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Abstract
n this study, we investigate the effectiveness of combined pressure depletion and thermal stimulation to produce CH4 gas from CH4 gas hydrates at permafrost conditions. CH4
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 CH4 gas hydrates were formed at a constant pressure between 60 and 85 bar and constant temperature between 0 and 4 °C. CH4
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 CH4 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 CH4 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 CH4 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 CH4
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.
Original language | English |
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Journal | Energy & Fuels |
Volume | 35 |
Issue number | 2 |
Pages (from-to) | 1178–1196 |
ISSN | 0887-0624 |
DOIs | |
Publication status | Published - 2021 |
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University of Bergen
Pandey, J. S. (Visiting researcher)
1 Sept 2019 → 20 Feb 2020Activity: Visiting an external institution › Visiting another research institution