibility of the application of classical sequence stratigraphy to continental stratum .We point out that the compulsory lake regresson often appears in later period of continental stratum development ,so large progradational stratum wedge come into being when lake level fall from the high relatively stable water level to the low water level, the bottom interface of this compulsory stratum wedge is conformable down lapping surface, it's top-interface is regional erosional boundary ,in this circumstance ,it is not feasible to take the bottom interface as sequence boundary ,and the top interface as sequence boundary is more correspond to the theory of classic sequence stratigraphy. Compulsory regressive stratum should be a new system tract on high level system tract in continental third grade sequence element ,continental sequence stratigraphy third grade element should be classified to four parts ;the element of the scheme of four division can not only be distinguished,but also has significance in theory and in practice.
2003, 21(2): 334-339.
Abstract:
In lower tertiary,There are a suit of saline lacustrine sediments in Wuyang and Xiangcheng subdepression. A clear correlation exist between sedimentary environment and organic geochemistry in studying area. The organic matter content in salt water-saline lacustrine sediments is the highest and the abundance in the front of delta and fan-delta higher while the content in the plain lower. In hydrocarbon source rocks, shale and oil shale are characterized by the high content of organic matter while gypseous and salt mudstone by the low , between them are dolomitic and carbonaceous mudstone and muddy dolomite and mudstone. The organic matter types are dominated by Ⅱ1 and secondly by Ⅰ.Also few Ⅱ2 exist. Generally, Ⅰand Ⅱ 1 organic matter exist in saline lake while Ⅱ2 and Ⅲ in the front and plain of delta and fan delta respectively. Biomarker compounds show that the source rocks are deposited in the high salinity and reducing to strong reducing environment. The n-alkanes of the source rock display a bimodal carbon number distribution with an odd-over-even predominance (OEP1). The content of pristine and gammacerane is high and the ratio of pristine/phytane is 0.04～0.72while the phytane/C 18 n-alkane greater than 4. The β-carrot alkane, hopene , hopanes and thionic aromatic hydrocarbons extend widely and the ratio of Ts/Tm is greater than unity. Dehydroxyltocopherols is widely spread with the 5 configurations of δ, 6-methyl-MTTC, β, γ and α. The hemi-saline water and saline facies can be distinguished availably by the triangle chart of Pr/Ph、Pr/nC17 and Ph/nC18 value.
In lower tertiary,There are a suit of saline lacustrine sediments in Wuyang and Xiangcheng subdepression. A clear correlation exist between sedimentary environment and organic geochemistry in studying area. The organic matter content in salt water-saline lacustrine sediments is the highest and the abundance in the front of delta and fan-delta higher while the content in the plain lower. In hydrocarbon source rocks, shale and oil shale are characterized by the high content of organic matter while gypseous and salt mudstone by the low , between them are dolomitic and carbonaceous mudstone and muddy dolomite and mudstone. The organic matter types are dominated by Ⅱ1 and secondly by Ⅰ.Also few Ⅱ2 exist. Generally, Ⅰand Ⅱ 1 organic matter exist in saline lake while Ⅱ2 and Ⅲ in the front and plain of delta and fan delta respectively. Biomarker compounds show that the source rocks are deposited in the high salinity and reducing to strong reducing environment. The n-alkanes of the source rock display a bimodal carbon number distribution with an odd-over-even predominance (OEP1). The content of pristine and gammacerane is high and the ratio of pristine/phytane is 0.04～0.72while the phytane/C 18 n-alkane greater than 4. The β-carrot alkane, hopene , hopanes and thionic aromatic hydrocarbons extend widely and the ratio of Ts/Tm is greater than unity. Dehydroxyltocopherols is widely spread with the 5 configurations of δ, 6-methyl-MTTC, β, γ and α. The hemi-saline water and saline facies can be distinguished availably by the triangle chart of Pr/Ph、Pr/nC17 and Ph/nC18 value.
2003, 21(2): 345-349.
Abstract:
In this paper, the authors have analyzed the main controlling factors that affect enrichment and high production of coalbed methane (CBM), such as generating and storing capacity of coal rock, permeability of coal reservoir and preservation conditions of CBM. Research shows that maceral and the degree of metamorphism of coal rock are key factors that control the generating and storing capacity of coal rock. Temperature, pressure and the content of mineral substance and water are also relevant to the storing capacity of coal rock. However, the permeability of coalbed is mainly controlled by fracture system of coal rock, which is relevant to the maturity of coal and the intensity of tectogenesis. The preservation of CBM pool is mainly controlled by the sealing capacity of roof and floor plate, tectonic activity and hydrodynamic environment. Because of its important role, we'd better strengthen the research on CBM pool forming conditions.
In this paper, the authors have analyzed the main controlling factors that affect enrichment and high production of coalbed methane (CBM), such as generating and storing capacity of coal rock, permeability of coal reservoir and preservation conditions of CBM. Research shows that maceral and the degree of metamorphism of coal rock are key factors that control the generating and storing capacity of coal rock. Temperature, pressure and the content of mineral substance and water are also relevant to the storing capacity of coal rock. However, the permeability of coalbed is mainly controlled by fracture system of coal rock, which is relevant to the maturity of coal and the intensity of tectogenesis. The preservation of CBM pool is mainly controlled by the sealing capacity of roof and floor plate, tectonic activity and hydrodynamic environment. Because of its important role, we'd better strengthen the research on CBM pool forming conditions.
2003, 21(2): 355-359.
Abstract:
A suite of 40 crude oil samples from 16 oil fields in the Qaidam basin were analyzed using IRMS, and features, main controlling factors and genetic types of carbon isotopic compositions for these crude oils were studied. The results show that differences in carbon isotopic compositions between the western Qaidam crude oils and the northen Qaidam crude ouils are evident. The western Qaidam crude oils are enriched in 13 C,while the northern Qaidam crude oils are enriched in 12 C. One finding is that carbon isotopic compositions of the western Qaidam curde oils from saline-hypersaline lacustrine environment are controlled mainly by oil-formed environments (e.g. salinity and humidity) and carbon isotopic compositions of the northern Qaidam crude oils from freshwater swampy-lacustrine environment rely mainly on their source natures. On the basis of their carbon isotopic compositions and Pr/Ph ratios,these oils could be divided into five genetic groups.
A suite of 40 crude oil samples from 16 oil fields in the Qaidam basin were analyzed using IRMS, and features, main controlling factors and genetic types of carbon isotopic compositions for these crude oils were studied. The results show that differences in carbon isotopic compositions between the western Qaidam crude oils and the northen Qaidam crude ouils are evident. The western Qaidam crude oils are enriched in 13 C,while the northern Qaidam crude oils are enriched in 12 C. One finding is that carbon isotopic compositions of the western Qaidam curde oils from saline-hypersaline lacustrine environment are controlled mainly by oil-formed environments (e.g. salinity and humidity) and carbon isotopic compositions of the northern Qaidam crude oils from freshwater swampy-lacustrine environment rely mainly on their source natures. On the basis of their carbon isotopic compositions and Pr/Ph ratios,these oils could be divided into five genetic groups.
2003, 21(2): 198-204.
Abstract:
The materials show that the loess possess bio-texture, edg-prismatic and crumb texture, and also have the illuvial component of CaCO3 coming from the soil and the atmospheric water, which reveals the reason of high CaCO3 content and calcification.In the cold and wet areas, the organic content in the loess is higher than that in the soils of desert-grasslands areas, which indicate the loess is the soils with the organic substance formed during the soil-forming process. The loess possess these conditions such as biology, climate ,fine-homogeneous parent material forming soil fast., available terrain and long enough time to change into mature soil during its the developmental process, which shows during the loess formation process, the five fundamental factors for soil-forming have been provided .In essence, the loess is soil, and it is made up of multiple gray-yellow paleosol developed under the conditions of cold and arid climate relatively. In addition, it is steady and mature paleosol under the unique climate condition at that time, the soil types of which are mainly chestnut soil, sierozem, brown soil and dark loessial soil but only minority is cinnamon soil. The formation model of the loess is the one that wind dust experience soil-forming processes in the areas of forest-grasslands, grasslands and desert-grasslands. The loess can indicate the cold and arid climate. In the loess plateau areas, the soil resource enriches mostly, the loess is the soil resource with superior soil texture, rich element and mineral component. The sub-divisions of soil profile isn't obvious owing to continue deposit of wind dust and the weak soil-forming processes. The physical and mechanical character of the loess is influenced by the soil-forming process to a great extent.
The materials show that the loess possess bio-texture, edg-prismatic and crumb texture, and also have the illuvial component of CaCO3 coming from the soil and the atmospheric water, which reveals the reason of high CaCO3 content and calcification.In the cold and wet areas, the organic content in the loess is higher than that in the soils of desert-grasslands areas, which indicate the loess is the soils with the organic substance formed during the soil-forming process. The loess possess these conditions such as biology, climate ,fine-homogeneous parent material forming soil fast., available terrain and long enough time to change into mature soil during its the developmental process, which shows during the loess formation process, the five fundamental factors for soil-forming have been provided .In essence, the loess is soil, and it is made up of multiple gray-yellow paleosol developed under the conditions of cold and arid climate relatively. In addition, it is steady and mature paleosol under the unique climate condition at that time, the soil types of which are mainly chestnut soil, sierozem, brown soil and dark loessial soil but only minority is cinnamon soil. The formation model of the loess is the one that wind dust experience soil-forming processes in the areas of forest-grasslands, grasslands and desert-grasslands. The loess can indicate the cold and arid climate. In the loess plateau areas, the soil resource enriches mostly, the loess is the soil resource with superior soil texture, rich element and mineral component. The sub-divisions of soil profile isn't obvious owing to continue deposit of wind dust and the weak soil-forming processes. The physical and mechanical character of the loess is influenced by the soil-forming process to a great extent.
2003, 21(2): 219-227.
Abstract:
The anastomosing fluvial system was considered as the same term of the braided fluvial system, but the anastomsing stream is distinct from the well-known meandering and braided river. Smith described the anastomosing fluvial system as "a low energy complex of several interconnected channels of variable sinuosity crossing a wetland and forming many elongate islands." Many Chinese rivers have anastomosing reaches, including some large rivers such as Changjiang River, Heilongjiang River, Zhujiang River and some middle-small rivers as Neijiang and Ganjiang River. Based on their physical geography and structural background, they can be divided into four types: plain anastomosing river, vale anastomosing river, lacustrine deltaic plain anastomosing river, marine deltaic plain anastomosing river. Three anastomosed river systems are described. They are anastomosing river in Qiqihaer section of Neijiang River, Ganjiang deltaplain anastomosing river and Zhujiang deltaplain anastomosing river. These rivers contain low gradient, high aggradation rates, multiple channel and large-area wetland between the channels. Channels, natural levees, crevasse-splay, floodplain, lakes, marshes and eolian dunes are important morphological and sedimentary units. Anastomosing channel-filling sediments are mainly composed of pebbly sand and medium to fine sands. Internally channel sandbody consist mainly of trough cross-bedding and oblique bedding. The other morphological units are mainly composed of fine-grained sediments. Some basic characteristics are as follows: climate and geography are not controlling factors of anastomosis; Low gradient is an essential condition for developing anastomosed river systems; Stable multiple channels are different from meandering and braided river; Wetland is major sedimentary unit; Primary factor of channel stabality is dense vegetation on the nature levees and high cohesiveness; Modern examples of anastomosed river systems are not common
The anastomosing fluvial system was considered as the same term of the braided fluvial system, but the anastomsing stream is distinct from the well-known meandering and braided river. Smith described the anastomosing fluvial system as "a low energy complex of several interconnected channels of variable sinuosity crossing a wetland and forming many elongate islands." Many Chinese rivers have anastomosing reaches, including some large rivers such as Changjiang River, Heilongjiang River, Zhujiang River and some middle-small rivers as Neijiang and Ganjiang River. Based on their physical geography and structural background, they can be divided into four types: plain anastomosing river, vale anastomosing river, lacustrine deltaic plain anastomosing river, marine deltaic plain anastomosing river. Three anastomosed river systems are described. They are anastomosing river in Qiqihaer section of Neijiang River, Ganjiang deltaplain anastomosing river and Zhujiang deltaplain anastomosing river. These rivers contain low gradient, high aggradation rates, multiple channel and large-area wetland between the channels. Channels, natural levees, crevasse-splay, floodplain, lakes, marshes and eolian dunes are important morphological and sedimentary units. Anastomosing channel-filling sediments are mainly composed of pebbly sand and medium to fine sands. Internally channel sandbody consist mainly of trough cross-bedding and oblique bedding. The other morphological units are mainly composed of fine-grained sediments. Some basic characteristics are as follows: climate and geography are not controlling factors of anastomosis; Low gradient is an essential condition for developing anastomosed river systems; Stable multiple channels are different from meandering and braided river; Wetland is major sedimentary unit; Primary factor of channel stabality is dense vegetation on the nature levees and high cohesiveness; Modern examples of anastomosed river systems are not common
2003, 21(2): 240-246.
Abstract:
According to the detailed observation of lots of rock core and sediment samples from drilled-holes and playa, authors have conducted a deeper research on diagenesis of the Quaternary salt strata of Luobei depression, Lop Nur lake. The studies showed that various kinds of diagenesis had occurred in the Quaternary salt-bearing strata, mainly including compaction, dissolution, re-crystallization, replacement, cementation, and fracturing. These actions exerted an enormous influence on the ability of strata holding brine. And their activities are closely related to the inter-crystalline fluid movement. Meanwhile, the “ diagenesis phrase” has been proposed, and its significance and role are also probed for assessing potash-bearing brine resources.
According to the detailed observation of lots of rock core and sediment samples from drilled-holes and playa, authors have conducted a deeper research on diagenesis of the Quaternary salt strata of Luobei depression, Lop Nur lake. The studies showed that various kinds of diagenesis had occurred in the Quaternary salt-bearing strata, mainly including compaction, dissolution, re-crystallization, replacement, cementation, and fracturing. These actions exerted an enormous influence on the ability of strata holding brine. And their activities are closely related to the inter-crystalline fluid movement. Meanwhile, the “ diagenesis phrase” has been proposed, and its significance and role are also probed for assessing potash-bearing brine resources.
2003, 21(2): 255-259.
Abstract:
Structural fault terrace is a kind of structural pattern developed on the margins of rift(especially in the early stage of rift)or fault basins reflecting step changes of depositional relief of slopes formed by different subsidence of marginal blocks. Some different types of fault terrace zones are interpreted from seismic profile under which we interpret seismic facies and sedimentary facies. Different types of fault terraces control different sedimentary types. The using of fault terrace may constrain the seismic interpretation with multiple resolutions. Well logging data may be used to test and confirm the controls of sedimentation on the terrace zones constraining seismic interpretation, and to study some details about sedimentary micro-facies and spatial distributions. The examples from seismic and well logging data are from Xujiaweizi fault depression of Songliao basin and Zhanhua sag of Bohaiwan basin. The example from field outcrop in Jiaolai Basin confirms this controlling process. Comparing with drilling and logging data, the information from outcrop is continuous and the analysis of outcrop may reveal details of sedimentation and stratigraphic architecture under control of structural fault terrace. Models of fault terrace and sedimentation may be applicable to oil and gas exploration.
Structural fault terrace is a kind of structural pattern developed on the margins of rift(especially in the early stage of rift)or fault basins reflecting step changes of depositional relief of slopes formed by different subsidence of marginal blocks. Some different types of fault terrace zones are interpreted from seismic profile under which we interpret seismic facies and sedimentary facies. Different types of fault terraces control different sedimentary types. The using of fault terrace may constrain the seismic interpretation with multiple resolutions. Well logging data may be used to test and confirm the controls of sedimentation on the terrace zones constraining seismic interpretation, and to study some details about sedimentary micro-facies and spatial distributions. The examples from seismic and well logging data are from Xujiaweizi fault depression of Songliao basin and Zhanhua sag of Bohaiwan basin. The example from field outcrop in Jiaolai Basin confirms this controlling process. Comparing with drilling and logging data, the information from outcrop is continuous and the analysis of outcrop may reveal details of sedimentation and stratigraphic architecture under control of structural fault terrace. Models of fault terrace and sedimentation may be applicable to oil and gas exploration.
2003, 21(2): 266-271.
Abstract:
Taking the Pingqiao horizontal well region of Ansai oil-field as an example, this paper deals with the method of 3D modeling of sedimentary microfacies using horizontal well and outcrop data and Marked Point Processes technique, in addition deeply study the quantitative architecture model of the delta front in study area. The oil-bearing strata of the study area is Chang 611 of Triassic Yanchang Formation, 20 m or so in thickness. The microfacies is distributary channel, splay and inter-channel shale. There are 10 vertical wells and 5 horizontal wells in the study area in addition to nearby outcrop. Research shows that the width of single channel sandbody is generally from 40 m to 100 m, smaller than the distance among vertical wells. There exist two kinds of reservoir architecture. One is labyrinth reservoir architecture, in which narrow and lenticular sand bodies are distributed discretely within lacustrine shale. The other is jigsaw-puzzle reservoir architecture, which consists of a series of channel sand bodies that laterally overlapped to continuous sandbodies, in which some lateral shaly or calcite non permeable barriers exist among single sandbodies. Geostatistical parameters for 3D microfacies modeling can be picked up effectively using horizontal well and nearby outcrop data. Research shows that Marked Point Processes method is adapt to 3D microfacies modeling of delta front reservoir with known sandbody geometry . The created microfacies model of the study atea is in line with dynamic production data.
Taking the Pingqiao horizontal well region of Ansai oil-field as an example, this paper deals with the method of 3D modeling of sedimentary microfacies using horizontal well and outcrop data and Marked Point Processes technique, in addition deeply study the quantitative architecture model of the delta front in study area. The oil-bearing strata of the study area is Chang 611 of Triassic Yanchang Formation, 20 m or so in thickness. The microfacies is distributary channel, splay and inter-channel shale. There are 10 vertical wells and 5 horizontal wells in the study area in addition to nearby outcrop. Research shows that the width of single channel sandbody is generally from 40 m to 100 m, smaller than the distance among vertical wells. There exist two kinds of reservoir architecture. One is labyrinth reservoir architecture, in which narrow and lenticular sand bodies are distributed discretely within lacustrine shale. The other is jigsaw-puzzle reservoir architecture, which consists of a series of channel sand bodies that laterally overlapped to continuous sandbodies, in which some lateral shaly or calcite non permeable barriers exist among single sandbodies. Geostatistical parameters for 3D microfacies modeling can be picked up effectively using horizontal well and nearby outcrop data. Research shows that Marked Point Processes method is adapt to 3D microfacies modeling of delta front reservoir with known sandbody geometry . The created microfacies model of the study atea is in line with dynamic production data.
2003, 21(2): 278-282.
Abstract:
Dongying Sag is one of the most important petroleum sags in Bohai gulf petroleum province. Its northern part, immediately south to Qingtuozi, Chenjiazhuang and Binxian Uplifts is a long narrow abrupt slope named Northern Slope. This slope is located south to marginal uplift and north to generative basin/center. It is formed during the swelling of Chenjiazhuang Uplift in early Eogene. Clastic deposits of great thickness were accumulated at the slope foot during Sha 3～4 stage. From the study, the sequence stratigraphic framework of Sha 3～4 deposits in this area is composed of 3 sequence, 8 para-sequence groups and 18 para-sequences. There are 3 genetic types of sandstone-conglomerate bodies include alluvial fan, near bank subaquatic fan and fan delta. The later 2 genetic types are the major oil-bearing fans. Anticline, upward finger out, fault block, lithologic and stratigraphic traps are the 5 major trap types there.
Dongying Sag is one of the most important petroleum sags in Bohai gulf petroleum province. Its northern part, immediately south to Qingtuozi, Chenjiazhuang and Binxian Uplifts is a long narrow abrupt slope named Northern Slope. This slope is located south to marginal uplift and north to generative basin/center. It is formed during the swelling of Chenjiazhuang Uplift in early Eogene. Clastic deposits of great thickness were accumulated at the slope foot during Sha 3～4 stage. From the study, the sequence stratigraphic framework of Sha 3～4 deposits in this area is composed of 3 sequence, 8 para-sequence groups and 18 para-sequences. There are 3 genetic types of sandstone-conglomerate bodies include alluvial fan, near bank subaquatic fan and fan delta. The later 2 genetic types are the major oil-bearing fans. Anticline, upward finger out, fault block, lithologic and stratigraphic traps are the 5 major trap types there.
2003, 21(2): 288-296,306.
Abstract:
According to traditional coal-forming theory, coal formation was thought to take place in the water (marine) regression period of the transgression and regression cycle, that is, the land facies coal forming model. The author's basic point of view that coal was formed during sea transgression is gradually becoming a theory or model of coal formation, which shows coal formation was transferred gradually to land during the transgression coal forming closely related to transgression. Peat formed in advance was submerged in seawater, as a result, the coal seam formed was of diachronism. This theory and model is originated from the analyzing result of the coal formation in epicontinental sea basin, which is a contribution to coal geology and bring up a new way in the analysis of coal formation. In particular, it puts forward a question on how to evaluate the function of coal seam, in terms of a special sedimentary body in sequence stratigraphy analysis. As the diachronism of coal seams was caused by the transgressive coal formation, whether the top surface or the bottom surface of a coal seam can be taken as an interface of different sequence units remains to be studied in detail. The sea level change of North China epicontinental sea basin in the late paleozoic period is of the feature of high frequency and complexity, that is, the sea level changed with different frequencies and grades and the superposition of them, to cause to form a special unit of sediment body. Long period of sea regression contains many short periods of transgression events; also, there may be relatively short period of regression in the course of transgression. The authors have studied the sedimentary series of transgression events in the coal-bearing strata and the characteristics of transgression sediments coming into contact with coal seams, summed up the points of transgression events and coal formation under the events, studied the mechanism of coal forming with transgression events, and put forward the theory of coal formation with transgression events in epicontinental sea coal aggregational basin. It is believed that the transgression events controlled the aggregation of coal in epicontinental sea basin, the rising of the base level provided favorable condition for the growth of peat swamp, while the large scale of transgression later on stopped the peat accumulation, which put the peat in a deoxidizing environment for a relatively short time for being preserved to form coal, and makes it impossible for very thick coal seams to be formed in such short period of peat swamp. That is to say, coal seams formed in such basin environment are mostly thin coal seams. The essential difference of coal formation with transgression events from that with transgression process is the isochronism. The latter is lacking in isochronism. There is no such continuous sedimentary series between sea facies layers and coal seams in the transgression event coal-forming model as in ordinary transgression process. The bottom floor of the coal seam is root clay, and there is interruption of sedimentation, which can be used as an important interface in dividing high-resolution sequences and the inside units. In the transgression event coal formation model has been proposed in the paper, the authors mainly emphasize the accidental event property. The transgression event played a controlling role in the aggregation of coal in the epicontinental sea basin. Peat accumulation results from the evolution of the environment caused by the rising of base level ahead of transgression. The peat accumulation can be said to take place during the period of sea level oscillation. If the accommodation needed for peat accumulation ion is stable for a long period, thick coal seam could be formed. The fact is that large scales of transgression enlarge the accommodation abruptly, which was not suitable for coal accumulation. Peat was submerged in deep water and coalification took place in a complete deoxidizing condition, also the gelatification was fairly complete. The happening proce
According to traditional coal-forming theory, coal formation was thought to take place in the water (marine) regression period of the transgression and regression cycle, that is, the land facies coal forming model. The author's basic point of view that coal was formed during sea transgression is gradually becoming a theory or model of coal formation, which shows coal formation was transferred gradually to land during the transgression coal forming closely related to transgression. Peat formed in advance was submerged in seawater, as a result, the coal seam formed was of diachronism. This theory and model is originated from the analyzing result of the coal formation in epicontinental sea basin, which is a contribution to coal geology and bring up a new way in the analysis of coal formation. In particular, it puts forward a question on how to evaluate the function of coal seam, in terms of a special sedimentary body in sequence stratigraphy analysis. As the diachronism of coal seams was caused by the transgressive coal formation, whether the top surface or the bottom surface of a coal seam can be taken as an interface of different sequence units remains to be studied in detail. The sea level change of North China epicontinental sea basin in the late paleozoic period is of the feature of high frequency and complexity, that is, the sea level changed with different frequencies and grades and the superposition of them, to cause to form a special unit of sediment body. Long period of sea regression contains many short periods of transgression events; also, there may be relatively short period of regression in the course of transgression. The authors have studied the sedimentary series of transgression events in the coal-bearing strata and the characteristics of transgression sediments coming into contact with coal seams, summed up the points of transgression events and coal formation under the events, studied the mechanism of coal forming with transgression events, and put forward the theory of coal formation with transgression events in epicontinental sea coal aggregational basin. It is believed that the transgression events controlled the aggregation of coal in epicontinental sea basin, the rising of the base level provided favorable condition for the growth of peat swamp, while the large scale of transgression later on stopped the peat accumulation, which put the peat in a deoxidizing environment for a relatively short time for being preserved to form coal, and makes it impossible for very thick coal seams to be formed in such short period of peat swamp. That is to say, coal seams formed in such basin environment are mostly thin coal seams. The essential difference of coal formation with transgression events from that with transgression process is the isochronism. The latter is lacking in isochronism. There is no such continuous sedimentary series between sea facies layers and coal seams in the transgression event coal-forming model as in ordinary transgression process. The bottom floor of the coal seam is root clay, and there is interruption of sedimentation, which can be used as an important interface in dividing high-resolution sequences and the inside units. In the transgression event coal formation model has been proposed in the paper, the authors mainly emphasize the accidental event property. The transgression event played a controlling role in the aggregation of coal in the epicontinental sea basin. Peat accumulation results from the evolution of the environment caused by the rising of base level ahead of transgression. The peat accumulation can be said to take place during the period of sea level oscillation. If the accommodation needed for peat accumulation ion is stable for a long period, thick coal seam could be formed. The fact is that large scales of transgression enlarge the accommodation abruptly, which was not suitable for coal accumulation. Peat was submerged in deep water and coalification took place in a complete deoxidizing condition, also the gelatification was fairly complete. The happening proce
2003, 21(2): 307-312.
Abstract:
On the basis of high-resolution sequence stratigraphy,the detailed study on the subdivision of different orders of the base-level cycles in middle Jurassic Yanan Formation has been performed in Yanshui river cross section,and a corresponding high-resolution sequence framework has been established in the middle part of Ordos Basin.There can be recognized 34 short,8 middle and 3 long base-level cycles.Simultaneously,the paper has also discussed the relationship between the stacking patterns of different cycles and sedimentary facies,deposition and tectonics,and furthermore,investigated the basinal filling history by the base-level cycle sequences.
On the basis of high-resolution sequence stratigraphy,the detailed study on the subdivision of different orders of the base-level cycles in middle Jurassic Yanan Formation has been performed in Yanshui river cross section,and a corresponding high-resolution sequence framework has been established in the middle part of Ordos Basin.There can be recognized 34 short,8 middle and 3 long base-level cycles.Simultaneously,the paper has also discussed the relationship between the stacking patterns of different cycles and sedimentary facies,deposition and tectonics,and furthermore,investigated the basinal filling history by the base-level cycle sequences.
2003, 21(2): 318-323.
Abstract:
On the base of the comprehensive analysis of seismic data, core and logging , we have discussed the method and principle of identifying sequence stratigraphical boundary with sonic logging, and its application in the study of sequence stratigraphy of Paleogene in Jiyang depression. The sequence boundary and the maximal lacustrine flooding surface (MLFS) are the key boundaries in the sequence strata. The sequence boundary corresponds to the unconformity surface or its corresponding conformity surface, and MLFS is the division surface between transgressive systems tract (TST) and high systems tract (HST), and condensed section (CS) can form near the MLFS. The regression line of the logarithm of interval transit-time of mud rocks versus its depth is a straight line in the basin under the normal imbedding and compacting conditions, but the unconformity usually leads to the formation of stratigraphical break, weathered crust and TST mud, and these characteristics also lead to the anomaly of the regression line, such as, the dislocation and different slope of the regression line above or below the unconformity surface and some anomaly of interval transit time below the unconformity surface, and they are the important identifying signs of sequence boundaries. The lithology of the CS is usually depth-water shale or mudstone, and it has high content of the organic substance and high interval transit time. The interval transit time is the highest at the location of the maximal lacustrine flooding surface, and becomes lower upward and downward in a sequence, and reach the lowest value at the location of the sequence boundary
On the base of the comprehensive analysis of seismic data, core and logging , we have discussed the method and principle of identifying sequence stratigraphical boundary with sonic logging, and its application in the study of sequence stratigraphy of Paleogene in Jiyang depression. The sequence boundary and the maximal lacustrine flooding surface (MLFS) are the key boundaries in the sequence strata. The sequence boundary corresponds to the unconformity surface or its corresponding conformity surface, and MLFS is the division surface between transgressive systems tract (TST) and high systems tract (HST), and condensed section (CS) can form near the MLFS. The regression line of the logarithm of interval transit-time of mud rocks versus its depth is a straight line in the basin under the normal imbedding and compacting conditions, but the unconformity usually leads to the formation of stratigraphical break, weathered crust and TST mud, and these characteristics also lead to the anomaly of the regression line, such as, the dislocation and different slope of the regression line above or below the unconformity surface and some anomaly of interval transit time below the unconformity surface, and they are the important identifying signs of sequence boundaries. The lithology of the CS is usually depth-water shale or mudstone, and it has high content of the organic substance and high interval transit time. The interval transit time is the highest at the location of the maximal lacustrine flooding surface, and becomes lower upward and downward in a sequence, and reach the lowest value at the location of the sequence boundary
2003, 21(2): 328-333.
Abstract:
It is prevalent and difficult to study oil-gas by inclusion in recent years. This paper presents time temperature index (TTI) method of judging hydrocarbon source condition by fluid inclusion in sedimentary rock. On the basis of fluid inclusion data of core in Ordos basin , TTI can be calculated out. We first calculate the capture temperatures and the capture pressure by the data of fluid inclusion microanalysis, then calculate the paleo-temperature gradient,the paleo-pressure gradient and the changable palaeo-temperature trajectory. Finally the time domain,the depth domain and the temperature domain of hydrocarbon-production can be worked out. We compare these calculated data with the data calculated in classic way , it shows that the inclusion TTI method is availabe and valid.
It is prevalent and difficult to study oil-gas by inclusion in recent years. This paper presents time temperature index (TTI) method of judging hydrocarbon source condition by fluid inclusion in sedimentary rock. On the basis of fluid inclusion data of core in Ordos basin , TTI can be calculated out. We first calculate the capture temperatures and the capture pressure by the data of fluid inclusion microanalysis, then calculate the paleo-temperature gradient,the paleo-pressure gradient and the changable palaeo-temperature trajectory. Finally the time domain,the depth domain and the temperature domain of hydrocarbon-production can be worked out. We compare these calculated data with the data calculated in classic way , it shows that the inclusion TTI method is availabe and valid.
2003, 21(2): 340-344.
Abstract:
The total organic carbon (TOC) of the mudstone formation in Songliao basin shows a regular distribution. Vertically, the high TOC value usually appears at base and decreases upwards in a given sediment unit. The regular change of TOC value as this is related to relative lake level change and sediment supply, and can be identified from the overlay log curves of sonic and resistance. Based on this method, it has been analyzed that the abundant of organic carbon and sequences of Nenjiang mudstone formation in Yingtai area, Songliao basin. The study show that the high content organic carbon appears at lower part of Nenjiang Formation, and the direction of sediment supply is from north to south. The content of organic carbon in source rock is higher in the south than north. Oil and gas exploration practice has proven that those results are true.
The total organic carbon (TOC) of the mudstone formation in Songliao basin shows a regular distribution. Vertically, the high TOC value usually appears at base and decreases upwards in a given sediment unit. The regular change of TOC value as this is related to relative lake level change and sediment supply, and can be identified from the overlay log curves of sonic and resistance. Based on this method, it has been analyzed that the abundant of organic carbon and sequences of Nenjiang mudstone formation in Yingtai area, Songliao basin. The study show that the high content organic carbon appears at lower part of Nenjiang Formation, and the direction of sediment supply is from north to south. The content of organic carbon in source rock is higher in the south than north. Oil and gas exploration practice has proven that those results are true.
2003, 21(2): 350-354.
Abstract:
On the basis of many methods, the main origin of deep layer natural gases in Duqiaobai area, Dongpu depression has been identified. The natural gases in Baimiao area mainly stemmed from the Tertiary Hydrocarbon source rock and Permo-Carboniferous coal-bearing strata in Qianliyuan depression. Shallow Es2 2—Es2 3 gas layer in structural high near to Lanliao fault zone possesses much high ratio 40 Ar/ 36Ar,which is coal formed gas and mixed gas .However, Es13—Es4 3 gas layer in structural low far from Lanliao fault zone has low ratio 40Ar/ 36Ar,which is petroligenic natural gas. Es3 3—Es4 3 gas layer is mainly petroligenic natural gas in Qiaokou area.Es3 3 gas layer in Duzhai area is petroligenic natural gas,which originated from the gas Es3 3source rock .And analysis on helium isotope of natural gas show that the deep-layer natural gases in Duzhai area and Qiaokou area is crust-derived gas and that it is mainly mixed gas of coal formed gas and petroligenic natural gas, with small portion of mantle-derived gas.
On the basis of many methods, the main origin of deep layer natural gases in Duqiaobai area, Dongpu depression has been identified. The natural gases in Baimiao area mainly stemmed from the Tertiary Hydrocarbon source rock and Permo-Carboniferous coal-bearing strata in Qianliyuan depression. Shallow Es2 2—Es2 3 gas layer in structural high near to Lanliao fault zone possesses much high ratio 40 Ar/ 36Ar,which is coal formed gas and mixed gas .However, Es13—Es4 3 gas layer in structural low far from Lanliao fault zone has low ratio 40Ar/ 36Ar,which is petroligenic natural gas. Es3 3—Es4 3 gas layer is mainly petroligenic natural gas in Qiaokou area.Es3 3 gas layer in Duzhai area is petroligenic natural gas,which originated from the gas Es3 3source rock .And analysis on helium isotope of natural gas show that the deep-layer natural gases in Duzhai area and Qiaokou area is crust-derived gas and that it is mainly mixed gas of coal formed gas and petroligenic natural gas, with small portion of mantle-derived gas.
2003, 21(2): 360-365.
Abstract:
Bimodal distribution was explored for n-alkanes in an oilsand sample from well Lunnan 14, Lunnan oilfield, Tarim Basin, NW China. GC-C-IRMS analyses indicated that the stable carbon isotopic compositions for nC 23～nC 32 n-alkanes (-32.02‰～-30.90‰) were isotopically heavier than that of nC 12～nC 22 n-alkanes (-33.72‰～-32.84‰) which reflect the contributions of two different organic matter inputs.In the mean time, high content mono-methyl branched alkane homologues were detected during the nC 23～nC 32 n-alkanes which have the same or similar stable carbon isotopic compositions (-30.52‰～-31.64‰) with nC 23～nC 32 n-alkanes. This seems to mean that they share the same genetic scheme. According to marvelous literatures and the measured stable carbon isotopic compositions, mono-methyl branched alkanes should be derived from microorganism, thus, a suspicion was put forward for the general biological precursor of which the high molecular weight n-alkanes (nC 23～nC 32) were derived from higher plant.
Bimodal distribution was explored for n-alkanes in an oilsand sample from well Lunnan 14, Lunnan oilfield, Tarim Basin, NW China. GC-C-IRMS analyses indicated that the stable carbon isotopic compositions for nC 23～nC 32 n-alkanes (-32.02‰～-30.90‰) were isotopically heavier than that of nC 12～nC 22 n-alkanes (-33.72‰～-32.84‰) which reflect the contributions of two different organic matter inputs.In the mean time, high content mono-methyl branched alkane homologues were detected during the nC 23～nC 32 n-alkanes which have the same or similar stable carbon isotopic compositions (-30.52‰～-31.64‰) with nC 23～nC 32 n-alkanes. This seems to mean that they share the same genetic scheme. According to marvelous literatures and the measured stable carbon isotopic compositions, mono-methyl branched alkanes should be derived from microorganism, thus, a suspicion was put forward for the general biological precursor of which the high molecular weight n-alkanes (nC 23～nC 32) were derived from higher plant.
