塔里木盆地顺北地区奥陶系凝析气地球化学特征及成因

Geochemical characteristics and genesis of Ordovician condensate gas in Shunbei area, Tarim Basin

  • 摘要: 为了给塔里木盆地顺北地区深层油气勘探提供理论依据,采用气体组分和组分碳、氢同位素分析方法,系统分析了顺北地区奥陶系凝析气化学组成与同位素特征,并与轮古东、玉科及塔中东西部奥陶系凝析气对比,探讨顺北地区凝析气成因及形成过程。顺北地区奥陶系凝析气以烃类气体为主,其中5号断裂带南段、4号断裂带及8号断裂带凝析气干燥系数多低于0.95,呈现湿气特征;而12号断裂带、14号断裂带及顺南地区天然气以干气为主。顺北地区凝析气非烃类气体主要包括少量二氧化碳、氮气及微量硫化氢;烷烃气组分碳、氢同位素序列总体呈正序分布,部分样品出现同位素倒转现象;从5号断裂带南段至顺南地区,天然气成熟度逐渐增加。顺北地区奥陶系凝析气主要为热成因油型气,5号断裂带南段、4号断裂带及8号断裂带天然气为干酪根裂解气与原油裂解气的混合气源,其中原油裂解气以裂解初期形成的湿气为主;12号断裂带、14号断裂带及顺南地区天然气则以高成熟度原油裂解气为主,表现为干气特征。通过天然气地球化学分析,揭示了顺北地区凝析气成因的区域差异性,为塔里木盆地深层油气资源评价和勘探部署提供了依据。

     

    Abstract: To provide a theoretical basis for deep oil and gas exploration in the Shunbei area of the Tarim Basin, gas component and carbon and hydrogen isotope analyses were used to systematically explore the chemical composition and isotopic characteristics of Ordovician condensate gas in the Shunbei area. These data were compared with those of Ordovician condensate gas from the eastern Lungu, Yuke, and eastern and western Tazhong areas to investigate the genesis and formation process of condensate gas in the Shunbei area. The Ordovician condensate gas in the Shunbei area was mainly composed of hydrocarbon gases. The dryness coefficients of condensate gas in the southern section of No.5 fault zone (F5), F4, and F8 were mostly below 0.95, showing wet gas characteristics, while the natural gas in F12, F14, and the Shunnan area was predominantly dry gases. The non-hydrocarbon gases of the condensate gas in the Shunbei area mainly include minor amounts of carbon dioxide, nitrogen, and trace amounts of hydrogen sulfide. The alkane carbon and hydrogen isotope sequences generally exhibited a positive sequence distribution, with isotope reversal occurring in some samples. From the southern section of F5 to the Shunnan area, the maturity of natural gas gradually increased. The Ordovician condensate gas in the Shunbei area was primarily thermogenic oil-type gas. The natural gas in the southern section of F5, F4, and F8 was a mixed source of kerogen-cracking gas and crude oil-cracking gas, with crude oil-cracking gas dominated by wet gas formed in the early stage of cracking. In contrast, the natural gas in F12, F14, and the Shunnan area was mainly crude oil-cracking gas with high maturity, showing dry gas characteristics. Through geochemical analysis of the natural gas, the regional differences in condensate gas genesis in the Shunbei area are revealed, providing a basis for the evaluation and exploration deployment of deep oil and gas resources in the Tarim Basin.

     

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