祁连山冻土区天然气水合物现场识别方法

Gas hydrate field identification methods in Qilian Mountain permafrost

天然气水合物是一种赋存在低温、高压条件下,陆上永久冻土区和海底沉积物中的规模巨大的新型能源。在冻土区的天然气水合物研究过程中,钻探取样和天然气水合物岩芯研究仍是识别和推断天然气水合物最直接有效的方法。因此,如何在钻探现场快速有效地识别出天然气水合物及相关异常特征就显得极其重要。近几年在祁连山天然气水合物勘探过程中,探索性地总结出适用于冻土区的天然气水合物现场识别方法,主要包括肉眼观测、孔口气涌观测、岩芯红外测温、岩芯裂隙孔隙水盐度测定、岩芯气体解析与组分测定和岩芯次生构造与伴生矿物鉴别等方法。利用该套现场识别方法和随钻岩芯编录,有效地查明了祁连山冻土区天然气水合物在岩芯中的产状和分布特征,为该区天然气水合物资源评价和试开采试验提供了重要依据。

Gas hydrate is a new type of potential energy that occurs within the land-based permafrost zone and marine sediments under low-temperature and high-pressure conditions.In the research on permafrost-associated gas hydrate,coring and investigation of gas hydrate-bearing cores remain the effective tools to identify and infer hydrate occurrence.The accurate identification of the gas hydrate and associated anomalous characteristics in the field is therefore very important.Based on gas hydrate exploration in the Qilian Mountain permafrost in recent years,the authors have tentatively summarized gas hydrates filed identification methods suitable for the permafrost zone.The methods mainly include the observation by naked eye,the observation of borehole gas blowout,the temperature measurement of the core by infrared ray,the salinity measurement of fracture and/or pore water,the gas volume and composition measurement from the core,as well as the identification of secondary structures and associated minerals in the core.With the help of the field identification methods anddocumentation with drilling,the occurrence and distribution characteristics of gas hydrate in the cores could be effectively revealed,thus providing geological data for the gas hydrate resource assessment and tentative production in the Qilian Mountain permafrost.