木里冻土带天然气水合物赋存区浅层土壤地球化学特征及指示意义

Geochemical behaviors of shallow soil in Muli permafrost and their significance as gas hydrate indicators

青海省祁连山木里是中国陆上唯一通过钻探发现天然气水合物样品的地区。在木里天然气水合物赋存区开展了土壤油气化探的研究工作,采用了顶空气、酸解烃和蚀变碳酸盐3种烃类检测技术,其中顶空气和酸解烃方法在木里冻土带比较有效,而蚀变碳酸盐方法相对较差。顶空气法提取的游离烃和酸解烃法提取的吸附烃显示:木里天然气水合物赋存区土壤中烃类气体组分复杂,除了主要成分甲烷外,还含有少量乙烷、丙烷、丁烷和戊烷。烃类气体既有热解成因,又有生物成因;气体类型包括油型气、煤成气和生物气。根据甲烷衬度异常图,结合研究区地质资料和发现天然气水合物的钻井资料,认为工区中东部的甲烷高异常区断裂发育,应该是天然气水合物的有利赋存区。

Muli,the only gas hydrate hosting area in China proved by core sampling ,is located in Qilian Mountain perma-frost area.Petroleum geochemical exploration was carried out with three hydrocarbon detection techniques （ HS,acidolysis hydrocarbon and altered carbonate survey methods ） in the area .The results show that the former two methods are more ef-fective than the latter one .Analysis of free hydrocarbons extracted through HS and absorbed hydrocarbons from acidolysis indicates that the components of hydrocarbon gas in soil of areas containing gas hydrate in Muli are complex .In addition to the major component of methane ,there are also small amount of ethane ,propane,butane and pentane .There are both hydrocarbon gas of pyrolytic origin and that of microbiogenic genesis .The hydrocarbon gas can be classified as oil-prone gas,coal-drived gas and biogas .Methane contrast diagram in combination with the geologic background and core samples in wells discovering gas hydrate reveal that its eastern-central part with well-developed faults and high methane anomaly may be a favorable target for gas hydrate exploration .