Visualization of CH 4 Hydrate Dissociation Under Permafrost Temperature Conditions Using High-Pressure Micromodel

• Main Authors: Pandey, Jyoti Shanker, Almenningen, Stian, von Solms, Nicolas, Ersland, Geir
• Format: Conference Object
• Language: English
• Published: 2020
• Subjects: Ice; permafrost
• Online Access: https://orbit.dtu.dk/en/publications/ea533ea2-5d15-4da8-a217-e2ac231f39d6; https://backend.orbit.dtu.dk/ws/files/236625902/GRS_Abstract.pdf

Methane (CH 4 ) gas hydrate formation, dissociation, and stability in permafrost sediments are essential to model these systems concerning global warming and in schemes of CH 4 recovery and/or carbon dioxide (CO 2 ) storage. It is known that CH 4 hydrate is thermodynamically less stable than CO 2 hydrate due to the lower activation energy of the decomposition. However, recent studies show that CH 4 hydrate’s dissociation slows down in subzero temperature due to the self-preservation mechanism. Thus, a fundamental understanding of CH 4 hydrate distribution, dissociation mechanism, and self-preservation in sediments at the pore-scale level, is essential to optimize the CH4 gas production method from permafrost-affected hydrate reservoirs. In this study, CH 4 hydrate dissociation was visualized using a high-pressure, water-wet, silicon-wafer based micromodel with pore network of actual sandstone rock. A total of nine runs were performed, and CH 4 hydrate was formed between 60-85 bar, and between 273.15 K-275 K. CH4 hydrate was dissociated between 270-275K by pressure depletion to evaluate the effect of hydrate and fluid saturation on dissociation rate, self-preservation, and risk of hydrate reformation. Below 273.15K, the CH 4 gas production was limited due to rapid formation of ice from liquid water liberated from initial hydrate dissociation. The liberated CH 4 gas was immobilized and trapped by the formed ice. Consequently, we demonstrate the ineffectiveness of depressurizing CH 4 hydrate without thermal stimulation. The results highlight the importance of initial hydrate/ice/gas saturations and free gas availability in characterizing hydrate dissociation patterns.