塔里木盆地库车坳陷不同构造单元天然气地球化学特征

Geochemical characteristics of natural gas from different structural units of the Kuqa Depression,the Tarim Basin

包建平 朱翠山 张秋茶 李梅 卢玉红

Bao Jianping Zhu Cuishan Zhang Qiucha Li Mei Lu Yuhong

塔里木盆地库车坳陷主要构造上的天然气地球化学特征分析结果表明,坳陷内部大北-克拉苏构造带上的天然气中甲烷占绝对优势,干燥系数接近于1.00,属于典型的干气;而前缘隆起带上的天然气中甲烷含量相对较低,其干燥系数一般小于0.95,属于典型的湿气。在碳同位素组成特征上,大北-克拉苏构造带上天然气中甲烷、乙烷碳同位素明显偏重,分别大于-31‰和-20‰;比较而言,前缘隆起带上的天然气中甲烷、乙烷碳同位素明显偏轻,分别小于-33‰和-20‰。成熟度计算结果表明,大北-克拉苏构造带上的天然气属于过成熟天然气,其镜质体反射率值为1.65%～2.25%;而前缘隆起带上的天然气属于高成熟天然气,其镜质体反射率值为1.00%～1.35%。由此表明,库车坳陷不同构造单元聚集了烃源岩中有机质在不同演化阶段生成的天然气。

Analysis of the geochemical characteristics of natural gas from the main structural units of the Kuqa Depression in Tarim Basin shows that the natural gas from Dabei-Kelasu structural belt is dominated by methane and has a dryness coefficient [C/(C-C)] near 1.00,indicating typical dry gas;while that from the frontal uplift zone has a relatively low content of methane and a dryness coefficient less than 0.95,indicating typical wet gas.In terms of carbon isotope compositions,the gas from the Dabei-Kelasu structural belt contains significantly heavier methane and ethane isotopes(>-31‰ and-20‰,respectively),while that from the frontal uplift zone has obviously lighter methane and ethane isotopes(<-33‰ and-20‰,respectively).Maturity calculation reveals that the gas from the Dabei-Kelasu structural belt belongs to over-mature gases with a vitrinite reflectance ranging between 1.65% and 2.25%,while that from the frontal uplift zone belongs to highly-mature gas with a vitrinite reflectance ranging from 1.00% to 1.35%.All these indicate that the natural gases in different structu-ral units in the Kuqa Depression were generated from the organic matters in the source rocks at different thermal evolution stages.

10.11743/ogg20070518