祁连山冻土区天然气水合物地球化学迁移机理探讨

陆域冻土区天然气水合物成矿机制较为复杂,水合物横向难以对比,形成机理不清楚,急需对天然气水合物迁移机理进行研究。文章根据祁连山冻土区天然气水合物发现区钻井揭示的地质和地球化学资料以及岩芯样品分析测试结果进行了综合分析。结果显示,研究区中侏罗统和上三叠统均为较好烃源岩,天然水合物气源以热解气为主,主要由上三叠烃源岩迁移和中侏罗统木里组烃源岩扩散提供,显示了多源多期次的特点。根据地质和地球化学分析,祁连山天然气水合物的形成经历了晚侏罗世—早白垩世的气体运移与聚集、中新世中晚期—上新世整体抬升、第四纪游离气体转化成天然气水合物矿藏3个阶段,经历了"先聚集-再抬升-后成藏"等过程,是构造-气候耦合作用的结果,初步建立了祁连山冻土区天然气水合物迁移机理。

A discussion on geochemical migration mechanism of natural gas hydrate in Qilian Mountain permafrost

The accumulation mechanism for natural gas hydrate (NGH) is sophisticated and it is difficult to conduct lateral correlation for NGH to figure out its mechanism. Therefore, it is urgent to conduct researches related to its accumulation mechanism. According to the NGH in the research well exploited in Muri, Qilian Mountain, the authors made a comprehensive analysis of its geological and geochemical data and the test results of core samples. It is revealed that the source rocks of Middle Jurassic and Upper Triassic can be regarded as the very good ones in the study area, and pyrolysis gas seems to have been the main source of the NGH, which was largely provided by the transfer and diffusion from the source rocks in Upper Triassic and Middle Jurassic respectively, exhibiting the features of multi-sources and multi-stages. Based on geological and geochemical analysis, the authors hold that the formation of NGH in Qilian Mountain experienced three phases, i.e., the gas migration and aggregation in Late Jurassic to Early Cretaceous, the overall uplift in Middle and Late Miocene to Pliocene and the free gas to NGH deposits in Quaternary. The whole process experienced aggregation, uplift and accumulation, resulting from coupling effect of tectonics and climate. On such a basis, the accumulation mechanism of the NGH in permafrost of Qilian Mountain can be initially established.