松辽盆地幔源CO2分布规律与运聚成藏机制

对CO₂碳同位素组成和³He/⁴He值分析表明,松辽盆地高含CO₂天然气藏中的CO₂皆为幔源成因.在对已发现含CO₂天然气分析的基础上,研究了松辽盆地CO₂在含量、层系和平面上的分布规律.研究结果表明,松辽盆地CO₂在含量上具有"两端元"的分布特征;受区域盖层和储层性质的控制,在层位上,CO₂主要富集于营城组和泉四段;在平面上,CO₂呈多个点状或狭长带状局限分布,其平面分布明显受控于深大断裂,与基底大断裂和火山岩体具有较好的伴生关系.幔源CO₂运聚成藏机制可概括为:深部热流底辟体的顶部是CO₂的储集库,基底大断裂向下收敛于拆离带并沟通CO₂气源,CO₂通过基底大断裂和古火山通道向上输导,并在适当圈闭中聚集成藏.运聚通道组合类型决定了气藏中CO₂的含量及含CO₂天然气的赋存层位,幔源CO₂的运聚通道可划分为3种组合类型.建立了松辽盆地含CO₂天然气藏的"三阶段"成藏模式.

Distribution and migration-accumulation mechanism of mantle-derived CO2 in Songliao Basin

The analysis on identifying indicators,such as CO₂ carbon isotope and ³He-to-⁴He ratio,shows that the high content CO₂ of gas reservoir in Songliao Basin can be distinguished as mantle origin.The content of CO₂ is characterized by two points of low and high.CO₂ is mainly concentrated in Yingcheng Formation (K₁yc) and the forth member of Quantou Formation (K₁q⁴) and controlled by regional cap rocks and reservoir quality.In the plane,CO₂ is locally distributed in point shape or thin-and-long banded shape and distinctly controlled by deep-large faults,which is associated with the large basement faults and volcanic rock bodies.The migration and accumulation mechanism of CO₂ was illustrated as follows.The top of deep heat-flow piercement is full of CO₂,and the large basement faults converge downward to the detachment zone and communicate CO₂ gas source.Then,CO₂ migrates upward the proper traps through basement faults and ancient volcanic conduits.The migration pathways of mantle-derived CO₂ can be divided into three combination types,which control the content and distribution of CO₂.The paper established the three-period pool-forming model of CO₂-containing gas pools in Songliao Basin.