青海哈拉湖东南缘多年冻土厚度及其影响因素研究——基于音频大地电磁探测

南祁连哈拉湖盆地是重要的含油气盆地,多年冻土分布广泛,具有良好的天然气水合物找矿前景,而多年冻土的分布特征是天然气水合物成藏的重要控制因素.应用音频大地电磁测深(AMT)对南祁连哈拉湖东南缘的多年冻土的下限进行探测,并对影响多年冻土厚度的因素进行了分析.结果表明:应用AMT能较好地划分多年冻土的厚度:区内的多年冻土厚度基本分布在30~ 130 m之间,整体呈现“中部与西北部厚,其他区域较薄”的分布特征,其中,中南部、中部与西北部的多年冻土厚度在80m以上,为天然气水合物提供了良好的盖层条件;区内多年冻土厚度的主要影响因素为地形、坡向(向阳面/背阴面)与地表径流,同时,断裂构造和地下水含量对冻土厚度也有一定的影响.高地、背阴面、非地表径流段、非断裂构造区域有利于形成较厚多年冻土层.

A study of the permafrost thickness and its influence factors based on AMT detection technology on the southeastern margin of Hala Lake,Qinghai Province

Permafrost regions are widely distributed in Hala Lake Basin in the Southern Qilian Mountain,and the basin is considered to be a favorable area for the accumulation of the natural gas hydrates with a great potential.The distribution of permafrost plays an important role in gas hydrate accumulation.The bottom of permafrost on the southeastern margin of Hala Lake was detected by AMT,and the factors affecting the permafrost thickness were analyzed.The detection results are as follows:It is found that using AMT to obtain the permafrost thickness is effective in the study area.Most of the permafrost thickness is between 30 meters and 130 meters,and the distribution of permafrost has the phenomenon that the central and the northwestern parts are thicker whereas other parts are thinner.In particular,the permafrost thickness of the areas including south-central area,central area and northwestern area is more than 80 meters,thus providing good conditions for the cap of the gas hydrate concentration.The main factors for the thickness of permafrost are terrain,slope and surface runoff.In addition,faults and underground water content are also factors influencing the thickness of permafrost.The conditions such as the highlands,the shady side,the non-runoff segment or the non-tectonic fault zone can facilitate greater thickness of permafrost.