2009 Vol. 34, No. 5
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2009, 34(5): 717-724.
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Abstract:
A significant tectonic event was recorded in late Oligocene sediments from ODP Site 1148 and Pearl River Mouth Basin.This tectonic event coincided with the seafloor spreading axis jump event across the Oligocene/Miocene boundary, leading to a series of changes not only in seafloor spreading direction but also types of sedimentary basins and sediment provenances, and representing the greatest tectonic activity in the South China Sea region since the Oligocene.Sedimentation breaks and slumps as well as obvious changes in sediment composition across the Oligocene/Miocene boundary indicate the existence of the tectonic event, which transformed the Pearl River Mouth Basin from a graben basin to a down-warped basin, and the sedimentary environment in the Baiyun Sag area from continental shelf in the late Oligocene to continental slope since the early Miocene.It played a key role in the transformation of the general topographic character in continental China and ended a period of accumulation of good source rock for petroleum offshore.Therefore, this tectonic event has a profound influence on the evolution of the South China Sea and East Asia.
A significant tectonic event was recorded in late Oligocene sediments from ODP Site 1148 and Pearl River Mouth Basin.This tectonic event coincided with the seafloor spreading axis jump event across the Oligocene/Miocene boundary, leading to a series of changes not only in seafloor spreading direction but also types of sedimentary basins and sediment provenances, and representing the greatest tectonic activity in the South China Sea region since the Oligocene.Sedimentation breaks and slumps as well as obvious changes in sediment composition across the Oligocene/Miocene boundary indicate the existence of the tectonic event, which transformed the Pearl River Mouth Basin from a graben basin to a down-warped basin, and the sedimentary environment in the Baiyun Sag area from continental shelf in the late Oligocene to continental slope since the early Miocene.It played a key role in the transformation of the general topographic character in continental China and ended a period of accumulation of good source rock for petroleum offshore.Therefore, this tectonic event has a profound influence on the evolution of the South China Sea and East Asia.
2009, 34(5): 725-732.
Abstract:
Trace element compositions in Upper Permian conodonts with low color alteration index were measured in situ by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) from a stratigraphic section of the Meishan in Changxing, Zhejiang Province.The results show that the Ce anomalies and rare earth element (REE) concentrations are characterized by fast fluctuation.These features indicate highly fluctuating environmental conditions including redox and instable ecosystem conditions during the P/T transition.The element compositions couple well with the paleo-oceanic environment and the biotic crisis.The study effective defines and offers new approach for the key issues to the biotic extinction and recovery process, time limit, paleo-ocean chemistry and paleoecology at the end of the Permian.
Trace element compositions in Upper Permian conodonts with low color alteration index were measured in situ by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) from a stratigraphic section of the Meishan in Changxing, Zhejiang Province.The results show that the Ce anomalies and rare earth element (REE) concentrations are characterized by fast fluctuation.These features indicate highly fluctuating environmental conditions including redox and instable ecosystem conditions during the P/T transition.The element compositions couple well with the paleo-oceanic environment and the biotic crisis.The study effective defines and offers new approach for the key issues to the biotic extinction and recovery process, time limit, paleo-ocean chemistry and paleoecology at the end of the Permian.
2009, 34(5): 733-742.
Abstract:
According to the vertical distribution of bivalves in the Lower Triassic Daye Formation at the Xiakou Section in Xingshan, Hubei Province, four bivalve biostratigraphic zones are recognized in ascending order: Claraia stachei-C.griesbachi Zone, Claraia concentrica-C.hubeiensis Zone, Eumorphotis multiformis-E.inaequicostata Zone, and Posidonia.circularis-P.cf. wengensis Zone.In addition, based on the occurrence and ecology of bivalves and their associations as well as the sedimentary facies, three communities are retrieved, i.e.Claraia concentrica-C.aurita Community, Eumorphotis inaequicostata-E.multiformis Community, and Posidonia circularis Community.The evolutionary succession of the communities indicates that the area was shallow in the early Dienerian and became deeper since then with the transgression in the Early Triassic.The turbulence of the Early Triassic environment prolongated the restoration of marine ecosystem after the end-Permian mass extinction.
According to the vertical distribution of bivalves in the Lower Triassic Daye Formation at the Xiakou Section in Xingshan, Hubei Province, four bivalve biostratigraphic zones are recognized in ascending order: Claraia stachei-C.griesbachi Zone, Claraia concentrica-C.hubeiensis Zone, Eumorphotis multiformis-E.inaequicostata Zone, and Posidonia.circularis-P.cf. wengensis Zone.In addition, based on the occurrence and ecology of bivalves and their associations as well as the sedimentary facies, three communities are retrieved, i.e.Claraia concentrica-C.aurita Community, Eumorphotis inaequicostata-E.multiformis Community, and Posidonia circularis Community.The evolutionary succession of the communities indicates that the area was shallow in the early Dienerian and became deeper since then with the transgression in the Early Triassic.The turbulence of the Early Triassic environment prolongated the restoration of marine ecosystem after the end-Permian mass extinction.
2009, 34(5): 743-751.
Abstract:
Well-preserved stratigraphic sequences composed of radiolarian chert and basalt were found in Pha Som metamorphic complex in Nan suture zone, northern Thailand.Bedded chert contains Follicucullus porrectus, fossils from late Middle Permian to early Late Permian.These cherts have high SiO2 (> 92.5%), low Al/ (Al+Fe+Mn) ratio (0.51 on average), and high Ce/Ce ratio (1.14 on average).These geochemical characteristics mentioned above indicate that the cherts deposited on continental margins.The basalt has high abundances of large ion lithophile elements (LILE), high field strength elements (HFSE), and light rare earth lements (LREE), suggesting characteristics of oceanic island basalt (OIB).The OIB characteristics of basalts and deep-sea-basin chert imply that the Nan suture zone was a small oceanic basin, which is similar to modern Southwest Pacific.The Nan Ocean presumably closed during the period from Late Permian to Late Triassic.
Well-preserved stratigraphic sequences composed of radiolarian chert and basalt were found in Pha Som metamorphic complex in Nan suture zone, northern Thailand.Bedded chert contains Follicucullus porrectus, fossils from late Middle Permian to early Late Permian.These cherts have high SiO2 (> 92.5%), low Al/ (Al+Fe+Mn) ratio (0.51 on average), and high Ce/Ce ratio (1.14 on average).These geochemical characteristics mentioned above indicate that the cherts deposited on continental margins.The basalt has high abundances of large ion lithophile elements (LILE), high field strength elements (HFSE), and light rare earth lements (LREE), suggesting characteristics of oceanic island basalt (OIB).The OIB characteristics of basalts and deep-sea-basin chert imply that the Nan suture zone was a small oceanic basin, which is similar to modern Southwest Pacific.The Nan Ocean presumably closed during the period from Late Permian to Late Triassic.
2009, 34(5): 752-758.
Abstract:
Petrographic microscope, XRD, infra-red spectrometer, electron spin resonance (ESR), Raman spectrometer, atomic absorption spectrometer were used to analyze the mineralogical and chemical composition of seawater and fresh water cultured pearls in this paper.The results show that pearls mainly consist of aragonite, with very few varterite and calcite.Fresh water cultured pearls are rich in Mn, but sea water cultured pearls rich in Na, K, Mg, and Sr.The enrichement character of freshwater pearl and seawater pearl is very similar to that of fresh water and seawater.There are detectable differences in chemical composition among different colored varieties.Violet pearls are slightly rich in Mg and Mn, orange pearls distinctively rich in Fe, and black seawater pearls probably have high organic contents.By contrast, white pearls contain little coloring elements such as Fe, Mg, and Cr.
Petrographic microscope, XRD, infra-red spectrometer, electron spin resonance (ESR), Raman spectrometer, atomic absorption spectrometer were used to analyze the mineralogical and chemical composition of seawater and fresh water cultured pearls in this paper.The results show that pearls mainly consist of aragonite, with very few varterite and calcite.Fresh water cultured pearls are rich in Mn, but sea water cultured pearls rich in Na, K, Mg, and Sr.The enrichement character of freshwater pearl and seawater pearl is very similar to that of fresh water and seawater.There are detectable differences in chemical composition among different colored varieties.Violet pearls are slightly rich in Mg and Mn, orange pearls distinctively rich in Fe, and black seawater pearls probably have high organic contents.By contrast, white pearls contain little coloring elements such as Fe, Mg, and Cr.
2009, 34(5): 759-768.
Abstract:
The carbonate cementation and secondary dissolution porosity in the deep-burial sandstones near the top overpressured surface (present-day depths: 4 400-6 200 m and temperatures: 105-145 ℃) in the central part of Junggar Basin are intimately related to the overpressured fluid activities.Periodic decreases of pore pressures and changes of formation hydrochemical conditions as sealing and releasing of overpressures along the top overpressured surface can result the processes of carbonate precipitation and aluminosilicate dissolving in the sandstones.Based on the data of diagenesis, carbonate cement content, sandstone property, carbon and oxygen isotope of carbonate cement, thermal maturity modeling of source rocks and so on, integrated studies indicate as fellows: The ferroan carbonate cements are the dominated cements formed in the late diagenesis stage, and the feldspar-related secondary dissolved pores are the most important pore types in the deep-burial sandstone reservoirs.The thickness scopes are more than 550 m, occurring 100 m below the top overpressured surface and over 450 m above the surface, while the carbonate cement contents reach or exceed the values of 15% to 30%.The thickness intervals are 250-300 m above the top overpressured surface while the carbonate cement contents reach or exceed the values of 25%.The depth intervals of up to 10%-20% secondary dissolving porosity are concomitant with the depth ranges of relative high carbonate cement contents.Since the late Cretaceous, the carbonate-riched fluid flows have been produced frequently as the development of hydrocarbon generation pressures from the deep Jurassic coal-bearing strata, and the carbonate cements have been influenced evidently by the overpressured and thermal fluids, implying that the late-stage ferroan calcite carbon is partly originated from the organic-matter thermal degradation.The secondary porosity zones in the deep-burial sandstones near the top overpressured surface have been formed during the processes of acid-fluid expulsion and migration due to upward releases of overpressures along the diagenetic barrier associated with the top carbonate mineralization zones.
The carbonate cementation and secondary dissolution porosity in the deep-burial sandstones near the top overpressured surface (present-day depths: 4 400-6 200 m and temperatures: 105-145 ℃) in the central part of Junggar Basin are intimately related to the overpressured fluid activities.Periodic decreases of pore pressures and changes of formation hydrochemical conditions as sealing and releasing of overpressures along the top overpressured surface can result the processes of carbonate precipitation and aluminosilicate dissolving in the sandstones.Based on the data of diagenesis, carbonate cement content, sandstone property, carbon and oxygen isotope of carbonate cement, thermal maturity modeling of source rocks and so on, integrated studies indicate as fellows: The ferroan carbonate cements are the dominated cements formed in the late diagenesis stage, and the feldspar-related secondary dissolved pores are the most important pore types in the deep-burial sandstone reservoirs.The thickness scopes are more than 550 m, occurring 100 m below the top overpressured surface and over 450 m above the surface, while the carbonate cement contents reach or exceed the values of 15% to 30%.The thickness intervals are 250-300 m above the top overpressured surface while the carbonate cement contents reach or exceed the values of 25%.The depth intervals of up to 10%-20% secondary dissolving porosity are concomitant with the depth ranges of relative high carbonate cement contents.Since the late Cretaceous, the carbonate-riched fluid flows have been produced frequently as the development of hydrocarbon generation pressures from the deep Jurassic coal-bearing strata, and the carbonate cements have been influenced evidently by the overpressured and thermal fluids, implying that the late-stage ferroan calcite carbon is partly originated from the organic-matter thermal degradation.The secondary porosity zones in the deep-burial sandstones near the top overpressured surface have been formed during the processes of acid-fluid expulsion and migration due to upward releases of overpressures along the diagenetic barrier associated with the top carbonate mineralization zones.
2009, 34(5): 769-777.
Abstract:
In order to assess correctly the flux of CH 4 emitted naturally from oil/gas basin, a static flux chamber method was applied to study natural emissions of methane to the atmosphere in oil-water interface of Yakela condensed oil/gas field in Tarim basin, Xinjiang.Using an online method which couples a gas chromatography/high-temperature conversion/isotope ratio mass spectrometry (GC/C/MS) together, 13C/12C ratios of the methane in flux chambers were measured.The results demonstrate that oxidation environments of soil and water are different in the oil-water interface because chambers lie in different places.So, fluxes of methane emission in the chambers are very different.The maximum daily flux of methane emission is 2.28 mg/m2·d and the minimum-1.32 mg/m2·d.The average daily flux of methane emission is 0.51 mg/m2·d with the standard deviation of 1.23 mg/m2·d.Although there are large differences in flux of methane emission in the oil-water interface, daily change laws are similar: the methane emission flux reaches the maximum at 5:00-6:00 am, and then it decreases gradually, and reaches the minimum at 17:00-18:00 pm, and then it gradually increases.Measurement of carbon isotope of methane shows that δ13C of methane becomes heavier with decreasing concentration in the afternoon and with increasing concentration in the morning.Thus it can be seen that the soil above the oil-water interface becomes a more oxidation environment because water contains O2. Methane is absorbed and oxidated constantly during migration to the earth's surface from deep oil/gas reservoir through microseepage and pervasion.Only a little methane which is not oxidized and degraded is discharged into the atmosphere through diffusing and convection.Even all methane is absorbed by soil in some areas, which leads to the sink of atmospheric methane.
In order to assess correctly the flux of CH 4 emitted naturally from oil/gas basin, a static flux chamber method was applied to study natural emissions of methane to the atmosphere in oil-water interface of Yakela condensed oil/gas field in Tarim basin, Xinjiang.Using an online method which couples a gas chromatography/high-temperature conversion/isotope ratio mass spectrometry (GC/C/MS) together, 13C/12C ratios of the methane in flux chambers were measured.The results demonstrate that oxidation environments of soil and water are different in the oil-water interface because chambers lie in different places.So, fluxes of methane emission in the chambers are very different.The maximum daily flux of methane emission is 2.28 mg/m2·d and the minimum-1.32 mg/m2·d.The average daily flux of methane emission is 0.51 mg/m2·d with the standard deviation of 1.23 mg/m2·d.Although there are large differences in flux of methane emission in the oil-water interface, daily change laws are similar: the methane emission flux reaches the maximum at 5:00-6:00 am, and then it decreases gradually, and reaches the minimum at 17:00-18:00 pm, and then it gradually increases.Measurement of carbon isotope of methane shows that δ13C of methane becomes heavier with decreasing concentration in the afternoon and with increasing concentration in the morning.Thus it can be seen that the soil above the oil-water interface becomes a more oxidation environment because water contains O2. Methane is absorbed and oxidated constantly during migration to the earth's surface from deep oil/gas reservoir through microseepage and pervasion.Only a little methane which is not oxidized and degraded is discharged into the atmosphere through diffusing and convection.Even all methane is absorbed by soil in some areas, which leads to the sink of atmospheric methane.
2009, 34(5): 778-784.
Abstract:
As one of the most important offshore basins in China, there exist many different kinds of fluid diapirs in the Pearl River Mouth basin, which have been introduced in some papers.However, the systemic study of these diapirs is still to be expected on its classification and origin, which can understand fluid migration better.Fluid diapir structure is a special style of fluid migrating upwards.The aim of this paper is to identify and classify the fluid diapir structure, to analyze the messages implied by the fluid diapir structure, to find out a new method of evaluating the fluid diapir structure characterized by the blank seismic reflection, and to discuss the origin of the diapirs according to basin modeling and structure analysis.On the basis of the investigation, we can come to the following conclusions: (1) There are four kinds of diapirs in the Pearl River Mouth basin including the turtleback-like arch, mud diapir, gas seepage, fault (or crack), which indicate different geological messages; (2) Structure activity rather than the overpressure is the primary driving pressure on diapirs.
As one of the most important offshore basins in China, there exist many different kinds of fluid diapirs in the Pearl River Mouth basin, which have been introduced in some papers.However, the systemic study of these diapirs is still to be expected on its classification and origin, which can understand fluid migration better.Fluid diapir structure is a special style of fluid migrating upwards.The aim of this paper is to identify and classify the fluid diapir structure, to analyze the messages implied by the fluid diapir structure, to find out a new method of evaluating the fluid diapir structure characterized by the blank seismic reflection, and to discuss the origin of the diapirs according to basin modeling and structure analysis.On the basis of the investigation, we can come to the following conclusions: (1) There are four kinds of diapirs in the Pearl River Mouth basin including the turtleback-like arch, mud diapir, gas seepage, fault (or crack), which indicate different geological messages; (2) Structure activity rather than the overpressure is the primary driving pressure on diapirs.
2009, 34(5): 785-791.
Abstract:
Studies of hydrocarbon charging events and ages have always been the hot and core issues of oil and gas migration and accumulation processes. In this research, systematic fluid inclusion analytical technology, such as fluorescent colors, micrcrobeam of fluorescent spectrum and the homogenization temperature (Th) of oil fluid inclusion, has been employed to find out that since the Carboniferous, there are three hydrocarbon charging events in the igneous reservoirs of Santanghu basin, and their charging ages are determined by Th projection on burial history curves method as follows: the first event occurred during 259-230 Ma, the second event 160-134 Ma, and the third event 72-0 Ma respectively. The regional hydrocarbon migration directions indicated by oil inclusion maturities suggest that the deep igneous reservoirs in the basin may have accumulated the earliest hydrocarbon (the Hercynian), which may be the favorable site for the next exploration.
Studies of hydrocarbon charging events and ages have always been the hot and core issues of oil and gas migration and accumulation processes. In this research, systematic fluid inclusion analytical technology, such as fluorescent colors, micrcrobeam of fluorescent spectrum and the homogenization temperature (Th) of oil fluid inclusion, has been employed to find out that since the Carboniferous, there are three hydrocarbon charging events in the igneous reservoirs of Santanghu basin, and their charging ages are determined by Th projection on burial history curves method as follows: the first event occurred during 259-230 Ma, the second event 160-134 Ma, and the third event 72-0 Ma respectively. The regional hydrocarbon migration directions indicated by oil inclusion maturities suggest that the deep igneous reservoirs in the basin may have accumulated the earliest hydrocarbon (the Hercynian), which may be the favorable site for the next exploration.
2009, 34(5): 792-798.
Abstract:
According to measurement of carbon isotopes of gaseous alkanes thermally cracked from the hydrocarbon sources and oil under closed system pyrolysis, the results suggest that the reversal occurrence for carbon isotopes of heavy gaseous alkanses (δ13C2 > δ13C3 > δ13C4) would be caused by single thermal dynamics, whereas the reversal trends of δ13C1 and δ13C2 (δ13C1 > δ13C2) could not be observed.The natural gases in the Qingshen gas field are characterized by the less negative δ13C1 values, reversal series of carbon isotopes for gaseous alkanes and high R/Ra values (R/Ra > 1.0), indicating natural gases should have stemmed from multi-sources.Based on the correlation of R/Ra and CO2/3He, R/Ra and CH4/3He, the genesis of natural gases from the Qingshen gas field were identified.The hydrocarbon gases in the Qingshen gas field are a mixture of alkanes, in which the heavy gaseous alkanes were derived from the thermal decomposition of organic matters due to the high geothermal gradient, whereas mixing of inorganic methane into organic gas caused the reversal of the carbon isotopic trend of CH4 and C2H6.
According to measurement of carbon isotopes of gaseous alkanes thermally cracked from the hydrocarbon sources and oil under closed system pyrolysis, the results suggest that the reversal occurrence for carbon isotopes of heavy gaseous alkanses (δ13C2 > δ13C3 > δ13C4) would be caused by single thermal dynamics, whereas the reversal trends of δ13C1 and δ13C2 (δ13C1 > δ13C2) could not be observed.The natural gases in the Qingshen gas field are characterized by the less negative δ13C1 values, reversal series of carbon isotopes for gaseous alkanes and high R/Ra values (R/Ra > 1.0), indicating natural gases should have stemmed from multi-sources.Based on the correlation of R/Ra and CO2/3He, R/Ra and CH4/3He, the genesis of natural gases from the Qingshen gas field were identified.The hydrocarbon gases in the Qingshen gas field are a mixture of alkanes, in which the heavy gaseous alkanes were derived from the thermal decomposition of organic matters due to the high geothermal gradient, whereas mixing of inorganic methane into organic gas caused the reversal of the carbon isotopic trend of CH4 and C2H6.
2009, 34(5): 799-805.
Abstract:
The experiments of hydrocarbon-generating dynamics in opening system on 18 samples of different lithology and kerogen types in western depression of Liaohe basin were carried out, and the results show that there exists huge difference between different kerogen types of the same lithology: the better the kerogen types, the lower of the average activity energy; while the larger of the corresponding reaction fraction of dominated frequency activity energy, the narrower distribution range of the activity energy, which shows that the kerogen type has a deciding function on hydrocarbon-generating of the source rock.By using the parallel first-order reaction model, taking the burial history and thermal history into comprehensive consideration, we did a quantitive study on the hydrocarbon-generating history of the source rock of the western depression, Liaohe basin.The results show that the Sha 3 and Sha 4 formations are the main source layers, which account for 63.9% and 18.5% the total amount of hydrocarbon-generating respectively.Sha 1-2 and Dongying formations are the secondary source rock layers, and the accumulative hydrocarbon generation amounts to 328.09×108 t of the four source rock layers in total.The Dongying deposition period is the main hydrocarbon-generating time.
The experiments of hydrocarbon-generating dynamics in opening system on 18 samples of different lithology and kerogen types in western depression of Liaohe basin were carried out, and the results show that there exists huge difference between different kerogen types of the same lithology: the better the kerogen types, the lower of the average activity energy; while the larger of the corresponding reaction fraction of dominated frequency activity energy, the narrower distribution range of the activity energy, which shows that the kerogen type has a deciding function on hydrocarbon-generating of the source rock.By using the parallel first-order reaction model, taking the burial history and thermal history into comprehensive consideration, we did a quantitive study on the hydrocarbon-generating history of the source rock of the western depression, Liaohe basin.The results show that the Sha 3 and Sha 4 formations are the main source layers, which account for 63.9% and 18.5% the total amount of hydrocarbon-generating respectively.Sha 1-2 and Dongying formations are the secondary source rock layers, and the accumulative hydrocarbon generation amounts to 328.09×108 t of the four source rock layers in total.The Dongying deposition period is the main hydrocarbon-generating time.
2009, 34(5): 806-810.
Abstract:
At present, oil recovery by CO2 driving is getting increasingly important.In order to probe into the flow mechanism of CO2 in miscible state, a high temperature and high pressure 3-D device was used to study miscible flooding of CO2 and oil.With this experiment, it is found that there is a big difference between the production and the injection volume.The complex flowing characteristics of CO2 flooding in porous media are observed in the recovery, water cut and gas-oil ratio curves.By analyzing water saturation distribution map which is measured by saturation probe, it is proved that CO2 and oil can be miscible.The viscosity of miscible liquid and flowing pressure decreases, which is one of the important mechanisms in enhanced oil recovery.At the same time, miscible CO2 and oil contacted with water can make up a similar 3 phase state.Experiment results also show that the main reason for the difference between the production and the injection is that CO2 can flow into micro pores in high density gas state while water and oil cann't.
At present, oil recovery by CO2 driving is getting increasingly important.In order to probe into the flow mechanism of CO2 in miscible state, a high temperature and high pressure 3-D device was used to study miscible flooding of CO2 and oil.With this experiment, it is found that there is a big difference between the production and the injection volume.The complex flowing characteristics of CO2 flooding in porous media are observed in the recovery, water cut and gas-oil ratio curves.By analyzing water saturation distribution map which is measured by saturation probe, it is proved that CO2 and oil can be miscible.The viscosity of miscible liquid and flowing pressure decreases, which is one of the important mechanisms in enhanced oil recovery.At the same time, miscible CO2 and oil contacted with water can make up a similar 3 phase state.Experiment results also show that the main reason for the difference between the production and the injection is that CO2 can flow into micro pores in high density gas state while water and oil cann't.
2009, 34(5): 811-818.
Abstract:
The top part of a giant IMAGE core MD05-2908 taken from the South Okinawa Trough was investigated for the sake of understanding the climate evolution in Donghai seacoast areas since the last millennium.Sporopollen and organic carbon isotope records of bulk sediments were used as proxies to trace the climate variations and terrigenous materials discharges.Time series were demarcated by 4 AMS 14 C dating ages.Comprehensive data of sporopollen and carbon isotopic composition, together with the paleoenvironmental records show that in the South Okinawa Trough the terrigenous material discharges fluctuated obviously for the past 1 000 years.Three relatively high terrigenous material discharge periods, corresponding to 1 100-1 040 a BP, 960-880 a BP and 800-480 a BP respectively and two quite low terrigenous material discharge periods, namely, 1 040-960 a BP and 480-230 a BP, can be identified from our records.In comparison with the stalagmite δ 13 C records (which were used to trace the East Asian Summer Monsoon) from Buddha Cave, Shaanxi Province, we found that the variations of terrigenous material discharges might be related closely to variations of the East Asian Summer Monsoon (EASM).Weaker EASM resulted in a convergence rain belt and longer residence time in the South China regions, which increased the efficiency of weathering and denudation of the source area.Moreover, increased rainfall enhanced the land runoff and as a result more terrigenous materials were transported to the South Okinawa Trough.
The top part of a giant IMAGE core MD05-2908 taken from the South Okinawa Trough was investigated for the sake of understanding the climate evolution in Donghai seacoast areas since the last millennium.Sporopollen and organic carbon isotope records of bulk sediments were used as proxies to trace the climate variations and terrigenous materials discharges.Time series were demarcated by 4 AMS 14 C dating ages.Comprehensive data of sporopollen and carbon isotopic composition, together with the paleoenvironmental records show that in the South Okinawa Trough the terrigenous material discharges fluctuated obviously for the past 1 000 years.Three relatively high terrigenous material discharge periods, corresponding to 1 100-1 040 a BP, 960-880 a BP and 800-480 a BP respectively and two quite low terrigenous material discharge periods, namely, 1 040-960 a BP and 480-230 a BP, can be identified from our records.In comparison with the stalagmite δ 13 C records (which were used to trace the East Asian Summer Monsoon) from Buddha Cave, Shaanxi Province, we found that the variations of terrigenous material discharges might be related closely to variations of the East Asian Summer Monsoon (EASM).Weaker EASM resulted in a convergence rain belt and longer residence time in the South China regions, which increased the efficiency of weathering and denudation of the source area.Moreover, increased rainfall enhanced the land runoff and as a result more terrigenous materials were transported to the South Okinawa Trough.
2009, 34(5): 819-828.
Abstract:
To discuss the non-synchronous change of accommodation space and sequence stacking patterns in both sides of a basin, using the SEDPAK two-dimensional stratigraphic modelling program, the "transformation system of the accommodation space" within a basin was simulated by considering the various parameters controlling the deposition of a sequence. The simulation results indicate that isochronous sequence stratigraphy within a basin may exhibit both synchronous and non-synchronous stacking patterns at different part of the basin. Synchronous stacking patterns were observed to be primarily developed during the lowstand system tracts and the late highstand system tracts. Non-synchronous stacking patterns were found to be often associated with the transgressive system tracts and the early highstand system tracts. The development of non-synchronous stacking patterns may occur under a number of circumstances within a basin with the right combination of various parameters. Nonsynchronous stacking patterns of isochronous sequence stratigraphy may provide new reference to identify system tracts interface and develop sequence stratigraphie correlation.
To discuss the non-synchronous change of accommodation space and sequence stacking patterns in both sides of a basin, using the SEDPAK two-dimensional stratigraphic modelling program, the "transformation system of the accommodation space" within a basin was simulated by considering the various parameters controlling the deposition of a sequence. The simulation results indicate that isochronous sequence stratigraphy within a basin may exhibit both synchronous and non-synchronous stacking patterns at different part of the basin. Synchronous stacking patterns were observed to be primarily developed during the lowstand system tracts and the late highstand system tracts. Non-synchronous stacking patterns were found to be often associated with the transgressive system tracts and the early highstand system tracts. The development of non-synchronous stacking patterns may occur under a number of circumstances within a basin with the right combination of various parameters. Nonsynchronous stacking patterns of isochronous sequence stratigraphy may provide new reference to identify system tracts interface and develop sequence stratigraphie correlation.
2009, 34(5): 829-834.
Abstract:
The aim of this paper is to test a new approach-tectono-sedimention analysis to gain insights into the controls of Laoyemiao transverse fold on the fan delta of Dongying Formation.By investigating the features of basin-bounding master fault (Xi'nanzhuang fault) and fold geometry in Laoyemiao region, we have determined that Laoyemiao fold is essentially a transverse fold produced by Xi'nanzhuang fault flexural.The fold with axes trending NW-SE was developed in sedimentary period of the 1 st Member of Shahejie Fm., and superimposed by Miocene NE trending strike-slip faults.Calculation of gravel content shows that the high values zone basically coincides with the hinge, which in turn reveals that the joint of the transverse fold and Xi'nanzhuang fault is the main drainage entry, and fold hinge provides major sediment long distance transportation pathway.From logging, seismic data and paleogeomorphology, the upper and lower slope break of transverse fold are identified.The sedimentary facies interpretation shows that they are consistent with the delimits of fan-delta plain and front, fan-delta front and pro-fan delta respectively.It can be proved that transverse fold constrains the facies distribution.Transverse folds caused by basin-bounding master fault are widely developed in sedimentary basins.The established model of sediment transportation for long distance and facies distribution of transverse fold is significant for favorable sandbodies prediction.
The aim of this paper is to test a new approach-tectono-sedimention analysis to gain insights into the controls of Laoyemiao transverse fold on the fan delta of Dongying Formation.By investigating the features of basin-bounding master fault (Xi'nanzhuang fault) and fold geometry in Laoyemiao region, we have determined that Laoyemiao fold is essentially a transverse fold produced by Xi'nanzhuang fault flexural.The fold with axes trending NW-SE was developed in sedimentary period of the 1 st Member of Shahejie Fm., and superimposed by Miocene NE trending strike-slip faults.Calculation of gravel content shows that the high values zone basically coincides with the hinge, which in turn reveals that the joint of the transverse fold and Xi'nanzhuang fault is the main drainage entry, and fold hinge provides major sediment long distance transportation pathway.From logging, seismic data and paleogeomorphology, the upper and lower slope break of transverse fold are identified.The sedimentary facies interpretation shows that they are consistent with the delimits of fan-delta plain and front, fan-delta front and pro-fan delta respectively.It can be proved that transverse fold constrains the facies distribution.Transverse folds caused by basin-bounding master fault are widely developed in sedimentary basins.The established model of sediment transportation for long distance and facies distribution of transverse fold is significant for favorable sandbodies prediction.
2009, 34(5): 835-840.
Abstract:
Sparse-spike deconvolution is an inverse issue which estimates the time and the amplitudes of the sparseness reflectivity (spikes) from the noisy seismic traces.Sparseness spike inverse is highly non-linear optimization problem that can be solved using the L1-L2 norm constrained method introduced in this paper.This method is characterized with its application of the log-barrier interior point to solve the sparseness inverse problem which is higher in terms of resolution and faster than conventional optimization methods.Resultsfrom the synthetic and real 3D data show that the physically meaningful high-resolution sparse-spike profile can be derived from the band-limited noisy data.Real data show that the method improves seismic resolution and estimates the thickness of thin bed which can reduce the uncertainty of resource estimation and oil field production.
Sparse-spike deconvolution is an inverse issue which estimates the time and the amplitudes of the sparseness reflectivity (spikes) from the noisy seismic traces.Sparseness spike inverse is highly non-linear optimization problem that can be solved using the L1-L2 norm constrained method introduced in this paper.This method is characterized with its application of the log-barrier interior point to solve the sparseness inverse problem which is higher in terms of resolution and faster than conventional optimization methods.Resultsfrom the synthetic and real 3D data show that the physically meaningful high-resolution sparse-spike profile can be derived from the band-limited noisy data.Real data show that the method improves seismic resolution and estimates the thickness of thin bed which can reduce the uncertainty of resource estimation and oil field production.
2009, 34(5): 841-847.
Abstract:
To understand the response of array laterolog to fracture in the fractured reservoir, based on the plane model of parallel fractures with equal space, the three-dimensional finite element method is used to simulate the responses of the high-definition array laterolog in fractured formation with different fracture parameters.The results show that conductivitites of array laterolog are linearly related to the porosity of fracture and the conductivity of pore fluid.A negative separation between the deep and shallow resistivity appears in the low-angle fractured formation, the positive appears in high-angle conditions.Apparent resistivity increases gradually with fracture density increasing under the same porosity of fracture conditions.If fracture density is large enough, the log response will not vary with essentially fracture density.Log response of crossing fracture is apparently different from that of the parallel fracture group with the same angle, and log response of crossing fracture is different under the different dip grouping system.Accordingly the array laterolog is sensitive to the fracture and its apparent resistivity can be used to determine the fracture porosity and the separation between the deep and shallow apparent resistivity can be used to study the fracture attitude.The above researches have contributions to the application of array laterolog in the fractured reservoir evaluation.
To understand the response of array laterolog to fracture in the fractured reservoir, based on the plane model of parallel fractures with equal space, the three-dimensional finite element method is used to simulate the responses of the high-definition array laterolog in fractured formation with different fracture parameters.The results show that conductivitites of array laterolog are linearly related to the porosity of fracture and the conductivity of pore fluid.A negative separation between the deep and shallow resistivity appears in the low-angle fractured formation, the positive appears in high-angle conditions.Apparent resistivity increases gradually with fracture density increasing under the same porosity of fracture conditions.If fracture density is large enough, the log response will not vary with essentially fracture density.Log response of crossing fracture is apparently different from that of the parallel fracture group with the same angle, and log response of crossing fracture is different under the different dip grouping system.Accordingly the array laterolog is sensitive to the fracture and its apparent resistivity can be used to determine the fracture porosity and the separation between the deep and shallow apparent resistivity can be used to study the fracture attitude.The above researches have contributions to the application of array laterolog in the fractured reservoir evaluation.
2009, 34(5): 848-854.
Abstract:
In order to study the difference and its controlling mechanism of gas adsorption on coals with different body structures, such parameters as the macroscopic petrographic constituents, the adsorption capacity and pore structure of undeformed and mylonitic coal samples of Jiaozuo coalfield, were measured. The experimental results show that the mylonitic coal is of higher ability of absorption and desorption than that of the undeformed coal. With the rising of temperature, the mylonitic coal is more evident than undeformed coal in the tendency of decline in absorption and increase in desorption. The study concludes that the pores in different pore diameter increases after the coal body is deformed, so the gas-containing capacity of mylonitic coals is stronger. Especially, the contents of macroand meso-pore are higher in mylonitic coals, so the desorption becomes easier. Moreover, other factors, including the coal rank rise, the vitrinite content increase and inertinite content decrease after the coal body is deformed, lead to the increase of absorption ability. The study also concludes that the ash content is not the main controlling factor on the adsorption difference between two types of coals with different coal body structures.
In order to study the difference and its controlling mechanism of gas adsorption on coals with different body structures, such parameters as the macroscopic petrographic constituents, the adsorption capacity and pore structure of undeformed and mylonitic coal samples of Jiaozuo coalfield, were measured. The experimental results show that the mylonitic coal is of higher ability of absorption and desorption than that of the undeformed coal. With the rising of temperature, the mylonitic coal is more evident than undeformed coal in the tendency of decline in absorption and increase in desorption. The study concludes that the pores in different pore diameter increases after the coal body is deformed, so the gas-containing capacity of mylonitic coals is stronger. Especially, the contents of macroand meso-pore are higher in mylonitic coals, so the desorption becomes easier. Moreover, other factors, including the coal rank rise, the vitrinite content increase and inertinite content decrease after the coal body is deformed, lead to the increase of absorption ability. The study also concludes that the ash content is not the main controlling factor on the adsorption difference between two types of coals with different coal body structures.
2009, 34(5): 855-860.
Abstract:
Based on engineering survey and experiments, slide mass structure and the mechanical parameters of Dagouwan landslide were obtained.FLAC3D was employed to analyze the stability and the deformation mechanism of Dagouwan landslide at different working conditions and water levels.The results of analysis show that: when the water level rose to 452 m, there showed a continuous crack at the back of the landslide from one side of gully to another, and the shear outlet of the landslide was located in the thick deposits of the slope at 580 m, but the whole slope still showed stability; when the water level rose to 488 m, another independent landslide formed from the toe of the landslide to 570 m.Interactions between two landslides caused the failure of the whole slope.The phenomenon had been confirmed during the two field explorations.The failure reasons of the landslide can be concluded as the loose structure of the landslide, high frequency of showers and the fluctuation of the water level in the reservoir, which finally led to the form of this complex retrogressive-progressive landslide.
Based on engineering survey and experiments, slide mass structure and the mechanical parameters of Dagouwan landslide were obtained.FLAC3D was employed to analyze the stability and the deformation mechanism of Dagouwan landslide at different working conditions and water levels.The results of analysis show that: when the water level rose to 452 m, there showed a continuous crack at the back of the landslide from one side of gully to another, and the shear outlet of the landslide was located in the thick deposits of the slope at 580 m, but the whole slope still showed stability; when the water level rose to 488 m, another independent landslide formed from the toe of the landslide to 570 m.Interactions between two landslides caused the failure of the whole slope.The phenomenon had been confirmed during the two field explorations.The failure reasons of the landslide can be concluded as the loose structure of the landslide, high frequency of showers and the fluctuation of the water level in the reservoir, which finally led to the form of this complex retrogressive-progressive landslide.
2009, 34(5): 861-869.
Abstract:
The primary consolidation ration, utmost primary consolidation and the calculational methods of primary consolidation degree have been draw in the last paper (Study on the Theory Primary Consolidation of Saturated Soft Clay), they lie on the initial moisture and liquid limit, but they are independent of consolidate stress.Qua continuation, the connection of moisture and time during one dimensional consolidation has been searched.According to the one-dimensional-consolidated model and assumption, the second-order partial differential equations which moisture as the dependent variable has been established according to the one-dimensional-consolidated model and assumption.Through specific boundary conditions and initial conditions, using separation of variables and trigonometric functions orthogonal winner of the consolidation process of understanding the relationship between water content and style.The new formula of coefficient of primary consolidation and time factor has been obtained.They are similar in form with Terzaghi consolidation equation, but they are different in the substance, the former has searched change of the water content of soft clay, but the latter has searched change of excess pore water pressure.The new expressions of primary consolidation, the average degree of consolidation and remainder of primary consolidation have been drawn by the new one-dimensional primary consolidation equation.According to engineering data, it has been indicated that permeability coefficient, excess pore water pressure head, and the proportion of soft clay have not affected the new coefficient of primary consolidation Θ, except moisture.
The primary consolidation ration, utmost primary consolidation and the calculational methods of primary consolidation degree have been draw in the last paper (Study on the Theory Primary Consolidation of Saturated Soft Clay), they lie on the initial moisture and liquid limit, but they are independent of consolidate stress.Qua continuation, the connection of moisture and time during one dimensional consolidation has been searched.According to the one-dimensional-consolidated model and assumption, the second-order partial differential equations which moisture as the dependent variable has been established according to the one-dimensional-consolidated model and assumption.Through specific boundary conditions and initial conditions, using separation of variables and trigonometric functions orthogonal winner of the consolidation process of understanding the relationship between water content and style.The new formula of coefficient of primary consolidation and time factor has been obtained.They are similar in form with Terzaghi consolidation equation, but they are different in the substance, the former has searched change of the water content of soft clay, but the latter has searched change of excess pore water pressure.The new expressions of primary consolidation, the average degree of consolidation and remainder of primary consolidation have been drawn by the new one-dimensional primary consolidation equation.According to engineering data, it has been indicated that permeability coefficient, excess pore water pressure head, and the proportion of soft clay have not affected the new coefficient of primary consolidation Θ, except moisture.
2009, 34(5): 870-876.
Abstract:
In order to investigate tetrachoroethylene (PCE) biodegradation potential by some enhanced factors, the experiment was carried out under natural groundwater condition by batch experiment.Microorganism cultured in the laboratory was added to the microcosm with acetic acid as electron donor and yeast powder as nitrogen source.Experimental results indicate that PCE could be dechlorinated to trichloroethylene (TCE) and dichloroethylene (DCEs) under 20 ℃.TCE was the primary dehalogenation product, and small amounts of dichloroethylenes (DCEs) were also detected.No significant further DCEs degradation was detected.The degradation rate of PCE was 0.184 8 d-1, and the half life was 3.75 d.Under 12 ℃ condition, PCE biodegradation could occur; however, the terminal product was only TCE without DCEs, and degradation rate of PCE was 0.076 1 d-1, which was relatively slow compared to that under 20 ℃.
In order to investigate tetrachoroethylene (PCE) biodegradation potential by some enhanced factors, the experiment was carried out under natural groundwater condition by batch experiment.Microorganism cultured in the laboratory was added to the microcosm with acetic acid as electron donor and yeast powder as nitrogen source.Experimental results indicate that PCE could be dechlorinated to trichloroethylene (TCE) and dichloroethylene (DCEs) under 20 ℃.TCE was the primary dehalogenation product, and small amounts of dichloroethylenes (DCEs) were also detected.No significant further DCEs degradation was detected.The degradation rate of PCE was 0.184 8 d-1, and the half life was 3.75 d.Under 12 ℃ condition, PCE biodegradation could occur; however, the terminal product was only TCE without DCEs, and degradation rate of PCE was 0.076 1 d-1, which was relatively slow compared to that under 20 ℃.
