Recently abiogenic alkanes have been found in various locations in the world and other celestial bodies. The chemical composition of abiogenic alkane gases varies widely. The content of methane is low and nearly no C2...Recently abiogenic alkanes have been found in various locations in the world and other celestial bodies. The chemical composition of abiogenic alkane gases varies widely. The content of methane is low and nearly no C2+ is found in the abiogenic alkane gases from fluid inclusions in volcanic rocks or hot springs in China. In the unsedimented submarine hydrothermal vent system C1/C2+ ratios are much greater than those for the thermogenic gases, mostly >800 and in some cases up to 8,000. In the Songliao Basin, China, C1/C2+ of some abiogenic gases are often less than 150. Abiogenic alkane gases which have been found in nature often have carbon isotopic reversal among C1–C4 alkanes (δ13C1>δ13C2>δ13C3>δ13C4), whereas both regular and reversed hydrogen isotope distribution pattern among C1–C4 alkanes have been reported. The δ13C of abiogenic methane is mainly greater than ?30‰ though laboratory synthesized methane can have δ13C as low as ?57‰, and its δD1 values vary widely and overlap with biogenic gases. High 3He/4He ratios often indicate the addition of mantle-derived helium and are related to abiogenic gases. However, some biogenic gases can also have high 3He/4He ratios up to 8. The CH4/3He end-member is often lower than 106 for abiogenic alkane gases while greater than 1013 for biogenic gases, and the values between these two end-members often reflect the mixing of biogenic and abiogenic gases.展开更多
Recently,methane of possible abiogenic origin has been reported from many localities within the Earth’s crust.However,little is known about the mechanisms of abiogenic methane formation during such processes.The Fisc...Recently,methane of possible abiogenic origin has been reported from many localities within the Earth’s crust.However,little is known about the mechanisms of abiogenic methane formation during such processes.The Fischer-Tropsch reaction as a well known process for converting CO<sub>2</sub> to hydrocarbon gas by reaction with H<sub>2</sub> may take place on a metallic iron or iron oxide catalyst and also may take place on展开更多
For the first time,the property of deep abiogenic methane-containing high-thermobaric fluid to decompose organic residues in the Earth’s crust and form coal seams was established.
Exploration and development of large gas fields is an important way for a country to rapidly develop its natural gas industry.From 1991 to 2020,China discovered 68 new large gas fields,boosting its annual gas output t...Exploration and development of large gas fields is an important way for a country to rapidly develop its natural gas industry.From 1991 to 2020,China discovered 68 new large gas fields,boosting its annual gas output to 1925×108m3in 2020,making it the fourth largest gas-producing country in the world.Based on 1696 molecular components and carbon isotopic composition data of alkane gas in 70 large gas fields in China,the characteristics of carbon isotopic composition of alkane gas in large gas fields in China were obtained.The lightest and average values ofδ^(13)C_(1),δ13C2,δ13C3andδ13C4become heavier with increasing carbon number,while the heaviest values ofδ^(13)C_(1),δ13C2,δ13C3andδ13C4become lighter with increasing carbon number.Theδ^(13)C_(1)values of large gas fields in China range from-71.2‰to-11.4‰(specifically,from-71.2‰to-56.4‰for bacterial gas,from-54.4‰to-21.6‰for oil-related gas,from-49.3‰to-18.9‰for coal-derived gas,and from-35.6‰to-11.4‰for abiogenic gas).Based on these data,theδ^(13)C_(1)chart of large gas fields in China was plotted.Moreover,theδ^(13)C_(1)values of natural gas in China range from-107.1‰to-8.9‰,specifically,from-1071%o to-55.1‰for bacterial gas,from-54.4‰to-21.6‰for oil-related gas,from-49.3‰to-13.3‰for coal-derived gas,and from-36.2‰to-8.9‰for abiogenic gas.Based on these data,theδ^(13)C_(1)chart of natural gas in China was plotted.展开更多
We have combined the analytical data of the carbon isotope distribution pattern, R/Ra and CH4/3He values of abiogenic and biogenic (referring to the thermogenic and bacterial or microbial) alkane gases in China with t...We have combined the analytical data of the carbon isotope distribution pattern, R/Ra and CH4/3He values of abiogenic and biogenic (referring to the thermogenic and bacterial or microbial) alkane gases in China with those of alkane gases from USA, Russia, Germany, Australia and other countries. Four discrimination criteria are derived from this comparative study: 1) Carbon isotopic composition is generally greater than ?30‰ for abiogenic methane and less than ?30‰ for biogenic methane; 2) Abiogenic alkane gases have a carbon isotopic reversal trend (δ13C1> δ13C2> δ13C3> δ13C4) with δ13C1> ?30‰ in general; 3) Gases with R/Ra >0.5 and δ13C1? δ13C2>0 are of abiogenic origin; 4) Gases (methane) with CH4/3He?106 are of abiogenic origin, whereas gases with CH4/3He?1011 are of biogenic origin.展开更多
The hydrocarbons and other organic compounds generated through abiogenic or inorganic processes are closely related to two science subjects, i.e., energy resources and life＇s origin and evolution. ＂The earth＇s prim...The hydrocarbons and other organic compounds generated through abiogenic or inorganic processes are closely related to two science subjects, i.e., energy resources and life＇s origin and evolution. ＂The earth＇s primordial abiogenic hydrocarbon theory＂ and ＂the serpentinization of abiogenic hydrocarbon theory＂ are the two mainstream theories in the field of related studies. Ser- pentinizafion generally occurs in slow expanding mid-ocean ridges and continental ophiolites tectonic environment, etc. The abiogenic hydrocarbons and other organic compounds formed through the serpentinization of ultramafic rocks provide energy and raw materials to support chemosynthetic microbial communities, which probably was the most important hydration reac- tion for the origin and early evolution of life. The superposition of biological and abiological processes creates big challenge to the identification of the abiogenic organic materials in serpentinite-hosted ecosystem. Whether abiotic （inorganic） process can form oil and gas resource is a difficult question that has been explored continuously by scientific community for more than a century but has not yet been solved. However, some important progress has been made. The prospecting practice of abiogenic hydrocarbons in commercial gases from the Songliao Basin, China, provides an important example for exploring abiogenic natural gas resources.展开更多
This paper discusses the kinetic fractionation, composition and distribution characteristics of carbon and hydrogen isotopes for various alkane gases formed in different environments, by different mechanisms and from ...This paper discusses the kinetic fractionation, composition and distribution characteristics of carbon and hydrogen isotopes for various alkane gases formed in different environments, by different mechanisms and from different sources in nature. It is demonstrated that the biodegradation or thermodegradation of complex high-molecule sedimentary organic material can form microbial gas or thermogenic gas. The δ13C1 value ranges from ?110% to ?50% for microbial gases but from ?50% to ?35% (even heavier) for thermogenic gases. Controlled by the kinetic isotope fractionation, both microbial and thermogenic gases have δ13C and δ D values characterized by normal distribution, i.e. δ13C1< δ 13C2< δ 13C3< δ 13C4 and $ \delta D_{CH_4 } < \delta D_{C_2 H_6 } < \delta D_{C_3 H_8 } < \delta D_{C_4 H_{10} } $ , and by a positive correlation between the δ 13C and δ D values. Simple carbon-bearing molecules (CH4, CO and CO2) can form abiogenic alkane gases via polymerization in the abiological chemical process in nature, with δ13C1 heavier than ?30‰ Moreover, controlled by the kinetic isotope fractionation, abiogenic alkane gases are characterized by a reverse distribution of δ 13C values and a normal trend of δ D values, namely δ13C1> δ 13C2> δ 13C3> δ 13C4 and $ \delta D_{CH_4 } < \delta D_{C_2 H_6 } < \delta D_{C_3 H_8 } < \delta D_{C_4 H_{10} } $ . The δ 13C values and δ D values are negatively correlated. Natural gases from 26 commercial gas wells distributed in the Xujiaweizi and Yingshan-Miaotaizi faulted depressions in the Songliao Basin, China, show δ13C1 values ranging from ?30.5% to ?16.7% with a very narrow δ D range between ?203‰?196‰ These gases are characterized by a reverse distribution of δ 13C values but a normal distribution of δ C values, and a negative correlation between their δ 13C and δ C values, indicating an abiological origin. The present study has revealed that abiogenic hydrocarbons not only exist in nature but also can make significant contribution to commercial gas reserviors. It is estimated that the reserve volume of alkane gases with abiogenic characteristics in these 26 gas wells in the Songliao Basin is over 500×108 m3. The prospecting practice in the Songliao Basin has demonstrated that abiogenic alkane gases are of a promising resource, and it provides an example for the investigation of and search for abiogenic commercial natural gases worldwide.展开更多
NATURAL gases usually refer to the inflammable gases dominated by methane from the angle of research on energy gases. Three genetic types of natural gases can be recognized according to the process of methane generati...NATURAL gases usually refer to the inflammable gases dominated by methane from the angle of research on energy gases. Three genetic types of natural gases can be recognized according to the process of methane generation: (ⅰ) biogenic (bacterial) gas, mainly the gas formed by the decomposition of organic matter in sediments under the action of anaerobic bacteria; (ⅱ) thermogenic gas, mainly the gas formed by the degradation of organic matter in sediments under the action of certain temperature and pressure; (ⅲ) abiogenic gas, mainly the展开更多
Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysi...Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysis, we found that： （1） up to 82 mole% methane exists in the primary inclusions hosted in the reservoir volcanic rocks; （2） high CH4 inclusions recognized in the volcanic rocks correspond to CH4-bcaring CO2 reservoirs that are rich in helium and with a high ^3He/^4He ratio and which show reversed order of 813C in alkane; （3） in gas reservoirs of such abiotic methane （〉80%） and a mix of CH4 and CO2, the enclosed content of CH4 in the volcanic inclusions is usually below 42 mole%, and the reversed order of δ^13C in alkane is sometimes irregular in the corresponding gas pools; （4） a glassy inclusion with a homogeneous temperature over 900℃ also contains a small portion of CH4 although predominantly CO2. This affinity between gas pool and content of inclusion in the same volcanic reservoirs demonstrates that magma-originated gases, both CH4 and CO2, have contributed significantly to the corresponding gas pools and that the assumed hydrocarbon budget of the bulk earth might be much larger than conventionally supposed.展开更多
FTT experiments with water as a hydrogen source and three types of possible carbon sources in the subsurface(diiron nonacarbonyl,siderite and formic acid,representing CO,CO_(2)and a simple organic acid,respectively)we...FTT experiments with water as a hydrogen source and three types of possible carbon sources in the subsurface(diiron nonacarbonyl,siderite and formic acid,representing CO,CO_(2)and a simple organic acid,respectively)were carried out in this study.Our experimental results showed that n-alkanes with the highest carbon number of C_(33)were produced when CO was used as a carbon source(series A);a variety of polycyclic aromatic hydrocarbons(PAHs)were detected in series B with CO_(2)as a carbon source;gaseous hydrocarbons were also detected with formic acid added(series C).The different products in the three series showed that there were different hydrocarbon generation mechanisms and reaction processes with different carbon sources.The generation of long-chain n-alkanes in series A provided experimental support for the formation of abiogenic petroleum underground,which was of significance to early membranes on the Earth.PAHs in series B provide experimental support for the possibility of an abiotic source of reduced carbon on other planets.The carbon isotopes of gaseous hydrocarbons produced by CO exhibited a partial reversed order(δ^(13)C_(1)<δ^(13)C_(2)>δ^(13)C_(3)>δ^(13)C_(4)>δ^(13)C_(5)),while the gaseous hydrocarbons produced by CO_(2)and HCOOH showed a positive order(δ^(13)C_(1)<δ^(13)C_(2)<δ^(13)C_(3)<δ^(13)C_(4)<δ^(13)C_(5)).Based on these,the alkylene mechanism and the carbonyl insertion mechanism were used to reasonably explain these characteristics.展开更多
Methane-rich fluids were recognized to be hosted in the reservoir volcanic rocks as primary inclusions. Samples were collected from core-drillings of volcanic gas reservoirs with reversed δ13C of alkane in the Xujiaw...Methane-rich fluids were recognized to be hosted in the reservoir volcanic rocks as primary inclusions. Samples were collected from core-drillings of volcanic gas reservoirs with reversed δ13C of alkane in the Xujiaweizi depression of the Songliao Basin. The volcanic rocks are rhyolite dominant being enriched in the more incompatible elements like Cs, Rb, Ba, Th, U and Th with relative high LREE, depleted HREE and negative anomalies of Ti and Nb, suggesting a melt involving both in mantle source and crustal assimilation. Primary fluids hosted in the volcanic rocks should have the same provenance with the magma. The authors concluded that the enclosed CH4 in the volcanics are mantle/magma-derived alkane and the reversed δ13C of alkane in the corresponding gas reservoirs is partly resulted from mixture between biogenic and abiogenic gases.展开更多
基金supported by the China Postdoctoral Science Foundation (20070420393)China Postdoctoral Special Science Foundation (20081095)PetroChina Science and Technology Project (07-01C-01-07)
文摘Recently abiogenic alkanes have been found in various locations in the world and other celestial bodies. The chemical composition of abiogenic alkane gases varies widely. The content of methane is low and nearly no C2+ is found in the abiogenic alkane gases from fluid inclusions in volcanic rocks or hot springs in China. In the unsedimented submarine hydrothermal vent system C1/C2+ ratios are much greater than those for the thermogenic gases, mostly >800 and in some cases up to 8,000. In the Songliao Basin, China, C1/C2+ of some abiogenic gases are often less than 150. Abiogenic alkane gases which have been found in nature often have carbon isotopic reversal among C1–C4 alkanes (δ13C1>δ13C2>δ13C3>δ13C4), whereas both regular and reversed hydrogen isotope distribution pattern among C1–C4 alkanes have been reported. The δ13C of abiogenic methane is mainly greater than ?30‰ though laboratory synthesized methane can have δ13C as low as ?57‰, and its δD1 values vary widely and overlap with biogenic gases. High 3He/4He ratios often indicate the addition of mantle-derived helium and are related to abiogenic gases. However, some biogenic gases can also have high 3He/4He ratios up to 8. The CH4/3He end-member is often lower than 106 for abiogenic alkane gases while greater than 1013 for biogenic gases, and the values between these two end-members often reflect the mixing of biogenic and abiogenic gases.
文摘Recently,methane of possible abiogenic origin has been reported from many localities within the Earth’s crust.However,little is known about the mechanisms of abiogenic methane formation during such processes.The Fischer-Tropsch reaction as a well known process for converting CO<sub>2</sub> to hydrocarbon gas by reaction with H<sub>2</sub> may take place on a metallic iron or iron oxide catalyst and also may take place on
文摘For the first time,the property of deep abiogenic methane-containing high-thermobaric fluid to decompose organic residues in the Earth’s crust and form coal seams was established.
基金Supported by the National Natural Science Foundation of China(41472120)General Project of National Natural Science Foundation of China(42272188)+1 种基金Special Fund of PetroChina and New Energy Branch(2023YQX10101)Petrochemical Joint Fund of Fund Committee(U20B6001)。
文摘Exploration and development of large gas fields is an important way for a country to rapidly develop its natural gas industry.From 1991 to 2020,China discovered 68 new large gas fields,boosting its annual gas output to 1925×108m3in 2020,making it the fourth largest gas-producing country in the world.Based on 1696 molecular components and carbon isotopic composition data of alkane gas in 70 large gas fields in China,the characteristics of carbon isotopic composition of alkane gas in large gas fields in China were obtained.The lightest and average values ofδ^(13)C_(1),δ13C2,δ13C3andδ13C4become heavier with increasing carbon number,while the heaviest values ofδ^(13)C_(1),δ13C2,δ13C3andδ13C4become lighter with increasing carbon number.Theδ^(13)C_(1)values of large gas fields in China range from-71.2‰to-11.4‰(specifically,from-71.2‰to-56.4‰for bacterial gas,from-54.4‰to-21.6‰for oil-related gas,from-49.3‰to-18.9‰for coal-derived gas,and from-35.6‰to-11.4‰for abiogenic gas).Based on these data,theδ^(13)C_(1)chart of large gas fields in China was plotted.Moreover,theδ^(13)C_(1)values of natural gas in China range from-107.1‰to-8.9‰,specifically,from-1071%o to-55.1‰for bacterial gas,from-54.4‰to-21.6‰for oil-related gas,from-49.3‰to-13.3‰for coal-derived gas,and from-36.2‰to-8.9‰for abiogenic gas.Based on these data,theδ^(13)C_(1)chart of natural gas in China was plotted.
基金the Science and Technology Project of PetroChina (Grant No.07-01C-01-07)
文摘We have combined the analytical data of the carbon isotope distribution pattern, R/Ra and CH4/3He values of abiogenic and biogenic (referring to the thermogenic and bacterial or microbial) alkane gases in China with those of alkane gases from USA, Russia, Germany, Australia and other countries. Four discrimination criteria are derived from this comparative study: 1) Carbon isotopic composition is generally greater than ?30‰ for abiogenic methane and less than ?30‰ for biogenic methane; 2) Abiogenic alkane gases have a carbon isotopic reversal trend (δ13C1> δ13C2> δ13C3> δ13C4) with δ13C1> ?30‰ in general; 3) Gases with R/Ra >0.5 and δ13C1? δ13C2>0 are of abiogenic origin; 4) Gases (methane) with CH4/3He?106 are of abiogenic origin, whereas gases with CH4/3He?1011 are of biogenic origin.
基金supported by National Natural Science Foundation of China (Grant Nos. 41172133, 41272146, 41103022)
文摘The hydrocarbons and other organic compounds generated through abiogenic or inorganic processes are closely related to two science subjects, i.e., energy resources and life＇s origin and evolution. ＂The earth＇s primordial abiogenic hydrocarbon theory＂ and ＂the serpentinization of abiogenic hydrocarbon theory＂ are the two mainstream theories in the field of related studies. Ser- pentinizafion generally occurs in slow expanding mid-ocean ridges and continental ophiolites tectonic environment, etc. The abiogenic hydrocarbons and other organic compounds formed through the serpentinization of ultramafic rocks provide energy and raw materials to support chemosynthetic microbial communities, which probably was the most important hydration reac- tion for the origin and early evolution of life. The superposition of biological and abiological processes creates big challenge to the identification of the abiogenic organic materials in serpentinite-hosted ecosystem. Whether abiotic （inorganic） process can form oil and gas resource is a difficult question that has been explored continuously by scientific community for more than a century but has not yet been solved. However, some important progress has been made. The prospecting practice of abiogenic hydrocarbons in commercial gases from the Songliao Basin, China, provides an important example for exploring abiogenic natural gas resources.
基金Supported by National Natural Science Foundation of China (Grant Nos. 49233060, 40572087)Key Technologies R & D Programme (Grant Nos.96110010602, 2008ZX05008)the Foundation of Chinese Academy of Sciences (Grant No. K2000315)
文摘This paper discusses the kinetic fractionation, composition and distribution characteristics of carbon and hydrogen isotopes for various alkane gases formed in different environments, by different mechanisms and from different sources in nature. It is demonstrated that the biodegradation or thermodegradation of complex high-molecule sedimentary organic material can form microbial gas or thermogenic gas. The δ13C1 value ranges from ?110% to ?50% for microbial gases but from ?50% to ?35% (even heavier) for thermogenic gases. Controlled by the kinetic isotope fractionation, both microbial and thermogenic gases have δ13C and δ D values characterized by normal distribution, i.e. δ13C1< δ 13C2< δ 13C3< δ 13C4 and $ \delta D_{CH_4 } < \delta D_{C_2 H_6 } < \delta D_{C_3 H_8 } < \delta D_{C_4 H_{10} } $ , and by a positive correlation between the δ 13C and δ D values. Simple carbon-bearing molecules (CH4, CO and CO2) can form abiogenic alkane gases via polymerization in the abiological chemical process in nature, with δ13C1 heavier than ?30‰ Moreover, controlled by the kinetic isotope fractionation, abiogenic alkane gases are characterized by a reverse distribution of δ 13C values and a normal trend of δ D values, namely δ13C1> δ 13C2> δ 13C3> δ 13C4 and $ \delta D_{CH_4 } < \delta D_{C_2 H_6 } < \delta D_{C_3 H_8 } < \delta D_{C_4 H_{10} } $ . The δ 13C values and δ D values are negatively correlated. Natural gases from 26 commercial gas wells distributed in the Xujiaweizi and Yingshan-Miaotaizi faulted depressions in the Songliao Basin, China, show δ13C1 values ranging from ?30.5% to ?16.7% with a very narrow δ D range between ?203‰?196‰ These gases are characterized by a reverse distribution of δ 13C values but a normal distribution of δ C values, and a negative correlation between their δ 13C and δ C values, indicating an abiological origin. The present study has revealed that abiogenic hydrocarbons not only exist in nature but also can make significant contribution to commercial gas reserviors. It is estimated that the reserve volume of alkane gases with abiogenic characteristics in these 26 gas wells in the Songliao Basin is over 500×108 m3. The prospecting practice in the Songliao Basin has demonstrated that abiogenic alkane gases are of a promising resource, and it provides an example for the investigation of and search for abiogenic commercial natural gases worldwide.
文摘NATURAL gases usually refer to the inflammable gases dominated by methane from the angle of research on energy gases. Three genetic types of natural gases can be recognized according to the process of methane generation: (ⅰ) biogenic (bacterial) gas, mainly the gas formed by the decomposition of organic matter in sediments under the action of anaerobic bacteria; (ⅱ) thermogenic gas, mainly the gas formed by the degradation of organic matter in sediments under the action of certain temperature and pressure; (ⅲ) abiogenic gas, mainly the
文摘Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysis, we found that： （1） up to 82 mole% methane exists in the primary inclusions hosted in the reservoir volcanic rocks; （2） high CH4 inclusions recognized in the volcanic rocks correspond to CH4-bcaring CO2 reservoirs that are rich in helium and with a high ^3He/^4He ratio and which show reversed order of 813C in alkane; （3） in gas reservoirs of such abiotic methane （〉80%） and a mix of CH4 and CO2, the enclosed content of CH4 in the volcanic inclusions is usually below 42 mole%, and the reversed order of δ^13C in alkane is sometimes irregular in the corresponding gas pools; （4） a glassy inclusion with a homogeneous temperature over 900℃ also contains a small portion of CH4 although predominantly CO2. This affinity between gas pool and content of inclusion in the same volcanic reservoirs demonstrates that magma-originated gases, both CH4 and CO2, have contributed significantly to the corresponding gas pools and that the assumed hydrocarbon budget of the bulk earth might be much larger than conventionally supposed.
基金funded by a grant from the National Key R&D Program of China(Grant No.2017YFC0603102)partially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA14010102)a Chinese NSF grant(Grant No.41973069)。
文摘FTT experiments with water as a hydrogen source and three types of possible carbon sources in the subsurface(diiron nonacarbonyl,siderite and formic acid,representing CO,CO_(2)and a simple organic acid,respectively)were carried out in this study.Our experimental results showed that n-alkanes with the highest carbon number of C_(33)were produced when CO was used as a carbon source(series A);a variety of polycyclic aromatic hydrocarbons(PAHs)were detected in series B with CO_(2)as a carbon source;gaseous hydrocarbons were also detected with formic acid added(series C).The different products in the three series showed that there were different hydrocarbon generation mechanisms and reaction processes with different carbon sources.The generation of long-chain n-alkanes in series A provided experimental support for the formation of abiogenic petroleum underground,which was of significance to early membranes on the Earth.PAHs in series B provide experimental support for the possibility of an abiotic source of reduced carbon on other planets.The carbon isotopes of gaseous hydrocarbons produced by CO exhibited a partial reversed order(δ^(13)C_(1)<δ^(13)C_(2)>δ^(13)C_(3)>δ^(13)C_(4)>δ^(13)C_(5)),while the gaseous hydrocarbons produced by CO_(2)and HCOOH showed a positive order(δ^(13)C_(1)<δ^(13)C_(2)<δ^(13)C_(3)<δ^(13)C_(4)<δ^(13)C_(5)).Based on these,the alkylene mechanism and the carbonyl insertion mechanism were used to reasonably explain these characteristics.
基金Supported by NSFC project No. 40372066 and SRFDP No. 20030183042
文摘Methane-rich fluids were recognized to be hosted in the reservoir volcanic rocks as primary inclusions. Samples were collected from core-drillings of volcanic gas reservoirs with reversed δ13C of alkane in the Xujiaweizi depression of the Songliao Basin. The volcanic rocks are rhyolite dominant being enriched in the more incompatible elements like Cs, Rb, Ba, Th, U and Th with relative high LREE, depleted HREE and negative anomalies of Ti and Nb, suggesting a melt involving both in mantle source and crustal assimilation. Primary fluids hosted in the volcanic rocks should have the same provenance with the magma. The authors concluded that the enclosed CH4 in the volcanics are mantle/magma-derived alkane and the reversed δ13C of alkane in the corresponding gas reservoirs is partly resulted from mixture between biogenic and abiogenic gases.
