To study the composition, affecting factors of the stable hydrogen isotopes of alkane gases and their application to identification of the natural gas origin and maturities, the chemical and isotopic compositions of 1...To study the composition, affecting factors of the stable hydrogen isotopes of alkane gases and their application to identification of the natural gas origin and maturities, the chemical and isotopic compositions of 118 gas samples of Carboniferous- Permian in the Ordos Basin, and of Triassic in the Sichuan Basin, combined with 68 gas samples from the Sinian and Cambrian reservoirs in the Sichuan Basin, and Ordovician and Siliurian reservoirs of Tarim Basin, are analyzed comprehensively. The following conclusions are obtained:(1) Natural gases in the study area and strata of the Ordos and Sichuan basins are dominated by alkane gases, and the dryness coefficients and maturities of the Carboniferous-Permian gases in the Ordos Basin are higher than the gases in the Triassic Xujiahe Formation of the Sichuan Basin, while the hydrogen isotopes of the latter ones are much enriched in 2H than the former.(2) The δ2HCH4-C1/C2+3 genetic identification diagram of natural gas was drawn, and the diagrams of hydrogen isotopic differences between the heavy alkane gases and methane vs. hydrogen isotopes of alkane gases can also be used in natural gas genetic identification.(3) The δ2HCH4-Ro formulas of coal-formed gas in different areas of the two basins are given, and the δ2HC2H6-δ2HCH4 is a new index for maturity, and the (δ2HC2H6-δ2HCH4)-Ro formula of the coal-formed gas can be used to calculate the maturity of the natural gas.(4) The stable hydrogen isotopes of alkane gases are affected by parent materials in source rocks, maturity, mixing and the aqueous medium conditions, among which the aqueous paleo-salinity is the key factor. To sum up, the hydrogen isotopes of alkane gases are affected by multiple factors, and they are significant to the identification of the origin, and maturity of natural gas, and the water environment during the deposition of source rocks.展开更多
Coalbed gases (CBG) in Enhong syncline are characterized by high concentration of C2+ (C2-5 ), with the highest content of ethane over 30%. However, the concentrations of C2+ are not evenly distributed in the syncline...Coalbed gases (CBG) in Enhong syncline are characterized by high concentration of C2+ (C2-5 ), with the highest content of ethane over 30%. However, the concentrations of C2+ are not evenly distributed in the syncline. Based on the analysis of δ13C1 , δ13C2 , δ13C3 , δ13CO2 , δDCH4 of CBG and their origin diagrams in the normal and abnormal areas, this research shows that gases in both areas are thermogenic gases and the reason for the uneven distribution of C2+ is that the microbial degradation action on gases is stronger in the normal area than in the abnormal area. The secondary biologic gases in the normal area are mainly characterized by that the carbon isotopes become obviously lighter in methane and become heavier in ethane, whereas the molecular and isotopic compositions of CO2 change little. These features indicate that the secondary biologic gases are mainly generated by the microbial degradation of C2+ , not generated by the reduction of CO2 . The degradation process is selective to make the residual ethane being enriched in 13C and the generated methane rich in 12C.展开更多
The geochemical characteristics of natural gases discovered in the Bozhong Depression are systematically described in this paper. The natural gases are composed mainly of hydrocarbon gases. Natural gases occurring in ...The geochemical characteristics of natural gases discovered in the Bozhong Depression are systematically described in this paper. The natural gases are composed mainly of hydrocarbon gases. Natural gases occurring in the Paleogene and older reservoirs are wet gases, whereas those in the Neogene reservoirs are dry gases. Methane and ethane in the gases are significantly different in carbon isotopic composition. The methane carbon isotopic composition of the gases in structure BZ28-1 and the ethane carbon isotopic composition of the gases in structure QHD30-1 are characterized by the heaviest values, respectively. The natural gases are in the mature to highly mature stages. The hydrocarbon gases are of organic origin and can be classified as oil-type gases, coal-derived gases and mixed gases with the third one accounting for the major portion.展开更多
基金Supported by the China National Science and Technology Major Project(2016ZX05004-001)
文摘To study the composition, affecting factors of the stable hydrogen isotopes of alkane gases and their application to identification of the natural gas origin and maturities, the chemical and isotopic compositions of 118 gas samples of Carboniferous- Permian in the Ordos Basin, and of Triassic in the Sichuan Basin, combined with 68 gas samples from the Sinian and Cambrian reservoirs in the Sichuan Basin, and Ordovician and Siliurian reservoirs of Tarim Basin, are analyzed comprehensively. The following conclusions are obtained:(1) Natural gases in the study area and strata of the Ordos and Sichuan basins are dominated by alkane gases, and the dryness coefficients and maturities of the Carboniferous-Permian gases in the Ordos Basin are higher than the gases in the Triassic Xujiahe Formation of the Sichuan Basin, while the hydrogen isotopes of the latter ones are much enriched in 2H than the former.(2) The δ2HCH4-C1/C2+3 genetic identification diagram of natural gas was drawn, and the diagrams of hydrogen isotopic differences between the heavy alkane gases and methane vs. hydrogen isotopes of alkane gases can also be used in natural gas genetic identification.(3) The δ2HCH4-Ro formulas of coal-formed gas in different areas of the two basins are given, and the δ2HC2H6-δ2HCH4 is a new index for maturity, and the (δ2HC2H6-δ2HCH4)-Ro formula of the coal-formed gas can be used to calculate the maturity of the natural gas.(4) The stable hydrogen isotopes of alkane gases are affected by parent materials in source rocks, maturity, mixing and the aqueous medium conditions, among which the aqueous paleo-salinity is the key factor. To sum up, the hydrogen isotopes of alkane gases are affected by multiple factors, and they are significant to the identification of the origin, and maturity of natural gas, and the water environment during the deposition of source rocks.
基金supported by the Key Program of the National Natural Science Foundation of China (No. 40730422)the Key Special Project of the National Science and Technology of China (No.2011ZX05034)the Fundamental Research Funds for the Central Universities of China (No. 2010QNA51)
文摘Coalbed gases (CBG) in Enhong syncline are characterized by high concentration of C2+ (C2-5 ), with the highest content of ethane over 30%. However, the concentrations of C2+ are not evenly distributed in the syncline. Based on the analysis of δ13C1 , δ13C2 , δ13C3 , δ13CO2 , δDCH4 of CBG and their origin diagrams in the normal and abnormal areas, this research shows that gases in both areas are thermogenic gases and the reason for the uneven distribution of C2+ is that the microbial degradation action on gases is stronger in the normal area than in the abnormal area. The secondary biologic gases in the normal area are mainly characterized by that the carbon isotopes become obviously lighter in methane and become heavier in ethane, whereas the molecular and isotopic compositions of CO2 change little. These features indicate that the secondary biologic gases are mainly generated by the microbial degradation of C2+ , not generated by the reduction of CO2 . The degradation process is selective to make the residual ethane being enriched in 13C and the generated methane rich in 12C.
文摘The geochemical characteristics of natural gases discovered in the Bozhong Depression are systematically described in this paper. The natural gases are composed mainly of hydrocarbon gases. Natural gases occurring in the Paleogene and older reservoirs are wet gases, whereas those in the Neogene reservoirs are dry gases. Methane and ethane in the gases are significantly different in carbon isotopic composition. The methane carbon isotopic composition of the gases in structure BZ28-1 and the ethane carbon isotopic composition of the gases in structure QHD30-1 are characterized by the heaviest values, respectively. The natural gases are in the mature to highly mature stages. The hydrocarbon gases are of organic origin and can be classified as oil-type gases, coal-derived gases and mixed gases with the third one accounting for the major portion.
