琼东南盆地陵水凹陷天然气成因类型及来源

Genetic types and origin of natural gas in Lingshui sag,Qiongdongnan basin

陵水13-2、陵水17-2大气田的发现使得陵水凹陷成为琼东南盆地天然气勘探的热点地区。综合利用天然气及烃源岩地球化学分析资料并结合地质条件,分析了陵水凹陷天然气组分特征、成因类型及来源,结果表明:该凹陷天然气干燥系数较低,其中凹陷北坡为反映凝析气藏组分特征的湿气,南坡为反映富含凝析油气藏特征的偏干湿气;该凹陷天然气中乙烷等重烃碳同位素值较重,轻烃C7富含甲基环己烷,反映天然气为典型煤型气;该凹陷北坡天然气成熟度低于南坡,天然气碳同位素指纹特征以及凝析油低含蜡量、高含陆源输入的奥利烷和双杜松烷等生物标志物特征均与崖城13-1气田类似,指示天然气主要来自该凹陷渐新统海陆过渡相煤系及浅海相泥质烃源岩,其中凹陷北坡天然气混有中新统低成熟浅海相泥质烃源岩的贡献。

Lingshui sag becomes a hot area of natural gas exploration in Qiongdongnan basin because of the dis- covery of LS 13-2 and 17-2 large gas fields. Composition characteristics, genetic types and origin of natural gas in Lingshui sag were analyzed by utilizing geochemical analysis information of natural gas and source rocks, combined with geological conditions. It is concluded that the gas drying coefficient is low in Lingshui sag, in which the gas in northern slope is wet gas, reflecting condensate gas reservoir characteristics, and the gas in southern slope is partial dry wet gas, reflecting gas reservoir characteristics with rich condensate oil. Carbon i- sotope ratios of heavy hydrocarbons such as ethane in the sag are heavier, and lighter hydrocarbon C7 is rich in methyl cyclohexane, which indicates the typical coal-type gas. The lower natural gas maturity in north- ern slope of the sag than that of southern slope, fingerprint characteristics of natural gas carbon isotope, low wax content of condensate oil, high content of biological markers of terrigenous input such as oleanane and bicadinane are similar to YC 13-1 gas field, indicating the gas mainly from Oligocene marine-continen- tal transitional facies coal measure strata and neritic facies mud hydrocarbon source rocks. Part of natural gas in northern slope of the sag is from Miocene low mature neritic facies mud source rocks.