A collection of data obtained from analytical methods in geochemistry along with the reservoir engineering and geologic data were used to investigate the reservoir continuity in the Cretaceous Fahliyan, Gadavan, Kazhd...A collection of data obtained from analytical methods in geochemistry along with the reservoir engineering and geologic data were used to investigate the reservoir continuity in the Cretaceous Fahliyan, Gadavan, Kazhdumi and Sarvak reservoirs of the super-giant Azadegan oilfield, SW Iran. The geochemical data indicate that the oil samples, with medium to high level of thermal maturity, have been generated from the anoxic marine marl/carbonate source rock(s). The Sargelu(Jurassic) and Garau(Cretaceous) formations are introduced as the main source rocks for the studied oils. The dendrogram obtained from the cluster analysis of high-resolution gas chromatography data introduces two main oil groups including Fahliyan reservoir, and Kazhdumi along with Sarvak/Gadvan reservoirs. This is confirmed by C7 Halpern star diagram, indicating that, the light oil fraction from Fahliyan reservoir is distinct from the others. Also, different pressure gradient of the Fahliyan Formation(over-pressured) relative to other reservoirs(normally-pressured) show the presence of compartments. The relation between toluene/n-heptane and n-heptane/methylcyclohexane represents the compartmentalization due to maturation/evaporative fractionation for Fahliyan and water washing for other studied reservoirs. Also, the impermeable upper part of the Fahliyan Formation and thin interbedded shaly layers in the Kazhdumi, Sarvak and Gadvan formations have controlled reservoir compartmentalization.展开更多
Having studied the biomarker composition and maturity of dissolved hydrocarbons from Ordovician formation waters, the authors presented molecular geochemical evidence for the controversial origin of natural gases in c...Having studied the biomarker composition and maturity of dissolved hydrocarbons from Ordovician formation waters, the authors presented molecular geochemical evidence for the controversial origin of natural gases in central Ordos Basin.The dissolved hydrocarbons in Well Shan 12 and Well Shan 78 are relatively high in abundance of tricylic terpane, pregnane series and dibenzothiophene series and low in Pr/Ph and hopane/sterane ratios, indicating the source input of marine carbonates. In contrast, the dissolved hydrocarbons in Well Shan 81 are free from tricyclic terpane and pregnane series, with trace dibenzothiophene series and high Pr/Ph and higher hopane/sterane ratios, which are the typical features of terrestrial organic matter. Furthermore, Well Shan 37 and Well Shan 34 are between the two situations, having a mixed source of marine carbonate and terrestrial organic matter. The maturity of biomarkers also supports the above suggestions. These results are consistent with the geological background and source rock distribution in this region.展开更多
The absolute amounts and relative distributions of neutral nitrogen compounds in the Tabei oilfield (e.g. blocks Ln1-Ln11) showed remarkable migration fractionation in the vertical direction. From Ordovician reservoir...The absolute amounts and relative distributions of neutral nitrogen compounds in the Tabei oilfield (e.g. blocks Ln1-Ln11) showed remarkable migration fractionation in the vertical direction. From Ordovician reservoirs (O) to oil legs T-Ⅲ and T-Ⅰ of Triassic reservoirs in blocks LN1-LN11, the concentrations of + decreased from {1.59}μg/g, {0.49}μg/g to {0.17}μg/g (oil). The ratios of various alkylcarbazole isomers, such as 1,8-dimethylcarbazole/nitrogen-partially shielded isomers and 1,8-dimethylcarbazole/nitrogen-exposed isomers, were adopted as the indicators of petroleum migration. The ratios increased from {0.13}, {0.20} to {0.67} and from {0.42}, {0.87} to {3.30}, corresponding to those of Ordovician oil leg and oil legs T-Ⅲ and T-Ⅰ. In going from the south to the north of the Tabei oilfield, the absolute concentrations of neutral nitrogen compounds decreased drastically, and the nitrogen-shielded isomers were enriched relative to nitrogen-exposed isomers and nitrogen-partially shielded isomers. Crude oils in the Tabei oilfield migrated laterally from the Jilake structure to the Sangtamu fault uplift and Lunnan fault uplift, and crude oils in the same fault uplift migrated and remigrated vertically from Ordovician reservoirs, to oil legs T-Ⅲ to T-Ⅰ of Triassic reservoirs.展开更多
We have investigated the distributions of alkylcarbazoles in a series of crude oils with different biodegradation extents, in combination with biomarker parameters, stable carbon isotopic ratios and viscosities. The a...We have investigated the distributions of alkylcarbazoles in a series of crude oils with different biodegradation extents, in combination with biomarker parameters, stable carbon isotopic ratios and viscosities. The analyses showed that slight biodegradation has little effect on alkylcarbazoles. The concentrations of C\-0-, C\-1-, and C\-2-carbazoles seem to display a slight decrease with biodegradation through the moderately biodegraded stage, and an abrupt decrease to the heavily biodegraded stage. The relative concentrations of C\-0-, C\-1-, and C\-2-carbazoles do not show any apparent change in the non-heavily biodegraded stages, but through non-heavily biodegraded to heavily biodegraded stages, the percentages of C\-0- and C\-1-carbazoles decrease, and those of C\-2-carbazoles increase significantly, which may indicate that C\-2-carbazoles are more resistant to biodegradation than lower homologous species. As to C\-2-carbazole isomers, the relative concentrations of the pyrrolic N-H-shielded, pyrrolic N-H partially shielded and pyrrolic N-H-exposed isomers do not show any obvious variation in the non-heavily biodegraded oil, but there is an abrupt change through the mid-biodegraded stage to the heavily biodegraded stage.展开更多
Isotachophoresis results indicate that the total concentrations of organic acids in Ordovician formation waters range from 9.17 mg/L to 94.49 mg/L and are obviously higher than those of Permo-Carboniferous formation w...Isotachophoresis results indicate that the total concentrations of organic acids in Ordovician formation waters range from 9.17 mg/L to 94.49 mg/L and are obviously higher than those of Permo-Carboniferous formation waters. But both of them have the same compositional characteristics, i.e., acetic acid >>formic acid >propanoic acid >butanoic acid. The total alkyl phenol contents of Ordovician formation waters range from {0.57} mg/L to {4.73} mg/L, averaging {1.77} mg/L. Among the samples for phenol detection, {47.06%} samples contain less than {1.0 mg/L}, {35.29%} samples {1.0}-{3.0} mg/L, and only {17.65%} samples more than {3.0 mg/L} alkyl phenol.The concentrations of organic acids and alkyl phenols in the Majiagou formation waters are of obviously heterogeneous distribution. There are several areas where the concentrations of organic acids and phenols are high in central Ordos Basin. These organic acid- and phenol-high areas (organic acids {>45} mg/L and phenols {>2.0 mg/L}) are consistent with natural gas reservoir enriched areas in central Ordos Basin.展开更多
The Ediacaran-Cambrian transition is characterized by numerous events such as the emergence of large multi-cellular metazoans and surface environmental disturbances.Based on geological evidence,it has been proposed th...The Ediacaran-Cambrian transition is characterized by numerous events such as the emergence of large multi-cellular metazoans and surface environmental disturbances.Based on geological evidence,it has been proposed that this transition coincided with the increase in the atmospheric oxygen level that was key to the evolution of life.Even though ancient redox conditions can be inferred from the composition of sedimentary iron mineral species,this method is not necessarily applicable to all rocks.In the Earth system,the cycling of iron is of considerable interest owing to its sensitivity to redox conditions.Information regarding the paleo-oceanic iron cycle is revealed in the iron isotopic composition of ironbearing minerals.Unfortunately,only limited iron isotopic data exists for Ediacaran-to Cambrianperiod oceans.To circumvent this deficiency,we drilled a fossiliferous Ediacaran to Early Cambrian sedimentary succession in the Three Gorges region,South China.We analyzed the iron isotope ratios(δ^(56/54)Fe)of pyrite grains in the drill cores using laser ablation multi collector inductively coupled plasma mass spectrometry.The results demonstrate large variations inδ^(56/54)Fe,from-1.6 to 1.6‰,and positive iron isotope ratios are observed in many successions.The presence of positiveδ^(56/54)Fe in pyrite indicates that the ferrous iron in the seawater was partially oxidized,suggesting that seawater at Three Gorges was ferruginous during the Ediacaran and Early Cambrian periods.However,aggregated pyrite grains in organic carbon-rich black shales at Member 4 of the Doushantuo Formation and the base of the Shuijingtuo Formation yield near-zeroδ^(56/54)Fe values;this suggests that the ocean was transiently dominated by sulfidic conditions during these periods.Notably negativeδ^(56/54)Fe values,lower than-1‰,can be interpreted as a signature of DIR.The DIR also might contribute in part to the re-mineralization of organic matter during the largest negative carbon isotope anomaly in the Ediacaran.展开更多
Organic petrology is a marginal science that is quite practicable. At present, it has developed into a routine research tool that is widely applied in petroleum exploration and assessment. Based on several years’ res...Organic petrology is a marginal science that is quite practicable. At present, it has developed into a routine research tool that is widely applied in petroleum exploration and assessment. Based on several years’ research of the authors, this paper presents the advances in organic petrological studies on immature source rocks, including the classification and characteristics of macerals, the composition of macerals and types of organic matter, the abundance and evolution of organic matter, oil-prone macerals, hydrocarbon generation and expulsion. All these results show that organic petrology is of considerable value pertaining to its application in the assessment of immature oil and gas. The immature source rocks consist of various macerals with obvious heterogeneity, contain different hydrocarbon-generating macerals with different oil thresholds and oil peaks, and show a two-staged evolutionary pattern of organic matter.展开更多
Geochemical methods can be used to optimize heavy oil reservoir management. The distribution of some biomarkers in oils is different with the degree of biodegradation. Geochemical parameters can be used to predict oil...Geochemical methods can be used to optimize heavy oil reservoir management. The distribution of some biomarkers in oils is different with the degree of biodegradation. Geochemical parameters can be used to predict oil viscosity and thus to preliminarily evaluate the difficulties involved in oil production. The results of viscosity prediction for oils from reservoir S\+2\-3 in block Leng 43 and preliminary evaluation of oil production difficulty are consistent with the geological data.展开更多
The Francevillian Group in Gabonese Republic was recently established as a typical sedimentary sequence for the Paleoproterozoic.However,its age is rather poorly constrained,mainly based on Rb-Sr and Nd-Sm datings.Thi...The Francevillian Group in Gabonese Republic was recently established as a typical sedimentary sequence for the Paleoproterozoic.However,its age is rather poorly constrained,mainly based on Rb-Sr and Nd-Sm datings.This study reports new zircon data obtained from Chaillu massif and N＇goutou complex,which constrain the protolith age of the basement orthogneisses and the igneous age of an intrusive granite,respectively.Most zircons from the orthogneisses are blue and exhibit oscillatory zoning in cathode-luminescence images.Zircons with lower common lead abundances tend to be distributed close to the concordia curve.Two age clusters around 2860 Ma and 2910 Ma are found in zircons plotted on the concordia curve.Based on the Th/U ratios of zircons,these ages correspond to the protolith ages of the orthogneisses,and the zircons are not metamorphic in origin.Syenites and granites were collected from the N＇goutou complex that intrudes into the FA and FB units of the Francevillian Group.The granitoids exhibit chemical composition of A-type granite affinity.Half of zircons separated from the granite are non-luminous,and the remaining half exhibit obscure internal textures under cathode-luminescence observation.All zircon grains contain significant amounts of common lead;the lead isotopic variability is probably attributed to the mixing of two components in the zircons.The zircon radiogenic ^（207）Pb/^（206）Pb ratio is 0.13707 ± 0.0010.corresponding to a ^（207）Pb/^（206）Pb age of 2191 ± 13 Ma.This constrains the minimum depositional age of the FA and FB units.Furthermore,the FB unit consists of manganese-rich carbonate rocks and organic carbon-rich black shales with macroscopic fossils.Based on our age constraints,these organisms appeared in the study area just after the last Paleoproterozoic Snowball Earth event,in concert with global scale oxidation event encompassing the Snowball Earth.展开更多
基金National Iranian Oil Company-Exploration Directorate(NIOC-EXP)the Petroleum Geology and Geochemistry Research Center(PGGRC)of Shahid Chamran University of Ahvaz.
文摘A collection of data obtained from analytical methods in geochemistry along with the reservoir engineering and geologic data were used to investigate the reservoir continuity in the Cretaceous Fahliyan, Gadavan, Kazhdumi and Sarvak reservoirs of the super-giant Azadegan oilfield, SW Iran. The geochemical data indicate that the oil samples, with medium to high level of thermal maturity, have been generated from the anoxic marine marl/carbonate source rock(s). The Sargelu(Jurassic) and Garau(Cretaceous) formations are introduced as the main source rocks for the studied oils. The dendrogram obtained from the cluster analysis of high-resolution gas chromatography data introduces two main oil groups including Fahliyan reservoir, and Kazhdumi along with Sarvak/Gadvan reservoirs. This is confirmed by C7 Halpern star diagram, indicating that, the light oil fraction from Fahliyan reservoir is distinct from the others. Also, different pressure gradient of the Fahliyan Formation(over-pressured) relative to other reservoirs(normally-pressured) show the presence of compartments. The relation between toluene/n-heptane and n-heptane/methylcyclohexane represents the compartmentalization due to maturation/evaporative fractionation for Fahliyan and water washing for other studied reservoirs. Also, the impermeable upper part of the Fahliyan Formation and thin interbedded shaly layers in the Kazhdumi, Sarvak and Gadvan formations have controlled reservoir compartmentalization.
文摘Having studied the biomarker composition and maturity of dissolved hydrocarbons from Ordovician formation waters, the authors presented molecular geochemical evidence for the controversial origin of natural gases in central Ordos Basin.The dissolved hydrocarbons in Well Shan 12 and Well Shan 78 are relatively high in abundance of tricylic terpane, pregnane series and dibenzothiophene series and low in Pr/Ph and hopane/sterane ratios, indicating the source input of marine carbonates. In contrast, the dissolved hydrocarbons in Well Shan 81 are free from tricyclic terpane and pregnane series, with trace dibenzothiophene series and high Pr/Ph and higher hopane/sterane ratios, which are the typical features of terrestrial organic matter. Furthermore, Well Shan 37 and Well Shan 34 are between the two situations, having a mixed source of marine carbonate and terrestrial organic matter. The maturity of biomarkers also supports the above suggestions. These results are consistent with the geological background and source rock distribution in this region.
文摘The absolute amounts and relative distributions of neutral nitrogen compounds in the Tabei oilfield (e.g. blocks Ln1-Ln11) showed remarkable migration fractionation in the vertical direction. From Ordovician reservoirs (O) to oil legs T-Ⅲ and T-Ⅰ of Triassic reservoirs in blocks LN1-LN11, the concentrations of + decreased from {1.59}μg/g, {0.49}μg/g to {0.17}μg/g (oil). The ratios of various alkylcarbazole isomers, such as 1,8-dimethylcarbazole/nitrogen-partially shielded isomers and 1,8-dimethylcarbazole/nitrogen-exposed isomers, were adopted as the indicators of petroleum migration. The ratios increased from {0.13}, {0.20} to {0.67} and from {0.42}, {0.87} to {3.30}, corresponding to those of Ordovician oil leg and oil legs T-Ⅲ and T-Ⅰ. In going from the south to the north of the Tabei oilfield, the absolute concentrations of neutral nitrogen compounds decreased drastically, and the nitrogen-shielded isomers were enriched relative to nitrogen-exposed isomers and nitrogen-partially shielded isomers. Crude oils in the Tabei oilfield migrated laterally from the Jilake structure to the Sangtamu fault uplift and Lunnan fault uplift, and crude oils in the same fault uplift migrated and remigrated vertically from Ordovician reservoirs, to oil legs T-Ⅲ to T-Ⅰ of Triassic reservoirs.
基金ThisprojectwasfinanciallysupportedbytheYouthKnowledge InnovationFoundationofCNPC (No .0 0Z130 4)
文摘We have investigated the distributions of alkylcarbazoles in a series of crude oils with different biodegradation extents, in combination with biomarker parameters, stable carbon isotopic ratios and viscosities. The analyses showed that slight biodegradation has little effect on alkylcarbazoles. The concentrations of C\-0-, C\-1-, and C\-2-carbazoles seem to display a slight decrease with biodegradation through the moderately biodegraded stage, and an abrupt decrease to the heavily biodegraded stage. The relative concentrations of C\-0-, C\-1-, and C\-2-carbazoles do not show any apparent change in the non-heavily biodegraded stages, but through non-heavily biodegraded to heavily biodegraded stages, the percentages of C\-0- and C\-1-carbazoles decrease, and those of C\-2-carbazoles increase significantly, which may indicate that C\-2-carbazoles are more resistant to biodegradation than lower homologous species. As to C\-2-carbazole isomers, the relative concentrations of the pyrrolic N-H-shielded, pyrrolic N-H partially shielded and pyrrolic N-H-exposed isomers do not show any obvious variation in the non-heavily biodegraded oil, but there is an abrupt change through the mid-biodegraded stage to the heavily biodegraded stage.
文摘Isotachophoresis results indicate that the total concentrations of organic acids in Ordovician formation waters range from 9.17 mg/L to 94.49 mg/L and are obviously higher than those of Permo-Carboniferous formation waters. But both of them have the same compositional characteristics, i.e., acetic acid >>formic acid >propanoic acid >butanoic acid. The total alkyl phenol contents of Ordovician formation waters range from {0.57} mg/L to {4.73} mg/L, averaging {1.77} mg/L. Among the samples for phenol detection, {47.06%} samples contain less than {1.0 mg/L}, {35.29%} samples {1.0}-{3.0} mg/L, and only {17.65%} samples more than {3.0 mg/L} alkyl phenol.The concentrations of organic acids and alkyl phenols in the Majiagou formation waters are of obviously heterogeneous distribution. There are several areas where the concentrations of organic acids and phenols are high in central Ordos Basin. These organic acid- and phenol-high areas (organic acids {>45} mg/L and phenols {>2.0 mg/L}) are consistent with natural gas reservoir enriched areas in central Ordos Basin.
基金supported by JSPS grants(Nos.24840021,18740318,23340152,25610148) from the Ministry of Education, Culture, Sports, Science and Technology, Japan
文摘The Ediacaran-Cambrian transition is characterized by numerous events such as the emergence of large multi-cellular metazoans and surface environmental disturbances.Based on geological evidence,it has been proposed that this transition coincided with the increase in the atmospheric oxygen level that was key to the evolution of life.Even though ancient redox conditions can be inferred from the composition of sedimentary iron mineral species,this method is not necessarily applicable to all rocks.In the Earth system,the cycling of iron is of considerable interest owing to its sensitivity to redox conditions.Information regarding the paleo-oceanic iron cycle is revealed in the iron isotopic composition of ironbearing minerals.Unfortunately,only limited iron isotopic data exists for Ediacaran-to Cambrianperiod oceans.To circumvent this deficiency,we drilled a fossiliferous Ediacaran to Early Cambrian sedimentary succession in the Three Gorges region,South China.We analyzed the iron isotope ratios(δ^(56/54)Fe)of pyrite grains in the drill cores using laser ablation multi collector inductively coupled plasma mass spectrometry.The results demonstrate large variations inδ^(56/54)Fe,from-1.6 to 1.6‰,and positive iron isotope ratios are observed in many successions.The presence of positiveδ^(56/54)Fe in pyrite indicates that the ferrous iron in the seawater was partially oxidized,suggesting that seawater at Three Gorges was ferruginous during the Ediacaran and Early Cambrian periods.However,aggregated pyrite grains in organic carbon-rich black shales at Member 4 of the Doushantuo Formation and the base of the Shuijingtuo Formation yield near-zeroδ^(56/54)Fe values;this suggests that the ocean was transiently dominated by sulfidic conditions during these periods.Notably negativeδ^(56/54)Fe values,lower than-1‰,can be interpreted as a signature of DIR.The DIR also might contribute in part to the re-mineralization of organic matter during the largest negative carbon isotope anomaly in the Ediacaran.
文摘Organic petrology is a marginal science that is quite practicable. At present, it has developed into a routine research tool that is widely applied in petroleum exploration and assessment. Based on several years’ research of the authors, this paper presents the advances in organic petrological studies on immature source rocks, including the classification and characteristics of macerals, the composition of macerals and types of organic matter, the abundance and evolution of organic matter, oil-prone macerals, hydrocarbon generation and expulsion. All these results show that organic petrology is of considerable value pertaining to its application in the assessment of immature oil and gas. The immature source rocks consist of various macerals with obvious heterogeneity, contain different hydrocarbon-generating macerals with different oil thresholds and oil peaks, and show a two-staged evolutionary pattern of organic matter.
文摘Geochemical methods can be used to optimize heavy oil reservoir management. The distribution of some biomarkers in oils is different with the degree of biodegradation. Geochemical parameters can be used to predict oil viscosity and thus to preliminarily evaluate the difficulties involved in oil production. The results of viscosity prediction for oils from reservoir S\+2\-3 in block Leng 43 and preliminary evaluation of oil production difficulty are consistent with the geological data.
基金supported by a grant for"Chronostratigraphy for the Mesoproterozoic strata in Jixian,North China(No.26800259)"and"Hadean BioScience(No.26106002)"from the Ministry of Education,Culture,Sports,Science,and Technology,Japan
文摘The Francevillian Group in Gabonese Republic was recently established as a typical sedimentary sequence for the Paleoproterozoic.However,its age is rather poorly constrained,mainly based on Rb-Sr and Nd-Sm datings.This study reports new zircon data obtained from Chaillu massif and N＇goutou complex,which constrain the protolith age of the basement orthogneisses and the igneous age of an intrusive granite,respectively.Most zircons from the orthogneisses are blue and exhibit oscillatory zoning in cathode-luminescence images.Zircons with lower common lead abundances tend to be distributed close to the concordia curve.Two age clusters around 2860 Ma and 2910 Ma are found in zircons plotted on the concordia curve.Based on the Th/U ratios of zircons,these ages correspond to the protolith ages of the orthogneisses,and the zircons are not metamorphic in origin.Syenites and granites were collected from the N＇goutou complex that intrudes into the FA and FB units of the Francevillian Group.The granitoids exhibit chemical composition of A-type granite affinity.Half of zircons separated from the granite are non-luminous,and the remaining half exhibit obscure internal textures under cathode-luminescence observation.All zircon grains contain significant amounts of common lead;the lead isotopic variability is probably attributed to the mixing of two components in the zircons.The zircon radiogenic ^（207）Pb/^（206）Pb ratio is 0.13707 ± 0.0010.corresponding to a ^（207）Pb/^（206）Pb age of 2191 ± 13 Ma.This constrains the minimum depositional age of the FA and FB units.Furthermore,the FB unit consists of manganese-rich carbonate rocks and organic carbon-rich black shales with macroscopic fossils.Based on our age constraints,these organisms appeared in the study area just after the last Paleoproterozoic Snowball Earth event,in concert with global scale oxidation event encompassing the Snowball Earth.
