| Summary: | Gas hydrates are ice-like crystalline solids consisting of water and gas (predominantly methane). The methane gas bound in hydrate structures and their worldwide occurrence make them interesting not only as a potential energy source but also as a possible climate-relevant factor. Estimations predict that a certain amount of atmospheric CH4 may originate through dissociation of global gas hydrates, which may exacerbate global warming (Ruppel and Kessler, 2017). In turn, climate warming is not only directly affecting the hydrate distribution, but also perturbing the hydrate stability field, leading to the release of CH4 from hydrate-bearing sediments. Gas hydrates, particularly those associated within or below shallow permafrost, are likely to be affected by the climate processes. For instance, gas hydrates in Qilian Mountain permafrost (QMP) are found below thin permafrost layers at a shallow depth of around 133~396 m. They might be vulnerable to dissociation due to global warming resulting in a possible higher CH4 gas emission in this area. Considering the environmental effect, a proper understanding of hydrate dissociation behavior under specific conditions is important for the stability of natural gas hydrate deposits with respect to climate change. This study focuses on the potential dissociation process of gas hydrates in QMP. Before the observation of hydrate dissociation, mixed gas hydrates are synthesized from pure water and gas mixtures containing CH4, C2H6, C3H8, CO2 at conditions close to those in QMP (3.0 MPa, 278 K) with respect to feed gas composition, pressure and temperature. Formed hydrate crystals are analyzed in x-y-z directions applying confocal in situ Raman spectroscopic measurements to identify structures and guest compositions. The dissociation process is based on the thermal conduction simulating global warming and the results are discussed under several isobaric conditions. The Raman spectra continuously record changes in the hydrate phase for each selected crystal over the whole ...
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