1995 Vol. 13, No. 2
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Display Method:
1995, 13(2): 14-21.
Abstract:
In this paper the existence style of hydrocarbons in the clay minerals has been analysed and the surface acid of clay minerals has been determined. Meanwhile, the simulating experiment has been carried out by mixing low-mature source rock and its kerogen extracts with different clay minerals. Through the experiment of alcohol dehydration reaction catalysed by clay minerals, the clay mineral catalysis of hydrocarbons to produce transitional zone nature gas has been discussed. The chief conclusions are as follows:Montmorillonite is the main catalyst for the formation of transitional zone nature gas because there are large amounts of Al3+ replacing Si4+ in its crystal layers when M→I/M transition occurs during diagenesis.As a result, the electric change balance on the surface of montmorillonite is destroyed to form surface acids such as Bronsted and Lowes acids which cause long chain hydrocarbons broken to produce light hydrocarbons with short chain.
In this paper the existence style of hydrocarbons in the clay minerals has been analysed and the surface acid of clay minerals has been determined. Meanwhile, the simulating experiment has been carried out by mixing low-mature source rock and its kerogen extracts with different clay minerals. Through the experiment of alcohol dehydration reaction catalysed by clay minerals, the clay mineral catalysis of hydrocarbons to produce transitional zone nature gas has been discussed. The chief conclusions are as follows:Montmorillonite is the main catalyst for the formation of transitional zone nature gas because there are large amounts of Al3+ replacing Si4+ in its crystal layers when M→I/M transition occurs during diagenesis.As a result, the electric change balance on the surface of montmorillonite is destroyed to form surface acids such as Bronsted and Lowes acids which cause long chain hydrocarbons broken to produce light hydrocarbons with short chain.
1995, 13(2): 33-43.
Abstract:
The amino acids and fatty acids in sediments of Caohai, Chaiwopu, Liaohe, Jiyang and Subei Basins were quantitatively analysed in this study. Based on the results, the gas-generating tests of peat and mudstone were carried out to investigate distribution and compostition of fatty acids in the extract and kerogen. As a result, some points are drawn as follows:1. Amino acids in sediments are mainly present in the soluble organic matter and may produce hydrocarbons during early diagenesis stage,contributing to the formation of Bio - thermocatalytic Transition Zone Gases.2.α-fatty acids in sediments are mainly present in asphaltene and may produce hydrocarbon, contributing to the formation of immature oil during early diagenesis stage.3. Kerogen is rich in α,ω - fatty acids which are favourable to the generation of Bio-thermocatalytic Transition Gases during erly diagenesis stage, and produce hydrocarbon in mature oil druing oil generating stage.
The amino acids and fatty acids in sediments of Caohai, Chaiwopu, Liaohe, Jiyang and Subei Basins were quantitatively analysed in this study. Based on the results, the gas-generating tests of peat and mudstone were carried out to investigate distribution and compostition of fatty acids in the extract and kerogen. As a result, some points are drawn as follows:1. Amino acids in sediments are mainly present in the soluble organic matter and may produce hydrocarbons during early diagenesis stage,contributing to the formation of Bio - thermocatalytic Transition Zone Gases.2.α-fatty acids in sediments are mainly present in asphaltene and may produce hydrocarbon, contributing to the formation of immature oil during early diagenesis stage.3. Kerogen is rich in α,ω - fatty acids which are favourable to the generation of Bio-thermocatalytic Transition Gases during erly diagenesis stage, and produce hydrocarbon in mature oil druing oil generating stage.
1995, 13(2): 48-58.
Abstract:
A large number of valuable analytic data of the chemical compositions and isotopes of natural gases have been obtained from 532 natural gas samples of 19 oil - gas - bearing basins in China. On the basis of the comprehensive research of the characteristics of natural gases it has been considered that the space distribution of the content and isotopic composition of rare gases in natural gases were controlled by tectonic settings. According to the 3He/ 4He values the distribution of the He isotopes in the oil - bearing basins can be divided into four areas: (1) eastern active area, where the natural gases of the basins near the Tancheng - Lujiang Fault have an average 3He/ 4He value of 10 -6, suggesting the addition of the mantle - derived volatile components, and the natural gases of the basins far from the Tancheng - Lujiang Fault have a mean 3He/ 4He value of 10 -7; (2) middle stable area, where the natural gases of the basins have an average 3He/ 4He value of 4× 10 -8, minimum of 5 × 10 -9, which means that He was monoradioactive; (3) northwest substable area,where the natural gases of the basins have a range of 3He/4He values from 10 -8 to 10 -7; and (4) southwest area of Hainal Island, along both sides of Honghe River Fault, where the natural gases of the basins have a range of 3He/ 4He ratio from 10 -8 to 10 -7 and averages 10 -7, indicating that He was crust - derived. A reverse Y- shaped origin model of rare gases has been proposed and two-origin types have been provided:(a) Crust - and mantte - derived type, distributed in the eastern active area, where the 40Ar/ 36Ar and 3He/ 4He values of rare gases increase with the addition of mantle - derived gases and (b) crust - derived type, distributed in the stable and substable area of Centrol and West China, cbaractermng that the 40Ar/ 36Ar values of rare gases increase but the 3He/4He values decrease with geological ages. Meanwhile, the time - accumulating - effect of Ar and He isotopes in natural gases is also researched. The formula which can be used to calculate the ages of crust -derived gas source rocks using He and Ar isotopic methods is suggested.The formula can be applied to tracing and comparating gas source rocks, which is of practical signficance for gas exploration. In addition, the rare gas geochemistry, hydrocarbon gas geochemistry, and the related geological backgrounds of the central north gas area of Erdos Basin, the Chuandong gas area of Sichuan Basin,the Ya 13 -1 gas fields and the Dengfang- Ledong gas zone have comprehensively been researched and some new views on the three large - or middle - sized gas areas have been suggested.
A large number of valuable analytic data of the chemical compositions and isotopes of natural gases have been obtained from 532 natural gas samples of 19 oil - gas - bearing basins in China. On the basis of the comprehensive research of the characteristics of natural gases it has been considered that the space distribution of the content and isotopic composition of rare gases in natural gases were controlled by tectonic settings. According to the 3He/ 4He values the distribution of the He isotopes in the oil - bearing basins can be divided into four areas: (1) eastern active area, where the natural gases of the basins near the Tancheng - Lujiang Fault have an average 3He/ 4He value of 10 -6, suggesting the addition of the mantle - derived volatile components, and the natural gases of the basins far from the Tancheng - Lujiang Fault have a mean 3He/ 4He value of 10 -7; (2) middle stable area, where the natural gases of the basins have an average 3He/ 4He value of 4× 10 -8, minimum of 5 × 10 -9, which means that He was monoradioactive; (3) northwest substable area,where the natural gases of the basins have a range of 3He/4He values from 10 -8 to 10 -7; and (4) southwest area of Hainal Island, along both sides of Honghe River Fault, where the natural gases of the basins have a range of 3He/ 4He ratio from 10 -8 to 10 -7 and averages 10 -7, indicating that He was crust - derived. A reverse Y- shaped origin model of rare gases has been proposed and two-origin types have been provided:(a) Crust - and mantte - derived type, distributed in the eastern active area, where the 40Ar/ 36Ar and 3He/ 4He values of rare gases increase with the addition of mantle - derived gases and (b) crust - derived type, distributed in the stable and substable area of Centrol and West China, cbaractermng that the 40Ar/ 36Ar values of rare gases increase but the 3He/4He values decrease with geological ages. Meanwhile, the time - accumulating - effect of Ar and He isotopes in natural gases is also researched. The formula which can be used to calculate the ages of crust -derived gas source rocks using He and Ar isotopic methods is suggested.The formula can be applied to tracing and comparating gas source rocks, which is of practical signficance for gas exploration. In addition, the rare gas geochemistry, hydrocarbon gas geochemistry, and the related geological backgrounds of the central north gas area of Erdos Basin, the Chuandong gas area of Sichuan Basin,the Ya 13 -1 gas fields and the Dengfang- Ledong gas zone have comprehensively been researched and some new views on the three large - or middle - sized gas areas have been suggested.
1995, 13(2): 70-76.
Abstract:
A lot of theoretical and practical studies have been done on applying the carbon and hydrogen isotopic compositions of gaseous hydrocarbons to indentify the type of natural gas and trace the type and maturation of potential gas source rocks. However, there are few studies on the application of the isotopic character of natural gas to gas migration. The main argument point on the above case is whether the isotopic fractionation occurs druing gas migration. In this paper, according to the characteristics of the carbon isotopic composition from acidlysis gas, canned gas and natural gas of Ordos and other oil - gas bearing basins, the changes of carbon isotope compositions of gaseous hydrocarbons during gas migration are discussed and the following conclusions are obtained.1.While natural gas migrates a long distance through micro fractures and the pore system in strata, a certain isotopic fractionation for methane occurred but little isotopic fractionation for heavier hydrocarbons.2. A relatively good concordant and comparative relation exsits between the carbon isotope compositions of heavier hydrocarbons from acidlysis gas of source rocks and those from natural gas orginated from the same source rocks. The correlation of direct gas and its source rocks was carried on from this coincidence.3. The carbon isotope ratios of methane from canned gas are equal to those of natural gas at gas production layers and show much heavier than the normal increase tendency with depth near gas production layers.The exsitence of gas layers may be indicated according to the vertical isotope characters of methane from canned gas.
A lot of theoretical and practical studies have been done on applying the carbon and hydrogen isotopic compositions of gaseous hydrocarbons to indentify the type of natural gas and trace the type and maturation of potential gas source rocks. However, there are few studies on the application of the isotopic character of natural gas to gas migration. The main argument point on the above case is whether the isotopic fractionation occurs druing gas migration. In this paper, according to the characteristics of the carbon isotopic composition from acidlysis gas, canned gas and natural gas of Ordos and other oil - gas bearing basins, the changes of carbon isotope compositions of gaseous hydrocarbons during gas migration are discussed and the following conclusions are obtained.1.While natural gas migrates a long distance through micro fractures and the pore system in strata, a certain isotopic fractionation for methane occurred but little isotopic fractionation for heavier hydrocarbons.2. A relatively good concordant and comparative relation exsits between the carbon isotope compositions of heavier hydrocarbons from acidlysis gas of source rocks and those from natural gas orginated from the same source rocks. The correlation of direct gas and its source rocks was carried on from this coincidence.3. The carbon isotope ratios of methane from canned gas are equal to those of natural gas at gas production layers and show much heavier than the normal increase tendency with depth near gas production layers.The exsitence of gas layers may be indicated according to the vertical isotope characters of methane from canned gas.
1995, 13(2): 86-92.
Abstract:
Thermal modelling of gas expelled from source rocks of Yacheng Formation and Meishan Formation in Ying-Qiong Basin was made. The total amount of gases generated and expelled from Yacheng Formation is larger than that from Meishan Formation, suggesting that the gas generation potential of Yacheng Formation is higher than that of Meishan Formation. The similarity of the percentage of C1, C2-C4 and C5-C7 of the gases from Ya13 -1 field to that of the normalized gases produced at high evolution stage implies that the gases of Ya13 - 1 field may come from the source rocks with high maturity. There are similarity and difference between the composition of C6 and C7 of the gases from Ya13 -1 field and that of the normalized gases produced during the experiment. The stable carbon isotope composition of the saturated fraction of the condensate of Ya13 - 1 field and the extracts of Yacheng Formation, Meishan Formation, Ying-Huang Formation indicates that the gases of Ya13 - 1 gas field may come from multiple source rocks.
Thermal modelling of gas expelled from source rocks of Yacheng Formation and Meishan Formation in Ying-Qiong Basin was made. The total amount of gases generated and expelled from Yacheng Formation is larger than that from Meishan Formation, suggesting that the gas generation potential of Yacheng Formation is higher than that of Meishan Formation. The similarity of the percentage of C1, C2-C4 and C5-C7 of the gases from Ya13 -1 field to that of the normalized gases produced at high evolution stage implies that the gases of Ya13 - 1 field may come from the source rocks with high maturity. There are similarity and difference between the composition of C6 and C7 of the gases from Ya13 -1 field and that of the normalized gases produced during the experiment. The stable carbon isotope composition of the saturated fraction of the condensate of Ya13 - 1 field and the extracts of Yacheng Formation, Meishan Formation, Ying-Huang Formation indicates that the gases of Ya13 - 1 gas field may come from multiple source rocks.
1995, 13(2): 112-119.
Abstract:
Early Palaeozoic marine hydrocarbon source rocks in China are characterized by high maturity, low amount of organic matter, especially lack of structured macerals, which leads to difficulties in determining conventional matruity parameters such as vitrinite reflectance and exinite fluorescence. Objective determination of the maturation level of these source rocks is an urgent matter for oil and gas exploration. In this paper, the authors, having investigated the detailed organic petrological characterstics of Early Palaeozoic marine source rocks, sampled mainly from Tarim Basin and found that bitumen, micrinite, marine vitrinite and graptolite are not only very common in the source rocks, but their reflectance has a good relationship with the depth or maturity. The results of thermal - simulating tests show that bitumen and graptolite reflectance within the "oil window", marine vitrinite throughout the hydrocarbon - generating stages and micrinite renectance after the oil - generating peak are of a near straight linear relation with vitrinite reflectance, and that all of them can be used as reliable maturation parameters.On the basis of this work, a preliminary plan is put forward which is based on the four parameters used to evaluate the maturity of Early Palaeozoic marine hydrocarbon source rocks.The analysis of a series of typical source rocks from Tarim Basin shows that this method not only solves successfully the determination of the maturity of source rocks, but also provides additional important information on oil and gas generation.
Early Palaeozoic marine hydrocarbon source rocks in China are characterized by high maturity, low amount of organic matter, especially lack of structured macerals, which leads to difficulties in determining conventional matruity parameters such as vitrinite reflectance and exinite fluorescence. Objective determination of the maturation level of these source rocks is an urgent matter for oil and gas exploration. In this paper, the authors, having investigated the detailed organic petrological characterstics of Early Palaeozoic marine source rocks, sampled mainly from Tarim Basin and found that bitumen, micrinite, marine vitrinite and graptolite are not only very common in the source rocks, but their reflectance has a good relationship with the depth or maturity. The results of thermal - simulating tests show that bitumen and graptolite reflectance within the "oil window", marine vitrinite throughout the hydrocarbon - generating stages and micrinite renectance after the oil - generating peak are of a near straight linear relation with vitrinite reflectance, and that all of them can be used as reliable maturation parameters.On the basis of this work, a preliminary plan is put forward which is based on the four parameters used to evaluate the maturity of Early Palaeozoic marine hydrocarbon source rocks.The analysis of a series of typical source rocks from Tarim Basin shows that this method not only solves successfully the determination of the maturity of source rocks, but also provides additional important information on oil and gas generation.
1995, 13(2): 128-139.
Abstract:
There are lots of complicated controlling factors on tight clastic gas reservoirs, especially those with long burial history and great burial depth. According to reserches on the relationship between porosity and burial history as well as diagenetic stages of several Meso - Cenozoic gas - bearing basins in China, this paper has proposed a subdivision scheme of reservoir pore types in terms of their occurrence, which includes four types,that is, intergranular pore, intergranular dissolution pore, intraconstituent pore and fissures. Furthermore,the contributions to the improvenment of reservoir properties resulted from different pore types have been analysed. In addition, the controlling mechanism on the properties of elastic gas reservoirs has also been disscussed by individually dissecting multiple factors, such as physical and chemical properties of detrital grains;argillic matrix and authigenic clay minerals; sedimentation rate and burial history; grain size and sorting; agenesis of mudstone; tectonic setting and movement, vitrinite reflectance and organic maturity, and so on.As a result of the study, the authors believe that the properties of elastic gas reservoirs are comprehensively controlled by multiple factors. Pore spaces of reserviors, which have a short burial history and shallow burial depth, are mainly composed of primary pores. Depositional environment and physical property of detrital grains are dominant controlling factors. As for those tight reservoirs with a long burial history and great depth,the pore spaces are extremely complex, in which the intergranular and intraconstituent dissolution pores are very common. And the influencing factors are diversified, including depositional environment, tectonic setting, physical and chemical properties of detrital grain, burial history, nature of pore fluid and its influx state as well as diagenetic evolution characteristics of mudstone and organic matter. However, in different basins, all the factors mentioned above have played different role in controlling the reservoir evolution,and their action procedures are changable, but above all, the burial history and pore fluid conditions are theleading elements in controlling the properties of tight gas reservoirs.
There are lots of complicated controlling factors on tight clastic gas reservoirs, especially those with long burial history and great burial depth. According to reserches on the relationship between porosity and burial history as well as diagenetic stages of several Meso - Cenozoic gas - bearing basins in China, this paper has proposed a subdivision scheme of reservoir pore types in terms of their occurrence, which includes four types,that is, intergranular pore, intergranular dissolution pore, intraconstituent pore and fissures. Furthermore,the contributions to the improvenment of reservoir properties resulted from different pore types have been analysed. In addition, the controlling mechanism on the properties of elastic gas reservoirs has also been disscussed by individually dissecting multiple factors, such as physical and chemical properties of detrital grains;argillic matrix and authigenic clay minerals; sedimentation rate and burial history; grain size and sorting; agenesis of mudstone; tectonic setting and movement, vitrinite reflectance and organic maturity, and so on.As a result of the study, the authors believe that the properties of elastic gas reservoirs are comprehensively controlled by multiple factors. Pore spaces of reserviors, which have a short burial history and shallow burial depth, are mainly composed of primary pores. Depositional environment and physical property of detrital grains are dominant controlling factors. As for those tight reservoirs with a long burial history and great depth,the pore spaces are extremely complex, in which the intergranular and intraconstituent dissolution pores are very common. And the influencing factors are diversified, including depositional environment, tectonic setting, physical and chemical properties of detrital grain, burial history, nature of pore fluid and its influx state as well as diagenetic evolution characteristics of mudstone and organic matter. However, in different basins, all the factors mentioned above have played different role in controlling the reservoir evolution,and their action procedures are changable, but above all, the burial history and pore fluid conditions are theleading elements in controlling the properties of tight gas reservoirs.
1995, 13(2): 150-159.
Abstract:
This paper mainly discusses the classification of sedimentary basins in accordance with the structure of oil and gas - bearing basins. The group basins can be classified into three large classes and eight types: (1)graben -downwarp basin. It is divided into three subtypes, that is, unitary structure, dualistic and polyunitary stucture; (2) uplift - depessions - downwarp basin. It is also divided into unitary structure, dualistic and polyunitary sturcture; (3) craton downwarp basin. It is divided into interrapt and inheritance subtype.Owing to the different sedimentary basins with different oil - gas- bearing properties, this kind of basin classification is of important theoretic and proctical significance.
This paper mainly discusses the classification of sedimentary basins in accordance with the structure of oil and gas - bearing basins. The group basins can be classified into three large classes and eight types: (1)graben -downwarp basin. It is divided into three subtypes, that is, unitary structure, dualistic and polyunitary stucture; (2) uplift - depessions - downwarp basin. It is also divided into unitary structure, dualistic and polyunitary sturcture; (3) craton downwarp basin. It is divided into interrapt and inheritance subtype.Owing to the different sedimentary basins with different oil - gas- bearing properties, this kind of basin classification is of important theoretic and proctical significance.
1995, 13(2): 169-177.
Abstract:
While oil and gas from a deep reservior migrates near surface along the micro fracture of sedimentary rocks covering above the reservior, the original geochemical characteristics of soil are changed. Thus, the recognizable geochemical anomaly is formed in the near surface soil. After analyzing soil hydrocarbons, soil secondary carbonate (△C), soil mercury and the carbon isotope of methane and △C, and so on, we may supply an important information on determinating oil - gas migration, discovering geochemical anomaly related to deep oil and gas reserviors, and, thereby, may suggest the existence of deep oil and gas in buried reserviors.According to our study on the geochemistry of soil hydrocarbons, soil secondary carbonate and soil mercury, different geochemical indicators and methods are of different results in various geochemical landscapes.
While oil and gas from a deep reservior migrates near surface along the micro fracture of sedimentary rocks covering above the reservior, the original geochemical characteristics of soil are changed. Thus, the recognizable geochemical anomaly is formed in the near surface soil. After analyzing soil hydrocarbons, soil secondary carbonate (△C), soil mercury and the carbon isotope of methane and △C, and so on, we may supply an important information on determinating oil - gas migration, discovering geochemical anomaly related to deep oil and gas reserviors, and, thereby, may suggest the existence of deep oil and gas in buried reserviors.According to our study on the geochemistry of soil hydrocarbons, soil secondary carbonate and soil mercury, different geochemical indicators and methods are of different results in various geochemical landscapes.
1995, 13(2): 4-13.
Abstract:
Carbon isotopic compositions of crude oil and natural gas can similarly indicate their characteristics of association. In this paper, types of oil - gas assemblage are classified based on the data of isotopic compositions of crude oil and natural gases in Liaohe Oilfield, of which hydrocarbon geochemistry has been studied well.With the study of Liaohe Oilfield, the relationship of the oil - gas isotopic composition of bio, thermo catalytic transitional zone (BTCTZ) in China is researched systematically and their types of oil - gas assemblage are divided, and the geochemical characteristics of different oil - gas assemblages for BTCTZ are discussed as well.According to the carbon isotopic composition of oils and methane and ethane of gases as well as to the geologic setting of Liaohe Basin, four types of oil - gas assemblages are divided, i. e., (1) the oil - gas assemblage of similar evolutionary stage and congenetic sapropel matters; (2) the assemblage of similar evolutionary stage of sapropel - humus matters; (3) the assemblage of similar evolutionary stage from homologous humus and (4) the oil- gas assemblage of mixture that the oils and gases would come from congenetic organic matters but different evolutionary stage, or similar evolutionary stage but different type of organic matters,or different matters with different evolutionary stage. All of the assemblages can be subdivided in terms of their evolutionary stage of the organic matter and have specific geochemical features and relationship of the isotopic compositions. From all of the assemblages, the oil - gas associations of different BTCTZ are researched emphatically.Because oil and gas from the same type and evolutionary stage of organic matter take corresponding distribution pattern of the carbon and hydrogen isotopic composition, the varied difference of them may identify the features of oil and gas generated from different type and evolutionary stage of organic matter. The systematic study of numerous oil and gas isotope data from more than ten sedimentary basins in China showsthat there are four oil - gas assemblages of BTCTZ, which are listed as follows:(1) The oil - gas assemblage of BTCTZ of sapropel organic matter. Its BTCTZ gas and immature - lowmature oil sourced from the same sapropel matter during similar evolutionary stage. its indictors are δ13C1 between - 52～- 45‰, δ13'Coil below - 28‰, δ13C2 below- 30‰, δDCH4 below - 250‰ and δDoil below -160‰.(2) The oil- gas assemblage of BTCTZ of sapropel - humic organic matter. It resembles type (1) but organic matter is sapropel - humus and δ13C1 between - 52～- 45‰, δ13Coil between - 28～- 25‰, δ13C2 between - 38～-26‰, δDCH4 between - 280～- 180‰ and δDoil between - 180～- 120‰.(3) The assemblage of BTCTZ gas from humus and oil from saporpel matter. This kind of gas is BTCTZ gas produced by humic organic matters and the oil may be from saropel - humic orgonic matter during the higher eviutionary stage. its isotopic compositions are δ13C1 between - 60～- 52‰, δ13Ciol between - 28～- 25‰.(4)The assemblage of BTCTZ gas from sapropel - humic organic matter and oil from saporpel matter.It's gas and oil originated from the same organic matter or different organic matters, but the evolutionary stage for oil was little higher than that for gas, and the mixture feature is obvious. Its carbon isotopic compositions are δ13C1 between - 60～- 52‰, and δ13Coil beolw - 28‰.The studies of isotopic composition relationship between gases and oils lead us to understand more about the origin and evolution of natural gas, particularly of BTCTZ gas. With the studies in this paper, it can be seen that almost all gases and oils in BTCTZ are the results of evolution from congeneitic matter in the same stage, and the existence of gases and oils in BTCTZ has been verified. It also corrects the concept that the BTCTZ gas was mixtule of biogenic gas and thermocatalytic gas. The studies show that the BTCTZ is an important stratum for oil and gas accumulation during the evolution of organic m
Carbon isotopic compositions of crude oil and natural gas can similarly indicate their characteristics of association. In this paper, types of oil - gas assemblage are classified based on the data of isotopic compositions of crude oil and natural gases in Liaohe Oilfield, of which hydrocarbon geochemistry has been studied well.With the study of Liaohe Oilfield, the relationship of the oil - gas isotopic composition of bio, thermo catalytic transitional zone (BTCTZ) in China is researched systematically and their types of oil - gas assemblage are divided, and the geochemical characteristics of different oil - gas assemblages for BTCTZ are discussed as well.According to the carbon isotopic composition of oils and methane and ethane of gases as well as to the geologic setting of Liaohe Basin, four types of oil - gas assemblages are divided, i. e., (1) the oil - gas assemblage of similar evolutionary stage and congenetic sapropel matters; (2) the assemblage of similar evolutionary stage of sapropel - humus matters; (3) the assemblage of similar evolutionary stage from homologous humus and (4) the oil- gas assemblage of mixture that the oils and gases would come from congenetic organic matters but different evolutionary stage, or similar evolutionary stage but different type of organic matters,or different matters with different evolutionary stage. All of the assemblages can be subdivided in terms of their evolutionary stage of the organic matter and have specific geochemical features and relationship of the isotopic compositions. From all of the assemblages, the oil - gas associations of different BTCTZ are researched emphatically.Because oil and gas from the same type and evolutionary stage of organic matter take corresponding distribution pattern of the carbon and hydrogen isotopic composition, the varied difference of them may identify the features of oil and gas generated from different type and evolutionary stage of organic matter. The systematic study of numerous oil and gas isotope data from more than ten sedimentary basins in China showsthat there are four oil - gas assemblages of BTCTZ, which are listed as follows:(1) The oil - gas assemblage of BTCTZ of sapropel organic matter. Its BTCTZ gas and immature - lowmature oil sourced from the same sapropel matter during similar evolutionary stage. its indictors are δ13C1 between - 52～- 45‰, δ13'Coil below - 28‰, δ13C2 below- 30‰, δDCH4 below - 250‰ and δDoil below -160‰.(2) The oil- gas assemblage of BTCTZ of sapropel - humic organic matter. It resembles type (1) but organic matter is sapropel - humus and δ13C1 between - 52～- 45‰, δ13Coil between - 28～- 25‰, δ13C2 between - 38～-26‰, δDCH4 between - 280～- 180‰ and δDoil between - 180～- 120‰.(3) The assemblage of BTCTZ gas from humus and oil from saporpel matter. This kind of gas is BTCTZ gas produced by humic organic matters and the oil may be from saropel - humic orgonic matter during the higher eviutionary stage. its isotopic compositions are δ13C1 between - 60～- 52‰, δ13Ciol between - 28～- 25‰.(4)The assemblage of BTCTZ gas from sapropel - humic organic matter and oil from saporpel matter.It's gas and oil originated from the same organic matter or different organic matters, but the evolutionary stage for oil was little higher than that for gas, and the mixture feature is obvious. Its carbon isotopic compositions are δ13C1 between - 60～- 52‰, and δ13Coil beolw - 28‰.The studies of isotopic composition relationship between gases and oils lead us to understand more about the origin and evolution of natural gas, particularly of BTCTZ gas. With the studies in this paper, it can be seen that almost all gases and oils in BTCTZ are the results of evolution from congeneitic matter in the same stage, and the existence of gases and oils in BTCTZ has been verified. It also corrects the concept that the BTCTZ gas was mixtule of biogenic gas and thermocatalytic gas. The studies show that the BTCTZ is an important stratum for oil and gas accumulation during the evolution of organic m
1995, 13(2): 22-32.
Abstract:
The formation of oil and gas is not a simple process of the transformation among organic matters. In other words, it is a result of the interaction between organic- inorganic matters which take place at the early diagenetic stage. The essence of this process is the elastic aluminosilicate mineral dissolution and diagenetic evolution of clay minerals during diagenesis in the transitional zone. In general, sandstone undergoes a series of diagenesis including compaction, cementation, dissolution, replacement and formation of authigenic minerals, while mudstone mainly changes its clay mineral composition by way of the M→I/M→I and M→C/M→C transformation which could produce proton acid when organic acid dissolves sandstone and replaces Si4+ in montmorillonite with Al3+ in pore water. The proton acid plays an important role in catalysis for the formation of the transitional zone natural gas.
The formation of oil and gas is not a simple process of the transformation among organic matters. In other words, it is a result of the interaction between organic- inorganic matters which take place at the early diagenetic stage. The essence of this process is the elastic aluminosilicate mineral dissolution and diagenetic evolution of clay minerals during diagenesis in the transitional zone. In general, sandstone undergoes a series of diagenesis including compaction, cementation, dissolution, replacement and formation of authigenic minerals, while mudstone mainly changes its clay mineral composition by way of the M→I/M→I and M→C/M→C transformation which could produce proton acid when organic acid dissolves sandstone and replaces Si4+ in montmorillonite with Al3+ in pore water. The proton acid plays an important role in catalysis for the formation of the transitional zone natural gas.
1995, 13(2): 44-47.
Abstract:
This paper made a thermally simulating experiment on modern peat under low temperatures and longer time, and discussed the genetic mechanism of transitional zone gas. Gannan peat has relatively higher yields of gaseous and liquid hydrocarbons under simulation. Liquid hydrocarbons are made up of thermolytic oil and residual chloroform "A". The former is dominated by C6-C14 light hydrocarbons, and the latter is dominated by NSO compounds and asphaltenes. With increasing thermal evolution, the relative content of saturated and aromatic hydrocarbons increases whereas that of NSO compounds and asphaltenes decreases rapidly. Gas compositions for simulated peat are dominated by non- hydrocarbon gases, such as CO2 and N2. With increasing simulation temperatures, gaseous hydrocarbon yields increase rapidly. Gaseous hydrocarbons include C1 -C5 hydrocarbon gases, mainly methane. Carbon isotope values of mathane produced at temperature of 200～400℃ are-53. 82～-33. 62‰.The research indicates that at low thermal evolution stage associated with humic acid decomposition and kerogen rearrangement, bio - thermal catalytic transitional zone gas with lighter carbon isotope value of methane can be generated.
This paper made a thermally simulating experiment on modern peat under low temperatures and longer time, and discussed the genetic mechanism of transitional zone gas. Gannan peat has relatively higher yields of gaseous and liquid hydrocarbons under simulation. Liquid hydrocarbons are made up of thermolytic oil and residual chloroform "A". The former is dominated by C6-C14 light hydrocarbons, and the latter is dominated by NSO compounds and asphaltenes. With increasing thermal evolution, the relative content of saturated and aromatic hydrocarbons increases whereas that of NSO compounds and asphaltenes decreases rapidly. Gas compositions for simulated peat are dominated by non- hydrocarbon gases, such as CO2 and N2. With increasing simulation temperatures, gaseous hydrocarbon yields increase rapidly. Gaseous hydrocarbons include C1 -C5 hydrocarbon gases, mainly methane. Carbon isotope values of mathane produced at temperature of 200～400℃ are-53. 82～-33. 62‰.The research indicates that at low thermal evolution stage associated with humic acid decomposition and kerogen rearrangement, bio - thermal catalytic transitional zone gas with lighter carbon isotope value of methane can be generated.
1995, 13(2): 59-69.
Abstract:
The thermogenic gas can be divided into coal type gas originated from humic organic matter and oil type gas formed by sapropel organic matter according to the type of organic matter. The stable isotopic compositions of hydrocarbons of coal type gas and oil type gas from main oil - gas- bearing basins in Chins are relatively systematically studied in this paper. The results show that it is not certain that the methane of coal type gas always enriches the heavy carbon isotope in comparison with oil type gas. At the stage from immature to low mature, there is no obvious difference in carbon isotopic compositions of methane between coal type gas and oil type gas. From low mature stage, in comparison with oil type gas, the methane of coal type gas gradually enriches heavy carbon isotope with the increasing of thermal evolution. When vitrinite renectance (Ro) reaches about 1. 0, the difference in δ13C1 between coal type gas and oil type gas is the largest,about 7～8‰, then gradually decreases with increasing thermal evolution. After thermal evolution reaches the stage of over - maturity(Ro2. 2% ), the carbon isotope composition of coal type gas is basically similar to that of oil type gas. The carbon isotope compositions of heavy gaseous hydrocarbons (ethane to butane) of coal type gas and oil type gas are mainly controlled by the carbon isotopic composition of organic matter in source rock. Therefore, the carbon isotopic composition of heavy gaseous hydrocarbon is an effective indicator for the identification of coal and oil type gas. In general, the δ13C2 of coal type gas is more than -28‰,while the δ13C2 of oil type gas is less than - 28‰. Thermal evolution has no obvious innuence on carbon isotopic composition of heavy hydrocarbons of coal type gas. However, it has certain influence on carbon isotopic composition of heavy hydrocarbons of oil type gas. With the increase of thermal evolution, the ethane of oil type gas gradually enriches heavy carbon isotopes. The hydrogen isotopic composition of methane and heavy gaseous hydrocarbons of coal type gas is mainly related to the salinity of water under which the source rock was deposited. The coal type gas formed by the source rock deposited in terrestrial freshwater environment relatively enriches protium of hydrogen isotope. However, the coal type gas derived from the marine source rock relatively enriches deuterium of hydrogen isotope. In addition, with the increase of carbon number from methane to butane, the hydrogen isotopic composition of hydrocarbons of coal type gas successively becomes heavier, i. e.,δD1<δＤ2<δＤ3<δＤ4.
The thermogenic gas can be divided into coal type gas originated from humic organic matter and oil type gas formed by sapropel organic matter according to the type of organic matter. The stable isotopic compositions of hydrocarbons of coal type gas and oil type gas from main oil - gas- bearing basins in Chins are relatively systematically studied in this paper. The results show that it is not certain that the methane of coal type gas always enriches the heavy carbon isotope in comparison with oil type gas. At the stage from immature to low mature, there is no obvious difference in carbon isotopic compositions of methane between coal type gas and oil type gas. From low mature stage, in comparison with oil type gas, the methane of coal type gas gradually enriches heavy carbon isotope with the increasing of thermal evolution. When vitrinite renectance (Ro) reaches about 1. 0, the difference in δ13C1 between coal type gas and oil type gas is the largest,about 7～8‰, then gradually decreases with increasing thermal evolution. After thermal evolution reaches the stage of over - maturity(Ro2. 2% ), the carbon isotope composition of coal type gas is basically similar to that of oil type gas. The carbon isotope compositions of heavy gaseous hydrocarbons (ethane to butane) of coal type gas and oil type gas are mainly controlled by the carbon isotopic composition of organic matter in source rock. Therefore, the carbon isotopic composition of heavy gaseous hydrocarbon is an effective indicator for the identification of coal and oil type gas. In general, the δ13C2 of coal type gas is more than -28‰,while the δ13C2 of oil type gas is less than - 28‰. Thermal evolution has no obvious innuence on carbon isotopic composition of heavy hydrocarbons of coal type gas. However, it has certain influence on carbon isotopic composition of heavy hydrocarbons of oil type gas. With the increase of thermal evolution, the ethane of oil type gas gradually enriches heavy carbon isotopes. The hydrogen isotopic composition of methane and heavy gaseous hydrocarbons of coal type gas is mainly related to the salinity of water under which the source rock was deposited. The coal type gas formed by the source rock deposited in terrestrial freshwater environment relatively enriches protium of hydrogen isotope. However, the coal type gas derived from the marine source rock relatively enriches deuterium of hydrogen isotope. In addition, with the increase of carbon number from methane to butane, the hydrogen isotopic composition of hydrocarbons of coal type gas successively becomes heavier, i. e.,δD1<δＤ2<δＤ3<δＤ4.
1995, 13(2): 77-85.
Abstract:
In some oil - bearing basins of China, the abnormal pressures do not develop, for example the oil - bearing formation of Tertiary in Liaohe Basin and the Jurassic coal measure in Tuba Basin, which are characterized by the near - hydrostatic pressure. Faults and fractures are the main paths of oil and gas migration, and tectonic stress is the principle dynamics of producing faults and fractures. The writer applies graphs of Mohr's stress circle and failure envelope to discuss this mechanism.According to the abnormal records of ground water table and oil - gas production before, at end after the time of strong earthquake in Eastern China during the latest 30 years, the author indicates that the oil - gas migration along the faults is closely related to the seismic pumping mechanism. The active fault leads to the stress relaxation in faults. especially in its upper part, and then the fluid now from the surrounding rocks towards fault. Based on the fluid potential difference between upper and lower part in fault and buoyance, the oil - gas- water may move periodically and gush out in a mixed phase.
In some oil - bearing basins of China, the abnormal pressures do not develop, for example the oil - bearing formation of Tertiary in Liaohe Basin and the Jurassic coal measure in Tuba Basin, which are characterized by the near - hydrostatic pressure. Faults and fractures are the main paths of oil and gas migration, and tectonic stress is the principle dynamics of producing faults and fractures. The writer applies graphs of Mohr's stress circle and failure envelope to discuss this mechanism.According to the abnormal records of ground water table and oil - gas production before, at end after the time of strong earthquake in Eastern China during the latest 30 years, the author indicates that the oil - gas migration along the faults is closely related to the seismic pumping mechanism. The active fault leads to the stress relaxation in faults. especially in its upper part, and then the fluid now from the surrounding rocks towards fault. Based on the fluid potential difference between upper and lower part in fault and buoyance, the oil - gas- water may move periodically and gush out in a mixed phase.
1995, 13(2): 105-111.
Abstract:
Black argillite samples from North China and Lower Yangtze Region are selected to study in detail by methods of organic petrology. Organic matters of North China samples are mainly from terrestrial plant, and those of Lower Yangtze samples mainly derived from water plant. Exinite in argillite has estuary configration, it shows that exinite has generated a large amount of gas in maturation process. Thus, exinite of argillite plays an important role in gas resource of North China.Gas-generating indices (GI) are put forward on the basis of the maceral composition and gas amount of single maceral in experiment. GI value stands for gas-generating potentail of source rocks. Gas-source rocks are divided into good, fairly good, general and poor types according to their GI values. Argillite of Lower Yangtze Region is a good gas-source rock, and that of North China is fairly good one. They have stronger gas-generating potential than coal.
Black argillite samples from North China and Lower Yangtze Region are selected to study in detail by methods of organic petrology. Organic matters of North China samples are mainly from terrestrial plant, and those of Lower Yangtze samples mainly derived from water plant. Exinite in argillite has estuary configration, it shows that exinite has generated a large amount of gas in maturation process. Thus, exinite of argillite plays an important role in gas resource of North China.Gas-generating indices (GI) are put forward on the basis of the maceral composition and gas amount of single maceral in experiment. GI value stands for gas-generating potentail of source rocks. Gas-source rocks are divided into good, fairly good, general and poor types according to their GI values. Argillite of Lower Yangtze Region is a good gas-source rock, and that of North China is fairly good one. They have stronger gas-generating potential than coal.
1995, 13(2): 120-127.
Abstract:
In this paper, source rocks from major Chinese coal-bearing petroliferous basins were studied by Pyrolysis-Gas Chromatography (PY-GC) technique, and compositional characters of pyrolysates and their significance were discussed in detail. Differences in pyrolysate compositions of different coal-bearing source rocks are principally reflected upon the abstract amounts of C+5 n-alkanes and n-alkenes, as well as upon the constitutinn of aromatic compounds. We selected C1-C5, C6-C14 and C+15 n-alkanes and n-alkenes as three terminal represents of pyrolysate composition, and their relative amounts could be effectivelly employed to distinct types and features of hydrocarbon generation in coal-bearing source rocks.All the results show that PY-GC technique is an effective approach for coal-generated hydrocarbon evaluation, and this technique is worthy of widespread application.
In this paper, source rocks from major Chinese coal-bearing petroliferous basins were studied by Pyrolysis-Gas Chromatography (PY-GC) technique, and compositional characters of pyrolysates and their significance were discussed in detail. Differences in pyrolysate compositions of different coal-bearing source rocks are principally reflected upon the abstract amounts of C+5 n-alkanes and n-alkenes, as well as upon the constitutinn of aromatic compounds. We selected C1-C5, C6-C14 and C+15 n-alkanes and n-alkenes as three terminal represents of pyrolysate composition, and their relative amounts could be effectivelly employed to distinct types and features of hydrocarbon generation in coal-bearing source rocks.All the results show that PY-GC technique is an effective approach for coal-generated hydrocarbon evaluation, and this technique is worthy of widespread application.
1995, 13(2): 140-149.
Abstract:
The formation of carbonate gas reserviors has a close relation with the diagenetic environment, which controls the development of primary and secondary porosities in carbonate reservoirs. In terms of burial depth and features of water medium, the diagenetic environment can be divided into three types, i. e., marine,burial and epidiagenetic environments, of which the most favorable porosity zone is shallow flat, beach and reef environments and meteoric vadose zone in epidiagenetic environment.The mechanisms responsible for the formation of carbonate reserviors are dolomitization and karstification. The fact that the excellent pore--type resrviors are commonly present in dolomite has been confirmed in many gas fields in China. The strata in which the giant gas fields formed are Sinian, Carboniferous in Sichun Basin and Ordovician in Ordos and Tarim Basin. The dolomitization developed in different stages can all produce excellent intercrystal and intergranular porosities as well as secondary porosity. The gas field reseryiors relevant to the karstification in China account for 83% in the total numbers of the proved gas fields. Theintensity and depth of karstification vary directly with the exposure time. Accordingly, the time for the slight karstification is approximately 5--20 Ma, the intermediate 40 Ma and the extensive 100-- 200 Ma, of which the first and the second contain the best porosity. Therefore, when assessing reservoir quality, this fator should be taken into consideration.The experiment results of comparision study on dissolubility and corrosion between different types of carbonate rocks indicate that limestone is greater than dolomitite in dissolublity, but inversrely in physical destruction quantity leading to the frequent observation of dolomitite breccia and solution cave in limestone in geohistory. The pure limestone appears to have the large dissolubility and rapid dissolution rate, and the average dissolubility of limestone is larger than that of dolomitite by 36%. In addition to composition, the texture is also the main factor affecting the dissolubility. Thus, dolomitite is easy to form dissolution pore along the intercrystal fissure, and micrite limestone, possessing a large specific surface area than sparite, is of rapid dissolution rate. For this reason, the karstification of ancient limestone is better developed than dolomitite,which makes the limestone an excellent reservoir in gas fields of China.On the basis of the integrated featrues of carbonate reservoir with different ages in different areas of China, the author has poroposed a diagenetic model on the reservoir formation, which describes the formation ofreservoir undergoes three important episodes in different diagenetic stages. The first episode to form secondary porosity on a large scale is closely related to the dissolution as a result of organic acid released fromthe transformation of organic matters to hydrocarbons, and the organic matter is in immature stage with burial depth less than 1000m. This episode spans at least 100 Ma. The second episode is in epidiagenesis when meteoric water leaks and dissolves the carbonate rock. Most gas reservoirs are formed in this period. The dissolution occurs in 5--200 Ma after sediment consolidation. The third episode is developed on the basis of the former dissolution and corrosion, and, while considerable karstification and collapse take place, resulting in pore fillings re dissolved and after repetition of filling and dissolution, the reservior has changed its oringinal features completely, in which only those effective porosities with no pore fillings or semi filled are contributed to the reservior formation.
The formation of carbonate gas reserviors has a close relation with the diagenetic environment, which controls the development of primary and secondary porosities in carbonate reservoirs. In terms of burial depth and features of water medium, the diagenetic environment can be divided into three types, i. e., marine,burial and epidiagenetic environments, of which the most favorable porosity zone is shallow flat, beach and reef environments and meteoric vadose zone in epidiagenetic environment.The mechanisms responsible for the formation of carbonate reserviors are dolomitization and karstification. The fact that the excellent pore--type resrviors are commonly present in dolomite has been confirmed in many gas fields in China. The strata in which the giant gas fields formed are Sinian, Carboniferous in Sichun Basin and Ordovician in Ordos and Tarim Basin. The dolomitization developed in different stages can all produce excellent intercrystal and intergranular porosities as well as secondary porosity. The gas field reseryiors relevant to the karstification in China account for 83% in the total numbers of the proved gas fields. Theintensity and depth of karstification vary directly with the exposure time. Accordingly, the time for the slight karstification is approximately 5--20 Ma, the intermediate 40 Ma and the extensive 100-- 200 Ma, of which the first and the second contain the best porosity. Therefore, when assessing reservoir quality, this fator should be taken into consideration.The experiment results of comparision study on dissolubility and corrosion between different types of carbonate rocks indicate that limestone is greater than dolomitite in dissolublity, but inversrely in physical destruction quantity leading to the frequent observation of dolomitite breccia and solution cave in limestone in geohistory. The pure limestone appears to have the large dissolubility and rapid dissolution rate, and the average dissolubility of limestone is larger than that of dolomitite by 36%. In addition to composition, the texture is also the main factor affecting the dissolubility. Thus, dolomitite is easy to form dissolution pore along the intercrystal fissure, and micrite limestone, possessing a large specific surface area than sparite, is of rapid dissolution rate. For this reason, the karstification of ancient limestone is better developed than dolomitite,which makes the limestone an excellent reservoir in gas fields of China.On the basis of the integrated featrues of carbonate reservoir with different ages in different areas of China, the author has poroposed a diagenetic model on the reservoir formation, which describes the formation ofreservoir undergoes three important episodes in different diagenetic stages. The first episode to form secondary porosity on a large scale is closely related to the dissolution as a result of organic acid released fromthe transformation of organic matters to hydrocarbons, and the organic matter is in immature stage with burial depth less than 1000m. This episode spans at least 100 Ma. The second episode is in epidiagenesis when meteoric water leaks and dissolves the carbonate rock. Most gas reservoirs are formed in this period. The dissolution occurs in 5--200 Ma after sediment consolidation. The third episode is developed on the basis of the former dissolution and corrosion, and, while considerable karstification and collapse take place, resulting in pore fillings re dissolved and after repetition of filling and dissolution, the reservior has changed its oringinal features completely, in which only those effective porosities with no pore fillings or semi filled are contributed to the reservior formation.
1995, 13(2): 160-168.
Abstract:
The tectonic kinematic process of the oil-gas bearing basins is controlled by tectonic dynamic conditions.Under the conditions of different tectonic dynamic, different prototype basins were formed. On the basis of studying tectonic dynamic condition of Palaeozoic Era in Northwest China and Mesozoic-Cenozoic Era in the Chinese continent, this paper has discussed the formation and quality of different oil-gas bearing basins.The tectonic kinematic processes of the basins are of cyclicity which controls the cyclicity of the formation and development of depositon, subsidence and oil- gas generating depression center of the basins, and restricted sedimentary sequence in depression, and also limited continuous subsidence of oil-gas bearing depression which result in the formation of multistage subsidence through vertical superimposing of different prototype basins, and multistage continuous hydrocarbon - producing process of source rocks.Multiphase tectonic activity supplies the oils and gases of different epoches and various types with condition of migration, accumulation and preservation, and it is the premise for the formation of oil - gas fields with multiple sources.
The tectonic kinematic process of the oil-gas bearing basins is controlled by tectonic dynamic conditions.Under the conditions of different tectonic dynamic, different prototype basins were formed. On the basis of studying tectonic dynamic condition of Palaeozoic Era in Northwest China and Mesozoic-Cenozoic Era in the Chinese continent, this paper has discussed the formation and quality of different oil-gas bearing basins.The tectonic kinematic processes of the basins are of cyclicity which controls the cyclicity of the formation and development of depositon, subsidence and oil- gas generating depression center of the basins, and restricted sedimentary sequence in depression, and also limited continuous subsidence of oil-gas bearing depression which result in the formation of multistage subsidence through vertical superimposing of different prototype basins, and multistage continuous hydrocarbon - producing process of source rocks.Multiphase tectonic activity supplies the oils and gases of different epoches and various types with condition of migration, accumulation and preservation, and it is the premise for the formation of oil - gas fields with multiple sources.
