陆域冻土区天然气水合物地球化学勘查中顶空气轻烃应用模式试验

Study on application mode of headspace gas light hydrocarbon in geochemical exploration of natural gas hydrate in permafrost regions

为探索顶空气轻烃技术在陆域冻土区天然气水合物地球化学勘查中的应用,选择祁连山木里已知天然气水合物矿区和哈拉湖未知区作为方法技术的试验区。试验指标包括土壤顶空气、土壤酸解烃、岩芯顶空气轻烃测井、甲烷碳同位素。研究表明:祁连山木里已知天然气水合物矿藏上方,土壤顶空气轻烃组分以甲烷为主,甲烷所占比例非常高,90.6%的样品C1含量都在78%以上,甲烷含量显著高于常规油气盆地;未发现天然气水合物的哈拉湖试验区,无明显的土壤顶空气轻烃异常现象。顶空气轻烃异常模式为:平面上,矿藏上方近地表土壤中存在明显的顶空气甲烷强异常;剖面上,在天然气水合物稳定带上方呈现“前缘晕”异常特征;其空间分布与祁连山水合物矿藏展布空间具有套合关系。甲烷碳同位素和烃类组成判断地表油气化探异常为热解成因,与祁连山冻土区天然气水合物的气体为同一成因来源。陆域冻土区天然气水合物顶空气轻烃地球化学勘查技术试验结果表明:顶空气轻烃地球化学方法既可以判断水合物成因类型,也可以圈出水合物矿藏范围。

In order to explore the application of the headspace gashydrocarbon technology in gas hydrates geochemical exploration in land permafrost regions,the known natural gas hydrate mining area of Qilian Muli and the unknown Hala Lake are chosen as the test areas.The test indices include soil top air,soil acid solution hydrocarbon,debris roof air logging and methane carbon isotope.The research shows that the methane as the main component of the headspace gas hydrocarbon above the known natural gas hydrate mining area of Qilian Muli is of high percentage,significantly higher than the conventional oil basins,and 90.6percent of C1content is above 78%.In the plane,there is an obvious anomaly of soil headspace gas methane above the mine,and on the section,there is“frontal halo”anomalous characteristics above the stable zone of the hydrate,the spatial distribution of which has close relation with Qilian mountain hydrate mineral spread distribution.The surface oil-gas geochemical anomaly is of pyrolysis origin based on the judgment of methane carbon isotopes and hydrocarbons,the same origin as the gas hydrate of Qilian mountain permafrost region.There are no obvious characteristics of headspace gashydrocarbon anomaly in the Hala Lake test area where natural gas hydrate is not discovered.The test result of geochemical exploration techniques of natural gas hydrates in the land area of permafrost region indicates that the technology can be used to determine the genetic type of hydrate,as well as the range of hydrate deposits.