摘要:
本文在论述新疆维吾尔自治区东部吐鲁番—哈密盆地台北凹陷天然气地质与地球化学特征的基础上,讨论了天然气的来源,对采自吐哈盆地十余个天然气样进行了气体组分和碳、氢、氦同位素分析。天然气甲烷含量为60.85～84.40%,干湿指数（C1/C+2）为1.57～6.37,属湿气.甲烷碳氢同位素组成(δ13C1、δD)分别为-43.0～-49.4‰和-220～-281‰.乙烷的δ13C2-20.1～-34 0‰,δD:-259～-257‰。丙烷的δ13C3-21.3～-26.7‰,δD:-114～-203‰。丁烷的δ13C4-22.2～-28.2‰,δD:-93～-116‰。天然气中氦的同位素组成（He/He）为（3.17～7.01）×10.目前主要产层属侏罗系,天然气一般与轻质油同藏,侏罗系中于酪根类型主要为Ⅲ型,R。值为0.4～1.0%。地质地球化学资料表明台北凹陷天然气与来自侏罗系的轻质油可能不完全同源,相当一部分天然气也许来自古生界。天然气中的氦为地壳来源的氦。
Abstract:
Origin of gaseous hydrocarbon is discussed on the basis of geochemical characteristics of natural gas in Taibei depression of the Turpan -Hami Basin, Northwestern China. More than 10 gas samples were collected from the production wells. Molecular composition and carbon, hydrogen and helium isotope composition of natural gas were analyzed. The gases contain 60. 85 - 84. 40% mathane and 13. 04-38. 76% heavy hydrocarbons (Cu2+). Values of wetness (C1/C2+) are between 1. 57 to 6. 37. The gases are isotopically characterized by δ18C1 = -43. 0～-49. 4‰, δDc1 = - 220～-271‰, δ18C2 = -20.1～-34. 0‰. δDc2= -259～-257‰. δ18C3= -21.3～-26. 7‰, δDc3= -114～-203‰, δ18C4= -22. 2～-28. 2‰, δDc4 =-93～-116‰, and 3He/4He = (3. 17-7. 01)×10-6. Estimated maturity of natural gas is different from that of Jurassic sediment organic matter. Based on the carbon isotope composition of mathane, ethane and propane, values of vit-rinite reflectance (R.) are calculated. The data indicate that natural gas in Taibei depression of the Tuipan -Hami Basin is wet gas, and belongs to thermocatalytical natural gas, that the gases may be generated in different stages, which causes the gases have larger △13C2-1 values, and that the gases may be partially derived from Jurassic System, and partially from Pre - jurassic strata.
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