对云南保山、陆良和曲靖盆地第三系天然气进行了研究,查明气组份以甲烷为主,其在烃气中所占比例超过了97%,尤其在陆良盆地的3个样品中均为99.4%以上。指出天然气轻烃分布具有如下特点:保山盆地天然气轻烃分布比较正常,曲靖盆地检测到微量轻烃化合物,陆良盆地天然气很难检测到轻烃。又指出保山天然气轻烃组成主要以环烷烃和链烷烃为主,在链烷烃中支链烷烃含量较高,天然气C7轻烃组成以环烷烃为主,在环烷烃中二甲基环戊烷含量最高(在50%左右),其次是甲基环己烷(30%~40%之间),正庚烷含量最低(一般在10%左右);从轻烃的组成来看,保山盆地天然气主要来源于Ⅱ型有机质,从C7轻烃组成对比来看,曲靖盆地天然气中甲基环己烷含量比保山盆地高,其天然气主要来源于腐殖型母质。认为合理运用轻烃指标能够对天然气生源作出识别和对成熟度做出初步判断。

 Researched on the natural gas of Tertiary in BaoShan，LuLiang and QuJing basin i n YunNan province ,we can conclude that the methane's proportion is more than 97 % in component of hydrocarbon,especially that of three samples of LuLiang basin  all above 99.4%，it belongs to typical biogas. Light hydrocarbon's distribution  has some traits as follows：it is very normal in BaoShan basin and a little in Q uJing basin, while it is difficult to detect in LuLiang basin; Light hydrocarbon  composition is mainly composed of Cycloalkane and Alkane in BaoShan basin , the  content of branch-alkane is more high in Alkane; The composition of Light hydr ocarbon in the C ₇ range is dominated by Cycloalkane which is consisted of Dime thyl cyclopentane(about 50%)，Methyl cyclohexane (30%~40%), n-heptane(about 10%), so it can be concluded that natural gas root in the type Ⅱ.At the same ti me, the natural gas in QuJing comes from type Ⅲ because the content of Methyl c yclopentane in QuJing basin is higher than that of BaoShan basin through the con trast of Light hydrocarbon in the C₇ range. So we can identify the generation  resource of natural gas and estimate the maturity by use of the light hydrocarbo n index correctly.