石油学报 ›› 2014, Vol. 35 ›› Issue (1): 26-36.DOI: 10.7623/syxb201401003

• 地质勘探 • 上一篇    下一篇

川东北元坝与河坝地区陆相储层天然气成因

王万春1, 张晓宝1, 刘若冰2, 罗厚勇1, 王国仓1   

  1. 1. 中国科学院油气资源研究重点实验室 甘肃兰州 730000;
    2. 中国石油化工股份有限公司勘探南方分公司 四川成都 610041
  • 收稿日期:2013-07-08 修回日期:2013-10-22 出版日期:2014-01-25 发布日期:2013-12-09
  • 通讯作者: 王万春,女,1962年9月生,1984年获兰州大学学士学位,2006年获中国科学院研究生院博士学位,现为中国科学院地质与地球物理研究所兰州油气资源研究中心副研究员,主要从事地球化学研究工作。Email:lgas@lzb.ac.cn
  • 作者简介:王万春,女,1962年9月生,1984年获兰州大学学士学位,2006年获中国科学院研究生院博士学位,现为中国科学院地质与地球物理研究所兰州油气资源研究中心副研究员,主要从事地球化学研究工作。Email:lgas@lzb.ac.cn
  • 基金资助:
    国家重点基础研究发展计划(973)项目(2012CB214801)和中国科学院重要方向项目(KZCX2-YW-Q05-03)资助。

Origin of natural gas in terrestrial reservoirs in Yuanba and Heba regions in northeastern Sichuan Basin, China

Wang Wanchun1, Zhang Xiaobao1, Liu Ruobing2, Luo Houyong1, Wang Guocang1   

  1. 1. Key Laboratory of Petroleum Resources Research, Chinese Academy of Sciences, Lanzhou 730000, China;
    2. Sinopec Exploration Southern Company, Chengdu 610041, China
  • Received:2013-07-08 Revised:2013-10-22 Online:2014-01-25 Published:2013-12-09

摘要: 在川东北地区石油地质背景特征的基础上,探讨了元坝与河坝地区陆相储层天然气的成因。元坝地区侏罗系储层天然气重烃气体含量较高;多数样品甲烷δ13C和δD值分别在-42.2‰ ~-34.4‰ 和-208‰ ~-168‰ ,乙烷δ13C值在-31.4‰ ~-21.4‰ ,甲烷δ13C和δD值之间相关性好;天然气主要来源于侏罗系自流井组或千佛崖组陆相烃源岩。元坝地区须家河组储层天然气重烃气体含量低;甲烷δ13C和δD值分别为-31.7‰ ~-29.2‰ 和-170‰ ~-148‰ ,乙烷δ13C值在-27.7‰ ~-26.5‰ ;天然气主要来源于元坝地区上三叠统须家河组高—过成熟的腐殖型烃源岩。元坝地区陆相储层天然气成因的主控因素是陆相烃源岩发育及其成熟度。河坝地区陆相储层天然气重烃气体含量变化大;甲烷δ13C值大多重于-32‰ ,甲烷δD值分布范围较大,在-186‰ ~-122‰ ,乙烷δ13C值在-33.2‰ ~-29.6‰ ;甲烷δD与δ13C值之间相关性很差,部分样品甲烷与乙烷的δ13C值倒转,表明河坝地区陆相储层天然气成因复杂,有来源于陆相须家河组的天然气,也有来源于海相烃源岩的天然气,以及海相与陆相来源天然气的混合气。河坝地区陆相储层天然气成因的主控因素是海相与陆相多套烃源岩与不同级别断裂。陆相储层天然气中CO2的δ13C值多轻于-12‰ ,属于有机质热分解成因。稀有气体3He/4He比值在0.003 3Ra~0.018 1Ra,分布于地壳来源或放射性成因的范围内,表明天然气中没有幔源稀有气体的贡献。

关键词: 川东北, 陆相储层, 天然气成因, 碳同位素, 氢同位素, 稀有气体同位素

Abstract: The origin of natural gas in terrestrial reservoirs of Yuanba and Heba regions is investigated by analyzing the geochemical characteristics of natural gases and surveying the regional background of petroleum geology in the northeastern Sichuan Basin, China. Results show that: 1) In Yuanba region, natural gases from the Jurassic clastic rock reservoirs contain high levels of heavy hydrocarbon gases. The δ13C and δD values of methane respectively range from -42.2‰ to -34.4‰ and -208‰ to -168‰, whereas the δ13C values of ethane range from -31.4‰ to -21.4‰ in most gas samples. There is a strong correlation between the δ13C and δD values of methane in gas samples tested, and the gases are mainly originated from terrestrial source rocks of the Jurassic Ziliujing and Qianfoya Formation. Differently, natural gases from the Xujiahe Formation contain low levels of heavy hydrocarbon gases; the δ13C and δD values of methane in natural gas samples respectively range from -31.7‰ to -29.2‰ and -170‰ to -148‰, whereas the δ13C values of ethane range from -27.7‰ to -26.5‰. The gases are mainly originated from high-to-over-maturity humic terrestrial source rocks of the Upper Triassic Xujiahe Formation. The origin of natural gases is mainly controlled by the development of terrestrial source rocks and their maturity. 2) In Heba region, natural gases from the terrestrial reservoirs contain varying levels of heavy hydrocarbon gases. The δ13C values of methane are mostly greater than -32.0‰ and the corresponding δD values widely range from -186‰ to -122‰; the δ13C values of ethane range from -33.2‰ to -29.6‰. There is a poor correlation between the δ13C and δD values of methane in gas samples. The δ13C values of methane and ethane are reversed in a few cases, suggesting the complex origin of the gases that include those from terrestrial source rocks of the Xujiahe Formation and marine source rocks, as well as mixed gases from the above two origins. The development of marine and terrestrial source rocks as well as fractures of various levels is the main factor that controls the origin of natural gases in this region. 3) The δ13C values of carbon dioxide in natural gas samples are mostly less than -12‰, indicating that the gases are mainly generated through organic matter decomposition. Noble gas isotopic ratios of helium (3He/4He, 0.003 3Ra~0.018 1Ra) are distributed in the range of values for deep crust or radiogenic decay, demonstrating a lack of mantle-derived noble gas in the samples tested.

Key words: northeastern Sichuan Basin, terrestrial reservoir, natural gas genesis, carbon isotope, hydrogen isotope, noble gas isotope

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