松辽盆地南部深层无机CO2对烃类气成藏控制机理

High-purity carbon dioxide natural gas reservoir has been discovered in the exploration of deep organic origin of hydrocarbon gas in the south of Songliao basin (mantle origin is considered previously), which leads to great confusion in exploration and optimization of hydrocarbon gas reservoir. Based on years of research of reservoir forming time, stage and sequence of CO2 gas reservoir and hydrocarbon gas reservoirs, by study of volcanic degassing experiments and displacement tests of hydrocarbon gas reservoirs by CO2, two major problems were solved: 1) Verifying the contribution of CO2 emanated from Volcanic degassing to high-purity CO2, and demonstrate the genesis of inorganic CO2；2) discussing displacement and replacement process of CO2 gas reservoir generated at a later stage to hydrocarbon gas reservoirs generated at an earlier stage, especially the coupling difference and hydrocarbon accumulation mechanism. Based on the properties above, it is benefit for further study of effect of CO2 at later stage in Songliao basin. Furthermore, hydrocarbon gas accumulation mechanism, controlling factors and distribution law are expected to be improved. At the same time, it is conducive to determine the location of favorable exploration areas. The ultimate goal is to increase the success rate of hydrocarbon gas reservoir exploration.

在松辽盆地南部深层有机成因烃类气藏的勘探中，多处发现了高纯度的无机成因CO2气藏（以往多数学者认为是幔源成因），给烃类气藏的勘探优选带来很大的困惑。本项目拟在前期对CO2 气藏和烃类气藏成藏时间、期次和序次等成藏特征多年研究的基础上，通过火山岩脱气实验和CO2 对烃类气的驱替试验，重点解决两个问题：1）核查以火山岩脱气方式释放出的CO2 量对形成高纯CO2 气藏的贡献，论证无机CO2 的成因类型；2）探讨后期产生的CO2 气藏对早期形成的烃类气藏排替、置换过程，重点查明两类气的耦合差异成藏机理。最终为研究松辽盆地深层受后期CO2 影响、改造的烃类气藏成藏机理、控制因素、分布规律和有利勘探区优选等科学问题提供依据，提高烃类气藏勘探的成功率。

松辽盆地南部断陷期地层中发现CH4气藏、无机CO2气藏和两类气体的混合气藏。以往的研究中多数人认为无机CO2成因是以幔源为主，壳、幔混合为辅。对无机CO2成因是营城组火山岩脱气的产物认识存有争议，同时对两类气体差异成藏机理认识不清。通过对营城组火山岩加温脱出CO2气体量测试，及CO2驱替营城组火山岩中CH4气体置换实验，研究无机CO2的成因和两类气体差异成藏机理，建立两类气体的成藏模式，为未来寻找烃类和无机CO2富集区奠定理论基础。.营城组火山岩脱气实验证实，火山岩脱出CO2气体量与样品粒级基本呈现负相关性，凝灰岩脱出CO2气体量与温度呈现正相关性；在相同粒级、相同温度条件下，岩石脱出CO 2的气体量火山凝灰岩大于火山熔岩。加热温度低于300℃之前，脱出的是岩石颗粒表面的吸附气，当持续加热温度达400℃-600℃时，开始大量脱出岩石颗粒表面紧密的吸附气。结果证实营城组火山岩随埋藏深度增加地温升高，是可以脱出无机CO2气体的，火山岩脱出的CO2可以成为松辽盆地无机CO2气体来源方式之一，但在温度<200℃时脱出的无机CO2气体量较低，对现存高含CO2气藏的贡献量很小。.在有压差存在的条件下，无机CO2可以将火山岩中的CH4全部置换掉。长岭断陷哈尔金构造中营城组为火山岩体控制的高含CO2与CH4的混合气藏，CH4在火山岩中先期成藏后，经历构造运动使原有的深源断裂活化，此时幔、壳源无机CO2进入营城组火山岩烃类气藏，CO2对火山岩中的CH4进行驱替，被置换出的CH4烃类气体向上运移至登娄库组砂岩层中富集形成次生气藏。无机CO2的突发性供给是登娄库组不具备生烃条件又有烃类气藏形成的主控因素。而高含无机CO2的大部分气藏应该是新近世期的产物，主要分布在深源断裂附近的圈闭中。