【摘要】 至2003年底,中国发现6个千亿立方米以上储量规模的大气田,其中5个在鄂尔多斯盆地(苏里格、乌审旗、榆林、大牛地、靖边),1个在塔里木盆地(克拉2)。根据150个气样的组分、143个气样烷烃碳同位素和21个气样氦同位素的分析数据,这些大气田天然气具有以下地球化学特征①高含烷烃气,低含二氧化碳。烷烃气含量均在90%以上,多数在95%以上,二氧化碳含量基本低于3%,主要在1.5%之下。②烷烃碳同位素组成重,具有煤成气特征。δ13C1值为-38.5‰～-26.2‰,主峰值为-35‰～-32‰;δ13C2值为-35.3‰～-17.8‰,一般为-28‰～-24‰;δ13C3值为-29.9‰～-19.1‰,一般为-27‰～-23‰;δ13C4值为-25.6‰～-20.3‰,一般为-23.5‰～-22‰;δ13CiC4>δ13CnC4。大气田气源岩是石炭系-二叠系和中、下侏罗统煤系。③3He/4He值为n×10-7～n×10-8,具壳源氦特征。CH4/3He为n×1010～n×1011,说明CH4为有机成因。图5表6参41更多还原

【Abstract】 By the end of 2003, 6 giant gas fields each with reserves of over 100 billion cubic meters （bcm） have been discovered in China, 5 of which, Sulige, Wushenqi, Yulin, Daniudi and Jingbian gas fields are located in Ordos Basin, and Kela 2 gas field, is located in Tarim Basin. According to the gas compositions of 150 gas samples, the alkane carbon isotope data of 143 gas samples, and helium isotopic data of 21 gas samples, the geochemical characters of the giant gas fields are as follows: ① The gases have a high alkane content of over 90% and the CO₂ content lower than 3%, mainly lower than 1.5%; ② The generally high δ 13 C values of C 1 -C 4 gaseous hydrocarbons in gases confirmed significant contribution from humic source rocks, mainly the Permian-Carboniferous and the Middle-Lower Jurassic coal measures. The dominant ranges for δ 13 C 1 , δ 13 C 2 , δ 13 C 3 and δ 13 C 4 values in the Upper Paleozoic trapped gases are -35‰ to-32‰,-28‰ to-24‰,-27‰ to-23‰, and-23.5‰ to-22‰, respectively. The δ 13 C iC₄ value is higher than that of the δ 13 C nC₄ . ③ The 3He/4He value is from n×10 -8 to n×10 -7 suggesting crustal origin. The CH₄/3He value is from n× 10 10 to n×10 11 showing that the CH 4 is of organic origin.更多还原