祁连山冻土区天然气水合物地质控制因素分析

Geological controlling factors of gas hydrate occurrence in Qilian Mountain permafrost,China

对祁连山冻土区天然气水合物勘探区DK-2至DK-6钻孔地层、岩心粒度、断层破碎带以及冻土层属性进行了综合分析。结果表明,研究区水合物储存首要控制因素是可为深部气源提供流体通道的区域主断层,其他小断层和破碎带可为水合物提供部分流体来源及储存空间,气体来源以深部热解气为主;不同沉积环境地层中水合物赋存层段的粒级组分含量不同,局部粗碎屑沉积亦可为天然气水合物提供有利储存空间;而水合物的储存不仅受冻土层厚度控制,还可能与冻土层岩性有很大关系,有利的"盖层"(低孔隙度、低渗透率)可能更利于水合物的赋存。此外,江仓组地层也可能对天然气水合物有一定的岩相控制作用。

In order to search after the control of geological factors over gas hydrate storage in Qilian Mountain permafrost, the grain size, fault fracture zone and permafrost properties of DK-2 to DK-6 borehole core samples have been discussed in detail. It has been considered that the gas hydrate occurrence in the study area is principally controlled by regional main faults, which can offer fluid channel for deep gas source. And the small fault and fracture zone could provide part of the fluid source and storage space. The source of gas mainly consists of deeper thermogenic gas. In addition, the main particle size fraction bearing gas hydrate is different in varied sedimentation, and local coarse clastic sediment can supply favorable storage space. Moreover, not only the thickness, but also the strata of permafrost are important for the existence of gas hydrate. A favorable grain size of cap rock is probably conductive to the occurrence of hydrate. Besides, the Jiangcang Formation may also have a certain degree of facies-control role to gas hydrate.