漠河盆地浅部气体特征及对天然气水合物形成的意义

Shallow gas characteristics in Mohe Basin,Northeast China and its significance to gas hydrate formation

烃类气源是天然气水合物形成的关键因素之一,气源问题长期困扰着中国东北冻土带的天然气水合物勘探。通过对中国东北漠河盆地4口地质浅井数百个岩心气体样品测试数据的研究可以得出:漠河盆地浅部(地表以下约1 200 m以浅的范围)的烃类气体含量多为10~100 mL/L,个别超过100 mL/L。通常泥质类岩石、破碎带和盆地深部的含气量较高,含碳或碳质泥岩的含气量更高。漠河盆地冻土带浅部主要为生物气;中深部(深度为1 200~2 300 m)可能主要是混合气;深部(深度>2 300 m)应该有热解成因的常规天然气。浅部生物气为漠河冻土带天然气水合物形成的主要气源,这对中国东北地区乃至中国陆域天然气水合物的勘探具有重要意义。

Hydrocarbon gas source is one of key factors for gas hydrate formation,and for long time is a puzzle during the gas hydrate exploration in the permafrost of Northeast China.In this study,hundreds of gas samples from the drilled cores of four wells in Mohe Basin were analyzed in detail,and it is obtained that the hydrocarbon gas content in the shallow part of Mohe Basin(above 1 200 m under subsurface)is in the range of 10-100 mL/L,and several individual contents exceed 100 mL/L.In general,the muddy rocks,fracture zones and deeper formations(>2 300 m)have high gas contents,while the carbon-bearing or carbonaceous mudstones have higher gas contents.The hydrocarbon gas in the shallow part of Mohe Permafrost is dominated by biogas;at the depth of 1 200-2 300 m,mixed gas could exist;conventional natural gas formed by pyrolysis shall occur in the deep formations.The shallow biogas is the main gas source for gas hydrate formation in the Mohe Permafrost,Northeast China,which has a great significance to guide the exploration of gas hydrate in the Northeast China and even the whole China land.