曾母盆地中部地区天然气与凝析油地球化学特征及成因

在广泛收集和总结前人资料的基础上，依据曾母盆地中部地区10个天然气样品的地球化学组成及碳同位素组成特征，系统分析了天然气地球化学特征及成因；同时对与天然气相伴生的凝析油的生物标志化合物特征进行分析，探讨了其油源。研究表明，曾母盆地中部地区天然气中烃类气体以甲烷为主，干燥系数(C₁/C _1-5)值介于0.68~0.97之间，既有干气也有湿气，天然气碳同位素具有正序列排列特征，其中δ¹³C₁值介于-45.6‰~-31.5‰之间，δ¹³C₂值介于-32.7‰~-24‰之间，δ¹³C₃值介于-30.1‰~-23.4‰之间，为干酪根初次裂解的有机成因气，既有油型气，又有煤型气；而非烃类气体以CO₂和N₂为主，含量介于11.44%~80.18%之间，且CO₂碳同位素值较高，介于-10.8‰~-2.4‰之间，为无机成因；与天然气伴生的凝析油具有较高的姥植比，高含量的奥利烷和双杜松烷，与盆地内发育的煤系泥质烃源岩地球化学特征具有较好的可比性，表明凝析油油源为煤系烃源岩。

Geochemical Characteristics and Origin of Natural Gas and Condensate in the Central Zone of Zengmu Basin

Based on the collection of a great number of data,according to the chemical composition and carbon isotope composition of 10 natural gas samples from the central zone of Zengmu Basin,the geochemical characteristics and origin of natural gas in this area were analyzed systematically.At the same time,the biomarker features of condensate oil associated with gas were analyzed,and its oil source was discussed.Research shows that,the alkane gases in the central zone of the basin are mainly composed of methane,and the dryness coefficient ranges from 0.68 to 0.97,indicating the existence of both dry and wet gases.Carbon isotope values have positive sequence among the C₁-C₃ alkanes.δ¹³C₁ varies from -45.6‰ to -31.5‰,δ¹³C₂ varies from -32.7‰ to -24‰,and δ¹³C₃ varies from -30.1‰ to -23.4‰.All these indicate that the hydrocarbon gases are of biogenic origin and belong to the primary kerogen cracking gas.while the non-hydrocarbon gas are mainly composed of CO₂ and N₂ and δ¹³C_CO2 varies from -10.8‰ to -2.4‰,which shows that CO₂ is of abiogenic origin condensate oil associated with natural gas have high Pr/Ph ratio,high content of oleanane and bicadinane,which have the genetic relationship with coal-measure source rocks.