塔里木盆地大北气田凝析油中分子化合物组成与成因

Composition and origin of molecular compounds in the condensate oils of the Dabei gas field, Tarim Basin, NW China

塔里木盆地库车坳陷大北气田是中国目前发现的构造极为复杂、埋藏超深的微含凝析油大气田。运用全二维气相色谱-飞行时间质谱仪对5个凝析油样品分析发现,正构烷烃系列保存完整,含有丰富的金刚烷类化合物。根据甲基金刚烷类指数计算出凝析油相当于烃源岩镜质体反射率为1.3%～1.6%阶段的产物。依据天然气碳同位素组成与镜质体反射率拟合公式计算出天然气成熟度相当于镜质体反射率为1.3%～1.7%,反映出天然气和凝析油属于同期且在高成熟阶段生成。大北气田成藏条件优越,古近系发育巨厚膏盐岩,直接覆盖于白垩系优质砂岩储集层之上,煤系烃源岩生烃强度大、持续强充注,盐下冲断构造成排展布,断裂极为发育,提供了良好的运移通道,这些因素共同控制了大北大型气田的形成。

The Dabei gas field in the Kuqa Depression of the Tarim Basin is the most complex and deep continental condensate gas field in China. Comprehensive two-dimensional gas chromatography-time of flight mass spectrometer(GC×GC-TOFMS) analysis was conducted on five condensate oil samples from this field. The results show that the samples have n-alkane series in complete preservation and rich adamantanes. According to the methyladamantane index, the condensate oil is the product of the source rock with vitrinite reflectance(Ro) of 1.3%–1.6%. According to the gas maturity calculated through carbon isotope and vitrinite reflectance, the natural gas is corresponding to Ro of 1.3%–1.7%, reflecting that the natural gas and condensate oil are basically formed during the same period at the high maturity stage of source rock. The Dabei gas field has favorable geological conditions for hydrocarbon accumulation: thick salt rock in the Paleogene acts as a regional high-quality caprock directly overlying the high-quality sandstone reservoir of the Cretaceous, the coal source rocks have high hydrocarbon generation intensity and provide continuous oil and gas, and the subsalt thrust structures develop in rows with rich faults, providing migration pathways for oil and gas migration. These factors together controlled the formation of the Dabei gas field.