Abstract:

The structure characteristics of natural gas hydrates play a significant role in the exploration and evaluation of natural gas hydrate resource. In this paper, the hydrate samples, recovered from DK8 -19, DK11-14 and DK12-13 holes in the Juhugeng drilling area in Qinghai, were investigated by micro-Raman spectroscopy for the structure characteristics. The results show that gas hydrates are widely distributed in the Juhugeng drilling area. In the vertical direction, gas hydrate are distributed discontinuously between the depth of 126.1 and 322.2 m. The Raman characteristics of gas hydrates from the three sites with different depths are almost the same, and show structure Ⅱ hydrate with various gas molecules. Besides hydrocarbons such as CH₄, C₂H₆, C₃H₈ and C₄H₁₀, N₂ is generally observed in these gas hydrates samples. In addition, the Raman signals attributed to H₂S in hydrate phase is found in the gas hydrate sample at depth of 126.1 m from DK8-19 hole, and it is the first time that H₂S in hydrate phase is found in Qilian Mountain hydrates,suggesting that H₂S gas molecules exist in some particular areas and gas hydrates form. The Raman spectroscopic characteristics of natural gas hydrates recovered from the Juhugeng drilling area may provide some new revelations for the study on the accumulation and distribution of gas hydrates located in the permafrost area in Qinghai.

Key words: Juhugeng drilling area, natural gas hydrate, laser micro-Raman spectroscopy, permafrost area, structure characteristic