松辽盆地长岭断陷下白垩统天然气成因及气源分析

Genesis Type and Source Analysis in Lower Cretaceous of Changling Depression in Songliao Basin

松辽盆地南部长岭断陷下白垩统登娄库气藏的成分复杂、来源多样,其成因及来源的确定对进一步的油气勘探有指导意义。从天然气组分、同位素特征等方面入手,对长岭断陷下白垩统天然气组分特征、成因类型进行分析,并结合地质分析确定天然气来源。认为除长岭2号和长岭6号气田为二氧化碳气藏外,长岭断陷下白垩统以烃类气藏为主。依据稳定碳同位素特征判定,哈尔金构造天然气是同源不同期的煤成气,伏龙泉构造泉一、三段天然气为油型气,登娄库组天然气为混合气,双坨子构造天然气主要是混合气,大老爷府构造天然气为油型气;而二氧化碳气藏则为幔源无机成因气。烃类气藏中显著的稳定碳同位素倒转现象为天然气扩散残余导致。以天然气成因分析为基础,结合地质分析认为,营城组和沙河子组是该地区烃类气体的主要供烃源。

The component and generation of natural gases are complicated in Lower Cretaceous of Changling depres-sion in Songliao Basin. It is significance to confirm the generation and source rock of natural gases, which is impor-tance to oil exploration in this area. On the basis of the component analysis and carbon isotope characteristics, the genesis types of natural gases in Lower Cretaceous were identified. The natural gas was coal-type gas in Haerjin structure, and oil-type gas in Dalaoyefu structure and upper part of Fulongquan structure, and mixing-type gas in Shuangtuosi structure and lower part of Fulongquan structure. The dioxide carbon gas in No. 2 and No. 6 Changling structure is inorganic genetic gas of mantle source. The abnormal sequence of stable carbon isotopes in hydrocarbon accumulation was properly caused by gas diffusion. Combined with the genesis type of natural gases and geology conditions, the main source rocks were confirmed to be Yingcheng Formation and Shahezi Formation.