在线富集-气相色谱法分析天然气中痕量轻烃

建立了高演化天然气在线富集-气相色谱分析方法,将干燥系数大于0.95的高演化天然气流经自行研制的富集反吹装置,痕量轻烃组分在富集管中冷冻液化并富集,对未液化的组分进行反吹,通过加热富集管使已液化的轻烃组分气化并进入色谱仪进行检测.分析结果表明,化合物的分析范围明显扩大,甲烷溶剂效应降低,达到对C10之前轻烃指纹进行分析的目的；对普光7井天然气样品进行3次重复性实验,所得甲基环己烷指数、正庚烷值、异庚烷值、Mango K1指数的实测最大重复性(r值)为0.22、0.23、0.02、0.00,分别小于国家标准要求的0.82、0.75、0.11、0.04,方法稳定可靠.通过本方法得到的轻烃参数可有效地应用于天然气成因类型、热演化程度探讨中.

Analysis of Trace Light Hydrocarbon in Natural Gas by an On-line Preconcentration-Gas Chromatography

A method for the analysis of high mature natural gas by Gas Chromatography with on-line preconcentration technique is introduced. High mature natural gas with greater than 0.95 of dry coefficient flowed through a self-developed enrichment back-blow device to trap the trace light hydrocarbons. After the back blow of un-liquefied components, the trapped trace light hydrocarbons were gasified and transferred into Gas Chromatography with carrier gas by heating the cold trapped components, which significantly expanded the analysis range of light hydrocarbons according to the results. The light hydrocarbons that were less than C₁₀ were successfully analyzed with this method. The results of three experiments of natural gas in Puguang 7 showed a good reproducibility in indices of methylcyclohexane, n-heptane, iso-heptane and Mango K₁ which were 0.22, 0.23, 0.02 and 0.00, respectively, lower than the national standard, 0.82, 0.75, 0.11 and 0.04. Meanwhile the solvent effect caused by methane has been dramatically reduced. The parameters obtained with this on-line analysis method can be effectively applied to the studies of origin and maturity of natural gas.