湘鄂西龙马溪组页岩解析气同位素组成特征及应用
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摘要
湘鄂西地区位于中扬子板块,研究区龙马溪组富有机质页岩的有机质类型以Ⅱ1型为主,Ⅱ2型次之,TOC含量高,有机质热成熟度高,页岩矿物以脆性矿物为主,黏土矿物次之。通过分析三个实验阶段(20℃、65℃、90℃)解析气样发现,气体中CH_4含量较高(90. 34%～99. 64%),含有少量非烃气体。龙马溪组页岩气CH_4碳同位素值为-41. 9‰～-30. 8‰,C_2H_6碳同位素值为-42. 3‰～-36. 2‰,δ~2H_(CH4)为-193. 4‰～-156. 0‰,随着成熟度的增加,CH_4碳同位素、C_2H_6碳同位素以及CH_4氢同位素都有升高的趋势。烃类气体碳同位素具有明显的倒转现象,即δ~(13)C_1>δ~(13)C_2。根据解析实验三个阶段的气体同位素特征和测得的各阶段含气特征建立游离气与吸附气所占比例的计算公式,进一步推算出解析过程总含气量中所含有的游离气量以及吸附气量。
The Longmaxi Formation organic-rich shale,featured by high total organic carbon( TOC) and high thermal maturity,is located in western Hunan and Hubei region of the middle Yangtze plate. Organic matter in the region are type Ⅱ1 to type Ⅱ2 kerogen and are dominated by the former. In the region,brittle minerals( dominant) and clay minerals are abundant in the organic-rich shale. The CH_4 content of the gas samples is high( 90. 34% to 99. 64%),and the gas also contains minor non-hydrocarbon components,as revealed by the experiment under 20℃,65℃,and 90℃. CH_4 carbon isotopes of the hydrocarbon gases are of-41. 9% to-30. 8‰,whilst those of C_2H_6 and δ~2 H_(CH4) are of-42. 3% to-36. 2‰ and-193. 4% to-156. 0‰,respectively. With increasing maturity,carbon isotopes of CH_4 and C_2H_6,and hydrogen isotope of CH_4 all become heavier. Carbon isotopes of the hydrocarbon gases show clear reversals,i. e. δ~(13) C_1> δ~(13) C_2. Accurate calculation of the free gas and adsorbed gas in the shale gas is of substantial guiding significance for the future exploration and development. Therefore,our work establish the calculation formula of the proportion of free gas and adsorbed gas according to the gaseous isotope characteristics of the three temperature stages of the experiment and the gas bearing characteristics measured at each stage. The free gas volume and the amount of adsorbed gas contained in the total gas content could thus be determined.
The Longmaxi Formation organic-rich shale,featured by high total organic carbon( TOC) and high thermal maturity,is located in western Hunan and Hubei region of the middle Yangtze plate. Organic matter in the region are type Ⅱ1 to type Ⅱ2 kerogen and are dominated by the former. In the region,brittle minerals( dominant) and clay minerals are abundant in the organic-rich shale. The CH_4 content of the gas samples is high( 90. 34% to 99. 64%),and the gas also contains minor non-hydrocarbon components,as revealed by the experiment under 20℃,65℃,and 90℃. CH_4 carbon isotopes of the hydrocarbon gases are of-41. 9% to-30. 8‰,whilst those of C_2H_6 and δ~2 H_(CH4) are of-42. 3% to-36. 2‰ and-193. 4% to-156. 0‰,respectively. With increasing maturity,carbon isotopes of CH_4 and C_2H_6,and hydrogen isotope of CH_4 all become heavier. Carbon isotopes of the hydrocarbon gases show clear reversals,i. e. δ~(13) C_1> δ~(13) C_2. Accurate calculation of the free gas and adsorbed gas in the shale gas is of substantial guiding significance for the future exploration and development. Therefore,our work establish the calculation formula of the proportion of free gas and adsorbed gas according to the gaseous isotope characteristics of the three temperature stages of the experiment and the gas bearing characteristics measured at each stage. The free gas volume and the amount of adsorbed gas contained in the total gas content could thus be determined.
引文
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[12]黄家国,许开明,郭少斌,等.基于SEM、NMR和X-CT的页岩储层孔隙结构综合研究[J].现代地质,2015,29(1):198-205.
[13]林拓,张金川,李博,等.湘西北地区龙马溪组页岩气聚集条件与含气性分析[J].新疆石油地质,2014,35(5):507-510.
[14]周中毅,贾蓉芬.碳酸盐岩生油岩的有机地球化学、岩石学特征[J].地球化学,1974(4):278-298.
[15]傅家谟,刘德汉.碳酸盐岩有机质演化特征与油气评价[J].石油学报,1982(1):1-8.
[16]马永生.中国海相油气勘探[M].北京:地质出版社,2006:1-530.
[17] DAI J,ZOU C,LIAO S,et al. Geochemistry of the extremely high thermal maturity Longmaxi shale gas,southern Sichuan Basin[J]. Organic Geochemistry,2014,74:3-12.
[18]钟宁宁,卢双舫,黄志龙,等.烃源岩TOC值变化与其生排烃效率关系的探讨[J].沉积学报,2004,22(增刊):73-78.
[19] DAI J,ZOU C,DONG D,et al. Geochemical characteristics of marine and terrestrial shale gas in China[J]. Marine&Petroleum Geology,2016,76:444-463.
[20]秦胜飞.塔里木盆地库车坳陷异常天然气的成因[J].勘探家,1999(3):21-23.
[21]韩中喜,李剑,垢艳侠,等.甲、乙烷碳同位素用于判识天然气成因类型的讨论[J].天然气地球科学,2016,27(4):665-671.
[22]戴金星,秦胜飞,陶士振,等.中国天然气工业发展趋势和天然气地学理论重要进展[J].天然气地球科学,2005,16(2):127-142.
[23]戴金星,倪云燕,邹才能,等.四川盆地须家河组煤系烷烃气碳同位素特征及气源对比意义[J].石油与天然气地质,2009,30(5):519-529.
[24] BURRUSS R C,LAUGHREY C D. Carbon and hydrogen isotopic reversals in deep basin gas:Evidence for limits to the stability of hydrocarbons[J]. Organic Geochemistry, 2010, 41:1285-1296.
[25] MA Y,ZHONG N,LI D,et al. Organic matter/clay mineral intergranular pores in the Lower Cambrian Lujiaping Shale in the north-eastern part of the upper Yangtze area,China:A possible microscopic mechanism for gas preservation[J]. International Journal of Coal Geology,2015,137:38-54.
[26] YANG F,NING Z,WANG Q,et al. Pore structure characteristics of lower Silurian shales in the southern Sichuan Basin,China:Insights to pore development and gas storage mechanism[J].International Journal of Coal Geology,2016,156:12-24.
[27] LIU Y,ZHANG J,TANG X. Predicting the proportion of free and adsorbed gas by isotopic geochemical data:A case study from lower Permian shale in the southern North China basin(SNCB)[J]. International Journal of Coal Geology,2016,156:25-35.
[28]田辉,肖贤明,李贤庆,等.海相干酪根与原油裂解气甲烷生成及碳同位素分馏的差异研究[J].地球化学,2007,36(1):71-77.
[2]张水昌,赵文智,王飞宇,等.塔里木盆地东部地区古生界原油裂解气成藏历史分析——以英南2气藏为例[J].天然气地球科学,2004,15(5):441-451.
[3]赵文智,王兆云,张水昌,等.有机质“接力成气”模式的提出及其在勘探中的意义[J].石油勘探与开发,2005,32(2):1-7.
[4]赵文智,王兆云,何海清,等.中国海相碳酸盐岩烃源岩成气机理[J].中国科学:地球科学,2005,35(7):638-648.
[5]戴金星.天然气中烷烃气碳同位素研究的意义[J].天然气工业,2011,31(12):1-6.
[6] TANG Y,PERRY J K,JENDEN P D,et al. Mathematical modeling of stable carbon isotope ratios in natural gases[J].Geochimica et Cosmochimica Acta,2000,64:2673-2687.
[7]于聪,龚德瑜,黄士鹏,等.四川盆地须家河组天然气碳、氢同位素特征及其指示意义[J].天然气地球科学,2014,25(1):87-97.
[8]戴金星,夏新宇,秦胜飞,等.中国有机烷烃气碳同位素系列倒转的成因[J].石油与天然气地质,2003,24(1):1-6.
[9]张金川,汪宗余,聂海宽,等.页岩气及其勘探研究意义[J].现代地质,2008,22(4):640-646.
[10]孟强,王晓锋,王香增,等.页岩气解析过程中烷烃碳同位素组成变化及其地质意义——以鄂尔多斯盆地伊陕斜坡东南部长7页岩为例[J].天然气地球科学,2015,26(2):333-340.
[11] LOUCKS R G,REED R M,RUPPEL S C,et al. Morphology,genesis,and distribution of nanometer-scale pores in siliceous mudstones of the Mississippian Barnett Shale[J]. Journal of Sedimentary Research,2009,79:848-861.
[12]黄家国,许开明,郭少斌,等.基于SEM、NMR和X-CT的页岩储层孔隙结构综合研究[J].现代地质,2015,29(1):198-205.
[13]林拓,张金川,李博,等.湘西北地区龙马溪组页岩气聚集条件与含气性分析[J].新疆石油地质,2014,35(5):507-510.
[14]周中毅,贾蓉芬.碳酸盐岩生油岩的有机地球化学、岩石学特征[J].地球化学,1974(4):278-298.
[15]傅家谟,刘德汉.碳酸盐岩有机质演化特征与油气评价[J].石油学报,1982(1):1-8.
[16]马永生.中国海相油气勘探[M].北京:地质出版社,2006:1-530.
[17] DAI J,ZOU C,LIAO S,et al. Geochemistry of the extremely high thermal maturity Longmaxi shale gas,southern Sichuan Basin[J]. Organic Geochemistry,2014,74:3-12.
[18]钟宁宁,卢双舫,黄志龙,等.烃源岩TOC值变化与其生排烃效率关系的探讨[J].沉积学报,2004,22(增刊):73-78.
[19] DAI J,ZOU C,DONG D,et al. Geochemical characteristics of marine and terrestrial shale gas in China[J]. Marine&Petroleum Geology,2016,76:444-463.
[20]秦胜飞.塔里木盆地库车坳陷异常天然气的成因[J].勘探家,1999(3):21-23.
[21]韩中喜,李剑,垢艳侠,等.甲、乙烷碳同位素用于判识天然气成因类型的讨论[J].天然气地球科学,2016,27(4):665-671.
[22]戴金星,秦胜飞,陶士振,等.中国天然气工业发展趋势和天然气地学理论重要进展[J].天然气地球科学,2005,16(2):127-142.
[23]戴金星,倪云燕,邹才能,等.四川盆地须家河组煤系烷烃气碳同位素特征及气源对比意义[J].石油与天然气地质,2009,30(5):519-529.
[24] BURRUSS R C,LAUGHREY C D. Carbon and hydrogen isotopic reversals in deep basin gas:Evidence for limits to the stability of hydrocarbons[J]. Organic Geochemistry, 2010, 41:1285-1296.
[25] MA Y,ZHONG N,LI D,et al. Organic matter/clay mineral intergranular pores in the Lower Cambrian Lujiaping Shale in the north-eastern part of the upper Yangtze area,China:A possible microscopic mechanism for gas preservation[J]. International Journal of Coal Geology,2015,137:38-54.
[26] YANG F,NING Z,WANG Q,et al. Pore structure characteristics of lower Silurian shales in the southern Sichuan Basin,China:Insights to pore development and gas storage mechanism[J].International Journal of Coal Geology,2016,156:12-24.
[27] LIU Y,ZHANG J,TANG X. Predicting the proportion of free and adsorbed gas by isotopic geochemical data:A case study from lower Permian shale in the southern North China basin(SNCB)[J]. International Journal of Coal Geology,2016,156:25-35.
[28]田辉,肖贤明,李贤庆,等.海相干酪根与原油裂解气甲烷生成及碳同位素分馏的差异研究[J].地球化学,2007,36(1):71-77.
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