The natural gas in the Yinggehai Basin is mainly coal related gas from Miocene series. Currently,there is not clear cognition on whether the natural gas type can be further divided and which source rock it came from, which restrains the exploration process of natural gas in this area. For solving the above problems,by fine dissection of the geochemical features of the natural gas in this basin,we analyzed them by geochemical data and thermal sim-ulation experiments of the source rock. The study results show that:(1)several parameters (δ13 C2 ,δ13 C1—δ13 C2 and C2/iC4 etc.)can be used to effectively subdivide the natural gas in this basin into type M and type S;(2)gas source analysis reveals that the above two types of natural gas individually came from the source rocks in the Meis-han Formation and the Sanya Formation. The carbon isotope values of heavy hydrocarbons in type M and type S nat-ural gas are consistent with the carbon isotope values of the source rocks in the Meishan Formation and the Sanya Formation,respectively. Type M natural gas has similar geochemical feature to the pyrolysed hydrocarbons from the mudstone in the Meishan Formation. This study provides theory support for natural gas exploration and hydrocarbon accumulation researches that are becoming more complex in this Basin.%莺歌海盆地天然气主要为来自中新统的煤型气,目前对天然气类型是否可以进一步细分以及具体来自中新统哪套烃源岩并无清晰认识,制约了该区天然气的勘探进程.针对以上问题,通过对盆地内天然气地球化学特征的详细剖析,结合烃源岩地球化学及热模拟实验等资料进行分析.研究结果表明:δ13 C2、δ13 C1—δ13 C2和C2/iC4等参数可有效将盆内天然气细分为M型和S型;气源分析揭示二者分别来自梅山组与三亚组烃源岩.M型和S型天然气的重烃碳同位素值分别与梅山组和三亚组烃源岩的碳同位素值一致;而M型天然气与梅山组泥岩热解烃地球化学特征相似.该研究为盆地日趋复杂的天然气勘探与成藏研究工作提供理论支撑.
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