漠河盆地多年冻土带生物气的发现及对陆域天然气水合物勘查的重要意义

东北漠河盆地多年冻土带不仅具有生物气形成的温度、地下水盐度、地下水Eh值和pH值等环境条件,而且具有生物气形成所需的丰富有机质。漠河盆地MK-2井的数据显示,井深870 m内的烃类气体干燥系数C₁/C_1-5> 98 %,70 % 以上的甲烷碳同位素δ¹³C₁< -55 ‰,几乎所有的甲烷氢同位素δD< -250 ‰,表现出明显的生物成因特征。区域和井下样品的生物标志物分析表明,几乎所有样品都含有25-降藿烷系列化合物,展示了漠河盆地多年冻土带微生物活动的普遍性。这一系列直接和间接标志,充分证实了漠河盆地生物气的存在,大大拓展了该区域天然气水合物的成藏气源,扩大了东北地区水合物的成藏潜力和勘查前景。这对东北地区乃至中国陆域多年冻土带的天然气水合物勘查都具有重要指导意义。

Occurrence of biogenic gas in the permafrost of Mohe Basin and its implication for gas hydrate exploration in continental permafrost,China

The permafrost soil of Mohe in northeastern China has proper environment conditions for the formation of biogas, such as temperature, salinity, Eh and pH values of groundwater, and rich organic matters. According to the data from Well MK-2, Mohe Basin, the dry coefficient of hydrocarbon gas C₁/C_1-5 is higher than 98 % within the well depth of 870 m, while carbon isotopes for more than 70 % of methane δ¹³ C₁ are less than -55 ‰, and hydrocarbon isotopes for almost all of methane δD are less than -250 ‰, showing significant biogenetic characteristics. Meanwhile, analyses on the biomarkers of regional and downhole samples indicate that almost all of the samples contain 25-norhopane series compounds, suggesting the widespread microbe activities in the permafrost soil. This series of direct and indirect markers have fully confirmed the existence of biogas in Mohe, which has greatly extended the sources of gas hydrate accumulation in this region and enlarged the accumulation potential and exploration prospect of gas hydrate in northeastern China. It is of important guiding significance to explore gas hydrate in onshore permafrost zones of northeastern China and the whole China.