松辽盆地长岭断陷老英台—达尔罕凸起CO_2分布特征及成因分析

DISTRIBUTION CHARACTERISTICS AND GENESIS OF CO_2 IN THE LAOYINGTAI-DAERHAN UPLIFT,THE CHANGLING FAULT SAG,THE SONGLIAO BASIN

松辽盆地长岭断陷老英台凸起区广泛分布CO2气层或与烃类气体伴生的CO2,其含量和组成非均质性明显,不同井区或同一井区不同层位气层中CO2的相对含量及同位素组成均可能存在明显差别,表明其成因十分复杂。揭示研究区CO2的成因机理,不仅具有理论意义,对研究区天然气勘探也具有重要的现实意义。根据CO2组成、同位素分布特征,结合伴生烃类气体分析,可知研究区深层CO2既有无机成因,也有有机成因,或者两者混合成因。其中,CO2含量相对较高的营城组气层中的CO2主要为无机成因气,而CO2含量较低的登娄库组气层中的CO2为有机成因或有机—无机混合成因。登娄库组有机成因CO2与烃类气为同期成藏;营城组CO2有与烃类气同期形成的,但大规模的无机成因的CO2为新近纪之后晚期成藏的。

CO2 gas or CO2 accompanied with hydrocarbon gas is widely distributed in the Laoyingtai Up lift of the Changling Fault Sag, the Songliao Basin. Contents and compositions of CO2 are different. Relative contents of CO2 and isotopic compositions may be obviously different between different wells or different gas formations in the same well, indicating complicate genesis. Studies of genetic mechanism of CO2 are important not only in theory, but also for natural gas exploration in the region. Based on CO2 composition and isotopic distribution features, combined with hydrocarbon gas studies, CO2 deep in the study area is both organic and inorganic origin, or mixed. CO2 in the Yingcheng Formation which contains much CO2 is mainly inorganic origin. CO2 in the Denglouku Formation which contains little CO2 is organic origin or mixed. Organic origin CO2 in the Denglouku Formation accumulates at the same time with hydrocarbon gas. Part of CO2 in the Yingcheng Formation accumulates at the same time with hy drocarbon gas; however, large accumulations of inorganic origin CO2 take place after Neogene.