地学前缘 ›› 2020, Vol. 27 ›› Issue (3): 262-268.DOI: 10.13745/j.esf.sf.2020.4.8

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龙泉山构造区隧道浅层天然气来源定量研究

张小林1(), 苏培东2,*(), 苏少凡2, 马云长2, 杨枫3   

  1. 1.中国中铁二院工程集团有限责任公司, 四川 成都 610000
    2.西南石油大学 地球科学与技术学院, 四川 成都 610500
    3.西南交通大学 土木工程学院, 四川 成都 610031
  • 收稿日期:2019-11-26 修回日期:2019-12-25 出版日期:2020-05-20 发布日期:2020-05-20
  • 通讯作者: 苏培东
  • 作者简介:张小林(1972—),男,高级工程师,主要从事工程地质、岩土工程方面的科研工作。E-mail: 176727655@qq.com
  • 基金资助:
    国家自然科学基金项目“炭质千枚岩隧道瓦斯生成及运移规律研究”(51804261);中铁二院工程集团有限责任公司科研项目“铁路工程非煤系地层有害气体成因机制与危险性评价研究”(科-2018-33-2);四川省科技厅应用基础研究项目“川西高原变质岩区隧道有毒有害气体成因机制与评价模型研究”(19YYJC1060)

Quantitative study of shallow natural gas source in tunnels in the Longquanshan structural zone

ZHANG Xiaolin1(), SU Peidong2,*(), SU Shaofan2, MA Yunchang2, YANG Feng3   

  1. 1. China Railway Eryuan Engineering Group Co., Ltd,Chengdu 610000, China
    2. College of Earth Sciences and Technology, Southwest Petroleum University, Chengdu 610500, China
    3. Civil Engineering College, Southwest Jiaotong University, Chengdu 610031, China
  • Received:2019-11-26 Revised:2019-12-25 Online:2020-05-20 Published:2020-05-20
  • Contact: SU Peidong

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摘要：

龙泉山含油气构造带是川西油气区和川中油气区分界构造,地层主要为侏罗系和白垩系红层,属非煤地层,不具生烃能力;但穿越龙泉山构造带的多条隧道,施工中都受到了浅层天然气危害。为查明浅层天然气来源,更准确地预测非煤地层隧道中瓦斯分布特征,为隧道工程服务,文章以成都地铁18号线龙泉山隧道为例,采用现场成分测试、气相色谱、稳定碳同位素、稀有气体同位素和生物标志化合物实验,对龙泉山含油气构造带浅层天然气的来源进行了定量研究。研究表明龙泉山含油气构造带浅层天然气主要成分以CH4、N2、CO2为主,其中CH4浓度达到57.65%~75.23%;浅层天然气稳定碳同位素实验表明δ13C1、δ13C2和δ13C3的值分别在40‰、26‰和25‰上下;稀有气体同位素实验表明气样源岩年代介于225~249 Ma;生物标志化合物实验表明规则甾烷比值介于0.90~1.07。龙泉山构造带浅层天然气主要来源于下伏三叠系须家河组地层,深部气体主要通过断层及节理裂隙向上运移,在浅部砂岩、节理裂隙发育区和局部构造高点富集,从而对隧道工程形成危害。成都地铁18号线龙泉山隧道横穿龙泉山含油气构造,隧道掌子面瓦斯绝对涌出量达到2.13~4.99 m3/min,浅层天然气的分布受龙泉驿断层、卧龙寺向斜、龙泉山背斜和马鞍山断层控制。龙泉驿断层和马鞍山断层是深部三叠系须家河组天然气向上运移通道,断层破碎带及其伴生、派生节理裂隙发育区以及龙泉山背斜转折端是浅层天然气有利富集区,浅层天然气浓度高,隧道风险大。

关键词: 隧道, 浅层天然气, 气源, 龙泉山含油气构造

Abstract:

The Longquanshan oil-bearing structural belt is at the boundary between the western and central Sichuan oil and gas fields. Its non-coal strata are mainly Jurassic and Cretaceous red layers producing no hydrocarbons. Yet tunnel constructions across the Longquanshan tectonic belt are often confronted with shallow gas hazard. To ascertain the source of shallow natural gas and provide more accurate prediction on gas distribution characteristics in the non-coal strata tunnels, we studied the Chengdu Metro Line 18 Longquanshan Tunnel as an example, using field composition testing, gas chromatography and stable carbon isotopes to quantitatively characterize the source of shallow natural gas in the area. Previous research predicted that the main components of the shallow natural gas were CH4 (57.65%-75.23%), N2, and CO2. We showed that δ13C1, δ13C2 and δ13C3 values were 40‰, 26‰ and 25‰, respectively, by stable isotopic analysis, and the age of gas source rocks was between 225 and 249 Ma from rare gas isotope experiments. Using biomarker compounds we determined the regular sterane ratio to be between 0.90 and 1.07. Large amounts of shallow natural gas, originated from the underlying Triassic Xujiahe Formation, escaped from the Longquanshan tunnel. The deep gas migrated mainly upward through faults and joint fissures. Enrichment in shallow sandstones, joint fissure development areas, and local structural highs all pose danger to tunnel engineering. The Chengdu Metro Line 18 Longquanshan Tunnel lies cross the Longquanshan petroleum structure. The absolute gas emission from the palm face of the tunnel reached 2.13-4.99 m3/min. The distribution of shallow natural gas is controlled by the Longquanyi fault, Wolongsi syncline, Longquanshan anticline, and Ma'anshan fault. The Longquanyi and Ma'anshan faults provide upward migration pathways in the deep Triassic Xujiahe Formation, where the two faults are associated with derived joint and fissure development areas, while the turning section of the Longquanshan anticline is favorable for shallow natural gas accumulation. Together these geological factors contribute to the high gas concentration and high risk for tunnel construction in the area.

Key words: tunnel, shallow natural gas, gas source, Longquanshan oil-bearing structure

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