Stability analysis of methane hydrates for gas storage application

Abstract Solidified Natural Gas (SNG) technology offers an attractive option for compact and safe, large-scale natural gas storage. Gas storage technologies are gaining traction due to the increasing demand for natural gas and the expected transition to hydrogen gas-based economies in the near future. Introduction of thermodynamic promoters like THF into the classical methane-water system enables rapid gas uptake at moderate pressure and temperature due to sII hydrate formation, with highly stable storage characteristics. Herein, we compare the stability of cylindrical mixed methane-THF (sII) and pure methane (sI) hydrate pellets, produced using freshwater. Storage pressure for both types of pellets was 1 atmosphere (atm) whereas the storage temperature was 268 K for sII hydrate and 268 K and 253 K for sI hydrate. While only 7.06% gas evolution occurs from a methane-THF (sII) hydrate pellet stored at 1 atm and 268 K over a 10 day period, % gas evolution from two pure methane (sI) hydrate pellets stored at 268 K for similar duration was 41.45% and 37.05% individually. Correspondingly, % gas evolution from an sI pellet stored at 253 K was 51.09%. We also report 2 year uninterrupted stability testing of methane-THF (sII) hydrate pellets produced using both fresh and seawater, stored at atmospheric pressure and temperatures of 271 K and 268 K, respectively. To the best of our knowledge, this is the longest storage of any type of methane hydrates ever reported, showcasing the extraordinary stability of sII hydrates produced using both fresh and seawater. The results obtained in the present study resolve the challenge of hydrate stability in SNG technology and strengthen its commercial viability by reducing downstream complications related to hydrate storage.