鄂尔多斯盆地奥陶系盐下天然气地球化学特征及成因
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摘要
探讨鄂尔多斯盆地奥陶系盐下天然气的成因类型及来源,为勘探部署提供理论依据。以天然气地球化学特征分析为基础,结合成藏组合特点剖析,通过烷烃气及轻烃组分碳同位素组成比对、δ~(13)C_1—RO相关性分析等综合判识天然气成因类型与来源。结果显示,鄂尔多斯盆地奥陶系盐下天然气组分以烃类气体为主,烃类组分含量平均为94.1%。烃类气体中甲烷占优势,甲烷化系数[C_1/∑(C_1—C_n)]随区域热演化程度的不同而变化明显,从靖边—乌审旗—神木地区,甲烷化系数依次由0.99→0.95→0.85逐渐减小。除高含硫天然气外,奥陶系盐下天然气的δ~(13)C_1值、δ~(13)C_2值整体偏低,δ~(13)C_1值分布于-45.90‰～-37.29‰之间,平均为-39.58‰,δ~(13)C_2值分布于-35.58‰～-25.77‰之间,平均为-29.9‰。奥陶系膏盐岩下高含硫天然气的甲烷、乙烷碳同位素值显著偏高,是硫酸盐热化学还原反应(TSR)的结果。综合各项地球化学指标气气、气源比对,结果显示鄂尔多斯盆地奥陶系盐下天然气属于自生自储油型气,奥陶系海相气源岩是其主力供烃源岩。
The genetic type and source of Ordovician subsalt natural gas in Ordos Basin are discussed so as to provide theoretical basis for gas exploration.Based on the analysis of geochemical characteristics of natural gas,combined with the gas accumulation combination characteristics,the genetic type and source of Ordovician subsalt natural gas are comprehensively identified through the comparison of the stable carbon isotopic compositions of alkane gases and light hydrocarbons and the correlation analysis of δ~(13)C_1-RO.The results show that the Ordovician subsalt natural gas in Ordos Basin are mainly composed of hydrocarbon components and the average content is 94.1%.Methane in hydrocarbon gases is dominant and the methanation parameter(C_1/(∑C_1-C_n))varies obviously with the difference of regional thermal maturity.From Jingbian to Wushen and Shenmu areas,the methanation parameter gradually decreases from 0.99-0.95-0.85.Except for high sulfur natural gas,the δ~(13)C_1 and δ~(13)C_2 values of Ordovician subsalt gas are generally low.The δ~(13)C_1 value is in ranges from-45.90‰ to -37.29‰,with an average of -39.58‰.The δ~(13)C_2 value ranges from -35.58‰ to -25.77‰,with an average of-29.9‰.The carbon isotopic composition of methane and ethane in the high sulfur natural gas under the Ordovician gypsum-salt rock is significantly heavier,which is the result of the thermochemical sulfate reduction(TSR).The results of gas-gas and gas-source correlation of various geochemical index show that the Ordovician subsalt natural gas in Ordos Basin belongs to oil-type gas which is characterized by self-generation and self-accumulation,and the Ordovician marine source rocks are the chief source rocks of producing hydrocarbon.
The genetic type and source of Ordovician subsalt natural gas in Ordos Basin are discussed so as to provide theoretical basis for gas exploration.Based on the analysis of geochemical characteristics of natural gas,combined with the gas accumulation combination characteristics,the genetic type and source of Ordovician subsalt natural gas are comprehensively identified through the comparison of the stable carbon isotopic compositions of alkane gases and light hydrocarbons and the correlation analysis of δ~(13)C_1-RO.The results show that the Ordovician subsalt natural gas in Ordos Basin are mainly composed of hydrocarbon components and the average content is 94.1%.Methane in hydrocarbon gases is dominant and the methanation parameter(C_1/(∑C_1-C_n))varies obviously with the difference of regional thermal maturity.From Jingbian to Wushen and Shenmu areas,the methanation parameter gradually decreases from 0.99-0.95-0.85.Except for high sulfur natural gas,the δ~(13)C_1 and δ~(13)C_2 values of Ordovician subsalt gas are generally low.The δ~(13)C_1 value is in ranges from-45.90‰ to -37.29‰,with an average of -39.58‰.The δ~(13)C_2 value ranges from -35.58‰ to -25.77‰,with an average of-29.9‰.The carbon isotopic composition of methane and ethane in the high sulfur natural gas under the Ordovician gypsum-salt rock is significantly heavier,which is the result of the thermochemical sulfate reduction(TSR).The results of gas-gas and gas-source correlation of various geochemical index show that the Ordovician subsalt natural gas in Ordos Basin belongs to oil-type gas which is characterized by self-generation and self-accumulation,and the Ordovician marine source rocks are the chief source rocks of producing hydrocarbon.
引文
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[15]Zhang Jianyong,Liu Wenhui,Tenger,et al.Influences of TSRon gaseous hydrocarbon components and carbon isotopes:Revelations from high-temperature and high-pressure simulation experiments[J].Petroleum Geology&Experiment,2012,34(1):66-77.张建勇,刘文汇,腾格尔,等.TSR对气态烃组分及碳同位素组成的影响---高温高压模拟实验的证据[J].石油实验地质,2012,34(1):66-77.
[16]Zhang Shuichang,Zhu Guangyou,He Kun.The effects of thermochemical sulfate reduction on occurrence of oil-cracking gas and reformation of deep carbonate reservoir and the interaction mechanisms[J].Acta Petrologica Sinica,2011,37(3):809-826.张水昌,朱光有,何坤.硫酸盐热化学还原作用对原油裂解成气和碳酸盐岩储层改造的影响及作用机制[J].岩石学报,2011,37(3):809-826.
[17]Kong Qingfen,Zhang Wenzheng,Li Jianfeng,et al.Origin of natural gas in Ordovician in the west of Jingbian Gasfield,Ordos Basin[J].Natural Gas Geoscience,2016,27(1):71-80.孔庆芬,张文正,李剑锋,等.鄂尔多斯盆地靖西地区下古生界奥陶系天然气成因研究[J].天然气地球科学,2016,27(1):71-80.
[18]Hao Fang,Guo Tonglou,Zhu Yangming,et al.Evidence for multiple stages of oil cracking and thermochemical sulfate reduction in the Puguang Gas Field,Sichuan Basin,China[J].AAPG Bulletin,2008,92(5):611-637.
[19]Dai Jinxing,Song Yan,Guan Deshi,et al.The indicators for coal-formed gas identification[C]∥Editorial Committee of Symposium on Geological Research of Coal-formed Gas.Symposium on Geological Research of Coal-formed Gas.Beijing:Petroleum Industry Press,1987:156-170.戴金星,宋岩,关德师,等.鉴别煤成气的指标[C]∥《煤成气地质研究》编委会.煤成气地质研究.北京:石油工业出版社,1987:156-170.
[20]Chen Anding.The origin of natural gas and characteristics of gas source rocks[M]∥Yang Junjie,Pei Xigu.Natural Gas Geology in China(Vol.4):Ordos Basin[M].Beijing:Petroleum Industry Press,1996:79-82.陈安定.天然气成因及气源岩地球化学特征[M]∥杨俊杰,裴锡古.中国天然气地质学---卷四:鄂尔多斯盆地.北京:石油工业出版社,1996,79-82.
[2]Sun Longde,Zou Caineng,Zhu Rukai,et al.Formation,distribution and potential of deep hydrocarbon resources in China[J].Petroleum Exploration and Development,2013,40(6):641-649.孙龙德,邹才能,朱如凯,等.中国深层油气形成、分布与潜力分析[J].石油勘探与开发,2013,40(6):641-649.
[3]Jin Zhijun,Long Shengxiang,Zhou Yan,et al.A study on the distribution of saline-deposit in southern China[J].Oil and Gas Geology,2006,27(5):571-583,593.金之钧,龙胜祥,周雁,等.中国南方膏盐岩分布特征[J].石油与天然气地质,2006,27(5):571-583,593.
[4]Gu Zhidong,Yin Jifeng,Yuan Miao,et al.Accumulation conditions and exploration directions of natural gas in deep subsalt SinianCambrian System in the eastern Sichuan Basin,SW China[J].Petroleum Exploration and Development,2015,42(2):137-149.谷志东,殷积峰,袁苗,等.四川盆地东部深层盐下震旦系-寒武系天然气成藏条件与勘探方向[J].石油勘探与开发,2015,42(2):137-149.
[5]Yang Hua,Zhang Wenzheng,Zan Chuanli,et al.Geochemical characteristics of Ordovician subsalt gas reservoir and their significance for reunderstanding the gas source of Jingbian Gasfield,east Ordos Basin[J].Natural Gas Geoscience,2009,20(1):8-14.杨华,张文正,昝川莉,等.鄂尔多斯盆地东部奥陶系盐下天然气地球化学特征及其对靖边气田气源再认识[J].天然气地球科学,2009,20(1):8-14.
[6]Yang Hua,Bao Hongping,Ma Zhanrong.Reservoir-forming by lateral supply of hydrocarbon:A new understanding of the formation of Ordovician gas reservoirs under gypsolyte in the Ordos Basin[J].Naturral Gas Industry,2014,34(4):19-26.杨华,包洪平,马占荣.侧向供烃成藏---鄂尔多斯盆地奥陶系膏盐岩下天然气成藏新认识[J].天然气工业,2014,34(4):19-26.
[7]Zhu Guangyou,Zhang Shuichang,Liang Yingbo,et al.Isotopic evidence of TSR origin for natural gas bearing high H2S contents within the Feixianguan Formation of the northeastern Sichuan Basin,southwestern China[J].Science in China:Series D,2005,35(11):1037-1046.朱光有,张水昌,梁英波,等.川东北地区飞仙关组高含H2S天然气TSR成因的同位素证据[J].中国科学:D辑,2005,35(11):1037-1046.
[8]Zhu Guangyou,Dai Jinxing,Zhang Shuichang,et al.Generation mechanism and distribution characteristics of hydrogen sulfide bearing gas in China[J].Natural Gas Geoscience,2004,15(2):166-170.朱光有,戴金星,张水昌,等.含硫化氢天然气的形成机制及分布规律研究[J].天然气地球科学,2004,15(2):166-170.
[9]Zhu Guangyou,Zhang Shuichang,Li Jian,et al.Formation and distribution of hydrogen sulfide bearing gas in China[J].Petroleum Exploration and Development,2004,31(3):18-21.朱光有,张水昌,李剑,等.中国高含硫化氢天然气的形成及其分布[J].石油勘探与开发,2004,31(3):18-21.
[10]Cai Chunfang,Worden R H,Bottrell,et al.Thermochemical sulphate reduction and the generation of hydrogen sulphide and thiols(mercaptans)in Triassic carbonate reservoirs from the Sichuan Basin,China[J].Chemical Geology,2003,20(2):39-57.
[11]Worden R H,Smalley P C,Oxtoby N H.The effects of thermochemical sulfate reduction upon formation water salinity and oxygen isotopes in carbonate reservoirs[J].Geochimicaet Cosmochim Acta,1996,60(20):3925-3931.
[12]Orr W L.Changes in sulfur content and isotopic ratios of sulfur during petroleum maturation-Study of the Big Horn Basin Paleozoic oils[J].AAPG Bulletin,1974,50(11):2295-2318.
[13]Mache H G.Bacterial and thermochemical sulfate reduction in diagenetic settings-old and new insights[J].Sedimentary Geology,2001,140(1/2):143-175.
[14]Zhu Guangyou,Zhang Shuichang,Liang Yingbo,et al.Alteration of thermochemical sulfate reduction to hydrocarbons[J].Acta Petrolei Sinica,2005,26(5):54-58.朱光有,张水昌,梁英波,等.TSR对烃类气体组分和碳同位素的蚀变作用[J].石油学报,2005,26(5):54-58.
[15]Zhang Jianyong,Liu Wenhui,Tenger,et al.Influences of TSRon gaseous hydrocarbon components and carbon isotopes:Revelations from high-temperature and high-pressure simulation experiments[J].Petroleum Geology&Experiment,2012,34(1):66-77.张建勇,刘文汇,腾格尔,等.TSR对气态烃组分及碳同位素组成的影响---高温高压模拟实验的证据[J].石油实验地质,2012,34(1):66-77.
[16]Zhang Shuichang,Zhu Guangyou,He Kun.The effects of thermochemical sulfate reduction on occurrence of oil-cracking gas and reformation of deep carbonate reservoir and the interaction mechanisms[J].Acta Petrologica Sinica,2011,37(3):809-826.张水昌,朱光有,何坤.硫酸盐热化学还原作用对原油裂解成气和碳酸盐岩储层改造的影响及作用机制[J].岩石学报,2011,37(3):809-826.
[17]Kong Qingfen,Zhang Wenzheng,Li Jianfeng,et al.Origin of natural gas in Ordovician in the west of Jingbian Gasfield,Ordos Basin[J].Natural Gas Geoscience,2016,27(1):71-80.孔庆芬,张文正,李剑锋,等.鄂尔多斯盆地靖西地区下古生界奥陶系天然气成因研究[J].天然气地球科学,2016,27(1):71-80.
[18]Hao Fang,Guo Tonglou,Zhu Yangming,et al.Evidence for multiple stages of oil cracking and thermochemical sulfate reduction in the Puguang Gas Field,Sichuan Basin,China[J].AAPG Bulletin,2008,92(5):611-637.
[19]Dai Jinxing,Song Yan,Guan Deshi,et al.The indicators for coal-formed gas identification[C]∥Editorial Committee of Symposium on Geological Research of Coal-formed Gas.Symposium on Geological Research of Coal-formed Gas.Beijing:Petroleum Industry Press,1987:156-170.戴金星,宋岩,关德师,等.鉴别煤成气的指标[C]∥《煤成气地质研究》编委会.煤成气地质研究.北京:石油工业出版社,1987:156-170.
[20]Chen Anding.The origin of natural gas and characteristics of gas source rocks[M]∥Yang Junjie,Pei Xigu.Natural Gas Geology in China(Vol.4):Ordos Basin[M].Beijing:Petroleum Industry Press,1996:79-82.陈安定.天然气成因及气源岩地球化学特征[M]∥杨俊杰,裴锡古.中国天然气地质学---卷四:鄂尔多斯盆地.北京:石油工业出版社,1996,79-82.
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