松辽盆地南部浅层天然气地球化学特征及其成因分析

由于松辽盆地南部浅层天然气成因研究比较薄弱，通过采集伏龙泉地区泉头组天然气样品，对天然气组分、碳同位素、轻烃组分进行了分析。结果表明该地区天然气有油型气和生物降解气2种成因。第一类天然气甲烷碳同位素值在-35‰左右，甲烷及其同系物碳同位素呈正碳分布;甲基环己烷指数在20%左右、环己烷指数略高于10%，符合油型气的特征。由甲烷碳同位素计算的R₀值，以及轻烃中的庚烷值和异庚烷值均在高-过成熟的范围，因此是高成熟的油型气。第二类天然气甲烷碳同位素偏轻，丙烷碳同位素偏重;轻烃色谱图中以环烷烃为主峰，轻烃内组成中支链烷烃和环烷烃含量高，各项轻烃参数(甲基环己烷指数、庚烷值、K1值等)都在较大范围内波动，为生物降解气。这一研究对于今后该区天然气勘探与资源评价及其成藏机理研究具有重要意义。

Geochemical Characteristics and Genetic Analysis of Shallow-buried Natural Gas in South Songliao Basin

There is lack of genetic research on shallow-buried natural gas in South Songliao Basin. By analyzing the component，carbon isotope and light hydrocarbon of the natural gas samples collected in Quantou Formation，Fulongquan，it shows that in the study area there are two types of shallow gas:oil-gas and bio-degradation gas. The characteristics of the first type natural gas include:the methane carbon isotope value is about -35‰, carbon isotope of methane and its homologs are presented as normal carbon distribution; methylcyclohexane index is about 20%，and cyclohexane index is a little higher than 10%; the R₀ value which was calculated by methane carbon isotope，the heptane value and the isoheptane value are all in high to over mature range，which confirms that it is belong to high mature oil-gas. The second type natural gas is characterized by rich light methane carbon isotope and rich heavy butane carbon isotope;cycloalkanes is displayed as the main peak in gas chromatogram of light hydrocarbon; cycloalkanes and branched alkanes are highly abundant in light hydrocarbon; all of the light hydrocarbon parameters (methylcyclohexane index， heptane value，K1，etc.)are fluctuated in a wide range，which confirms that it is belong to bio-degradation gas. This research has great significance on natural gas exploration，resource evaluation and revealing the mechanism of oil and gas accumulation.