百色盆地第三系浅层气成因类型与形成机制

Genetic Type and Formaction Mechanism of Shallow Gas in Baise Basin

关键词:  浅层气  地球化学特征  成因类型  形成机制

Key words:  shallow gas  geochemical behavior  genetic type  formaction mechanism

摘要:

在分析百色盆地第三系浅层气地球化学特征的基础上,利用天然气的化学组成和稳定碳同位素比值关系对该盆地浅层气的成因类型进行鉴别,同时根据浅层气的赋存状态与空间展布规律,从浅层气的化学组成和碳同位素组成变化特征入手,结合其它地质、地化资料,探讨盆地浅层气的形成机制。认为百色盆地浅层气以烃类气体为主,其中甲烷占优势;甲烷碳同位素组成偏轻,具有生物成因气的碳同位素组成特征。随气藏埋深增加,浅层气中甲烷含量降低,C₂₊重烃增多;甲烷碳同位素组成变重;天然气密度升高。盆地浅层气可划分为三种成因类型:生物气、生物气-低熟混合气、油层菌解气。提出盆地具有沉积、成岩过程中的早期成气作用、抬升之后的后期成气作用和晚期复合成藏三种形成机制。

Abstract:

Based on studying the geochemical behavior of Tertiary shallow gas in Baise residual Basin,the authors identified the genetic type of shallow gas in this basin and divided it into three genetic type:bacterial gas,mixed-genic gas and pyrolyzed gas. Meanwhile,according to the existence form and spatial distribution rule,the chemical constituent and carbon isotope change character of shallow gas,combined with the other geology and geochemical datum,we discussed the formaction mechanism of shallow gas in Baise Basin,and expounded three formaction mechanisms:primeval generation of gas,latter generation of gas and last-complex formation of gas accumulation.