Pore-Scale Visualization of CH 4 Gas Hydrate Dissociation under Permafrost Conditions
n this study, we investigate the effectiveness of combined pressure depletion and thermal stimulation to produce CH 4 gas from CH 4 gas hydrates at permafrost conditions. CH 4 gas hydrate phase transitions were visualized using a high-pressure, water-wet, silicon-wafer micromodel with a pore network...
| Published in: | Energy & Fuels |
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| Main Authors: | , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2021
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| Subjects: | |
| Online Access: | https://orbit.dtu.dk/en/publications/d2777e86-23a3-4142-ab23-40f48c624a62 https://doi.org/10.1021/acs.energyfuels.0c03295 https://backend.orbit.dtu.dk/ws/files/238100229/DTU_Library_Copy.pdf |
| Summary: | n this study, we investigate the effectiveness of combined pressure depletion and thermal stimulation to produce CH 4 gas from CH 4 gas hydrates at permafrost conditions. CH 4 gas hydrate phase transitions were visualized using a high-pressure, water-wet, silicon-wafer micromodel with a pore network of actual sandstone rock. A set of eight experiments was performed in which CH 4 gas hydrates were formed at a constant pressure between 60 and 85 bar and constant temperature between 0 and 4 °C. CH 4 gas hydrates were then dissociated at a constant system temperature between −3 and −2 °C by pressure depletion to study the effect of hydrate and fluid saturation on the hydrate dissociation rate, self-preservation, and risk of ice formation. The hydrate dissociation rate and associated fluid flow were heavily affected by the hydrate saturation and initial hydrate distribution in the pore space. Specifically, the rate of CH 4 gas production was low at T < 0 °C due to rapid formation of ice and secondary hydrate from the unfrozen liquid water that was liberated from the initial hydrate dissociation. The liberated CH 4 gas was therefore immobilized and trapped and could not be produced without thermal stimulation. Thermal stimulation effectively melted the metastable hydrate and surrounding ice cover and thereby enhanced the CH 4 gas production. Visual observation showed that self-preserved hydrates in the metastable state dissociated before ice at T < 0 °C, providing experimental evidence of recently discovered CH 4 leaking from gas hydrates in permafrost-affected sediments. The reported results are important in order to understand and predict the influence of global warming on the dissociation of permafrost-affected gas hydrates. |
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