Abstract:

The noble-gas helium(He)and neon(Ne)are rare components of natural gas hydrates, and their concentration changes are almost unaffected by complex chemical reactions and near-surface microorganism activities. Discussion of rare-gas geochemical exploration can not only eliminate the strong interference of microorganisms, but can also improve the intensity of the near-surface gas geochemical anomalies including natural gas hydrates. In this paper, natural gas hydrates mining area in the Muli permafrost region of Qilian mountains was investigated, where the average headspace He and Ne contents is 7.99×10^-6 and 20.8×10^-6, respectively, both higher than the average atmospheric concentrations. It is found that He and Ne have strong penetrative power, and show clear geochemical anomaly halos above the known hydrate deposits/prospects. Drilling-hole profiles show that there is obvious upper gas anomaly above the hydrate accumulation horizon, and the noble-gas differentiation and vertical percolation occur during the rare gas hydrate formation in Qilian, while the noble-gas He and Ne carry migrates vertically in the form of “gas-like” geogas current. Our study demonstrates that He-Ne anomaly has a good indication of the gas hydrate deposits, and He-Ne exploration technology is an effective supplement for hydrate exploration in permafrost regions.

Key words: noble-gas, geochemical anomaly, natural gas hydrate, Qilian Mountains